Coating processes – Solid particles or fibers applied – Uniting particles to form continuous coating with...
Reexamination Certificate
2000-09-20
2003-07-08
Beck, Shrive P. (Department: 1762)
Coating processes
Solid particles or fibers applied
Uniting particles to form continuous coating with...
C427S202000, C427S374400, C427S385500, C264S460000, C526S242000
Reexamination Certificate
active
06589597
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a molding method or an ethylene/tetrafluoroethylene type copolymer (hereinafter referred to also as ETFE) powder. Particularly, it relates to a molding method for an ETFE powder whereby a coating film excellent in the surface smoothness can be obtained, and an ETFE powder therefor.
BACKGROUND ART
ETFE is excellent in heat resistance and chemical resistance and is therefore widely used as a material suitable for corrosion resistant lining or corrosion resistant containers, etc. As a processing method for corrosion resistant lining, there is a method wherein ETFE is powdered and subjected to a known method such as electrostatic powder coating, fluid bed coating or rotational molding to form coating films on various substrates. Further, as a processing method for corrosion resistant containers, there is a method wherein: ETFE is powdered and subjected to a mold, whereby a bottle molded product having any shape is obtained by a molding method such as rotational molding.
However, in a molding method for a powder, it sometimes tends to be difficult to increase the smoothness of the surface of the coating film, since no external shearing stress is exerted during the melting and solidification of a resin.
DISCLOSURE OF THE INVENTION
The present invention has an object to provide a molding method for a novel ETFE powder, whereby the surface smoothness of the coating film thereby obtained, can be remarkably improved. The present invention provides an ETFE powder which is made of ETFE of ethylene, tetrafluoroethylene and a fluorine-containing vinyl monomer copolymerizable therewith, said copolymer having a viscoelastic property represented by the formula (1) wherein the viscosity factor &phgr; in the formula (1) is at most 1×10
4
Pa·sec, and the anelasticity factor &egr; represented by the formula (2) as the sum of &egr;
i
in the formula (1) is at most 5×10
−4
Pa
−1
, and which has an average particle diameter of from 5 to 1,000 &mgr;m and an apparent density of at least 0.5 g/cc:
J
(
t
)
=
t
/
φ
+
∑
i
=
1
6
[
ϵ
i
(
1
-
exp
(
-
t
/
τ
i
)
)
(1)
ϵ
=
∑
i
=
1
6
ϵ
i
(2)
provided that in the formulae (1) and (2), J(t) is the amount of strain per unit stress under a predetermined stress, &phgr; is a viscosity factor, t is time, &egr; is an anelasticity factor, i is an integer of from 1 to 6, and &tgr;
i
is a constant (&tgr;
1
=0.135 sec, &tgr;
2
=0.368 sec, &tgr;
3
=1.000 sec, &tgr;
4
=2,718 sec, &tgr;
5
=7.389 sec, &tgr;
6
=20.086 sec)
Further, it provides a molding method for an ETFE powder characterized by depositing the above ETFE powder on a substrate surface, followed by heat melting and cooling for solidification to form a coating film.
BEST MODE FOR CARRYING OUT THE INVENTION
ETFE to be used in the present invention is one obtained by copolymerizing tetrafluoroethylene (hereinafter referred to as TFE), ethylene and a fluorine-containing vinyl monomer copolymerizable therewith, wherein the molar ratio of polymer units based on TFE/polymer units based on ethylene is preferably 90 to 50/10 to 50. If the molar ratio of polymer units based on TFE/polymer units based on ethylene is lower than 50/50, the decomposition temperature tends to be low, whereby the moldability tends to be impaired. On the other hand, if this molar ratio exceeds 90/10, by-product polytetrafluoroethylene is likely to be present in ETFE, and the formed coating film is likely to form gels, or the high surface smoothness intended by the present invention, tends to be impaired.
The fluorine-containing vinyl monomer to be used in the present invention is a fluorine-containing vinyl monomer copolymerizable with TFE and ethylene, and the following ones may, for example, be mentioned. The fluorine-containing vinyl monomers may be used alone or in combination as a mixture of two or more of them.
Poly (or mono) fluoroethylenes such as CF
2
═CFCl, and CF
2
═CH
2
.
Poly (or mono) fluoropropylenes such as CF
2
═CFCF
3
, and CF
2
═CHCF
3
.
(Poly (or mono) fluoroalkyl) ethylenes such as CH
2
═CH(CF
2
)
2
F, and CH
2
═CH(CF
2
)
4
F.
Poly (or mono) fluoroalkyl fluoroethylenes wherein the poly (or mono) fluoroalkyl group has from 2 to 10 carbon atoms, such as CH
2
═CF(CF
2
)
4
F, and CH
2
═CF(CF
2
)
3
H.
Perfluorovinyl ethers such as CF
2
═CFO(CF
2
CFXO)
m
Rf (wherein Rf is a C
1-6
perfluoroalkyl group, X is a fluorine atom or a trifluoromethyl group, and m is an integer of from 0 to 5).
Vinyl ethers having a carboxyl group or a sulfonate group, such as CF
2
═CFO(CF
2
)
3
COOCH
3
, and CF
2
═CFOCF
2
CF (CF
3
) OCF
2
CF
2
SO
2
F.
The proportion of polymer units based on the fluorine-containing vinyl monomer is usually from 1 to 10 mols, preferably from 2 to 7 mols, per 100 mols of the total amount of polymer units based on TFE and polymer units based on ethylene.
For ETFE in the present invention, it is important that the viscosity factor &phgr; defined by the above formula (1) is at most 1×10
4
Pa·sec, and the an elasticity factor &egr; defined by the above formula (2) is at most 5×10
−4
Pa
−1
.
The above formula shows the relation between the strain and the time when a very small stress is exerted in a molten state of the polymer heated at a temperature of at least the melting point. If the molten liquid is a Newtonian fluid, the strain increases linearly with time. Namely, it is considered to be a fluid whereby &egr;=0 in the formula (2). Whereas, ETFE is an agglomerate of linear molecules, and the molten liquid will not take an ideal Newtonian fluid behavior, since the molecules are entangled, and it shows a viscous behavior and an elastic behavior simultaneously against a very small stress, whereby the strain-time curve becomes non-linear. Namely, it is considered to be a fluid whereby &egr;>0 in the formula (2). If such ETFE is melted and left to stand still, the surface of the molten liquid becomes smooth and flat by free movement of molecules and the own weight of the molten liquid itself, while it shows an elastic behavior as the linear molecules are entangled one another, which prevents the surface from becoming completely flat and smooth.
ETFE in the present invention has a viscosity factor &phgr; of at most 1×10
4
Pa·sec, preferably from 500 to 7,000 Pa·sec. When the viscosity factor &phgr; is at most 1×10
4
Pa·sec, mutual free movement of the molecules can be promoted. If the viscosity factor &phgr; is larger than 1×10
4
Pa·sec, free movement of molecules will be suppressed, and a large stress and time will be required to obtain a smooth surface, and it tends to be difficult to obtain a smooth surface.
Further, ETFE to be used in the present invention has an anelasticity factor &egr; of at most 5×10
−4
Pa
−1
, preferably from 1×10
−5
to 1×10
−4
Pa
−1
. By adjusting the anelasticity factor &egr; to be at most 5×10
−4
Pa
−1
, elastic resistance can be made small. If the anelasticity factor &egr; is larger than 5×10
−4
Pa−1, the mutual entangling effect of molecules tends to be large, and it tends to show a more elastic behavior, whereby it tends to be difficult to obtain a smooth surface.
ETFE having a viscosity factor &phgr; of at most 1×10
4
Pa·sec can be obtained by controlling the molecular weight. If the molecular weight is too large, slipping of ETFE molecules one another will be suppressed, whereby the viscosity tends to be large, and the value of the viscosity factor &phgr; will not be satisfied. Specifically, the control of the molecular weight of ETFE can be accomplished by e.g. the temperature, the pressure and/or the addition of a chain transfer agent during the polymerization. Further, as an index of the molecular weight of ETFE, the melt index (MI) is employed.
Further, ETFE having an anelasti
Ono Mitsufumi
Takakura Teruo
Asahi Glass Company Limited
Beck Shrive P.
Fletcher, III William Phillip
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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