U.S. patent application number 14/132404 was filed with the patent office on 2014-07-17 for resin coated member and method of resin coating.
This patent application is currently assigned to National Institute For Materials Science. The applicant listed for this patent is National Institute For Materials Science. Invention is credited to Jin KAWAKITA, Masayuki KOMATSU, Seiji KURODA.
Application Number | 20140199516 14/132404 |
Document ID | / |
Family ID | 40259676 |
Filed Date | 2014-07-17 |
United States Patent
Application |
20140199516 |
Kind Code |
A1 |
KAWAKITA; Jin ; et
al. |
July 17, 2014 |
RESIN COATED MEMBER AND METHOD OF RESIN COATING
Abstract
A coating method through HVOF spraying that comprises generating
a combustion jet in a combustion chamber connected to one end of a
barrel while controlling the temperature of the combustion jet by
supply of an inert gas to the jet, feeding resin coating materials
into the temperature-controlled combustion jet and leading them to
pass through the barrel, and spouting the coating particles through
a spout port along with the combustion jet therethrough to thereby
coat the substrate surface; wherein the length of the barrel, the
temperature of the combustion jet and the physical properties of
the coating particles are defined so as to satisfy both the
following formulae (1) and (2). Numerical Formula 1 .alpha. .times.
t r > 0.5 ( 1 ) Numerical Formula 2 2.5 < Tav Tcp < 4.5 (
2 ) ##EQU00001##
Inventors: |
KAWAKITA; Jin; (Ibaraki,
JP) ; KURODA; Seiji; (Ibaraki, JP) ; KOMATSU;
Masayuki; (Ibaraki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
National Institute For Materials Science |
Ibaraki |
|
JP |
|
|
Assignee: |
National Institute For Materials
Science
Ibaraki
JP
|
Family ID: |
40259676 |
Appl. No.: |
14/132404 |
Filed: |
December 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12452611 |
Mar 18, 2010 |
8637121 |
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PCT/JP2008/062718 |
Jul 14, 2008 |
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14132404 |
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Current U.S.
Class: |
428/142 |
Current CPC
Class: |
B05B 7/205 20130101;
C09D 123/06 20130101; Y10T 428/24364 20150115; C23C 4/04 20130101;
Y10T 428/24355 20150115; B05D 1/10 20130101 |
Class at
Publication: |
428/142 |
International
Class: |
C09D 123/06 20060101
C09D123/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 13, 2007 |
JP |
2007-184340 |
Claims
1-7. (canceled)
8. A resin coated member of which the substrate surface is coated
with a coating material comprising a resin, characterized by having
a structure of such that the coating material breaks in the
micrometer-order random irregularities existing in the surface of
the substrate and integrated with the substrate.
9. The resin coated member as claimed in claim 8, wherein the
coating material comprises ultra-high-molecular weight
polyethylene.
Description
TECHNICAL FIELD
[0001] The present invention relates to a resin coated member where
the substrate surface is directly coated with a resin coating
material, and to a resin coating method for producing it.
BACKGROUND ART
[0002] Heretofore, since resins such as typically plastics are
excellent in corrosion resistance and transformation acceptablity,
it is often that the surfaces of various substrates such as iron,
aluminium and the like are coated for protection with resins such
as plastics, taking the advantages of the properties of those
resins, and thereafter the coated substrates are worked and
shaped.
[0003] In this case, a thick coating may be formed by casting a
molten plastic material onto a substrate; however, it is difficult
to form a uniform thin film having a thickness of, for example, at
most 100 microns. A resin such as an ultra-high-molecular weight
polyethylene or the like has poor fluidity, to which, therefore, a
coating method that comprises melting and fluidizing a powder could
not be applied.
[0004] As a thin coating method for an objective substrate with a
resin or the like, there is known a vapor deposition method or the
like, which, however, requires special facilities and is not
applicable at all to a large substrate; and therefore, in general,
a resin solution dissolved in a solvent is applied to such a
substrate.
[0005] The solvent-based resin coating has many problems in that
the solvent may degradate resins or may damage substrates and the
solvent may scatter to have some negative influences on the workers
and on the environment; and if possible, solvent-free resin coating
is desired.
[0006] On the other hand, regarding thin-film coating with an
inorganic material, HVOF spraying (high-velocity oxy fuel
spraying), which requires no solvent at all and which readily
attains spray coating of a substrate with an inorganic material
using a spray gun, has achieved many satisfactory results.
[0007] A technique of spraying a substrate with a heat-resistant
resin such as PEEK (polyether-ether ketone) or the like through
such HVOF spraying is disclosed in the following references (see
Patent References 1 and 2). However, according to these methods, it
is indispensable to previously roughen the surface of the substrate
and form on the substrate surface a bonding layer having good
adhesiveness to resin, for which, therefore, the working steps may
increase and the methods could not exceed the category of the
above-mentioned coating technique. In addition, the resin coating
members to be obtained are substantially those where the bonding
layer stands in the interface between the coating material and the
substrate. Further, in mere melt coating of the roughened surface
with PEEK by HVOF spraying, the coating material could not break
into the fine irregularities of the substrate surface, and strong
coating could not be realized.
Patent Reference 1: JP-A 2000-96203
Patent Reference 2: JP-A 2007-175881
[0008] In the above-mentioned background, the subject matter of the
present invention is to solve the prior-art problems and to provide
a coated member in which the coating resin and the substrate
strongly adhere to each other by a physical structure, and a resin
coating method for producing the coated member not requiring any
coating treatment at all.
DISCLOSURE OF THE INVENTION
[0009] For solving the above-mentioned problems, the invention is
characterized by the following:
[0010] The resin coated member of the invention 1 is a resin coated
member of which the substrate surface is coated with a coating
material comprising a resin, wherein the interface between the
coating material and the substrate surface has a structure of such
that the two break in each other with at least micron-pitch
irregularities.
[0011] The resin coated member of the invention 2 is that, in the
above invention 1, the coating particles are of
ultra-high-molecular weight polyethylene.
[0012] The resin coating method of the invention 3 is a coating
method through HVOF spraying that comprises generating a combustion
jet in a combustion chamber connected to one end of a barrel while
controlling the temperature of the combustion jet by supply of an
inert gas to the jet, feeding resin coating materials into the
temperature-controlled combustion jet and leading them to pass
through the barrel, and spouting the coating particles through a
spout port along with the combustion jet therethrough to thereby
coat the substrate surface; wherein the length of the barrel, the
temperature of the combustion jet and the physical properties of
the coating particles are defined so as to satisfy both the
following formulae (1) and (2):
Numerical Formula 1 .alpha. .times. t r > 0.5 ( 1 )
##EQU00002##
.alpha.: thermal diffusion coefficient of particles (m.sup.2/s), t:
heating time in barrel (s), r: radius of particles (m),
Numerical Formula 2 2.5 < Tav Tcp < 4.5 ( 2 )
##EQU00003##
Tav: average temperature of combustion jet in barrel (.degree. C.),
Tcp: cohesion critical temperature of particles (.degree. C.).
[0013] The resin coating method of the invention 4 is that, in the
above invention 3, the length of the barrel is at least 25 cm.
[0014] The resin coating method of the invention 5 is that, in the
above invention 3 or 4, the speed of the combustion jet is at least
mach 1.
[0015] The resin coating method of the invention 6 is that, in any
of the above inventions 3 to 5, the substrate is processed for
surface roughening.
[0016] The resin coating method of the invention 7 is that, in any
of the above inventions 3 to 6, the substrate is coated with
heating or cooling.
[0017] Based on the finding that the adhesion between resin and
substrate (mostly metal) is attained not by their mutual affinity
but by their physical structure, the present inventors have
repeated assiduous studies and, as a result, have developed a
method not requiring at all the above-mentioned coating
treatment.
[0018] The coated member of the invention 1 has an interface
structure in which the coating material resin and the substrate
break in each other with at least micron-pitch irregularities, and
therefore, the two can have extremely strong integrality
irrespective of their affinity.
[0019] In the invention 2, even with high-molecular-weight
polyethylene to which a coating method of melting and fluidizing
powder is not applicable, the interface structure of the type can
be realized.
[0020] According to the method of the inventions 3 to 7, the
above-mentioned resin-coated member can be produced in a good and
simplified manner.
DETAILED DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic cross-sectional view showing one
example of a spray gun usable in the invention
[0022] FIG. 2 is a graph illustrating the result of computing the
jet average temperature Tav in a barrel.
[0023] FIG. 3 is a flowchart showing one example of a resin coating
method of the invention.
[0024] FIG. 4 is a conceptual view showing one example of a method
of temperature control of a substrate.
[0025] FIG. 5 is a cross-sectional view showing one example of the
interface between the coating layer and the substrate in a resin
coated member of the invention.
[0026] FIG. 6 is an enlarged cross-sectional view of FIG. 5.
[0027] FIG. 7 is a view illustrating the test result of the
substrate protecting capability of the coating layer obtained with
a spray gun and its control system of the invention.
[0028] FIG. 8 includes views illustrating the observation result of
the resin-coated layer in the invention (A) and in a comparative
example (B).
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
(1) Combustion Chamber
(11) Combustion Zone
(12) Temperature Control Zone
(13) Inert Gas Supply Port
(13b) Control Valve
(14) Nozzle
(15) Fuel Supply Port
(16) Spark Plug
(2) Barrel
(20) Supply Port
(31) Cooling Water Supply Port
(32) Cooling Water Discharge Port
(A) Substrate
[0029] (L) Distance from supply port to spout port (La) Distance
between substrate surface and spout port (t) Heating Time in
barrel
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] The resin coating method and the resin coated member of the
invention are described, for example, with reference to the
constitution of a spray gun for HVOF spraying illustrated in FIG.
1.
[0031] The spray gun illustrated in FIG. 1 comprises a combustion
chamber (1) connected to one end of a barrel (2), in which the
combustion chamber (1) comprises, for example, a combustion zone
(11), a temperature control zone (12) and a nozzle (14), and the
combustion zone (11) is provided with a spark plug (16), a fuel
supply port (15) and an oxygen supply port (17) whereby the fuel
supply amount and the oxygen supply amount are controllable on the
supply side. The temperature control zone (12) is provided with an
inert gas supply port (13) so that the supply amount of an inert
gas is controlled by the control valve (13b) provided on the supply
side to thereby make it possible to control the temperature of the
combustion gas. The barrel (2) is provided with a supply port (20)
through which coating particles are injected thereinto under
pressure, on the side nearer to the combustion chamber.
[0032] In the drawing, (A) is a substrate to be coated, and the
distance between the surface of the substrate (A) and the spout
port is expressed by (La). In the spray gun of FIG. 1, the
constitutive members are so designed that they are composed of a
double-layered partition wall and provided with a supply port (31)
and a discharge port (32) for supplying and discharging cooling
water inside the space of the partition wall, thereby making it
possible to prevent the outer wall from being heated for stable
driving.
[0033] The resin coating method of the invention is a coating
method through HVOF spraying that comprises generating a combustion
jet in the combustion chamber (1) connected to one end of the
barrel (2) while controlling the temperature of the combustion jet
by supply of an inert gas to the jet, feeding resin coating
materials into the temperature-controlled combustion jet and
leading them to pass through the barrel (2), and spouting the
coating particles through a spout port along with the combustion
jet therethrough to thereby coat the surface of the substrate (A);
wherein the length of the barrel (L), the temperature of the
combustion jet and the physical properties of the coating particles
are defined so as to satisfy both the following formulae (1) and
(2):
Numerical Formula 3 .alpha. .times. t r > 0.5 ( 1 ) Numerical
Formula 4 2.5 < Tav Tcp < 4.5 ( 2 ) ##EQU00004##
[0034] In formula (1), a means the thermal diffusion coefficient of
the coating particles (m.sup.2/s), t means the time for which the
coating particles are heated inside the barrel (s), and r means the
radius of the coating particles (m). The thermal diffusion
coefficient of the coating particles is determined according to the
following formula:
.alpha.=k/.rho.Cp
wherein k: thermal conductivity (J/smK), .rho.: density
(kg/m.sup.3), Cp: specific heat (K/kgK)/ For the thermal
conductivity, the density and the specific heat, the data in
Material Handbook or the like may be referred to.
[0035] t can be obtained from the speed of the combustion jet to be
computed from the mass flow rate of the combustion gas and the
inert gas, and from the barrel length (L). The barrel length (L) is
defined as the distance from the supply port (20) to the spout port
at the tip of the barrel (2).
[0036] In the formula (2), Tav means an average temperature
(.degree. C.) of the combustion jet inside the barrel, and this can
be theoretically obtained by (a) computing the temperature of the
combustion jet in the temperature control zone from the mass flow
rate of the inert gas relative to the combustion gas, then (b)
computing the gas temperature profile in the flow direction in the
nozzle and the barrel from the viewpoint of fluid dynamics under
the condition, and (c) computing the average temperature Tav inside
the barrel from the gas temperature profile inside the barrel. Tcp
means the cohesion critical temperature (.degree. C.) of the
coating particles, and this is the softening temperature of the
resin constituting the particles .+-.10.degree. C. The expression
of .+-.10.degree. C. is because even resins of the same type may
slightly differ in the softening temperature thereof depending on
the additives therein and on the synthesis degree thereof, the
value range can include the difference so as to attain suitable
temperature expression.
[0037] The combustion jet temperature in HVOF spraying is generally
around 3000.degree. C. in a case of no cooling with an inert gas or
the like; however, with a spray gun having the constitution as
above, the combustion jet temperature could be controlled within a
range of approximately from 3000.degree. C. to 300.degree. C. owing
to the supply of an inert gas to the jet. In practice, the
temperature is controlled to fall within a suitable range of from
1000.degree. C. to 400.degree. C. or so depending on the
characteristics of the coating material.
[0038] The combustion jet speed is preferably a jet speed of at
least mach 1 (supersonic velocity) for attaining high-adhesion
resin coating in the resin coating method of the invention. More
preferably, it is at least mach 2. The combustion jet speed may be
controlled by controlling the flow rate of the fuel and oxygen to
be fired and that of the inert gas; and for example, inside the
barrel (2), the speed may be a supersonic velocity of around mach 2
in the following Examples. In this, the supply amount of the inert
gas may have some influence on the supply amount of fuel and oxygen
in the combustion zone (11); and when the insert gas is increased,
then the fuel and oxygen may be reduced, but as a result, the
temperature control may be possible not having any significant
influence on the combustion jet speed (to such a degree with no
influence on t). Specifically, even at a low temperature
corresponding to the resin, a supersonic combustion jet speed can
be realized.
[0039] As the fuel, usable are various known heat sources.
Typically, for example, there may be mentioned kerosene, acetylene,
etc. For realizing the above-mentioned combustion jet speed, a case
where kerosene is used as the fuel only as a guide may be
mentioned, in which the kerosene flow rate is within a range of
from 0.3 to 0.5 SLM or so and the oxygen flow rate is within a
range of from 500 to 900 SLM or so, though the data may vary
depending on the dimension and the shape of the combustion zone
(11) and the nozzle (14). Needless-to-say, it is not limitative. As
the inert gas, usable are nitrogen and rare gases such as He, Ar,
etc.
[0040] The barrel (2) is provided with a supply port (20) through
which coating particles are injected thereinto under pressure, on
the side nearer to the combustion chamber; and coating particles
are spouted out through a spout port on the other end along with
the temperature-controlled combustion jet therethrough.
[0041] The characteristic feature of the invention of the present
application is that, for realizing good coating, the barrel length
(L), the combustion jet temperature and the physical properties of
the coating particles are suitably defined so as to satisfy the
above-mentioned formula (1) and formula (2).
[0042] The formula (1) defines the right-hand value, which is a
function of the thermal diffusion coefficient of the coating
particles .alpha. (m.sup.2/s), the heating time inside the barrel t
(s) and the radius of the particles r (m), to be more than 0.5. The
combustion jet temperature is defined to be considerably lower than
the temperature in conventional spray guns, as so mentioned in the
above, and therefore, when the right-hand value is 0.5 or less,
then the coating particles could be heated insufficiently and a
good coating layer could not be formed. In case where the
right-hand value is larger, then the particles could be uniformly
heated as a whole in their collision and therefore it may be
considered that the particles could more surely break in the fine
irregularities in a broad range and could more readily adhere
thereto.
[0043] The value of Tav/Tcp in the formula (2) is a ratio of the
average temperature of the jet in the barrel Tav (.degree. C.) to
the cohesion critical temperature of the coating particles Tcp
(.degree. C.), and is defined to be more than 2.5 but less than
4.5. In case where the prevention of thermal degradation of the
coating particles is emphasized, then it is desirable that the
value of Tav/Tcp is shifted to the lowermost limit side, or that
is, the temperature of the combustion jet is lowered; however, when
the value is 2.5 or less, then the coating particles could be
insufficiently heated and a good, dense and adhesive coating layer
could not be formed. On the other hand, in case where the
densification of the coating layer and the adhesiveness thereof to
the substrate are emphasized, the value of Tav/Tcp may be shifted
to the uppermost limit side, or that is, the temperature of the
combustion jet may be made high. However, when the value is 4.5 or
more, then it is unfavorable since the coating particles may be
degraded and could not adhere to the substrate or the physical
properties of the coating layer may be degraded.
[0044] Regarding the above-mentioned distance (L) in the barrel,
the distance is from 10 to 20 cm or so in known spray guns.
However, with a barrel having the value L in that range, a good
coating layer could not be formed when coating particles having an
big thermal diffusion coefficient .alpha. and an extremely small
particle radius r (m) are not selected, which, however, is
impracticable. Accordingly, a special step of surface roughing of a
substrate or coating a substrate with a coating layer having good
adhesiveness to resin is said to be indispensable, as in the prior
art. Contrary to this, in the invention of the present application,
even when ordinary resin coating particles of which the thermal
diffusion coefficient a and the particle radius r (m) are within an
ordinary range are used, simple and good resin coating can be
realized so far as a spray gun of which the distance (L) satisfies
the above-mentioned formulae (1) and (2) is used. The value L of
the spray gun is not specifically defined, but from the past
inspection, the value is preferably at least 20 cm, practically at
least 25 cm, more preferably at least 30 cm. Typically, the value
is preferably from 35 to 50 cm or so in consideration of the
physical properties of the coating particles. The present inventors
have confirmed that the coating is well possible in case where the
total flying distance of the coating particles from the supply port
to the substrate is within a range of up to 700 mm. Accordingly, it
may be considered that the length to be computed by subtracting the
distance (La) between the spout port and the substrate from 700 mm
or so can be well defined as the distance (L).
[0045] In the resin coating method of the invention, the
temperature of the combustion jet is low in accordance with the
resin coating particles, and therefore, when the distance (L) of
the barrel is at most 20 cm or so like in the prior art, the resin
coating particles inside the barrel could not be sufficiently
heated; however, when the distance (L) is made not shorter than 25
cm, for example, it is made to be 40 cm or so, then the particles
could be sufficiently heated and good coating could be thereby
attained.
[0046] In a practical coating operation, even after the resin
coating particles have been applied to the substrate, the
combustion jet is still kept blown to the coated surface for a
certain period of time. In this case, when a spray gun in which the
distance (L) is longer than before as in the above, or that is, at
least 25 cm, for example 40 cm or so is used, then the temperature
of the combustion jet could be suitably lowered inside the barrel
and the coated resin could be prevented from being thermally
degraded.
[0047] In the resin coating method of the invention of the present
application mentioned in the above, resins heretofore used in
various coating compositions can be used as the coating particles
in the same manner as therein. For example, they include the
following:
[0048] Polyethylene (PE), polypropylene (PP), polystyrene (PS),
acrylonitrile/styrene resin (AS), acrylonitrile/butadiene/styrene
resin (ABS), methacrylic resin (PMMA), vinyl chloride (PVC),
polyamide (PA), polyacetal (POM), ultra-high-molecular polyethylene
(UHPE), polybutylene terephthalate (PBT), GF-reinforced
polyethylene terephthalate (GF-PET), polymethylpentene (TPX),
polycarbonate (PC), modified polyphenylene ether (PPE),
polyphenylene sulfide (PPS), polyether-ether ketone (PEEK),
liquid-crystal polymer (LCP), polytetrafluoroethylene (PTFE),
polyether imide (PEI), polyarylate (PAR), polysulfone (PSF),
polyether sulfone (PES), polyamidimide (PAI).
[0049] The particle size of the coating particles is not
specifically defined so far as the above-mentioned formulae (1) and
(2) are satisfied; however, in consideration of the thermal
diffusion coefficient .alpha. and others of the individual
materials, those having a particle size suitable for coating may be
selected and used.
[0050] The substrate to be coated is not also specifically defined,
for which are usable not only carbon steel but also various metals
and alloys as well as ceramics of inorganic materials and others
such as those mentioned below.
[0051] Metals (magnesium, aluminium, copper, iron, titanium, etc.)
and their alloy ceramics (oxides such as alumina; nitrides such as
TiN; carbides such as SiC; borides such as B4C), etc.
[0052] Keeping the substrate at a suitable temperature, for
example, resin substrates mentioned below may also be readily
coated.
[0053] Plastics (ordinary plastics such as polyethylene, polyvinyl
chloride, polypropylene, polystyrene; polyvinyl acetate, ABS resin,
AS resin, acrylic resin, polyacetal, polyimide, polycarbonate,
modified polyphenylene ether (PPE), polybutylene terephthalate,
polyarylate, polysulfone, polyphenylene sulfide, polyether-ether
ketone, polyimide resin, fluororesin, etc.
[0054] In the invention of this application, one preferred
embodiment comprises surface roughening the substrate. As the
surface-roughening means, employable is a known method of blasting,
etc. Preferably, the surface of the substrate is roughened to have
irregularities so as to increase the contact area thereof with the
coating material applied thereto. The roughness of the
irregularities is not specifically defined so far as it does not
have any influence on the uniformity and the strength of the
coating film; and the irregularities may be formed in the entire
surface or a part of the surface of the substrate. In the
invention, micron-pitch irregularities of at most 1 .mu.m may well
exhibit the function thereof. This is because, according to the
method of the invention of the present application, the coating
material is made to collide against the substrate at a high speed
along with a suitably temperature-controlled combustion jet
thereto, and therefore, the coating material can be step into even
extremely small irregularities in the surface of the substrate.
This may be considered because, even when the substrate has
micro-irregularities existing therein, some far larger physical
force may be generated as compared with the physical force negative
to the contact between the substrate and the coating material, such
as the surface tension of the coating material, air invasion,
etc.
[0055] Accordingly, not only by the irregularities of the substrate
of itself but also by the irregularities mechanically formed in the
substrate, the coating layer and the substrate may be mechanically
strongly bonded to each other.
[0056] In the invention of this application, the substrate to be
coated may be heated or cooled in coating it. In this case, the
substrate may be set at any desired temperature, and as one
embodiment in practice, a temperature range from a temperature at
which the coating particles soften to a temperature lower by about
50.degree. C. than it may be employed for the temperature as a
general guide. This is for the purpose of unifying the temperature
of the target surface when the coating particles adhere to the
substrate; and accordingly, coating of excellent adhesiveness for
good coating film condition can be attained. In particular, this is
effective in a case where the above-mentioned resin is used as the
substrate.
[0057] The resin coated member of the invention thus produced in
the manner as above is a resin coated member in which the surface
of the substrate is coated with a coating material of resin, and
the interface between the coating material and the substrate
surface has a structure where the substrate and the coating resin
break in each other with at least micron-pitch irregularities
therebetween and are directly integrated, for example, as
illustrated in FIG. 6. The micron-pitch irregularities may be
understood as irregularities of such that the distance between the
adjacent projections thereof is on an order of micrometer.
Typically, the distance between the adjacent projections may be at
most tens micrometers or so, preferably at most a few micrometers.
Preferably, the irregularities are in the entire interface between
the coating material and the substrate surface, but may be partly
in the interface, and there is no specific limitation thereon.
[0058] Characteristically, in the resin coated member of the
invention, the resin coating material can break in the inside of
even the micro-recesses of, for example, not larger than a few
micrometers, of which the width of the inner space is larger than
in the substrate surface part, therefore forming an intricate
resin/substrate interface constitution. This constitution can be
realized only by deep stepping of the coating material into the
depth of the substrate surface by the supersonic combustion jet;
and accordingly, the two may have an extremely strong integrality
by the mechanical structure thereof irrespective of their affinity
to each other.
[0059] In the prior art of resin coating with solvent, the contact
between the substrate surface and the resin is only by chemical
affinity of the two. Accordingly, for example, when the substrate
surface has irregularities, they may bring about some physical
force that could not be overcome by the affinity, for example,
bridge formation by the surface tension of the coating material,
solvent vapor accumulation, air invasion, etc.; and therefore, the
irregularities are undesirable. However, it is almost impossible to
mirror-finish the substrate surface and, as a result, in solvent
coating, it is impossible to make the coating material break in
micro-level irregularities.
[0060] Also in simple resin melt coating by conventional HVOF
spraying, it may be difficult for the molten material to break in
the micro-level irregularities in the substrate surface such as
those mentioned in the above, in consideration of the surface
tension and the affinity of the coating material melt as well as
air invasion, etc.
[0061] Contrary to this, in the invention of the present
application where a coating material is made to impact against a
substrate at a high speed over the sonic speed, it has become
possible for the first time to generate a physical force far larger
than the above-mentioned negative physical force (surface tension
of coating material, solvent vapor accumulation, air invasion,
etc.), and as a result, it may be considered that the coating
material could be made to step in even extremely small
irregularities with no influence of the negative physical force
thereon.
[0062] As the coating material, usable are resins for use in
various coating materials such as those mentioned in the above; and
as the substrate, usable are various metals and their alloy
ceramics and resin substrates such as those mentioned in the
above.
[0063] Now the invention is described in more detail with reference
to the following Examples. Needless-to-say, the invention is not
restricted by the following Examples.
EXAMPLES
Example 1
Spray Gun for HVOF Spraying
[0064] FIG. 1 is a schematic vertical cross-sectional view
illustrating the constitution of a spray gun used in the resin
coating method of the invention.
[0065] The spray gun comprises a combustion chamber (1) and a
barrel (2). The combustion chamber (1) comprises a combustion zone
(11), a temperature control zone (12) and a nozzle (14); and the
combustion zone (11) is provided with a spark plug (16), a fuel
supply port (15) and an oxygen supply port (17), and the fuel feed
rate and the oxygen feed rate can be controlled on the supply side.
The temperature control zone (12) is provided with an inert gas
supply port (13), and the temperature of the combustion gas can be
controlled by controlling the feed rate of the inert gas by the
control valve (13b) provided on the supply side. The combustion gas
generated in the combustion zone (11) is cooled in the temperature
control zone (12) by supply of a suitable amount of an inert gas
thereinto and its temperature is thereby controlled, and this is
fed to the barrel (2) as a combustion jet through the nozzle (14).
The speed of the combustion jet is supersonic of mach 2 or so in
the barrel (2), and the temperature of the combustion jet can be
controlled within a range of from 3000 to 400.degree. C. The
constitutive members are so designed that they are composed of a
double-layered partition wall and provided with a supply port (31)
and a discharge port (32) for supplying and discharging cooling
water inside the space of the partition wall, thereby making it
possible to prevent the outer wall from being heated for stable
driving. (A) is a substrate to be coated; and the distance between
the surface of the substrate (A) and the spout port is expressed as
(La).
[0066] Kerosene was used as the fuel of the combustion jet, and
nitrogen was used as the inert gas; and the average temperature in
the barrel, Tav was computed in this case, and the data are shown
in FIG. 2. In that manner, it is known that, when the feed rate of
the fuel and oxygen and the feed rate of the inert gas are suitably
controlled, then the temperature and Tav of the combustion jet can
be controlled.
Regarding Control of Spray Gun Condition
[0067] FIG. 3 is a flow chart describing one example of spray gun
control for realizing the coating method of the invention. In the
drawing, the area surrounded by the dash line is by computer
software operation.
[0068] The operation is according to the following process.
S1:
[0069] .alpha. (thermal diffusion coefficient of the coating
particles to be used (m.sup.2/s)), r (radius of the particles (m)),
Tcp (cohesion critical temperature of the particles (.degree. C.))
and t (heating time in barrel to be determined by the barrel length
L (s)) are inputted.
S2:
[0070] Based on the formula (1), it is determined as to whether or
not a predetermined spray gun can be used with the inputted data
(as to whether or not the data satisfy the formula (1)); and in
case where the data do not satisfy the formula, then a message of
"unserviceable" is expressed on a display or the like.
[0071] On the contrary, when the formula (1) is satisfied, then the
process goes ahead to S3, and the inputted Tcp data are fed to
S3.
S3:
[0072] Based on the Tcp data fed from S2, the acceptable range of
Tav (average temperature of jet in barrel (.degree. C.)) is
determined according to the formula (2), and this is fed to S4.
S4:
[0073] Based on the position information from the detector of
detecting the position of the valve for controlling the feed rate
of inert gas, the computed Tav at the current stage is compared
with the Tav range computed in the previous S3; and in case where
the former falls within the Tav range, then a message of
"serviceable" is displayed.
[0074] On the contrary, in case where the computed Tav is outside
the range, then the signal of + or - obtained in the computation
result are fed to S5.
S5:
[0075] The fed signal is determined as to whether it is plus or
minus. In a plus case, an increase signal is outputted to the valve
control solenoid; and in a minus case, a decrease signal is
thereto.
[0076] Until the signal of "serviceable" is expressed or the
operation stop is inputted, S4 and S5 are repeated so that the feed
rate of inert gas can be automatically controlled in accordance
with the physical properties of the coating particles or the
characteristics of the spray gun to be used.
[0077] The repetition interval must be not shorter than the time
interval of a period of time for which one-round solenoid operation
is finished, for enhancing the system stability and
reliability.
[0078] In case where the spray gun of FIG. 1 is used, the speed of
the combustion jet is determined by the amount of the combustion
gas to be generated in the initial stage (in case where the inert
gas is fed in a lowermost limit amount corresponding to resin) but
is not so much influenced by the feed rate of inert gas to such a
degree that it has some influence on t (heating time in barrel
(s)); however, t may vary depending on the size of the spray gun.
Accordingly, it is also possible to previously input a conversion
formula intrinsic to the experimentally-settled spray gun so that
the barrel length L inputted in the formula can be automatically
converted into t.
Resin Coating Experiment Result
[0079] Using a spray gun having the above-mentioned constitution in
the above-mentioned control system, resin coating was attained
under the conditions mentioned below, and the results are shown in
Table 1.
[0080] As the coating particles, used was an ultra-high-molecular
weight polyethylene, Mitsui Chemical's Mipelon XM220. Its thermal
diffusion coefficient .alpha. is 2.4, and its adhesion critical
temperature Tcp is 393K. As the fuel, used were kerosene at a flow
rate of 0.35 SLM and oxygen at a flow rate of 670 SLM. An inert gas
(nitrogen) was fed at a flow rate of 0, 500 or 1000 SLM.
[0081] The barrel distance (L) was 16 inches in Nos. 1 to 15, and 8
inches in Nos. 16 to 18. Under the condition, the heating time in
barrel, t was set as 0.8.times.10.sup.-3 sec, and
0.4.times.10.sup.-3 sec, respectively.
[0082] Controlling the temperature of the substrate (A) was tried
as in FIG. 4. The substrate temperature control was as follows:
Based on the difference between the measured system temperature and
the measured substrate temperature, in case where the measured
system temperature is high, the cooling device is put ON and the
heating device is cut OFF; but in case where the measured system
temperature is low, the operation is contrary to the above; whereby
the substrate is heated or cooled to make it have the preset
temperature.
[0083] As the substrate, used was carbon steel (SS400).
TABLE-US-00001 TABLE 1 Substrate Exper- temperature Formula Formula
Coating Layer iment Coating Particles Barrel Inert Gas control La n
(1) (2) thickness No material Tcp .alpha. d L t L/min Tav material
(.degree. C.) mm times >0.5 Tav/Tcp (.mu.m) condition 1 poly-
393 2.4 43 16 0.8 1000 1489 carbon no 200 4 0.64 3.79 33 .THETA.
ethylene steel 2 poly- '' '' '' '' 0.8 '' '' carbon no '' 4 0.64
3.79 43 .THETA. ethylene steel 3 poly- '' '' '' '' 0.8 '' '' carbon
no '' 1 0.64 3.79 4 .largecircle. ethylene steel 4 poly- '' '' ''
'' 0.8 '' '' carbon no '' 2 0.64 3.79 18 .THETA. ethylene steel 5
poly- '' '' '' '' 0.8 '' '' carbon 100 '' 1 0.64 3.79 18 .THETA.
ethylene steel 6 poly- '' '' '' '' 0.8 '' '' carbon 100 '' 2 0.64
3.79 24 .THETA. ethylene steel 7 poly- '' '' '' '' 0.8 '' '' carbon
100 '' 4 0.64 3.79 219 .THETA. ethylene steel 8 poly- '' '' '' ''
0.8 '' '' carbon 100 '' 6 0.64 3.79 66 ethylene steel (only at the
start point) 9 poly- '' '' '' '' 0.8 '' '' carbon no '' 2 0.64 3.79
27 .THETA. ethylene steel 10 poly- '' '' '' '' 0.8 1500 1342 carbon
no '' 4 0.64 3.41 7 .largecircle. ethylene steel 11 poly- '' '' ''
'' 0.8 '' '' carbon 100 '' 4 0.64 3.41 105 .THETA. ethylene steel
12 poly- '' '' '' '' 0.8 '' '' carbon 100 '' 10 0.64 3.41 233
.THETA. ethylene steel 13 poly- '' '' 162 '' 0.8 500 1654 carbon no
'' 4 0.18 4.21 5 .DELTA. ethylene steel 14 poly- '' '' '' '' 0.8
1000 1489 carbon 100 '' 4 0.18 3.79 5 .DELTA. ethylene steel 15
poly- '' '' '' '' 0.8 1500 1342 carbon 100 '' 4 0.18 3.41 x
ethylene steel 16 poly- '' '' 43 8 0.4 500 1822 carbon 100 '' 0.45
4.64 50 .diamond-solid. ethylene steel 17 poly- '' '' '' '' 0.4
1000 1605 carbon 100 '' 0.45 4.08 x ethylene steel 18 poly- '' ''
162 '' 0.4 500 1822 carbon 100 '' 4 0.12 4.64 x ethylene steel Tcp:
cohesion critical temperature of coating particles (K) d: diameter
of coating particles (.mu.m) .alpha.: thermal diffusion coefficient
of coating particles used (.times.10.sup.-7 m.sup.2/s) Tav: average
temperature of jet in barrel (K) L: barrel length (inch) t: heating
time in barrel (.times.10.sup.-3 s) La: distance between spout port
and substrate surface (mm) n: spray gun scanning frequency Inert
gas: nitrogen gas was used. .THETA.: Firmly adhered, dense and
smooth surface coating layer was formed. .largecircle.: Adhesion
efficiency was low, but the same coating layer as in .THETA. was
formed. : The surface was wrinkled, but in the other aspects, the
same coating layer as in .THETA. was formed. .DELTA.: The adhesion
power of the coating layer to the substrate was weak, and layer
readily dropped. .diamond-solid.: The coating layer discolored in
black. x: Not adhered.
[0084] As obvious from the results in Table 1, the coating under
the condition satisfying the above-mentioned formulae (1) and (2)
resulted in good resin coating of substrate in a uniform thickness,
and the formed coating layer was extremely dense. The thickness of
the coating layer could be readily controlled to a degree of from a
few .mu.m to a few hundred .mu.m.
[0085] The cross section of the coated substrate of Experiment No.
2 is shown in FIG. 5. The coating material broke in the depth of
the substrate surface through supersonic jetting thereof, and it is
understood that the coating firmly fixed to the substrate not only
by adhesion but also by mechanical profile. This aspect was
observed in more detail, as in FIG. 6, in which it is obvious that
the coating material broke in the irregularities of the substrate
surface existing at a pitch of at most 1 .mu.m.
[0086] On the other hand, under the condition not satisfying the
formulae (1) and (2), it was confirmed that the adhesiveness of the
coating layer to the substrate was poor, or the coating could not
be attained, or the coating layer was discolored or deteriorated by
thermal degradation. For example, even though the coating layer was
formed, it discolored in black.
[0087] Further, under the same condition as in Experiment No. 2, a
polyethylene coating (having a thickness of 50 microns) was formed
on a substrate of carbon steel SS400, and then a copper wire was
connected to the backside of the substrate, and the coated surface
except 2 cm.sup.2 left as such, was insulation-coated with a
silicon resin. The sample was dipped in artificial seawater at room
temperature for 5 days. The result is shown in FIG. 7. No rust
formed on the surface of the coating layer, and it is confirmed
that the coated surface kept the same condition as that before
dipping. It is known that, as coated with the uniform and dense
polyethylene coating layer, the resin coated member could have an
excellent barrier function even though the coating layer was thin
and had a thickness of 50 .mu.m.
Example 2
[0088] Using the spray gun as in Example 1, polyethylene was blown
onto a mirror-polished 304 stainless steel sheet. The coating
condition is mentioned below. FIG. 8 includes observation results
of the resin coating according to the method of the invention of
the present application (A) and the resin coating in a comparative
example (B).
[0089] Barrel length: (A) 8 inches, (B) 16 inches
[0090] Amount of nitrogen gas added: 500 L/min
[0091] Spray distance: 50 mm
[0092] Observation power: 100, 200, 500 magnifications
[0093] As in FIG. 8, (A) show parts swollen like the yolk of a
fried egg; but (B) show larger parts looking like the egg white of
a fried egg. This may be presumed because, in (A), the heating time
could be sufficient and the ratio of the molten polyethylene could
be larger and the deposited volume of polyethylene could also be
larger, and therefore the coating layer could be thick; but in (B),
the molten amount of polyethylene would be small and the volume
thereof would be also small.
INDUSTRIAL APPLICABILITY
[0094] According to the resin coating method of the invention, a
uniform and firm resin coating may be formed in a solvent-free
simplified manner, readily on already-constructed structures, etc.
In addition, the invention provides resin coated members improved
in the environment-resistant capabilities such as electric
insulation, corrosion resistance, rust resistance, antifouling,
chemical resistance, impact resistance, abrasion resistance,
bending resistance, tensile damage resistance, etc.
* * * * *