Fluoropolymer coating composition and coated article

Details Fluoropolymer coating composition and coated article Fluoropolymer coating composition and coated article

1998-10-22

2001-08-21

Chen, Vivian (Department: 1773)

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Physical dimension specified

C428S334000, C428S335000, C428S336000, C428S421000, C428S422000, C524S136000, C524S173000, C524S198000, C524S315000, C524S366000, C525S199000, C525S206000, C525S209000, C525S212000, C525S217000, C525S218000, C525S231000

Reexamination Certificate

active

06277487

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a fluoropolymer coating composition and a coated article.
BACKGROUND ART
An anionic surfactant has been hitherto added, as an auxiliary for forming a film, to a fluoropolymer coating composition. However there were drawbacks such that since foaming is apt to occur, pin holes are easy to be produced and that, since film forming property is insufficient and thick coating is difficult, corrosion resistance and non-sticking property are lowered due to abrasion of a coating film.
An object of the present invention is to provide the fluoropolymer coating composition which incorporates a specific polyether type resin particularly in the form of emulsion and is capable of coating thick and forming a coating film excellent in abrasion resistance, corrosion resistance and nonsticking property, and to provide the article coated with that fluoropolymer coating composition.
DISCLOSURE OF THE INVENTION
The present invention relates to the fluoropolymer coating composition which comprises fine particles of a fluoropolymer, 0.1 to 300% by weight of the polyether type resin on the basis of a weight of the above-mentioned fine particles, and a liquid carrier, and the polyether type resin is a resin represented by the formula (I):
R
1
—Y
1
—(A—B)—R
1
  (I)
wherein R
1
is the same or different and each is hydrogen or an alkyl having 1 to 20 carbon atoms, Y
1
is the same or different and each is ether, ester, urethane or thionyl, A is alkylene oxide residual group having at least 3 carbon atoms (A molecular weight of an alkylene oxide moiety obtained by polymerization is 1×10
3
to 1×10
4
), B is urethane, thionyl or phosphoric acid residual group (in the parenthesis is represented a residual group obtained through alternating copolymerization), and a temperature where the above-mentioned resin is decomposed and vaporized is in the range up to a decomposition temperature of the fluoropolymer.
Also the present invention relates to the article coated with the above-mentioned fluoropolymer coating composition as a top coat so as to form at least 30 &mgr;m thick molten coating film.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention provides the fluoropolymer having a major feature of particularly making thick coating possible by employing the specific polyether type resin in the form of emulsion.
The above-mentioned specific polyether type resin is a resin represented by the formula (I):
R
1
—Y
1
—(A—B)—R
1
  (I)
and is hydrophobic and dispersive in water and has no surface activity since no ethylene oxide residual group is contained. The specific polyether type resin is decomposed and vaporized in a temperature range up to a decomposition temperature of the fluoropolymer used in the present invention (namely, low temperature decomposition property).
It is preferable from the viewpoint of hydrophobic property that the above-mentioned R
1
is the same or different and each is hydrogen or an alkyl having 1 to 20 carbon atoms.
It is preferable from the viewpoint of thermal decomposition property that the above-mentioned Y, is the same or different and each is ether, ester, urethane or thionyl.
It is preferable from the viewpoint of hydrophobic property and dispersibility in water that the above-mentioned A is alkylene oxide residual group having not less than 3, preferably 3 or 4 carbon atoms and that a molecular weight of the alkylene oxide moiety obtained by polymerization is from 1×10
3
to 1×10
4
.
It is preferable from the viewpoint of thermal decomposition property that the above-mentioned B is urethane, thionyl or phosphoric acid residual group.
It is preferable that the group in the parenthesis of the formula (I) is a residual group obtained through alternating copolymerization
The polyether type resin represented by the formula (I) is hydrophobic and dispersive in water, and is used suitably in the form of resin emulsion from the viewpoint of stability and workability. Also since such a resin is emulsion, it is easily dispersed homogeneously with the fluoropolymer particles.
Examples of the resin represented by the formula (I) are, for instance, when the above-mentioned B is urethane,
(1) HO—&Brketopenst;&Parenopenst;CH
2
CH(CH
3
)O&Parenclosest;
n
—CONH—J
1
—NHCO&Brketclosest;
m
—OH
wherein m is an integer of 1 to 1000, n is an integer of 45 to 455, CONH—J
1
—NHCO represents, for example, tolylene diisocyanate (TDI) type urethane residual group, hexamethylene diisocyanate (HMDI) type urethane residual group, isophorone diisocyanate (IPDI) type urethane residual group, xylylene diisocyanate (XDI) type urethane residual group, diphenylmethane diisocyanate (MDI) type urethane residual group and the like,
(2) C
17
H
35
COO&Brketopenst;&Parenopenst;CH
2
CH(CH
3
)O&Parenclosest;
n
—CONH—J
1
—NHCO&Brketclosest;
m
—OC
17
H
35
wherein m, n and J
1
are the same as above, and the like. From the viewpoint of thermal decomposition property, the structure (1) is preferable.
Also when the above-mentioned X is thionyl, there are
(3) HO&Brketopenst;&Parenopenst;CH
2
CH(CH
3
)O&Parenclosest;
n
—J
2
&Brketclosest;
m
—OH
wherein m and n are the same as above, J
2
represents ═S═O,
(4) C
17
C
35
COO&Brketopenst;&Parenopenst;CH
2
CH(CH
3
)O&Parenclosest;
n
—J
2
&Brketclosest;
m
—CO
2
C
17
H
35
wherein m, n and J
2
are the same as above, and the like. From the viewpoint of thermal decomposition property, the structure (3) is preferable.
Also when the above-mentioned X is phosphoric acid residual group, there are
(5) HO&Brketopenst;&Parenopenst;CH
2
CH(CH
3
)O&Parenclosest;
n
—J
3
&Brketclosest;
m
—OH
wherein m and n are the same as above, J
3
represents a residual group of a phosphoric acid,
(6) C
17
H
35
COO&Brketopenst;&Parenopenst;CH
2
CH(CH
3
)O&Parenclosest;
n
—J
3
&Brketclosest;
m
—CO
2
C
17
H
35
wherein m, n and J
3
are the same as above, and the like. From the viewpoint of thermal decomposition property, the structure (5) is preferable.
In those examples, any of the groups in the brackets is a residual group obtained through alternating copolymerization.
The fluoropolymer of the present invention is one of homopolymers of monoethylenically unsaturated hydrocarbon monomer being completely substituted by fluorine, chlorine or those two atoms, copolymers of at least two of the above-mentioned monomers or mixtures comprising at least two of the homopolymers and the copolymers.
Example of the above-mentioned homopolymers is polytetrafluoroethylene (PTFE).
Examples of the above-mentioned copolymers are, for instance, a tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA) (the number of carbon atoms of the alkyl group is from 1 to 5) and tetrafluoroethylene-hexafluoropropylene (FEP) copolymer, and PFA is preferable in view of its excellent non-sticking property and heat resistance.
Examples of the above-mentioned mixtures of the homopolymers and the copolymers are, for instance, a mixture of PTFE and PFA, a mixture of PTFE and FEP, a mixture of PTFE, PFA and FEP, a mixture of PFA and FEP and the like, and the mixture of PTFE and PFA is preferable in view of its excellent non-sticking property and heat resistance.
A number average molecular weight of the above-mentioned fluoropolymer is from 2×10
4
to 1×10
7
, and 2×10
5
to 8×10
6
is preferable. When the number average molecular weight is less than 2×10
4
, the coating film tends to become fragile, and when more than 1×10
7
, there is a tendency that the particles are not fused with each other because its melt viscosity is too high.
The number average molecular weight of PTFE can be obtained, for example, through the measuring method described in Vol. 17, pages 3,253 to 3,257 of “
Journal of Applied Polymer Science
” (1973).
Also the number average molecular weight of FEP an be obtained through the method described in ASTM D-2116 by measuring a melt flow rate (MFR), calculating a melt viscosity (MV) based on the equation (1) and then calculating the number average molecular weight (Mn) based on

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