JPH11106699A - Article made of steel coated with tetrafluoroethylene copolymer composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an article made of steel having a bonded coated film composed of a tetrafluoroethylene copolymer, excellent in water resistance. SOLUTION: This article made of steel is coated with a composition comprising 100 pts.wt. of a melt flowable copolymer of a tetrafluoroethylene containing a reactive terminal group and a fluorovinyl compound and 0.1-20 pts.wt. of a polyester composed of an aromatic dicarboxylic acid and an aromatic diol as constituent units. Preferably the fluorovinyl compound is a perfluoroalkoxytrifluoroethylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel article having an adhesive coating having excellent water resistance of a tetrafluoroethylene copolymer composition.

[0002]

2. Description of the Related Art Copolymers of tetrafluoroethylene and a fluorovinyl compound are excellent in non-adhesion, chemical resistance, heat resistance and the like, and are used for piping in chemical industry, food industry, electronics industry, machinery industry, etc. It is used as a material for coating various stainless steel or steel articles such as storage tanks, hoppers, pulp, and other equipment, various machine parts, kitchenware, and the like. In such a coating, since the tetrafluoroethylene copolymer has poor adhesion to the substrate, as a pre-coating treatment, the substrate is subjected to sandblasting, phosphate treatment, chromate treatment, etc. A method has been proposed in which a primer composed of a mixture of a fluororesin and several tens percent of a heat-resistant resin such as polyimide, polyamideimide, polyethersulfone, or polyphenylenesulfide is applied.

[0003]

However, such a method has a problem that the coating step is complicated and the cost is high, and a problem that the adhesive strength of the coating layer to the substrate is easily reduced by contact with water.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tetrafluoroethylene copolymer composition which has excellent water-resistant adhesion to steel and does not require complicated pretreatment for steel. It is intended to provide a steel article covered with an object.

[0005]

Means for Solving the Problems As a result of research conducted to solve the above-mentioned problems, the present inventors have found that a melt-flowable copolymer of tetrafluoroethylene having a reactive terminal group and a fluorovinyl compound has a specific property. The present inventors have found that a composition containing a small amount of polyester has excellent melt adhesion to steel and is extremely excellent in water resistance, and thus completed the present invention.

The copolymer of the present invention with tetrafluoroethylene and a fluorovinyl compound has fluidity at a temperature not lower than the melting point, and is available from ASTM D-3307.
0.5 at 372 ° C. ± 1 ° C. when measured according to
~ 500g / 10min, preferably 0.5 ~ 50g / 10
Min melt flow rate (MFR). Suitable fluorovinyl compounds include perfluoroalkyltrifluoroethylene having 3 to 10 carbon atoms and formula [I]

[0007]

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(Where X is H or F, m is an integer of 0 to 7, and n is an integer of 0 to 4) or formula [II].

[0009]

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(In the formula, q is an integer of 0 to 3.). The content of the perfluorovinyl compound in the copolymer is usually selected from the range of 0.5 to 20 mol%. In the present invention, the above tetrafluoroethylene copolymer must have a reactive terminal group. The reactive end groups -COOH, -CONH _{2,
-CH 2 OH, -COOCH 3, -COF} , -CF = CF
_{And the} like. The presence of such a terminal group can be confirmed by measurement of an infrared absorption spectrum described later. Preferably, such at least one reactive end groups are present in a ratio of carbon 10 ⁶ 6 or more per one during tetrafluoroethylene copolymer.

The polyester of the present invention contains one or more aromatic dicarboxylic acids and one or more aromatic diols as constituent units.

Preferred aromatic dicarboxylic acids are those represented by the following general formula, and include, for example, terephthalic acid and isophthalic acid.

HOOC-Ar-COOH (where Ar is an o-phenylene group, an m-phenylene group,
An arylene group such as a p-phenylene group. Suitable aromatic diols are represented by the following general formula, and include, for example, p, p'-biphenol and 2,2-bis (4-hydroxyphenyl) -propane (bisphenol A).

[0014]

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Wherein n is 0 or 1, -X- is -O-,
_{-S -, - SO 2 -,} - CO-, an alkylene group or an alkylidene group, R ₁ ~ ₄ and R _'1 ~ ₄ is a hydrogen atom, a halogen atom or an alkyl group. The polyester used in the present invention can be synthesized from the aromatic dicarboxylic acid and the aromatic diol or a functional group derivative thereof by a known method such as interfacial polycondensation, solution polycondensation, and melt polycondensation. As the functional group derivative of the aromatic dicarboxylic acid, an acid halide, a dialkyl ester or a diallyl ester of the aromatic dicarboxylic acid can be used. As the functional group derivative of the aromatic diol, an alkali metal salt of an aromatic diol, a diester with an aliphatic monocarboxylic acid, or the like can be used.

The polyester used in the present invention contains the above-mentioned aromatic dicarboxylic acid and aromatic diol as essential constitutional units, but may contain other constitutional units such as aromatic hydroxycarboxylic acid. It is.

In the present invention, the polyester is blended in an amount of 0.1 to 20 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the tetrafluoroethylene copolymer. If the amount is less than 0.1 part by weight, a sufficient adhesive strength to the substrate of the composition cannot be obtained. Meanwhile, 2
If the amount exceeds 0 parts by weight, the adhesive strength tends to decrease, and the heat resistance and chemical resistance of the composition deteriorate. The particle diameter and shape of the polyester in the composition are not particularly limited, but are preferably about 20 μm or less in order to obtain a smooth coating film.

In the present invention, the adhesiveness of the composition to steel can be further improved by incorporating inorganic particles into the composition. Useful minerals can be selected from among those known as solid acids or solid bases, such as (1) Al
Metal oxides such as ₂ O ₃ , TiO ₂ , MgO, ZnO, SiO ₂ , and mixtures thereof, or SiO ₂ —Al ₂ O
_3, complex metal oxides such as _{K 2 O-TiO 2, (} 2)
Clay minerals such as acid clay, kaolinite, bentonite, montmorillonite, talc, mica, zeolite,
Silicate compounds such as silicate glass; (3) metal sulfates such as aluminum sulfate, calcium sulfate, etc.
(4) Metal carbonates such as potassium carbonate, and (5) metal hydroxides such as calcium hydroxide.

The shape of the inorganic substance is not particularly limited, and may be granular,
It can be scaly, fibrous or the like. The particle size is not particularly limited, but is 20 μm in consideration of the moldability of the composition and the surface smoothness of a coating or a lamination film.
The following particles are preferred. The optimum amount of the inorganic particles varies depending on factors such as the particle diameter and the specific surface area.
It is selected from the range of from 01 to 30% by weight.

In the present invention, for the purpose of improving the abrasion resistance and hardness of the coating layer, and other purposes, the above-mentioned components may be added to the composition, if necessary, in addition to polyimide, polyamide-imide, or a polyamic acid which is a precursor thereof. A heat-resistant resin such as polyether sulfone, polyphenylene sulfide, and polyether ether ketone can be blended.

The method of blending the above additives with the tetrafluoroethylene copolymer can be appropriately selected from conventional methods such as melt kneading, dry mixing, and wet mixing according to the coating method.

The steel articles referred to in the present invention include, for example, various industrial and household facilities and machinery and equipment which have been conventionally covered with a copolymer of tetrafluoroethylene and a fluorovinyl compound. Articles made of steel, including carbon steel and specialty steel, such as those parts, are not limited in shape and size as long as the coating operation is possible.

As a method of coating a steel article with the composition, various methods can be appropriately adopted depending on the shape of the article and the like. For example, a method in which a powdery composition is attached to the surface of an article by a powder coating method such as electrostatic spraying or fluid immersion, and then heated to a temperature higher than the melting point of the tetrafluoroethylene copolymer and baked, or a dispersed liquid composition is used. After applying it to the surface of the article and baking it in the same way, or
When coating the inner surface of a tube or a container, a method such as obtaining a coating layer by a rotary lining method using a powdery composition can be adopted. Further, in the case of a steel plate or the like, the film-shaped composition can be coated on a steel plate which has been heated in advance to the melting point of the tetrafluoroethylene copolymer by a roller or the like.

When coating a steel article with the composition, when the material is stainless steel, an adhesive coating having excellent water resistance can be obtained only by performing a normal degreasing treatment in advance. Of course, it is of course possible to further improve the adhesiveness. In the case of a material that easily generates rust, such as mild steel, it is desirable to remove rust by sandblasting in advance.

The coating layer of the composition of the present invention thus obtained contains a small amount of additives other than the tetrafluoroethylene copolymer. It retains the excellent properties of the polymer. The article coated with the composition of the present invention can of course be used as it is. However, if necessary, polytetrafluoroethylene or tetrafluoroethylene and fluorotetrafluoroethylene may be further coated on the coating layer of the composition of the present invention. It is also possible to form a coating layer such as a copolymer of a vinyl compound.

[0026]

The steel article having the coating of the tetrafluoroethylene copolymer composition of the present invention not only has a high initial adhesive strength of the coating layer but also has a coating layer which can be used for a long time under an environment in which it comes into contact with moisture. Has a small decrease in adhesive strength and is excellent in durability. In addition, since the ratio of additives other than the tetrafluoroethylene copolymer in the coating layer can be reduced, it is excellent in non-adhesion, heat resistance, chemical resistance, and the like. Furthermore, since a complicated pretreatment such as a phosphate treatment or a chromate treatment of the steel surface is not required for forming the coating layer, the production cost can be reduced.

[0027]

The present invention will be specifically described below with reference to examples and comparative examples. As the tetrafluoroethylene copolymer, a copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether (PPVE) (PF
A) was used. Melt flow rate (MFR), PP
The measurement of the VE content, the melting temperature and the reactive terminal group was carried out by the following methods.

Melt flow rate (MFR): Using a melt indexer manufactured by Toyo Seiki, ASTM D-330
After filling 5 g of the sample into a cylinder having an inner diameter of 9.53 mm maintained at 372 ° C. ± 1 ° C. and maintaining the sample for 5 minutes in accordance with Example 7, under a load of 49.03 N (piston and weight), an inner diameter of 2.1 mm and a length of It was extruded through an 8 mm orifice, and the extrusion speed (g / 10 minutes) at this time was determined as MFR.

Determination of PPVE content: Sample PFA was 35
From an infrared absorption spectrum (nitrogen atmosphere) of a film having a thickness of about 50 μm obtained by compressing at 0 ° C. and then cooling with water, the absorbance ratio is determined by the following equation, and a calibration curve obtained by a standard film having a known PPVE content in advance. Was used to determine the PPVE content of the sample.

[0030]

(Equation 1)

Measurement of melting temperature: D manufactured by PerkinElmer
Using SC7 type, sample amount 5mg and heating rate 10 ° C /
The melting peak temperature was determined from the melting curve obtained in minutes.

Determination of reactive end groups: Sample PFA was measured at 350
A film having a thickness of about 250 μm obtained by compressing at 17 ° C.,
The infrared absorption spectrum is measured using X-type FTIR,
Similarly, as a control, P
Regarding the FA film, the infrared absorption spectrum was measured, and then, using the software attached to the FTIR,
The difference spectrum between the sample and the control sample was obtained by the operation represented by the following equation.

Difference spectrum = A−F × B A: Infrared absorption spectrum of sample B: Infrared absorption spectrum of control sample F: Thickness correction coefficient of sample film Thickness correction coefficient of sample film is -CF _{2 in} PFA −
The absorbance of the difference spectrum in the absorption band at a wavelength of 4.25 μm according to the structure was determined to be 0. On the obtained difference spectrum, the absorbance corresponding to each reactive terminal group was determined based on the assignment in the following table, and the correction coefficient (CF) shown in the following table was used to calculate the absorbance in the copolymer according to the following formula. The number of reactive end groups was determined.

[0034]

(Equation 2)

EXAMPLES 1-5 AND COMPARATIVE EXAMPLE 1 PPVE content 3.4% by weight, MFR 15 g / 1 with 83 --CONH ₂ end groups per 10 ⁶ carbon atoms
0 minutes, PFA with a melting temperature of 307 ° C. and an average particle size of about 10 μm
100 parts by weight of powder and formula

[0036]

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Powder (average particle size: 8 μm) of amorphous polyester (U-Polymer U-100, manufactured by Unitika Ltd.) and glass beads (EMB-1) comprising the structural units
0, manufactured by Toshiba Barotini, average particle size: 6 μm) were uniformly dry-mixed at the ratio shown in Table 1 to obtain a powdery composition.

After this powder composition is dispersed in isopropyl alcohol, it is poured on a stainless steel plate (SUS 430, 100 × 50 × 1 mm) degreased with acetone in advance, air-dried, and then baked at 380 ° C. for 30 minutes. , Length 100mm, width 15mm, thickness about 40μm
Was formed. Next, a 1 mm thick PFA sheet containing no additive was placed on the stainless steel plate and heated at 330 ° C. for 5 minutes to fuse the PFA sheet to the adhesive coating layer to obtain a test piece. The 90 ° peel strength of the PFA sheet thus fused was measured at room temperature at a pulling speed of 50 mm / min, and this was taken as the initial peel strength. After boiling the same test piece in tap water for 8 to 40 hours, the peel strength was measured in the same manner, and the water resistance of the adhesion was evaluated. Table 1 shows the results.

Reference Example 10.0 g (0.054 mol) of p, p'-biphenol powder was completely dissolved in 500 ml of KOH aqueous solution (hereinafter referred to as solution A). Next, 10.90 g (0.054 mol)
Of terephthaloyl chloride powder in 300 ml of methylene chloride solution (hereinafter referred to as solution B). When the liquid A and the liquid B were mixed and vigorously shaken at room temperature, precipitation of a white powder was immediately observed in the mixed liquid. After shaking for about 5 minutes, the precipitated powder was separated by filtration, washed with water, then washed with an organic solvent such as methanol and acetone, and finally washed again with water. Thereafter, the obtained white powder was dried at 100 ° C. for 1 hour under atmospheric pressure to obtain a synthetic polyester.

Polyester yield: 14.8 g (yield = 86.8%) Polyester average particle size: 8.0 μm (Shimadzu centrifugal sedimentation type particle size distribution analyzer SA-CP4L solvent: methanol) Heated at ° C / min but was infusible.

Examples 6 and 7 100 parts by weight of the PFA powder of Example 1 and the polyester powder synthesized in Reference Example 1 were uniformly dry-blended at the ratio shown in Table 1 to obtain a powder composition. Using this composition, an adhesive coating layer was formed on a stainless steel (SUS430) plate in the same manner as in Example 1, and a 90 ° peel strength was measured by fusing a PFA sheet. Table 1 shows the results.

Example 8 An isopropyl alcohol dispersion of a powdery composition obtained by uniformly mixing 100 parts by weight of the PFA powder of Example 1 and 3 parts by weight of the polyester powder synthesized in the reference example was degreased in advance. Sandblasted stainless steel plate (SUS 3
04, 100 × 50 × 1 mm), air-dried, and baked at 330 ° C. for 5 minutes to form an adhesive coating layer having a thickness of about 40 μm. PFA powder (MP-10, manufactured by Mitsui DuPont Fluorochemicals) is further electrostatically coated on the adhesive coating layer, and then baked at 380 ° C. for 30 minutes to obtain an additive-free PFA having a thickness of about 60 μm. An overcoat layer was formed. The overcoat layer of the test piece thus obtained had a 90 ° initial peel strength of 1 N / mm or more. Further, even after the test piece was exposed to steam at 150 ° C. and 5 kg / cm for 300 hours, no peeling or blistering of the coating layer was observed.

Examples 9 to 14 and Comparative Example 2 PPVE content 3.0 wt.%, MFR 1.7 g / 39 with 39 --CONH ₂ end groups per 10 ⁶ carbon atoms.
Furfuryl alcohol, N-methylpyrrolidone, and ammonia containing 15% by weight of colloidal particles of PFA having a melting temperature of 309 ° C. and an average particle size of about 0.17 μm and 3% by weight of a polyamic acid which is a precursor of polyimide for 10 minutes A water-soluble organic liquid composed of water was prepared, and the polyester powder used in Example 1 or the polyester powder synthesized in Reference Example was mixed and dispersed at a ratio shown in Table 2 to obtain a primer composition. This primer composition was degreased in advance and sandblasted on a stainless steel plate (SUS430, 1).
00 × 50 × 1 mm), dried, and about 8μ thick
m of primer layers were formed. After further electrostatically coating PFA powder (MP-10) on this primer layer, 38
By baking at 0 ° C. for 30 minutes, an overcoating layer containing no additive and having a thickness of about 60 μm was formed. The test piece thus obtained was measured for 90 ° peel strength. Table 2 shows the results.

[0044]

[Table 1]

[0045]

[Table 2]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C09D 127/18 C09D 127/18 // (C09D 127/12 167: 02) (C09D 127/18 167: 02)

Claims (2)

[Claims] 1. A polyester containing from 100 to 100 parts by weight of a melt-flowable copolymer of tetrafluoroethylene having a reactive terminal group and a fluorovinyl compound and from 0.1 to 0.1% of a polyester containing aromatic dicarboxylic acid and aromatic diol as constituent units. 20
A steel article coated with a composition comprising parts by weight. 2. The steel article according to claim 1, wherein the fluorovinyl compound is perfluoroalkoxytrifluoroethylene.