JPS59147057A - Fluororesin composition for coating - Google Patents

Abstract

PURPOSE:To provide the titled composition giving a coating film driable without causing cracking and having excellent surface smoothness after baking, and suitable for the coating of iron, metals, etc., by adding methyl cellulose to an aqueous dispersion of a thermoplastic fluororesin. CONSTITUTION:The objective composition is obtained by compounding (A) an aqueous dispersion of a thermoplastic fluororesin (e.g. tetra-fluoroethylene/perfluoroalkyl vinyl ether copolymer) with (B) 2-10wt%, based on the thermoplastic fluororesin, of a methyl cellulose (e.g. hydroxypropyle methyl cellulose having a thermal gelatinization temperature of 60-70 deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluororesin composition for coating, and furthermore, the present invention relates to a fluororesin composition for coating, which has a thermofluidity that does not cause cracking of the coating film during coating and drying, and provides a smooth coating film surface after baking. This invention relates to an aqueous dispersion of fluororesin.

Thermofluid fluororesins such as tetrafluoroethylene perfluoroalkyl vinyl ether copolymer or tetrafluoroethylene/hexafluoropropylene copolymer have excellent chemical resistance unique to fluororesins, have a small coefficient of friction, and are non-adhesive. It is rich in fluororesins and has a lower melt viscosity than other fluororesins, so it can be melt-molded.

In recent years, aqueous dispersions of these thermofluid fluororesins have been developed,
Although it has become possible to easily obtain products coated with fluororesin by applying it onto a substrate using a spray gun or the like, it is still difficult to apply a uniform coating in some cases. That is, when it is applied and dried, cracks may occur in the coating film, resulting in a cracked coating film, and when it is baked, unevenness may occur on the coating film surface, making it impossible to obtain a smooth surface.

Such cracks in the coating film and lack of surface smoothness are undesirable because they directly impair the value of the product, and prevention thereof is desired.

In view of the current situation, the present inventors have conducted research to create an aqueous dispersion of a thermofluid fluororesin that prevents cracking during drying and has excellent surface smoothness after firing. This invention has been achieved. That is, the gist of the present invention is a fluororesin composition for coating, which is characterized by blending methylcellulose into an aqueous dispersion of a heat-flowable fluororesin.

The thermofluid fluororesin used in the present invention refers to a fluororesin that has a low melt viscosity and can be melt-processed, such as evatetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene/hegisafluoroethylene, etc. Propylene copolymer (FEP), polychlorotrifluoroethycine (paTFg), polypylidene fluoride (PVDF), polyvinyl fluoride (P
VF), tetrafluoroethylene-ethylene copolymer (ETFE), and the like. Among these, PFA, FEP and ETFE are particularly preferred.

To obtain these aqueous dispersions, for example, when using powder or granules, they can be obtained by pulverizing them with a ball mill or the like as necessary and then dispersing them in water. In addition, an aqueous dispersion or an aqueous emulsion of an organosol obtained by emulsion polymerization can be used as is. These aqueous dispersions may also contain other organic liquids, but it is not preferable to mix them in large amounts from the viewpoint of the working environment during coating.

, l/ As the methyl cellulose, in addition to methyl cellulose obtained by methyl etherifying cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, etc. which are further modified from the methyl cellulose can also be used. Furthermore, various degrees of polymerization and substitution degree (number of substituents per glucose group) of these methylcelluloses can be used. However, for ease of handling after mixing with an aqueous dispersion of heat-flowable fluororesin, that is, for ease of application with a spray gun and for maintaining uniformity of the coating film, it is necessary to
It is preferable that the viscosity of the aqueous solution is 4 Q Q cps or less at 20°C. Among various methyl celluloses, hydroxypropyl methyl cellulose is particularly effective in the present invention, and those with a thermal gelation temperature (2%) of 60 to 70°C are particularly preferred.

Adding methylcellulose to the heat-flowable fluororesin aqueous dispersion can prevent cracking of the coating film when the aqueous dispersion is applied onto a substrate and dried, and can also prevent cracking of the coating film after baking the coating film. It also has excellent surface smoothness, which is a significant effect in practical application of coatings. Such prevention of cracking of the coating film and maintenance of surface smoothness cannot be achieved by an aqueous dispersion of heat-flowable fluoropolymer alone, and by blending carboxymethylcellulose, hydroxyethylcellulose, or polyvinyl alcohol, which are water-soluble polymers similar to methylcellulose. It does not occur even in the aqueous dispersion. Furthermore, the aqueous dispersion blended with an inorganic filler such as silica, Aerosil or calcium carbonate and a resin such as an acrylic emulsion, an ionomer resin, or a polyolefin does not produce the effect described in item 1. In other words, even if something other than methylcellulose is blended, cracks will occur during drying of the coating film, or the surface of the coating film will become uneven after baking, making it impossible to obtain surface smoothness.

It is difficult to define the amount of methylcellulose based on the concentration of the aqueous dispersion of heat-flowable fluoropolymer, the type of methylcellulose, the desired coating thickness, etc.For example, if PFA is used, Against 4
% to 10% by weight, especially 6% to 8% by weight
L% is preferred. If the blending amount is less than 4% by weight, the surface smoothness of the coating film after firing cannot be obtained, and if it exceeds 10% by weight, methyl cellulose decomposition products tend to remain in the coating film even after firing, resulting in the formation of pinholes or Non-adhesive properties may be impaired.

Any known method may be used to blend methylcellulose into the aqueous dispersion of a heat-flowable fluororesin, such as adding it directly to the aqueous dispersion while stirring, or preparing an aqueous methylcellulose solution in advance and mixing it with the aqueous dispersion. Methods etc. can be exemplified.

In addition, in the present invention, the thickening effect of methylcellulose can be utilized to prevent sagging during application and to prevent repellency during overcoating.

The dripping during application is from an aqueous dispersion applied to a vertical surface.

It flows and causes uneven streaks and puddles on the paint film, and repellency occurs when overcoating.When forming a paint film using an aqueous dispersion, a sufficiently thick paint film cannot be obtained with one coat, and the nails become sticky. Undesirable as it often requires painting. To prevent such dripping and staining, for example, the coating thickness should be 10 to 30 mm.
If the objective is to increase the viscosity of the aqueous dispersion of heat-flowable fluororesin to 29 Q cps or more, sagging can be prevented by adding methylcellulose to the water dispersion.
Repelling can also be prevented by setting the value to 50 CTl5 or higher. Of course, even if a known thickener other than methylcellulose is used, dripping and repelling can be prevented as long as the viscosity is within the above range. The viscosity here is 27° measured by a B-type viscometer.
This is a value measured under CC56Qrp conditions.

The fluororesin composition for coating of the present invention may also contain various other known additives, such as fatty acids, sulfuric acid esters of higher alcohols, alkylbenzene sulfonic acids, argylnaphthalene sulfonic acids, and polynaphthalene sulfonic acids. and salts thereof, carboxylic acids, sulfonic acids, phosphoric acids and salts thereof, esters, polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene acyl esters, sorbitan fatty acid esters, etc. having fluoroalkyl groups. A surfactant may be used as a dispersing agent or a leveling agent, and higher alcohols such as octyl alcohol and cyclohexamer, ethylene glycol, polymethylsiloxane, etc. can be blended as an antifoaming agent. In addition, pigments, dyes, inorganic and organic fillers, etc. may also be blended.

Examples will be shown next, but the present invention is not limited to these examples unless the purpose of the invention is impaired.

Example 1 and Comparative Examples 1 to 7 PFA with a melt viscosity of 3xio ps at 372'C was
The formulations shown in Table 1 were added to an aqueous dispersion of Pi...A dispersed in weight percent. The resulting PI・'A aqueous dispersion composition was coated with a bar coater on an iron plate roughened with sandpaper so that the dry coating thickness was 20 to 25μ, and heated at 80"C.
After drying for 10 minutes at 380"C, it was baked for 10 minutes. Table 1 shows the visual judgment of the degree of cracking in the coating film during drying and the smoothness of the coating film surface after baking.・Very good crack prevention or surface smoothness, ○...
Good, △: Slight cracks or slightly good smoothness, ×: Cracks or no smoothness).

The following commercially available formulations were used.

Hydroxybrobyl methylcellulose: Medrow's ■65SH50 Shin-Etsu Chemical Silica; Mizukashiru ■P-527 Mizusawa Chemical Industry Calcium Carbonate; Hakuenka ■pz Shiraishi Industry Acrylic Emulsion;
Brimar ■TR-534 Rohm and Haas Japan Polyvinyl Alcohol Synthetic Chemical Industry Carboxymethyl Cellulose; Celogen ■pR Daiichi Kogyo Seiyaku Hydroxyethyl Cellulose; Natrosol ■250LR
Hercules Examples 2 to 5 The same PFR aqueous dispersion as in Example 1 was blended with the methi/dicellulose shown in Table 2, and the same tests as in Example 1 were conducted.

The results are shown in Table 2.

The following commercially available methylcellulose was used.

Methylcellulose; Metro-105M100 Shin-Etsu Chemical Hydroxypropyl methylcellulose; Metro-■ 60SH50, 65sH400, 90SH100
゜Shin-Etsu Chemical/Example 6 700 ppm each of a fluorosurfactant and a silicone antifoaming agent were added to the same aqueous dispersion of PFA and hydroxypropyl methylcellulose as in Example 1, and P
Water was added to adjust the FA content to 35% by weight. The resulting PFA aqueous dispersion had a viscosity of 950 cps using a 27" CC 160rp B-type viscometer. When this aqueous dispersion was applied onto a steel plate using a spray gun, there was no sagging during application or during drying. There were no cracks in the coating film or repellency during overcoating, and the surface smoothness of the coating film after firing was excellent.

Example 7 The same PFA aqueous dispersion as in Example 1 was mixed with 4 parts by weight of hydroxypropyl methyl cellulose based on PFA, and further 2 TdiLm of carboxymethyl cellulose (Celogen PR) and 100 p of a silico antifoaming agent were added.
pm was added. The resulting PFA aqueous dispersion is 2”’CC-6
The viscosity measured by Orp's B-type viscometer was 760 cps.

When this aqueous dispersion was applied to an aluminum plate, there was no dripping during application, cracking of the coating during drying, or repellency during overcoating, and the coating surface had excellent smoothness after firing. .

Example 8 FE with melt viscosity s x + o' ps at 372"C
5 parts by weight of methylcellulose (Metrose ■65SH50) and 100 ppm of the same surfactant and antifoaming agent as in Example 6 were added to an aqueous dispersion of P F'A in which 53% by weight of P was dispersed.
Water was added to adjust the FEP content to 35% by weight. The resulting FEP water dispersion is 27”C,6O
The viscosity measured by a B-type viscometer at rpm was 680 cps.

When applied to an iron plate in the same manner as in Example 6, no sagging occurred during application, no cracking of the coating film during drying, and no repellency during overcoating, and the surface smoothness of the coating film after baking was also excellent.

Applicant: Mitsui Petrochemical Industries, Ltd. Agent Kazu Yamaguchi Procedural amendment (voluntary) January 2nd, 1982 Mr. Kazuo Wakasugi, Commissioner of the Patent Office 1. Display of incident 1981 Patent Application No. 21691 2 Name of the invention Fluororesin composition for painting 3 Person making the amendment Relationship to the incident: Patent applicant (588) Mitsui Petrochemical Industries Co., Ltd. 4 agents〒100 2-5 Kasumigamana-chome, Chiyoda-ku, Tokyo 5 Spontaneous correction 6 Target of correction Claims and Detailed Description of the Invention in the Specification Z Correction details The scope of the claims is amended as shown in the attached sheet.

(2) Page 6 lines 7-10 of the specification "4% to 10% by weight, particularly 6% to 8% by weight, based on prΔ is preferable. If the amount is less than 4' weight%, the ``2% to 10% by weight, particularly 4 to 6% by weight of PFA is preferable. If the amount is less than 2% by weight, the surface smoothness of the coating film cannot be obtained. It is not possible to obtain the estrous properties of the coating film surface, and the correction is made to ``.

(3) In the specification, page 12, line 2, "PFR water teaching solution" should be corrected to "PFA water teaching solution J."

(4) In the specification, page 15, line 6, "PFA aqueous dispersion" is corrected to "FEP aqueous dispersion."

Claims (1) A fluororesin composition for coating, characterized in that methylcellulose is blended into an aqueous dispersion of a heat-flowable fluororesin.

(2) Claim 1 in which 2 to 10% by weight of methyl cellulose is blended with respect to the heat-flowable fluororesin.
The fluororesin composition for painting described in Section 1.

(3) The fluororesin composition for coating according to claim 1 or 2, wherein the methylcellulose is hydroxypropyl methylcellulose.

{4} Claim 3, wherein the thermal gelation temperature of hydroxypropyl methylcellulose is 60 to 70°C.
The fluororesin composition for painting described in Section 1.

Claims (4)

[Claims] (1) A fluororesin composition for coating, characterized in that it is made by blending methylcellulose into an aqueous dispersion of a heat-flowable fluororesin. (2) A fluororesin composition for coating according to item 1 of the patent application, which contains 4 to 10% by weight of methyl cellulose based on the heat-flowable fluororesin. (3) The fluororesin composition for coating according to claim 1 or 2, wherein the methylcellulose is hydroxypropylmethylcellulose. (4) The fluororesin composition for coating according to claim 6, wherein the hydroxypropyl methyl cellulose has a thermal gelation temperature of 60 to 70°C.