Coating resin composition

A coating resin composition is described, comprising from 50 to 99% by weight of a thermoplastic aromatic polyether ketone resin and from 50 to 1% by weight of a perfluoroalkoxy resin or a tetrafluoroethylene/hexafluoropropylene copolymer resin having hexafluoropropylene content of from 18 to 25% by weight. The composition, when applied to a steel plate, for example, produces a coating film which is greatly improved in water repellency while retaining the desirable properties of the polyether ketone, such as high heat resistance, good mechanical and electrical properties, and high chemical resistance.

FIELD OF THE INVENTION 
The present invention relates to a coating resin composition comprising a 
thermoplastic aromatic polyether ketone resin and a perfluoroalkoxy resin 
or a tetrafluoroethylene/hexafluoropropylene copolymer resin and 
particularly, to a coating resin composition from which a coating film 
which has good appearance, is free from pinholes and is good in water 
repellency and adhesion to a substrate can be obtained. 
BACKGROUND OF THE INVENTION 
It is known, as described in Japanese Patent Application (OPI) No. 90296/79 
(the term "OPI" as used herein means a "published unexamined Japanese 
patent application"), that thermoplastic aromatic polyether ketone resins 
are superior in heat resistance, flame resistance, mechanical and 
electrical properties, and chemical resistance. Because of these superior 
properties, it has been suggested to utilize the resin particularly in 
electrically insulating coating of electrical wires and cables. But the 
use of the resin is not limited to the coating of electrical wires or 
cables. That is, a further development is expected in various industries 
in the electrical or mechanical field by expanding its range for use by 
means of imparting electrically insulative coating, anti-corrosion 
property, etc. to various electrically conductive materials. 
In order to impart excellent properties of such thermoplastic aromatic 
polyether ketone resins such as electrical insulation and anti-corrosion 
properties to metal substrates, especially steel, aluminum and copper, 
extensive investigations on the coating of the thermoplastic aromatic 
polyether ketone resin have been made by the present inventors. As the 
results, there were previously proposed the following procedures for 
forming a good coating film: a method in which a polyether ketone having a 
specific particle diameter is applied onto the surface of a substrate, 
melted at a specific temperature, and then cooled to form a strong coating 
film (see Japanese Patent Application (OPI) Nos. 127768/83 and 130574/84; 
and a method in which a molten polyether ketone is fused onto the surface 
of a substrate and then cooled to form a strong coating film (see Japanese 
Patent Application No. 83289/83). 
The polyether ketone coating films obtained by the above methods retain the 
superior properties of the polyether ketone resin, i.e., high heat 
resistance, flame resistance, mechanical and electrical properties, 
chemical resistance, and resistance to boiling water, and further can 
impart high electrical insulation, corrosion resistance, and resistance to 
boiling water to the metal substrate, whereby they are proceeding 
development of useful products and are contributing to development of the 
industry. 
The polyether ketone resin does not undergo chemical deterioration even 
when exposed to boiling water or steam of more than 200.degree. C. Because 
of such superior resistance to boiling water and resistance to steam, the 
polyether ketone resin is expected to be used in various fields, e.g., 
nuclear power field, oil drilling field, etc. as well as various chemical 
equipments. The polyether ketone resin, however, is poor in water 
repellancy (a property to repel water). When it is, for example, applied 
to a level gage of boiling water, there are caused various problems such 
as an error in the detection of the boiling water dip surface and easy 
occurrence of scale. Thus it has been strongly desired to improve the 
water repellency in many applications using boiling water. 
As a result of extensive investigations, it has been found that a 
composition as described below can produce a coating film which is 
improved in water repellency without deteriorating the superior properties 
of the polyether ketone resin, such as resistance to boiling water and 
resistance to steam, exhibits good adhesion to a substrate, has good 
appearance, and further is free from pinholes, leading to accomplishment 
of the present invention. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a coating resin 
composition comprising from 50 to 99% by weight of a thermoplastic 
aromatic polyether ketone resin and from 50 to 1% by weight of 
perfluoroalkoxy resin or a tetrafluoroethylene/hexafluoropropylene 
copolymer resin having hexafluoropropylene content of from 18 to 25% by 
weight. 
DETAILED DESCRIPTION OF THE INVENTION 
The thermoplastic aromatic polyether ketone resin as used herein contains 
the following repeating unit: 
##STR1## 
singly or in combination with other repeating units, and has an inherent 
viscosity of from 0.3 to 2.6, preferably from 0.5 to 1.8. Examples of 
these other repeating units are shown below: 
##STR2## 
The proportion of the other repeating units is usually less than 25% by 
weight. If it exceeds 25% by weight, the above described characteristics 
of the polyether ketone are undesirably lost. The inherent viscosity as 
referred to herein is determined with respect to a solution of a polymer 
sample in concentrated sulfuric acid (density: 1.84 g/cm.sup.3), 
containing 0.1 g of the polymer sample per 100 cm.sup.3 of the solution, 
at 25.degree. C. 
The inherent viscosity was determined by the use of a viscometer having a 
solvent efflux time of about 2 minutes. This inherent viscosity 
principally corresponds to the molecular weight of the polymer. 
The inherent viscosity of the thermoplastic aromatic polyether ketone is 
from 0.3 to 2.6 and preferably from 0.5 to 1.8. If the inherent viscosity 
is less than 0.3, the ultimate coating film is low in heat resistance and 
brittle because of its low molecular weight. On the other hand, if exceeds 
2.6, the resulting resin composition is not satisfactory in melt fluidity 
because of its high melt viscosity and therefore, a coating film having a 
uniform thickness is difficult to produce; no satisfactory coating film 
can be obtained. When the inherent viscosity is between 0.3 and 2.6, good 
fluidity and satisfactory coating film performance can be obtained. In 
order to obtain a coating film having more improved surface appearance, 
adhesion strength and toughness, it is preferred for the inherent 
viscosity to be in the range of from 0.5 to 1.8. When the inherent 
viscosity is within the range of from 0.3 to 2.6, a melting point as 
measured by a differential calorimeter is from 330.degree. to 335.degree. 
C. and good heat stability and thermoplasticity can be obtained. 
The perfluoroalkoxy resin (hereinafter abbreviated to "PFA") as used herein 
is represented by the following general formula: 
##STR3## 
wherein Rf is a fluoroalkyl group, and --O--Rf is a perfluoroalkoxy group. 
PFA has a melting point of from 302.degree. to 310.degree. C., exhibits 
melt fluidity at temperatures more than the melting point thereof, has 
high heat resistance and chemical resistance, has a continuous service 
temperature of 260.degree. C., and is little affected by the usual acids, 
alkalis, oxidation-reduction agents, halogens, and organic solvents. 
PFA is sold under the trade name of Teflon PFA by E. I. Du Pont de Nemours 
& Co., Inc., U.S.A. and Mitsui Fluorochemicals Co., Ltd., Japan. 
The tetrafluoroethylene/hexafluoropropylene copolymer (hereinafter 
abbreviated to "FEP") is represented by the following general formula: 
##STR4## 
FEP has a melting point of from 250.degree. to 290.degree. C., exhibits 
melt fluidity at temperatures more than the melting point thereof, has 
high heat resistance and chemical resistance, and has a continuous service 
temperature of 200.degree. C. 
FEP is commercially available from E. I. Du Pont de Nemours & Co., Inc., 
U.S.A. (trade name: Teflon FEP) and Daikin Kogyo Co., Ltd. (trade name: 
Neofuron). Among commercially available FEPs, those copolymers having a 
hexafluoropropylene content of from 18 to 25% by weight are preferably 
used in the present invention because their physical properties and melt 
fluidity are well balanced. 
If the hexafluoropropylene content is less than 18% by weight, FEP is not 
satisfactory in melt fluidity and when the composition with a polyether 
ketone is applied on a substrate, the coating film applied is seriously 
large in irregularity and has pinholes; it fails to impart corrosion 
resistance to the substrate. On the other hand, if the hexafluoropropylene 
content exceeds 25% by weight, since the melting point serious drops, when 
the composition with a polyether ketone is applied on a substrate, a 
reduction in heat resistance is undesirably large. 
In compounding the polyether ketone with PFA or FEP, it is preferred that 
the proportion of the polyether ketone is from 50 to 99% by weight, with 
that of PFA or FEP being from 50 to 1% by weight, based on the total 
amount of the polyether ketone and PFA or FEP. If the proportion of the 
polyether ketone exceeds 99% by weight, i.e., the proportion of PFA or FEP 
is less than 1% by weight, the desired water repellency can be improved 
only insufficiently. On the other hand, if the proportion of the polyether 
ketone is less than 50% by weight and the proportion of PFA or FEP exceeds 
50% by weight, insufficient dispersion results and furthermore, the 
adhesion to the substrate is insufficient. Thus a satisfactory coating 
film cannot be obtained. 
With a composition comprising from 50 to 99% by weight of the polyether 
ketone and from 50 to 1% by weight of PFA or FEP, a coating film which is 
satisfactory in heat resistance, resistance to boiling water, water 
repellency, adhesion to a substrate, and appearance and is free from 
pinholes can be obtained. A composition comprising from 60 to 97% by 
weight of the polyether ketone and from 40 to 3% by weight of PFA or FEP 
is preferred, because a coating film which is more improved in the above 
properties can be obtained. 
Even when the proportion of the polyether ketone falls within the range of 
from 50 to 99% by weight, if fluorocarbon resins other than PFA and FEP 
are employed, the desired coating film cannot be obtained. 
That is, when polytetrafluoroethylene is, for example, concerned though it 
has a melting point of about 330.degree. C., it does not exhibit melt 
fluidity even at temperatures above the melting point thereof and hence, 
the resulting composition with a polyether ketone can form only a coating 
film on a substrate which is very irregular in the surface and does not 
have uniform surface appearance because of it poor dispersibility. 
Furthermore, pinholes are developed in the coating film because of poor 
fluidity. Thus it falls to impart corrosion resistance to a substrate. 
On the other hand, when fluorocarbon resins other than PFA and FEP, 
exhibiting melt fluidity, such as polychlorotrifluoroethylene, polyvinyl 
fluoride, polyvinylidene fluoride, an ethylene/tetrafluoroethylene 
copolymer, and ethylene/chlorotrifluoroethylene copolymer, are used, water 
repellency is not satisfactory so that the desired coating cannot be 
obtained. 
The composition of the present invention is not limited in the means of 
compounding the constituents; the polyether ketone and PFA or FEP can be 
compounded by any suitable technique such as a method in which powders of 
the polyether ketone and PFA or FEP are mixed by the use of, e.g., a 
mortar, a Henschel mixer, a ball mill, and a ribbon blender, a method in 
which the mixture is melt-kneaded to improve dispersibility, followed by 
granulating or powdering by grinding, and a method in which powders of the 
polyether ketone and PFA or FEP are independently deposited on the surface 
of a substrate and then mixed on the substrate. 
In forming a coating film from the composition on the substrate, any 
suitable technique can be employed, including powder coating methods such 
as powder spraying, electrostatic coating, and fluidized bed coating, 
compression molding, extrusion molding, and injection molding. Depending 
on the coating method, the composition of the present invention is applied 
in the form of powders, granules, or sheets. 
To the composition of the present invention can be added within the ranges 
that do not deteriorate the desired characteristics, usual additives such 
as an antioxidant, a heat stabilizer, an ultraviolet absorber, a 
lubricant, a releasing agent, a coloring agent (e.g., a dye and a 
pigment), a flame retardant, an auxiliary flame retardant, and an 
antistatic agent, or suitable reinforcing agents and fillers. These 
additives can be used alone or in combination of two or more thereof. 
The present inventin is described in greater detail with reference to the 
following examples, although it is not intended to be limited thereto.

EXAMPLES 1 TO 3 
A powdered thermoplastic aromatic polyetherketone resin having a repeating 
unit represented by: 
##STR5## 
having an inherent viscosity of 0.8, an average particle diameter of 100 
microns and a perfluoroalkoxy resin (Teflon PFA MP-10, a product of Mitsui 
Fluorochemicals Co., Ltd.; average particle diameter: 39 microns) were 
powder blended in a Henschel mixer in a proportion as shown in Table 1. 
The mixture of polyether ketone and perfluoroalkoxy resin was spray coated 
in a powder-jetting amount of 300 g/min at a voltage of 60 KV by the use 
of an electrostatic spray apparatus (Model CH-9015, manufactured by GEMA 
Corp.) on a surface of a steel plate (JIS S45C) which had been 
sand-blasted so that the average depth of irregularities was 5 to 10 
microns and an interval between irregularities was 10 to 20 microns, and 
then melt baked by heating at 380.degree. C. for 20 minutes. Thereafter, 
the resulting steel plate was taken out of the heating furnace and allowed 
to cool to room temperature in air. 
The thus-formed coating film was tested for the surface condition, 
pinholes, adhesion strength, heat resistance, and water repellency. The 
results are shown in Table 1. 
The pinhole test was performed with a discharge-type pinhole tester (Model 
TRC-20, manufactured by Sanko Denshi Kenkyujo). 
The adhesion strength was evaluated in terms of peeling strength as 
determined by a 180.degree. C. coating film-peeling test (peeling speed: 
50 mm/min), and the resistance to boiling water, in terms of peeling 
strength after soaking in 200.degree. C. boiling water for 100 hours. 
The water repellency was evaluated in terms of contact angle of a water 
droplet gently dropped on the surface of the coating film. The greater the 
contact angle, the better the water repellency. 
COMATIVE EXAMPLE 1 
The same procedure as in Example 1 was repeated except that the 
perfluoroalkoxy resin was not compounded and only the powdered polyether 
ketone resin was used. The results are shown in Table 1. 
COMATIVE EXAMPLE 2 
The same procedure as in Example 1 was repeated except that the amounts of 
the polyether ketone and the perfluoroalkoxy resin compound were changed 
to 40% by weight and 60% by weight, respectively. The results are shown in 
Table 1. 
EXAMPLE 4 
The same procedure as in Example 1 was repeated except that a 
tetrafluoroethylene/hexafluoropropylene copolymer resin (FEP powder having 
a hexafluoropropylene content of 20%) was used in place of the 
perfluoroalkoxy resin and that a mixture comprising 80% by weight of the 
polyether ketone and 20% by weight of FEP was used. The results are shown 
in Table 1. 
COMATIVE EXAMPLE 3 
The same procedure as in Example 4 was repeated except that the amounts of 
the polyether ketone and the tetrafluoroethylene/hexafluoropropylene 
copolymer resin compounded were changed to 40% by weight and 60% by 
weight, respectively. The results are shown in Table 1. 
COMATIVE EXAMPLE 4 
The same procedure as in Example 4 was repeated except that polyvinylidene 
fluoride (KF polymer powder, manufactured by Kureha Chemical Industry Co., 
Ltd.; abbreviated as "PVdF") was used in place of the 
tetrafluoroethylene/hexafluoropropylene copolymer resin. The results are 
shown in Table 1. 
COMATIVE EXAMPLE 5 
The same procedure as in Example 4 was repeated except that 
polytetrafluoroethylene (Fluon L169 powder, manufactured by Imperial 
Chemical Industries PLC; abbreviated as "PTFE") was used in place of the 
tetrafluoroethylene/hexafluoropropylene copolymer resin. The results are 
shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Peeling Strength (kg/cm) 
After 
Compositon (wt %) Soaking in 
Fluorine- 200.degree. C. Boil- 
Contact 
Polyether 
Based Before 
ing Water 
Angle 
Ketone 
Resin 
Appearance 
Pinhole 
Soaking 
for 100 Hrs 
(.degree.) 
__________________________________________________________________________ 
Example 1 
95 PFA 5 
Good None 4.3 3.8 78 
Example 2 
80 PFA 20 
" " 4.0 3.6 90 
Example 3 
70 PFA 30 
" " 3.8 3.4 93 
Comparative 
100 PFA 0 
" " 4.8 4.0 65 
Example 1 
Comparative 
40 PFA 60 
Poor " 1.5 0 100 
Example 2 dispersion 
Example 4 
80 FEP 20 
Good " 3.8 3.4 88 
Comparative 
40 FEP 60 
Poor " 1.3 0 96 
Example 3 dispersion 
Comparative 
80 PVdF 20 
Seriously 
" 3.4 2.8 68 
Example 4 colored 
Comparative 
80 PTFE 20 
Big irregu- 
Many 2.8 2.4 88 
Example 5 larities 
pinholes 
__________________________________________________________________________ 
As is apparent from Table 1, the coating films produced using the 
compositions of Examples 1 to 4 have good appearance, are free from 
pinholes, and are good in adhesion to a substrate and resistance to 
boiling water. In addition, it can be seen that the contact angle is large 
and the water repellency is excellent. 
When the polyether ketone is used singly, the water repellency is poor 
(Comparative Example 1); when the amounts of PFA and FEP compounded are 
too large, the dispersibility is low and the adhesion to a substrate is 
poor (Comparative Examples 2 and 3); and when a fluorocarbon resin other 
than PFA and FEP is used, the water repellency is poor (Comparative 
Example 4), or many pinholes are formed (Comparative Example 5); a 
satisfactory coating film cannot be obtained. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.