JP2009242711A - Coating composition - Google Patents

Abstract

Disclosed is a coating composition that achieves uniform coating even when a powder coating is used as a top coating, and can suppress pinholes in the top coating.
SOLUTION: A fluorine-containing polymer, a heat-resistant resin and a water-soluble inorganic salt are included, and the fluorine-containing polymer includes polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer and tetrafluoroethylene / perfluoro (alkyl vinyl ether). ) It is at least one selected from the group consisting of copolymers and has an average particle diameter of 0.01 to 5 μm, and the heat-resistant resin has an average particle diameter of 0.1 to 10.0 μm and is heat resistant. The solid content mass ratio of the resin to the fluoropolymer is 15:85 to 50:50, and the water-soluble inorganic salt is 0.0001 to 10 mass% with respect to the total solid content of the fluoropolymer and the heat-resistant resin. A coating composition characterized by the above.
[Selection figure] None

Description

The present invention relates to a coating composition.

Fluoropolymers such as polytetrafluoroethylene [PTFE] are excellent in properties such as heat resistance and electrical insulation, the molded product has a low coefficient of friction, and is excellent in non-adhesiveness. This surface property exhibits chemical resistance, water / oil repellency, releasability, slidability, and the like.

Since the fluoropolymer has such properties, for example, it is prepared as a coating composition, and is applied to an object to be coated to provide a coating film made of the fluoropolymer, thereby separating the mold. Wide range of applications in fields such as mold materials, office automation (OA) equipment rolls, household items such as irons, kitchen utensils such as frying pans and hot plates, food industry, electrical industry, and machine industry.

On the other hand, the fluoropolymer has a problem of poor adhesion to an object to be coated due to its non-adhesiveness. For the purpose of improving the adhesion, a primer containing a binder resin such as a heat-resistant resin and a fluorine-containing polymer is preliminarily coated on an object to be coated as an undercoat.

As an aqueous primer containing a fluoropolymer and a heat-resistant resin, a coating composition containing a fluoropolymer, colloidal silica, a specific polyamic acid and a liquid carrier (see, for example, Patent Document 1), polyethersulfone. , Polyamideimide and / or polyimide, and PTFE or other fluororesin having a specific content ratio (see, for example, Patent Document 2), heat-resistant resin, fluoropolymer, and specific amount of non-alkylphenol nonionic interface Examples thereof include a coating composition comprising an aqueous dispersion containing an activator (for example, see Patent Document 3).

However, when a powder coating material is applied onto an undercoat film formed from these aqueous primers, there is a problem that uniform application is difficult due to electrostatic repulsion between powders, and pinholes are generated in the coating film.

JP 52-14630 A International Publication No. 99/64523 Pamphlet JP 2004-204073 A

In view of the above situation, an object of the present invention is to provide a coating composition that can suppress pinholes in a top coat even when a powder paint is used as a top coat.

The present invention includes a fluorine-containing polymer, a heat-resistant resin, and a water-soluble inorganic salt. The fluorine-containing polymer includes polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer, and tetrafluoroethylene / perfluoro. It is at least one selected from the group consisting of (alkyl vinyl ether) copolymers, has an average particle size of 0.01 to 5 μm, and the heat resistant resin has an average particle size of 0.1 to 10.0 μm. The solid content mass ratio of the heat-resistant resin and the fluoropolymer is 15:85 to 50:50, and the water-soluble inorganic salt is added to the total solid content of the heat-resistant resin and the fluoropolymer. The coating composition is characterized by being 0.0001 to 10% by mass with respect to the coating composition.

The present invention is a coated article obtained by painting the coating composition.

The present invention is described in detail below.

The coating composition of the present invention contains a fluoropolymer, a heat resistant resin, and a water-soluble inorganic salt.

(Water-soluble inorganic salt)
Since the coating composition of the present invention contains a water-soluble inorganic salt, it is possible to prevent electrostatic repulsion of the overcoat powder coating and to obtain a coating film without pinholes.

The powder coating is generally applied by electrostatic coating on the primer coating. In electrostatic coating, the powder particles are opposite to the base material and the primer coating, and adhere to the primer coating. Therefore, the higher the applied voltage, the better the adhesion to the primer coating. When the conductivity of the primer coating is low, the particles are difficult to adhere, and the influence of electrostatic repulsion between the particles becomes relatively large and pinholes are easily generated.

The water-soluble inorganic salt is considered to play a role of imparting conductivity to the coating film formed from the coating composition of the present invention. Therefore, when the coating composition of the present invention is used as a primer, the primer coating film formed has excellent conductivity, and therefore pinholes are not easily generated in the top coating film formed from the powder coating.

The water-soluble inorganic salt is preferably an inorganic metal salt or an inorganic ammonium salt.

Examples of the inorganic metal salt include metal chloride, metal bromide, metal sulfate, metal chromate, and the like, and more specifically, sodium chloride, potassium chloride, potassium sulfate, magnesium chloride, and the like. . Examples of the inorganic ammonium salt include ammonium chloride and ammonium sulfate.

The said water-soluble inorganic salt is 0.0001-10 mass% with respect to the total solid of a fluorine-containing polymer and a heat resistant resin. If it is less than 0.0001% by mass, the effect of adding a water-soluble inorganic salt cannot be obtained, and if it exceeds 10% by mass, the corrosion resistance of the coating film may be reduced, or the effect corresponding to the content may not be obtained. .

The above “total solid content of fluoropolymer and heat-resistant resin” is obtained as the mass of the residue after the coating composition is dried at a temperature of 80 to 100 ° C. and baked at 380 to 400 ° C. for 45 minutes. is there.

(Fluoropolymer)
Since the coating composition of the present invention contains a fluoropolymer, in addition to being excellent in heat resistance and strength, when a top coat film is formed by coating a paint containing a fluororesin, A coating film excellent in adhesion with the top coating film can be obtained.

The fluoropolymers include polytetrafluoroethylene [PTFE], tetrafluoroethylene [TFE] / hexafluoropropylene [HFP] copolymer [FEP] and TFE / perfluoro (alkyl vinyl ether) [PAVE] copolymer [ At least one selected from the group consisting of PFA].

The PTFE may be a TFE homopolymer or a modified polytetrafluoroethylene [modified PTFE] as long as it is non-melt processable.

In the present specification, the non-melt processability means a property in which the melt flow cannot be measured at a temperature higher than the crystallization melting point in accordance with ASTM D-1238 and D-2116.

The modified PTFE is a copolymer of TFE and a small amount of monomer copolymerizable with TFE and cannot be melt-molded. Examples of the trace amount of monomer include fluoroolefin, fluorinated (alkyl vinyl ether), cyclic fluorinated monomer, and perfluoroalkylethylene.

Examples of the fluoroolefin include perfluoroolefins such as HFP.

Examples of the fluorinated (alkyl vinyl ether) include PAVE. Examples of the PAVE include perfluoro (methyl vinyl ether) [PMVE], perfluoro (ethyl vinyl ether) [PEVE], and perfluoro (propyl vinyl ether). [PPVE] and the like.

The trace monomer unit derived from the trace monomer is preferably 0.001 to 2% by mass, and 0.01 to 1% by mass of the total monomer units constituting the modified PTFE. Is more preferable.

In the present specification, the “monomer unit” such as the above-mentioned trace monomer unit is a part of the molecular structure of the fluorine-containing polymer and means a part derived from the corresponding monomer. The trace monomer unit derived from the trace monomer is a value obtained by performing an infrared absorption spectrum measurement on a fine powder obtained by coagulating, washing and drying the PTFE aqueous dispersion.

In the FEP, the HFP unit is more than 2% by mass, preferably 20% by mass or less, and more preferably 10 to 15% by mass.

As PAVE in said PFA, what has a C1-C6 alkyl group is preferable, and PMVE, PEVE, or PPVE is more preferable. The PFA has a PAVE unit of more than 2% by mass and preferably 5% by mass or less, and more preferably 2.5 to 4.0% by mass.

The HFP and PFA may be those obtained by polymerizing other monomers as long as they have the above-described composition. As said other monomer, when it is said FEP, PAVE is further mentioned, and when it is said PFA, HFP is further mentioned. The said other monomer can use 1 type (s) or 2 or more types.

Although the said other monomer changes with kinds, normally it is preferable that it is 1 mass% or less of the mass of a fluoropolymer. A more preferred upper limit is 0.5% by mass, and a still more preferred upper limit is 0.3% by mass.

The coating composition of the present invention may contain two or more fluoropolymers. That is, as the fluoropolymer, PTFE and PFA may be contained, PTFE and FEP may be contained, or PTFE, PFA and FEP may be contained.

The fluoropolymer is preferably PTFE, FEP, or a mixture of PTFE and FEP. Among these, PTFE is more preferable for heat resistance and economical reasons.

The fluoropolymer has an average particle size of 0.01 to 5 μm. If it is less than 0.01 μm, the mechanical stability of the particles comprising the fluoropolymer is poor, and the resulting coating composition may be inferior in mechanical stability and storage stability. If it exceeds 5 μm, the particles made of the fluoropolymer lack uniform dispersibility, and when coated with the resulting coating composition, a coating film with a smooth surface may not be obtained and the coating film properties may be inferior. is there. A more preferable upper limit is 0.5 μm, and a more preferable lower limit is 0.05 μm.

The mechanical stability is a property that hardly produces aggregates that cannot be redispersed even when strong stirring or shearing force is applied by a homogenizer or the like during liquid feeding and redispersion.

In this specification, the average particle diameter of the fluoropolymer is measured by observation with a transmission electron microscope.

(Heat resistant resin)
Since the coating composition of the present invention contains a heat-resistant resin, it is possible to obtain a coating film that is excellent in adhesion to an object to be coated and further has good corrosion resistance and water vapor resistance.

The heat resistant resin exhibits heat resistance at a temperature of 150 ° C. or higher. The heat-resistant resin generally has a molecular structure or a functional group that exhibits adhesion to the object to be coated, such as an amide bond or an imide bond, and thus exhibits adhesion to the object to be coated.

In the coating composition of the present invention, the fluoropolymer and the heat-resistant resin have a difference in surface tension. Therefore, the fluoropolymer floats when fired, so that the fluoropolymer is mainly disposed on the coating surface side. A coating film in which a heat-resistant resin is mainly disposed on the object side is formed.

Examples of the heat resistant resin include polyamideimide resin [PAI], polyimide resin [PI], polyethersulfone resin [PES], polyetherimide resin, polyetheretherketone resin, aromatic polyester resin, and polyphenylene sulfide [PPS]. And polyarylene sulfide resins represented by The coating composition of the present invention may contain one type of heat-resistant resin, or may contain two or more types.

The PAI is a resin made of a polymer having an amide bond and an imide bond in the molecular structure. The PAI is not particularly limited. For example, a reaction between an aromatic diamine having an amide bond in the molecule and an aromatic tetravalent carboxylic acid such as pyromellitic acid; an aromatic trivalent carboxylic acid such as trimellitic anhydride; It consists of a high molecular weight polymer obtained by a reaction with a diamine such as 4,4-diaminophenyl ether or a diisocyanate such as diphenylmethane diisocyanate; a reaction between a dibasic acid having an aromatic imide ring in the molecule and a diamine. Examples thereof include resins. As said PAI, what consists of a polymer which has an aromatic ring in a principal chain from the point which is excellent in heat resistance is preferable.

The PI is a resin made of a polymer having an imide bond in the molecular structure. The PI is not particularly limited, and examples thereof include a resin made of a high molecular weight polymer obtained by a reaction of an aromatic tetravalent carboxylic anhydride such as pyromellitic anhydride. As said PI, what consists of a polymer which has an aromatic ring in a principal chain from the point which is excellent in heat resistance is preferable.

The PES has the following formula:

It is resin which consists of a polymer which has a repeating unit represented by these.

The PES is not particularly limited, and examples thereof include a resin made of a polymer obtained by polycondensation of dichlorodiphenyl sulfone and bisphenol.

The heat-resistant resin is at least one selected from the group consisting of PAI and PI in that it can improve the adhesion to an object to be coated and can maintain this adhesion even at high temperatures. It is preferable.

The heat-resistant resin is selected from the group consisting of PES, PAI, and PI in that it has excellent adhesion to an object to be coated, has sufficient heat resistance, and has excellent corrosion resistance and water vapor resistance. More preferably, it is at least one kind. The heat resistant resin is more preferably a mixture of PES and PAI.

In the coating composition of the present invention, when PES and at least one selected from the group consisting of PAI and PI are contained as the heat-resistant resin, the solid content mass ratio of the PES to PAI and PAI is 85: It is preferable that it is 15-65: 35. If the PES is less than 65% by mass, the water vapor resistance of the coating film obtained from the coating composition may be reduced, and if it exceeds 85% by mass, the corrosion resistance of the coating film may be reduced.

The heat-resistant resin has an average particle size of 0.1 to 10 μm. When the average particle diameter of the heat resistant resin is within the above range, the resulting coating film has good corrosion resistance.

In the present specification, the average particle diameter of the heat-resistant resin is measured using an ultracentrifugal automatic particle size distribution measuring apparatus CAPA-700 manufactured by Horiba, Ltd.

In the coating composition of the present invention, the solid content mass ratio between the fluoropolymer and the heat-resistant resin is heat-resistant resin: fluoropolymer = 15: 85 to 50:50. If the heat-resistant resin is less than 15% by mass of the total solid content of the fluoropolymer and the heat-resistant resin, the heat-resistant resin is small, so that the adhesion between the resulting coating film and the object to be coated is insufficient. It becomes. If it exceeds 50% by mass, the amount of the fluoropolymer is small, so that the adhesion between the coating film and the top coating film becomes insufficient.

The solid content mass ratio is preferably heat-resistant resin: fluorinated polymer = 15: 85 to 40:60, and more preferably heat-resistant resin: fluorinated polymer = 20: 80 to 30:70.

The solid content mass ratio is calculated from the amounts of the fluoropolymer and heat-resistant resin blended at the time of preparation.

(Nonionic surfactant)
The coating composition of the present invention may contain a nonionic surfactant. In the present specification, the nonionic surfactant does not contain fluorine.

The nonionic surfactant preferably has an HLB value of 11 or less. When the HLB value of the nonionic surfactant is 11 or less, the mechanical stability, the wettability to an object to be coated, and the wettability of the top-coated fluororesin paint are excellent. Moreover, when HLB exists in the said range, it will become possible to reduce content of the fluorine-containing surfactant mentioned later.

In the present specification, the “HLB value” is calculated based on the Griffin calculation method. The HLB value is a unique value based on the molecular structure of the surfactant and is an index of the balance between the hydrophilicity and hydrophobicity of the surfactant. Generally, the higher the hydrophilicity, the larger the value and the higher the hydrophobicity. The smaller the value.

When the HLB value exceeds 11, the nonionic surfactant tends to agglomerate particles made of the fluoropolymer, resulting in insufficient mechanical stability of the resulting coating composition, and the resulting coating composition. When a top coat made of a fluorine-containing polymer is applied after coating the material to be coated and dried, repelling is likely to occur.

If the said HLB value is in the said range, it is more preferable that it is 5 or more at the point which does not deteriorate the dispersibility of the coating composition obtained. A more preferable lower limit of the HLB value is 7, and a particularly preferable lower limit is 9.

The nonionic surfactant is preferably a nonionic surfactant that does not have a molecular structure portion derived from alkylphenol in the molecular structure.

Examples of the nonionic surfactant include the following general formula (I):
R-O-A-H (I)
(In the formula, R is a linear or branched C8-19 saturated or unsaturated acyclic aliphatic hydrocarbon group or a C8-19 saturated cyclic aliphatic hydrocarbon. A represents a group and represents a polyoxyalkylene chain having 3 to 25 oxyethylene groups and 0 to 5 oxypropylene groups.

In the present specification, the carbon number of R, the number of oxyethylene groups, and the number of oxypropylene groups in the general formula (I) are the average of values in each molecule of the nonionic surfactant.

The acyclic aliphatic hydrocarbon group is an aliphatic hydrocarbon group having no cyclic structure. The saturated cycloaliphatic hydrocarbon group is an aliphatic hydrocarbon group having a saturated cyclic structure. The saturated cyclic aliphatic hydrocarbon group may have one or two or more saturated cyclic structures as long as the total number of carbon atoms is 8 to 19. In the saturated cyclic aliphatic hydrocarbon group, if the total number of carbon atoms including substituents is 8 to 19, the hydrogen atom bonded to the carbon atom of the saturated cyclic structure is linear or branched. It may be substituted with an alkyl group, and one or two or more hydrogen atoms may be substituted.

The above R in the general formula (I) is excellent in the dispersibility of particles made of a fluoropolymer, and the coating composition obtained is excellent in mechanical stability and storage stability. 16, a more preferred upper limit is 14, and a preferred lower limit is 10. R preferably has 13 carbon atoms. R is particularly preferably a saturated acyclic aliphatic hydrocarbon group having 13 carbon atoms, and examples thereof include a tridecyl group and an isotridecyl group.

Regarding A in the above general formula (I), if the number of oxypropylene groups exceeds 5, the solubility of the non-alkylphenol type nonionic surfactant is reduced, so that the dispersibility of the particles made of the fluoropolymer is lowered, The mechanical stability and storage stability of the coating composition may be poor. The smaller the number of oxypropylene groups, the better. The preferred upper limit is three. More preferably, the oxypropylene group is not present in the polyoxyalkylene chain.

Although the number of oxyethylene groups in the polyoxyalkylene chain depends on the number of carbon atoms of R, a preferred upper limit is 7 and a more preferred upper limit is 6.

The polyoxyalkylene chain preferably has 3 to 7 oxyethylene groups, 0 to 3 oxypropylene groups, 3 to 6 oxyethylene groups, and oxypropylene groups. It is more preferable that no is present.

In the bond of —O— in the above general formula (I) and the polyoxyalkylene chain of A in the above general formula (I), the carbon atom in the polyoxyalkylene chain is adjacent to —O— in the above general formula (I). For example, when the oxyethylene group in the polyoxyalkylene chain and -O- are bonded, the -O- and the adjacent oxyethylene group are -O- (CH ₂ CH ₂ O) — is bonded in an orientation represented by —.

In the coating composition of the present invention, one or more nonionic surfactants can be used as the nonionic surfactant. In this case, the HLB value can be calculated from the HLB value of each nonionic surfactant and the mixing ratio.

In the coating composition of the present invention, the nonionic surfactant is preferably 0.1 to 10% by mass with respect to the total solid content of the fluoropolymer and the heat-resistant resin. When the nonionic surfactant is less than 0.1% by mass with respect to the total solid content, particles of the fluoropolymer are likely to settle in the resulting composition, and the storage stability is poor. If it exceeds 10% by mass, the resulting composition will increase in viscosity and the coating workability will deteriorate. A preferable upper limit is 7 mass%, and a more preferable upper limit is 5 mass%.

The above “total solid content of fluoropolymer and heat-resistant resin” is obtained as the mass of the residue after the coating composition is dried at a temperature of 80 to 100 ° C. and baked at 380 to 400 ° C. for 45 minutes. is there.

(Fluorine-containing surfactant)
In the coating composition of the present invention, the fluorine-containing surfactant may be less than 500 ppm based on the fluorine-containing polymer.

The coating composition is excellent in mechanical stability and wettability to an object to be coated even when the fluorine-containing surfactant is less than 500 ppm based on the solid content mass of the fluorine-containing polymer.

The fluorine-containing surfactant is a compound having a fluorine atom and exhibiting surface activity. Examples of the fluorine-containing surfactant include perfluorocarboxylic acid or a salt thereof, perfluorosulfonic acid or a salt thereof, and among them, perfluorocarboxylic acid or a salt thereof is preferable. Examples of the perfluorocarboxylic acid include perfluoroalkyl carboxylic acids such as perfluorooctanoic acid.

The fluorosurfactant is preferably 200 ppm or less, and more preferably 100 ppm or less, based on the solid content mass of the fluoropolymer, for the purpose of recovery and the like.

In the present specification, the content of the above-mentioned fluorine-containing surfactant is determined by performing high-performance liquid chromatography (HPLC) under the following conditions after Soxhlet extraction is performed by adding an equal amount of methanol to the obtained coating composition. It was obtained by doing. A calibration curve obtained by HPLC measurement of the fluorine-containing surfactant concentration under the above eluate and conditions was used.

(Measurement condition)
Column; ODS-120T (4.6φ × 250 mm, manufactured by Tosoh Corporation)
Developing solution: acetonitrile / 0.6 mass% perchloric acid aqueous solution = 1/1 (vol / vol%)
Sample volume: 20 μL
Flow rate: 1.0 ml / min Detection wavelength: UV 210 nm
Column temperature: 40 ° C

The coating composition of the present invention may contain other resins as necessary. By blending the above-mentioned other resins, the film forming property, corrosion resistance, etc. of the coating film obtained from the coating composition can be improved.

The other resin is not particularly limited, and examples thereof include phenol resin, urea resin, epoxy resin, urethane resin, melamine resin, polyester resin, polyether resin, acrylic resin, acrylic silicone resin, silicone resin, and silicone polyester resin. Can be mentioned.

The coating composition of the present invention is used for a more general coating composition within the range of not impairing the characteristics of the present invention for the purpose of improving the properties of the coating film and the properties of the coating film obtained from the coating composition. It may be formed by blending additives.

The additive is not particularly limited and can be selected according to the use of the resulting coated article. For example, a leveling agent, solid lubricant, wood powder, quartz sand, carbon black, diamond, tourmaline, germanium, alumina , Silicon nitride, fluorite, clay, talc, extender pigments, various fillers, conductive fillers, glittering materials, pigments, fillers, pigment dispersants, anti-settling agents, moisture absorbers, surface conditioners, thixotropic agents , Viscosity modifier, anti-gelling agent, UV absorber, light stabilizer, plasticizer, anti-coloring agent, anti-skinning agent, anti-scratch agent, anti-mold agent, anti-bacterial agent, antioxidant, anti-static agent And silane coupling agents.

Examples of the bright material include mica, metal powder, glass beads, glass bubbles, glass flakes, and glass fibers.

The metal powder is not particularly limited, and examples thereof include powders of simple metals such as aluminum, iron, tin, zinc, gold, silver, and copper; powders of alloys such as aluminum alloy and stainless steel. It does not specifically limit as a shape of the said metal powder, For example, particle shape, flake shape, etc. are mentioned. When the coating composition of the present invention contains such a bright material, a coating film having an excellent appearance can be formed. The content of the glittering material is preferably 0.1 to 10.0% by mass with respect to the solid content of the coating composition.

Examples of the viscosity modifier include methyl cellulose and alumina sol.

The coating composition of the present invention preferably has a viscosity at 25 ° C. of 0.1 to 50000 mPa · s. If the viscosity is less than 0.1 mPa · s, sagging or the like is likely to occur during application on the object to be coated, and it may be difficult to obtain the desired film thickness. The workability may be deteriorated, the film thickness of the obtained coating film may not be uniform, and the surface smoothness and the like may be inferior. A more preferred lower limit is 1 mPa · s, and a more preferred upper limit is 30000 mPa · s. The said viscosity is a value obtained by measuring using a BM type single cylinder type rotational viscometer (made by Tokyo Keiki Co., Ltd.).

The coating composition of the present invention includes, for example, (1) after preparing a fluoropolymer aqueous dispersion, and (2) a heat-resistant resin and a water-soluble inorganic salt, and if necessary, a nonionic interface. It can be obtained by adding an activator, an aqueous medium, an additive and the like.

The aqueous medium is not particularly limited as long as it contains water, and examples thereof include a mixture of water and an organic solvent, water and the like. Examples of the organic solvent include N-methyl-2-pyrrolidone [NMP] and N, N-dimethylacetamide. The aqueous medium is preferably a mixture of water and an organic solvent.

In the step (1), after obtaining an aqueous dispersion containing a fluorine-containing polymer by a conventionally known method such as emulsion polymerization or suspension polymerization, an operation of removing the fluorine-containing surfactant from the aqueous dispersion. Fluoropolymer aqueous dispersion may be prepared by carrying out the process.

The operation for removing the fluorine-containing surfactant is not particularly limited, and examples thereof include a conventionally known operation such as an operation for contacting an anion exchange resin and a phase separation concentration by adding a nonionic surfactant. In these operations, the above-mentioned nonionic surfactant may be added as necessary for the purpose of stabilizing the resulting fluoropolymer aqueous dispersion.

In the fluoropolymer aqueous dispersion, the content of the fluoropolymer is preferably 35 to 70% by mass. A more preferable lower limit is 40% by mass, and a more preferable upper limit is 65% by mass.

The content of the fluoropolymer in the fluoropolymer aqueous dispersion is such that when the aqueous dispersion 1 g is dried in a blow dryer at 100 ° C. for 1 hour, further 300 ° C. for 1 hour, The ratio of the mass of the heating residue to the mass of the dispersion (1 g) is expressed as a percentage.

In the fluoropolymer aqueous dispersion, the fluorosurfactant may be 500 ppm or less based on the solid content mass of the fluoropolymer. The fluorine-containing surfactant may be 200 ppm or less or 100 ppm or less based on the solid content mass of the fluorine-containing polymer.

The content of the fluorosurfactant in the fluoropolymer aqueous dispersion was determined by high-performance liquid chromatography after Soxhlet extraction after adding an equal amount of methanol to the obtained fluoropolymer aqueous dispersion ( HPLC) can be determined by performing the following conditions. A calibration curve obtained by HPLC measurement of the fluorine-containing surfactant concentration under the above eluate and conditions was used.

(Measurement condition)
Column; ODS-120T (4.6φ × 250 mm, manufactured by Tosoh Corporation)
Developing solution: acetonitrile / 0.6 mass% perchloric acid aqueous solution = 1/1 (vol / vol%)
Sample volume: 20 μL
Flow rate: 1.0 ml / min Detection wavelength: UV 210 nm
Column temperature: 40 ° C

In the fluoropolymer aqueous dispersion, the nonionic surfactant is preferably 1 to 9% by mass based on the solid content of the fluoropolymer. A more preferable lower limit is 3% by mass, and a more preferable upper limit is 7% by mass.

The content (N) of the nonionic surfactant in the aqueous fluoropolymer dispersion was about 1 g (Xg) of the sample taken in an aluminum cup having a diameter of 5 cm and heated at 100 ° C. for 1 hour (Yg). Furthermore, the obtained heating residue (Yg) was calculated from the formula: N = [(Y−Z) / Z] × 100 (%) from the heating residue (Zg) heated at 300 ° C. for 1 hour. Is.

In the step (2), a heat-resistant resin and a water-soluble inorganic salt, and if necessary, a nonionic surfactant, an aqueous medium, an additive and the like are added to the aqueous dispersion obtained in the step (1). The above heat-resistant resin may be blended in advance into the above-mentioned fluoropolymer aqueous dispersion as an aqueous dispersion containing a heat-resistant resin.

In the step (2), other resins and additives may be added as necessary.

In the coating composition of the present invention, the fluorine-containing polymer has a solid content of 35 to 70% by mass, and the nonionic surfactant is 1 to 9% by mass with respect to the solid content of the fluorine-containing polymer. It is preferable to be obtained by adding a heat-resistant resin to the combined aqueous dispersion.

The coating composition of this invention can form a coating film on the said to-be-coated object by applying to a to-be-coated object. In the present specification, the term “coating” for the coating composition means a process comprising applying the coating composition, drying it if necessary, and then baking it.

The coating composition of the present invention can be, for example, a primer composition. When the said composition for coating | cover is used as a primer composition, in addition to adhesiveness with to-be-coated material, it can form a coating film with favorable adhesiveness with top coat film.

In the case where the coating composition of the present invention is used as a primer composition, a paint containing a fluororesin is preferable as the top coating to be applied onto the resulting coating film. In this case, the coating film is excellent between the top coating film because the fluoropolymer oriented on the coating film surface side as described above exhibits affinity with the fluoropolymer in the top coating film. Show good adhesion.

The coating film obtained from the coating composition of the present invention is formed by applying the coating composition on an object to be coated and drying it to obtain a coating film, followed by baking as necessary. Can do.

The material to be coated is not particularly limited, and examples thereof include simple metals such as iron, aluminum, and copper and metals such as alloys thereof; nonmetallic inorganic materials such as enamel, glass, and ceramics. Examples of the alloys include stainless steel.

The object to be coated is subjected to a surface treatment such as a degreasing treatment or a surface roughening treatment in advance in that the coating composition can be uniformly applied and the adhesion with the object to be coated is improved. It is preferable. The surface roughening treatment method is not particularly limited, and examples thereof include chemical etching with acid or alkali, anodization (alumite treatment), and sandblasting.

The application method is not particularly limited, and examples thereof include spray coating, roll coating, doctor blade coating, dip (immersion) coating, impregnation coating, spin flow coating, and curtain flow coating.

Although the said drying can be performed by a conventionally well-known method, it is preferable to carry out for 5 to 60 minutes at the temperature of 60-200 degreeC.

The coating film is usually not fired before the top coating is applied, but may be fired as necessary. It is preferable not to perform the baking before applying the top coating because it can simplify the process and reduce energy, labor, time, and the like.

The top coating film can be formed, for example, by applying a top coating material on the coating film or the coating film, and then baking.

The fluorine-containing polymer in the top coating is not particularly limited, and examples thereof include PTFE, PFA, FEP and the like. From the viewpoint of improving the interlayer adhesion between the coating and the top coating, the coating of the present invention. The same as the above-mentioned fluoropolymer in the composition for use, or those having similar properties such as the presence or absence of melt processability are preferred.

Examples of the top coating include a PTFE paint whose main component is PTFE, a PFA paint whose main component is PFA, an FEP paint whose main component is FEP, and the like.

The top coating composition may be formed by blending additives similar to various additives that can be used in the coating composition described above for the purpose of improving coating properties and properties of the resulting coating film. .

When the main component is PFA or FEP, the top coating material can be a powder coating material.

Examples of the method for applying the top coating include, in the case of a powder coating, electrostatic spray coating, fluidized dip coating, and a rolining method.

Firing after applying the top coating can be performed under the same conditions as firing performed after applying and drying the coating composition described above.

Each film thickness of the coating film obtained from the coating composition of the present invention and the top coating film is not particularly limited, but the film thickness of the coating film is 1 to 100 μm, and the film thickness of the top coating film is 10. It is preferable that it is -200 micrometers.

The application of the coating composition of the present invention is not particularly limited. For example, it can be applied as a coating material for products that require heat resistance, non-adhesiveness, slipperiness, and the like on the surface of the substrate.

Such applications include, for example, cooking utensils such as frying pans, grill pans, pressure cookers, various other pans, rice cookers, rice bowls, ovens, hot plates, baking molds, kitchen knives, gas tables; electric pots, ice trays Food industry containers such as kneading rolls, rolling rolls, conveyor hoppers, etc .; industries such as rolls for office automation equipment [OA], belts for OA, separation nails for OA, papermaking rolls, calendar rolls for film production, etc. Articles: Molds for foamed polystyrene molding, mold release such as release plates for plywood / decorative board production; kitchen supplies such as range hoods; frozen food production equipment such as conveyor belts; tools such as saws and files; Household items such as irons and irons; metal foils; sliding bearings for food processing machines, packaging machines, textile machines, etc .; sliding parts for cameras and watches; automobile parts And the like.

The coated article obtained by applying the coating composition exemplified above is also one aspect of the present invention.

Since the coating composition of the present invention has the above-described configuration, it is possible to prevent electrostatic repulsion of the overcoat powder coating and to obtain a coating film without pinholes.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. Hereinafter, “%” and “part” represent mass% and mass part, respectively.

In each example and comparative example, each physical property was measured by the following method.

(1) Particle diameter of heat-resistant resin The particle diameter was measured with an ultracentrifugal automatic particle size distribution measuring apparatus CAPA-700 manufactured by Horiba, Ltd.

(2) Fluoropolymer concentration in fluoropolymer aqueous dispersion The fluoropolymer aqueous dispersion was dried at a temperature of 80 to 100 ° C and measured as a residue after baking at 380 to 400 ° C for 45 minutes. .

(3) The average particle size of the fluoropolymer was measured by observation with a transmission electron microscope.

(4) Concentration of non-fluorine-containing nonionic surfactant The content (N) of non-fluorine-containing nonionic surfactant was about 1 g (Xg) of a sample taken in a 5 cm diameter aluminum cup and heated at 100 ° C. for 1 hour. From the heating residue (Yg) and the heating residue (Zg) obtained by heating the obtained heating residue (Yg) at 300 ° C. for 1 hour, the formula: N = [(Y−Z) / Z] × 100 (%)

(5) Concentration of fluorinated surfactant An equivalent amount of methanol was added to the obtained coating composition to perform Soxhlet extraction, followed by high performance liquid chromatography (HPLC) under the following conditions. A calibration curve obtained by HPLC measurement of the fluorine-containing surfactant concentration under the above eluate and conditions was used.

(Measurement condition)
Column; ODS-120T (4.6φ × 250 mm, manufactured by Tosoh Corporation)
Developing solution: acetonitrile / 0.6 mass% perchloric acid aqueous solution = 1/1 (vol / vol%)
Sample volume: 20 μL
Flow rate: 1.0 ml / min Detection wavelength: UV 210 nm
Column temperature: 40 ° C

Production Example 1 Preparation of Polyethersulfone Resin Aqueous Dispersion 60 parts of a polyethersulfone resin [PES] having a number average molecular weight of about 24,000 and 60 parts of deionized water are placed in a ceramic ball mill until the particles made of PES are completely pulverized. Stir for about 10 minutes. Next, 180 parts of N-methyl-2-pyrrolidone [NMP] was added and further pulverized for 48 hours to obtain a dispersion. The obtained dispersion was further stirred by a sand mill for 1 hour to obtain a PES aqueous dispersion having a PES concentration of about 20%. The particle diameter of the particles composed of PES in the PES aqueous dispersion was 2 to 3 μm.

Production Example 2 Preparation of Polyamideimide Resin Aqueous Dispersion Polyamideimide resin [PAI] varnish (containing 71% NMP) having a solid content of 29% was poured into water to precipitate PAI. This was pulverized for 48 hours in a ball mill to obtain an aqueous PAI dispersion. In the obtained PAI aqueous dispersion, the solid content was about 20%, and the average particle diameter of the particles composed of PAI was about 2 μm.

Production Example 3 Preparation of Polytetrafluoroethylene [PTFE] Aqueous Dispersion (1) Capacity A 5 L reactor was charged with PTFE dispersion (PTFE content 25%, average particle size 0.24 μm, ammonium perfluorooctanoate [PFOA]. Content: An amount equivalent to 2000 ppm of PTFE) was added, and after adjusting the pH to 9 with a 10% aqueous ammonia solution, 125 g of a polyether nonionic surfactant (HLB value = 13) was added with stirring at 120 rpm. And uniformly mixed at 40 ° C. in a warm water bath. Subsequently, the temperature of the hot water tank was raised while stirring, and the internal temperature reached 70 ° C., then the stirring was stopped and held at the internal temperature of 70 ° C. for 6 hours. Then, the separated supernatant phase was removed, and the aqueous PTFE dispersion was removed. The phases were separated.

The obtained PTFE aqueous dispersion (concentrated aqueous dispersion) had a PTFE concentration of 70.5%, a fluorine-free surfactant content equivalent to 3.0% of PTFE, and a PFOA content of 932 ppm of PTFE. The amount was equivalent to

Ion exchange water was added to this aqueous dispersion to adjust the PTFE content to 60% and the fluorine-free surfactant content to an amount corresponding to 3.0% of PTFE.

(2) The obtained PTFE aqueous dispersion 2000 g was charged in a column (diameter 2 cm) packed with 50 ml of an anion exchange resin (product name: Amberlite IRA 402J, manufactured by Rohm and Haas) at a temperature of 50 ° C. and a space velocity [SV The fluoropolymer aqueous dispersion was obtained by passing the solution under the conditions of 2.

The obtained PTFE aqueous dispersion has an average particle diameter of PTFE of 0.24 μm, a solid content of 60%, and a polyether nonionic surfactant (HLB value = 13) as a dispersant with respect to 100 parts of the solid content of PTFE. 3 parts was contained, and the PFOA content was an amount corresponding to 90 ppm of PTFE.

Example 324 g of the PES aqueous dispersion obtained in Production Example 1 and 108 g of the PAI aqueous dispersion obtained in Production Example 2 were mixed, and the PTFE aqueous dispersion obtained in Production Example 3 (2) was mixed with this. 431 g was added, 0.67% of methylcellulose was added to the solid content mass of PTFE, and polyoxyethylene tridecyl ether (HLB value = 9) was added to be 5.0 parts with respect to 100 parts of PTFE solid content. Then, 3.45 parts of a 10% aqueous solution of ammonium sulfate was added, and the solid content of PTFE was 24.0%, the solid content of PES was 6%, the solid content of PAI was 2%, and ammonium sulfate was 0.1% based on the solid content. A coating composition having a PFOA of 90 ppm based on the solid content of PTFE was obtained.

About the obtained coating composition, the coating-film external appearance was observed in the following procedure.

(Preparation of evaluation paint plate)
The surface roughness Ra value measured according to JIS B 1982 after degreasing the surface of a 2.0 mm thick aluminum plate (A-1050F, size 10 cm × 20 cm) with acetone is 2.5 to 3.5 μm. Sandblasting was performed to obtain a rough surface. After removing dust on the surface by air blowing, the coating composition obtained was dried using a gravity type spray gun RG-2 (trade name, manufactured by Anest Iwata, nozzle diameter 1.0 mm). It apply | coated by spray coating with the spraying pressure 0.2MPa so that it might become 10-15 micrometers. The obtained coating film was dried at 80 to 100 ° C. for 15 minutes and cooled to room temperature. On top of the resulting coating film, PFA powder paint NEOFLON PFA ACX-31 (trade name, manufactured by Daikin Industries, Ltd.) was used as an overcoat paint, using an electrostatic powder coating machine EPG2007 manufactured by Wagner. The coating was applied at 1 MPa and an applied voltage of 70 kV, and baked at 380 ° C. for 20 minutes to produce a top coating film having a thickness of about 70 μm, thereby obtaining a coating plate for evaluation.

(Appearance of coating film)
The appearance of the evaluation coating plate after firing was visually observed, and the number of pinholes generated by electrostatic repulsion was examined. Ten pinholes were generated due to electrostatic repulsion of the overcoat powder coating.

Comparative Example A coating composition was prepared in the same manner as in Example, except that ammonium sulfate was not added. The solid content of PTFE was 24.0%, the solid content of PES was 6%, the solid content of PAI was 2%, and PFOA A coating composition of 90 ppm based on the solid content of PTFE was obtained.

Using the obtained coating composition, an evaluation coated plate was produced and evaluated in the same manner as in the Examples. Thirty pinholes were generated due to electrostatic repulsion of the overcoat powder coating.

From the results of Examples and Comparative Examples, it was found that the number of pinholes generated was drastically reduced when ammonium sulfate was added.

Since the coating composition of the present invention can prevent electrostatic repulsion of the powder coating of the top coat and can obtain a coating film without a pinhole, it can serve as a primer in coating a coating material on various products. It can be preferably used.

Claims (6)

Including a fluorine-containing polymer, a heat-resistant resin, and a water-soluble inorganic salt,
The fluoropolymer is at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer and tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, and The average particle size is 0.01-5 μm,
The heat-resistant resin has an average particle diameter of 0.1 to 10.0 μm,
The solid content mass ratio between the heat-resistant resin and the fluoropolymer is 15:85 to 50:50,
The said water-soluble inorganic salt is 0.0001-10 mass% with respect to the total solid of the said fluoropolymer and the said heat resistant resin, The coating composition characterized by the above-mentioned. The coating composition according to claim 1, wherein the heat resistant resin is at least one selected from the group consisting of a polyamideimide resin and a polyimide resin. The heat resistant resin is a polyethersulfone resin and at least one selected from the group consisting of a polyamideimide resin and a polyimide resin,
The coating composition according to claim 1, wherein a solid content mass ratio of the polyethersulfone resin to the polyamideimide resin and the polyimide resin is 85:15 to 65:35. The coating composition according to any one of claims 1 to 3, wherein the water-soluble inorganic salt is an inorganic metal salt or an inorganic ammonium salt. It is a primer composition, The coating composition of any one of Claims 1-4. A coated article obtained by coating the coating composition according to any one of claims 1 to 5.