JPS6320466B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an epoxy resin coating that has excellent corrosion resistance and solvent resistance. In recent years, the number of large steel structures such as plants, bridges, and offshore structures has increased, and efforts have been made to prevent corrosion of steel materials in order to maintain the strength of such structures over long periods of time. Among these, so-called heavy-duty anti-corrosion coating, which is applied to the surface of steel materials, is becoming more important from the aspects of aesthetics, workability, and total cost. Therefore, the current situation is that it is impossible to apply heat-curable paints, and it is inevitably limited to paints that dry at room temperature. However, it has so far been almost impossible to obtain a paint that dries at room temperature and can fully exhibit the required performance as described above. Although it is often used in this type of heavy-duty anticorrosion paint because it has excellent corrosion resistance, the reality is that it does not have sufficient durability when exposed to severe corrosive conditions. Typical epoxy resin paints that dry at room temperature include a solution of bisphenol A type epoxy resin as the main ingredient, and amines or polyamines as a curing agent, and the two components are mixed immediately before painting. There is a so-called two-component room-temperature drying type, which is widely used. By the way, in order to increase the durability of such epoxy resin paints, methods such as simply mixing a novolak type phenolic resin with the above epoxy resin at room temperature in advance, or heating or heat-fusing it at a relatively low temperature of 180 degrees Celsius or less are used. The use of the product thus obtained is also known as described in JP-A-49-120928. However, the products obtained according to such a method are not so good because the addition reaction between the epoxy resin and the novolac type phenolic resin is not sufficiently carried out, and the degree of formation of the network molecular structure cannot be increased. It cannot be said that this is a practically effective means, as it does not show any improvement in the corrosion resistance of the coating, and on the other hand, the mechanical physical properties of the coating film, such as impact resistance, deteriorate significantly. Another possibility is to use a catalyst such as a tertiary amine to accelerate the reaction between these two resins, but such a catalyst is usually used as a catalyst to accelerate the curing of the epoxy resin itself. Furthermore, since it becomes an insoluble and infusible gel in a short period of time during preparation, it is extremely difficult to control the reaction, and this cannot be said to be an effective means. However, in light of the above-mentioned background, the inventors of the present invention have completed the present invention as a result of intensive studies to obtain an epoxy resin paint that has a high degree of corrosion resistance and provides a coating film with excellent mechanical properties. I've come to the point where I can. That is, the present invention uses an epoxy resin having an average of two or more epoxy groups in one molecule with an epoxy group equivalent of 1.0 and a phenolic hydroxyl group of 0.3.
The present invention provides an epoxy resin paint characterized by containing an epoxy resin prepolymer obtained by reacting a novolak type phenolic resin in an amount equivalent to ~0.55 equivalent at 190 to 230°C. Here, as the above-mentioned epoxy resin, all commercially available epoxy resins can be used, but among them, particularly representative ones include bisphenol A type, bisphenol F type, hydrogenated bisphenol type A, hydrogenated bisphenol type Various epoxy resins of the bisphenol F type, alicyclic, novolac type, polyoxyalkylene type, polyhydroxybenzene type, methylepichlorohydrin type or glycidylamine type, or derived from dimer acids, phthalic acid, tetrahydrophthalic acid or epichlorohydrin. On the other hand, the novolac type phenolic resin is ester-type epoxy resin or halogen-containing epoxy resin.
Use of substituted phenols such as cresol, p-tert-phenol, p-phenylphenol, p-nonylphenol, O-phenylphenol or 3,4-xylenol, or acidic condensates of resorcinol and formaldehyde, etc. However, in particular, the use of substituted phenolic resins improves the solubility of the so-called prepolymer, which is the addition reaction product with the epoxy resin, in organic solvents, and also reduces the viscosity of the prepolymer. In addition to speeding up pigment dispersion and increasing curing speed, it can also improve the mechanical properties and gloss of the cured coating film. Incidentally, in the present invention, the reason why such a novolac type phenolic resin is particularly selected is that the epoxy group present only at the molecular terminal of the epoxy resin reacts with the phenolic hydroxyl group in the novolac resin. The aim is to advance polymerization while maintaining the linear structure as much as possible, and this is an advantage that cannot be obtained by using resol type phenolic resins. The above-mentioned epoxy resin and novolac resin are then reacted at 190 to 230°C to form an epoxy resin prepolymer. The reaction time at this time is usually 0.5
-6 hours, and if the reaction time is prolonged, the epoxy resin will be cured and polymerized, which is not preferable. The appropriate ratio of each resin used in this reaction is such that the phenolic hydroxyl group in the latter resin is equivalent to 0.3 to 0.55 equivalent to 1.0 equivalent of epoxy group in the former resin. be. If the amount is less than 0.3 equivalent, it is not preferable because the corrosion resistance of the cured coating film cannot be sufficiently improved.On the other hand, when using a large amount of novolak resin exceeding 0.55 equivalent, the presence of epoxy resin increases accordingly. As the ratio decreases, this leads to disadvantages such as a decrease in the flexibility of the cured coating film and its adhesion to the base material. The epoxy resin prepolymer obtained as described above can be put to practical use as an epoxy resin composition as it is, or if necessary, the viscosity can be adjusted by adding a solvent, and depending on the purpose of use, it can be further used. It can also be used as an enamel-like epoxy resin composition in which suitable known and commonly used paint pigments or various additives are dispersed. Thus, in the epoxy resin prepolymer used in the present invention, since the reaction is carried out at a higher temperature than in conventional methods, the reaction between the epoxy groups and the phenolic hydroxyl groups occurs sufficiently, and the formation of a network molecular structure is facilitated. In order to be able to increase the degree of
To obtain a transparent epoxy resin prepolymer using a novolak type phenolic resin which gives a cured coating film with extremely excellent corrosion resistance and which is incompatible with epoxy resins at room temperature. becomes possible. In addition, the coating film obtained by curing the epoxy resin prepolymer used in the present invention with an amine curing agent exhibits excellent adhesion to the surface of a steel plate, and also has mechanical properties such as impact resistance. Because it exhibits excellent performance in terms of so-called corrosion resistance, such as corrosion resistance, water resistance, and chemical resistance, it is useful as a so-called heavy-duty anticorrosion paint used under extremely harsh environmental conditions. This prevents the peeling, swelling, and softening of the paint film over a long period of time, as well as the formation of blisters and the formation of rust on the steel surface. Furthermore, even when used, for example, to paint the inner surfaces of tanks such as product carrier ships that carry petroleum products, it is useful for protecting the base steel surface without contaminating the petroleum products. Next, the present invention will be explained in detail with reference to Reference Examples, Examples, and Comparative Examples. In the following, all parts and percentages are based on weight unless otherwise specified. Reference example: “Epicron 1050” in the four-necked flask of 1 and 2.
919 parts (equivalent to 1.9 equivalents) of [epoxy resin manufactured by Dainippon Ink and Chemicals Co., Ltd.; epoxy equivalent = 475],
121 parts (equivalent to 0.95 equivalent) of "Super Betsukasite 3011" (a novolac type phenolic resin made by the same company) were charged and reacted at 200°C for 4 hours with stirring, then cooled to 150°C, and then A reflux condenser was then attached to this flask, 446 parts of xylene was added, and the reaction product was dissolved under reflux to obtain a transparent liquid prepolymer with a resin solid content of about 70%. Hereinafter, this will be abbreviated as prepolymer (P-1). Reference example 2 “Epicron 850” (epoxy resin manufactured by the same company;
757 parts (equivalent to 4.0 equivalents) of epoxy equivalent = 190)
Example 1 was carried out in the same manner as in Example 1, except that 243 parts (equivalent to 1.6 equivalents) of "Barcam TD2618" (novolac type phenolic resin manufactured by the same company) were used, and the amount of xylene to be added was changed to 400 parts. A transparent liquid prepolymer having a resin solid content of about 70% was obtained. Hereinafter, this will be abbreviated as prepolymer (P-2). Reference Example 3 809 parts (equivalent to 4.6 equivalents) of "Epicron N-740" (epoxy resin manufactured by the same company; epoxy equivalent = 176) and both were mixed in a ratio of 0.7 moles of formaldehyde to 1 mole of carbolic acid. The resin solid content was approximately 70% in the same manner as in Example 2, except that 191 parts (equivalent to 1.8 equivalents) of a novolac type phenolic resin obtained by condensation in the presence of a hydrochloric acid catalyst was used. A transparent liquid prepolymer was obtained.
Hereinafter, this will be abbreviated as prepolymer (P-3). Reference example 4 “Epicron 1050” and “Super Betsukasite”
A transparent liquid prepolymer having a resin solid content of about 70% was obtained by carrying out the reaction in the same manner as in Reference Example 1, except that the reaction conditions with ``3011'' were changed to 225° C. for 5.5 hours. Hereinafter, this will be abbreviated as prepolymer (P-4). Reference example 5 By adding 919 copies of "Epicron 1050" and 121 copies of "Super Betsuka Site 3011", an additional 446 copies are prepared.
The procedure of Example 1 was changed to add 100% of xylene, continue boiling at 130°C for about 4 hours while heating and cooling under reflux, and take it out after cooling, and the resin solid content was about 70%. A translucent liquid control prepolymer was obtained. Hereinafter, this will be abbreviated as prepolymer (P'-1). Reference Example 6 A reaction was carried out in the same manner as in Reference Example 1, except that the reaction temperature was 175°C, to obtain a control prepolymer in the form of a translucent liquid having a resin solid content of approximately 70%. Hereinafter, this will be abbreviated as prepolymer (P'-2). Examples 1 to 4 and Comparative Examples 1 to 4 Each prepolymer obtained in Reference Examples 1 to 6,
"Ratsukamide TD971" [Dainippon Ink and Chemicals
Co., Ltd. (Amine Adduct Curing Agent: Theoretical Active Hydrogen Equivalent = 145) in the ratio shown in Table 1, and if necessary, xylene/n-butanol = 1/1 (weight ratio ) was added and mixed, and then immediately brushed onto a sandblasted steel plate to form a clear coating film with a film thickness of about 300 μm, and then cured in a room at 20°C for 7 days. . For each cured coating thus obtained, mechanical properties such as pencil hardness, grain density and impact resistance, and erosion resistance such as salt spray resistance, water resistance, methanol resistance and linseed oil fatty acid resistance were evaluated. The performance evaluation tests are summarized in the same table. When the epoxy resin prepolymer obtained according to the method of the present invention was used as the main material (Examples 1 to 4), the epoxy resin was used as the main material. (Comparative Examples 1 and 2), and when the control prepolymer was used as the base material (Comparative Example 3).
It can be seen that it has clearly superior coating film performance compared to 4) and 4).

[Table] ** Judgment criteria ◎…Excellent △…Acceptable

○…Good ×…Not good

Claims (1)

[Claims] 1. An epoxy resin having an average of two or more epoxy groups in one molecule and a novolac-type phenol formaldehyde resin are used in such a manner that the phenolic hydroxyl group in the latter novolac resin is 0.3 to 1.0 equivalent of the epoxy group in the former epoxy resin. An epoxy resin paint characterized by containing an epoxy resin prepolymer reacted at 190 to 230°C in a proportion of 0.55 equivalent.