JPS6324468B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a corrosion-resistant resin coating material with excellent adhesive properties. Specifically, it is obtained by undercoating a base material with a special resin using a powder coating method, and then overcoating a vinylidene fluoride resin thereon. As is well known, vinylidene fluoride resin is mechanically strong, has a high heat resistance, has excellent weather resistance, and has excellent chemical resistance, making it useful as a corrosion-resistant coding material for chemical equipment and metals in corrosive environments. It has extremely desirable properties as a long-life coating material for In addition, vinylidene fluoride resin is easy to melt process because its melting temperature and thermal decomposition temperature are 150°C or more apart, and if a resin with an appropriate degree of polymerization is selected, it can be processed without using any organic solvents or plasticizers. So-called powder coating is possible. However, if vinylidene fluoride resin is actually powder-coated on a substrate surface and used for a long period of time in a high-temperature, corrosive environment in the presence of water, problems such as floating and peeling of the coating occur. Particularly, due to the shape of the base material, these problems occur more frequently in the inner portion with a small radius of curvature. As a method to improve the adhesion of vinylidene fluoride resin to the substrate surface, it has been proposed to use an epoxy compound as an undercoat (US Pat. No. 3,111,426). Due to poor compatibility,
Adhesion is not necessarily good. In addition, a method has been proposed to improve adhesion by adding and mixing inorganic substances to vinylidene fluoride resin (Japanese Patent Publication No. 48-17543), but even with this method, if the inner radius of curvature is small due to the shape of the base material, internal It is difficult to say that it is a sufficient powder coating method as it may cause floating and peeling. The object of the present invention is to provide a coating material obtained by powder coating these vinylidene fluoride resins, which improves the adhesion between the base material and the vinylidene fluoride resin, and which has a small inner radius of curvature. The present invention provides a coating material that does not cause trouble even when used in a high-temperature, long-term corrosive environment in the presence of water. In powder coating of vinylidene fluoride resin, the present invention provides a partially saponified ethylene-vinyl acetate copolymer (), a polymer () obtained by graft polymerizing the saponified product () with an unsaturated carboxylic acid, and a saponified Undercoat a primer resin consisting of a resin selected from the group consisting of a mixture of the polymer () and a vinylidene fluoride resin, and a mixture of the polymer () and a vinylidene fluoride resin, and apply a vinylidene fluoride resin thereon. By overcoating, the adhesion between the vinylidene fluoride resin and the base material becomes stronger,
This is due to the discovery of a vinylidene fluoride resin coating material that uses a base material with a small radius of curvature and does not cause lifting or peeling even under high-temperature, long-term corrosive environments. The present invention will be explained in detail below. The vinylidene fluoride resin used in the undercoat and overcoat of the present invention is not only a homopolymer of vinylidene fluoride, but also has a vinylidene fluoride content of 90%, which has essentially the same properties.
Contains mol % or more of copolymer. Examples of copolymers that can be copolymerized with vinylidene fluoride include ethylene tetrafluoride, propylene hexafluoride, ethylene monochloride trifluoride, and vinyl fluoride. The degree of polymerization of the vinylidene fluoride resin used in the present invention is expressed as an intrinsic viscosity η _ioh = 0.6 _to 1.4
Preferably within the range of . If it is less than 0.6,
When the strength of the coating film becomes small and is greater than 1.4, it becomes difficult to form a continuous coating film. Here, η _ioh is a value expressed by the following formula. η _ioh = 1/Cln [η/η _p ] η: Viscosity of a dimethylformamide solution of the polymer with a concentration of 0.4 g/dl C at 30°C η _p : Viscosity of dimethylformamide at 30°C Used in the primer in the present invention Partially saponified ethylene-vinyl acetate copolymer () refers to a copolymer having a vinyl acetate content of 5 to 95% and a degree of saponification of 30 mol% or more. In addition, the unsaturated carboxylic acid in the polymer () obtained by graft polymerizing the saponified product with an unsaturated carboxylic acid is an α,β-unsaturated carboxylic acid such as acrylic acid, methacrylic acid, or maleic anhydride; The content of the unit is preferably 0.05 to 10% by weight in parentheses.
Examples of the polymer () include Dumilan D (trade name, manufactured by Mitsui Polychemical Co., Ltd.), and examples of the polymer (2) include Dumilan C (trade name, manufactured by Mitsui Polychemical Co., Ltd.). Polymers () and () each show good results when used alone, but they can also be used in combination with vinylidene fluoride resin. The mixing ratio is vinylidene fluoride resin content.
80% by weight or less in the mixture, more preferably 60% by weight
The following is desirable. These primer resins can be used as an undercoat by powder coating the base material as is, but a compound that chemically reacts with the hydroxyl and carboxyl groups in the resin to cause crosslinking is added to 100 parts by weight of the primer resin. It can be used by mixing up to 20 parts by weight. By mixing these compounds, the adhesion between the vinylidene fluoride resin of the overcoat and the base material is further strengthened, and the corrosion resistance is also improved. Such compounds include epoxy compounds, isocyanates, urea, phenols, acid anhydrides, acid chlorides, etc., and epoxy compounds are most preferred. The epoxy compound is preferably an epoxy resin, such as Evacrate, a trade name manufactured by Kansai Paint Co., Ltd., and the like. Also, inorganic substances may be mixed into the primer resin.
Inorganic substances include silica sand, graphite,
Materials with good water resistance, acid resistance, alkali resistance, and solvent resistance such as mica, talc, molybdenum disulfide, and chromium oxide are used, and the mixing amount is 100 parts by weight for 100 parts by weight of primer resin. Parts by weight or less are preferred. Mere mechanical mixing of the primer resin and the epoxy compound or inorganic powder is sufficient, and a common blender may be used. In addition, a powder obtained by heating, melting, and mixing a primer resin and an epoxy compound, causing a partial reaction, and then pulverizing the mixture may be used. Further, the inorganic substance may be used after being mixed with the vinylidene fluoride resin in advance. Whichever method is used for production, the viscosity of the final powder is preferably in the range of 60 to 325 mesh, but it is not necessary to make the particle size uniform. The base material used in the present invention is mainly made of iron, and other materials such as aluminum, stainless steel, titanium, and copper are also used. Porcelain as a non-metal,
Glass etc. can also be used. The present invention can be applied not only to plates, pipes, containers, etc., but also to substrates of complex shapes with a particularly small radius of curvature. The coating material of the present invention is manufactured as follows. That is, the surface of the base material to be coated is conditioned by sandblasting, shotblasting, gritblasting, etc. to remove rust, foreign matter, and chemical conversion treatment, and then transferred to a heating furnace to a temperature of 120 to 300℃. Preheat. The preheated substrate is coated with the primer resin powder described above on the surface to be coated by applying a method such as fluidized bed dipping, powder spraying, or electrostatic powder spraying. In order to form a continuous film of the adhered primer resin, it is preferable to return it to the heating furnace and continue heating. In the case of electrostatic powder spraying, it may be applied to the surface to be coated at room temperature and then heated and melted. Once a molten continuous film is formed, take it out again and
A primer resin powder is applied and the same operation is repeated to obtain an undercoat layer of a predetermined thickness. 1
Although it is possible to obtain a predetermined thickness in one coat, it is usually preferable to coat in two or more coats. After undercoating a primer resin to a predetermined thickness, a vinylidene fluoride resin is overcoated thereon. The overcoat is powder coated using almost the same method as described above. Even though the overcoat is made of vinylidene fluoride resin and is thin, it is possible to obtain complete coding without pinholes. Incidentally, pigments, fillers, crystal nucleating agents, etc. may be added depending on the case. At this time, a vinylidene fluoride resin containing an inorganic substance may be coated on the primer resin layer, and then a vinylidene fluoride resin may be overcoated. The coating material of the present invention has an undercoat thickness of 0.01
~1.0 mm, preferably 0.2-0.6 mm, overcoat in the range 0.1 mm-2.0 mm, preferably 0.1-1.0 mm. The thus obtained coating material could be used for a long time in a high temperature corrosive environment in the presence of water.
Examples will be described below, but the present invention is not limited to the examples as long as the invention is within the scope of the claims. Example 1-6, Comparative Example 1 Iron plate sandblasted to remove rust (SS-41)
A powder coating of vinylidene fluoride resin was applied to the entire surface of a 200 mm square and 6 mm thick piece as follows. A partially saponified product obtained by saponifying 90 mol% of an ethylene-vinyl acetate copolymer containing 30% by weight of vinyl acetate monomer units as a copolymer () was reacted with acrylic acid to introduce 2% by weight of an acrylic acid component. A graft polymer was used. This graft copolymer powder (60-325 mesh)
Alone, and this graft copolymer mixed with vinylidene fluoride resin powder (containing salt as a crystal nucleating agent) with η _ioh = 1.00 and particle size of 60 to 200 mesh produced by suspension polymerization in varying proportions; Furthermore, six types of plummer resins were prepared by mixing these with epoxy resin (Evacrat No. 3250 manufactured by Kansai Paint Co., Ltd.) as shown in Table 1. As Comparative Example 1, a primer resin containing only a mixture of vinylidene fluoride resin and epoxy resin was prepared. Next, seven iron plates were preheated using a heating furnace at 250°C, and then the primer resin was powder-coated by a powder spraying method, and then placed in the heating furnace again to be tightly fused. This operation was repeated twice to obtain a primer resin layer with a thickness of 0.4 mm. Next, vinylidene fluoride resin powder containing a crystal nucleating agent is overcoated three times using a heating furnace at 250°C to obtain an overcoat layer with a thickness of 0.6 mm. completed the ing. Table 1 shows the results of measuring the peel strength of the coated surfaces of the seven iron plates by making cuts with a width of 10 mm reaching the iron surface using a knife and immersing them in hot water at 50°C.

[Table] Peel strength is measured by cutting cuts that reach the iron surface of the coating on the material at approximately 10 mm intervals.
Insert two pieces into a 100mm length, with a membrane of about 30mm at one end of the 10mm width.
was peeled off from the material with a knife, held between clips, the clips were fixed on a spring scale, and the film was peeled off at 90°C. The stress at the time of peeling was measured and determined as peel strength (Kg/cm). As can be seen from Table 1, the adhesion of the coating material of the present invention was superior to that of the comparative example even after 30 days of immersion in hot water. Example 7-8 Instead of the graft copolymer in Examples 2 and 4, a saponified ethylene-vinyl acetate copolymer was used as Dumilan D-229 (trade name, manufactured by Mitsui Polychemical Co., Ltd.).
An iron plate was coated using the same method and operation as in Example 1, except that . A similar test was conducted, and the strength of peel change over time is shown in Table 2.

[Table] As is clear from the table, excellent results were obtained. Example 9 A composition obtained by adding 17.5 parts by weight of silica sand having a particle size of 150 to 325 mesh to the formulation of Example 2 (vinylidene fluoride resin 50, graft copolymer 50, epoxy resin 5, silica sand 17.5, numbers are parts by weight). ) was used as a primer resin to coat an iron plate in the same manner as in Example 2 to obtain a coating material. The peel strength was examined using the same test method as in Example 2, and the results were 8 Kg/cm before immersion and 6 Kg/cm ³ after 30 days of immersion in 50°C warm water.
There was little deterioration over time. Example 10 As the vinylidene fluoride resin, a copolymer of 95% by weight of vinylidene fluoride and 5% by weight of trifluoromonoethylene chloride with η _ioh = 1.05 and a particle size of 60 to 250 mesh was used as the vinylidene fluoride resin of Example 2. An iron plate was undercoated in the same manner as in Example 2, except that the resin was used in place of the resin and the temperature of the heating furnace was 240°C. This vinylidene fluoride copolymer resin was also used for the overcoat to a thickness of 0.5 mm. As a result of conducting the same test as in Example 2, the peel strength before immersion was 8 kg/cm, and the peel strength after 30 days immersion in 50° C. hot water was 7 kg/cm. When only a mixture of 100 parts by weight of vinylidene fluoride copolymer and 5 parts by weight of epoxy resin was undercoated, the adhesive strength was 10 kg/cm or more before dipping, but the adhesive strength was lost within 2 days after dipping. . Example 11 Covering materials were manufactured using different base materials. In Example 2, the iron plate was SUS316L,
Powder coating was carried out in the same manner as in Example 2, except that SUS304, aluminum, titanium, and ceramics were each used with a 10 mm square and a thickness of 3 mm, and the peel strength was measured in the same manner. The results are shown in Table 3. Table 3 also shows the results of powder coating with only vinylidene fluoride resin to a thickness of 1 mm without undercoating.

[Table] As is clear from the table, the present invention obtained excellent results for each material. Example 12 Sandblasted and desalted curvature radius 6.5
mm material SS-41 equilateral angle steel 50×50×4×200L
(Radius 6.5 mm) Powder coating of vinylidene fluoride resin was applied to the entire surface of the two pieces. A coating material was obtained in the same manner as in Example 2 using the primer resin of Example 2. One piece of this coated iron equilateral angle shape steel was immersed in hot water at 50℃, and after 3 months,
When the condition of the inner R part (corner part) was observed, no peeling of the coating film on the inner R part was observed. In addition, for the other piece, cuts reaching the iron surface were made at positions 10 mm on both sides from the center line of the inner radius, and an accelerated test for peeling was performed by immersing it in 50°C warm water.
Even after several months, no peeling of the inner R coating film was observed. Comparative Example 2 Two pieces of SS41 equilateral angle steel as in Example 12 were used, and η _ioh = 1.00 grain size 60-200 was used as the undercoat.
A powder obtained by mixing 100 parts by weight of a mesh vinylidene fluoride resin crystal nucleating agent-containing powder with 35 parts by weight of silica powder having a mesh size of 60 or less was used. Using a heating furnace at 250°C, undercoat both sides of the equilateral angle shape steel to a thickness of 0.4 mm, then apply vinylidene fluoride resin powder containing a crystal nucleating agent to 0.6 mm using a heating furnace at 250°C. The entire surface was coated to a thickness of 1.0 mm. When the inner R part was observed using the same test method as in Example 12, peeling was observed on the 5th day. In addition, in an accelerated test in which cuts reaching the steel surface were made at positions 10 mm on both sides from the center line of the inner radius, the coating film on the inner radius peeled off on the first day.

Claims (1)

[Scope of Claims] 1 Partially saponified product of ethylene-vinyl acetate copolymer (), said saponified product () applied to a base material by powder coating method
A resin selected from the group consisting of a polymer obtained by graft polymerizing with an unsaturated carboxylic acid (), a mixture of the saponified product () and a vinylidene fluoride resin, and a mixture of the polymer () and a vinylidene fluoride resin A vinylidene fluoride resin coating material obtained by undercoating a primer resin and then overcoating a vinylidene fluoride resin. 2. The resin coating material according to claim 1, wherein the vinylidene fluoride resin in the mixture of the saponified product () or the polymer () and the vinylidene fluoride resin is 80% by weight or less. 3. The resin coating material according to claim 1 or 2, wherein the primer resin contains an epoxy compound.