U.S. patent application number 11/334574 was filed with the patent office on 2006-06-08 for ethylene-vinyl alcohol copolymer composition, and powdery coating composition comprising it.
This patent application is currently assigned to KURARAY CO. LTD.. Invention is credited to Osamu Kazeto.
Application Number | 20060121270 11/334574 |
Document ID | / |
Family ID | 19092334 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060121270 |
Kind Code |
A1 |
Kazeto; Osamu |
June 8, 2006 |
Ethylene-vinyl alcohol copolymer composition, and powdery coating
composition comprising it
Abstract
An ethylene-vinyl alcohol copolymer (EVOH) composition comprises
100 parts by weight of a powder (A) having a particle size of from
22 to 850 .mu.m of an ethylene-vinyl alcohol copolymer (a) which
has an ethylene content of from 2 to 60 mol % and has a degree of
saponification greater than 95%, and from 0.0001 to 2 parts by
weight of inorganic particles (B) having primary particles with a
mean particle size of from 1 to 100 nm. The EVOH powder coating
composition of the present invention forms a coating film having
good uniformity when applied to a substrate as powder coating, even
when it contains 1 part by weight or more water relative to 100
parts by weight of EVOH resin.
Inventors: |
Kazeto; Osamu;
(Kurashiki-City, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KURARAY CO. LTD.
Kurashiki-City
JP
|
Family ID: |
19092334 |
Appl. No.: |
11/334574 |
Filed: |
January 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10962604 |
Oct 13, 2004 |
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11334574 |
Jan 19, 2006 |
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10232327 |
Sep 3, 2002 |
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10962604 |
Oct 13, 2004 |
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Current U.S.
Class: |
428/327 ;
428/402; 428/403; 524/437; 524/493; 524/557 |
Current CPC
Class: |
C08K 2201/013 20130101;
Y10T 428/2998 20150115; Y10T 428/25 20150115; Y10T 428/254
20150115; Y10T 428/2982 20150115; C08K 5/09 20130101; C08K 3/01
20180101; C09D 5/03 20130101; C08K 5/09 20130101; C08K 3/01
20180101; C09D 129/02 20130101; Y10T 428/2991 20150115; C09D 129/02
20130101; Y10T 428/31692 20150401; C09D 129/02 20130101; C08L 29/02
20130101; C08L 2666/54 20130101; Y10T 428/2993 20150115; C08L
2666/54 20130101; C08L 29/02 20130101; C08L 2666/28 20130101 |
Class at
Publication: |
428/327 ;
428/402; 428/403; 524/493; 524/437; 524/557 |
International
Class: |
B32B 5/16 20060101
B32B005/16; B32B 27/00 20060101 B32B027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 2001 |
JP |
2001/265944 |
Claims
1. A composition comprising: 100 parts by weight of a powder (A)
having a particle size of 22 to 850 .mu.m, and 0.0001 to 2 parts by
weight of inorganic particles (B) having primary particles with a
mean particle size of from 1 to 100 nm, wherein powder (A)
comprises an ethylene-vinyl alcohol copolymer (a) having an
ethylene content of from 2 to 60 mol %, and a degree of
saponification of more than 95%.
2. The composition of claim 1, wherein the inorganic particles (B)
adhere to the surface of the powder (A).
3. The composition of claim 1, wherein the ethylene-vinyl alcohol
copolymer (a) has an amount of carboxylic acid ranging from 10 to
5000 ppm, based on the weight of the ethylene-vinyl alcohol
copolymer (a).
4. The composition of claim 3, wherein the carboxylic acid is at
least one carboxylic acid selected from the group consisting of
acetic acid, propionic acid and lactic acid.
5. The composition of claim 1, wherein the ethylene-vinyl alcohol
copolymer (a) has an amount of alkali metal salt ranging from 5 to
500 ppm (expressed as ppm by weight of the elemental alkali metal
in the ethylene-vinyl alcohol copolymer (a)).
6. The composition of claim 1, wherein the ethylene-vinyl alcohol
copolymer (a) has an amount of carboxylic acid ranging from 10 to
5000 ppm (based on the weight of the ethylene-vinyl alcohol
copolymer (a)) and an amount of alkali metal salt ranging from 5 to
500 ppm (expressed as ppm by weight of the elemental alkali metal
in the ethylene-vinyl alcohol copolymer (a)), and the ratio by
weight of the carboxylic acid to the alkali metal salt ranges from
0.1 to 15.
7. The composition of claim 1, wherein the ethylene-vinyl alcohol
copolymer (a) has an amount of alkaline earth metal salt ranging
from 5 to 250 ppm (expressed as ppm by weight of the elemental
alkaline earth metal in the ethylene-vinyl alcohol copolymer
(a)).
8. The composition of claim 1, wherein the ethylene-vinyl alcohol
copolymer (a) has an amount of carboxylic acid ranging from 10 to
5000 ppm (based on the weight of the ethylene-vinyl alcohol
copolymer (a)) and an amount of alkaline earth metal salt ranging
from 5 to 250 ppm (expressed as ppm by weight of the elemental
alkaline earth metal in the ethylene-vinyl alcohol copolymer (a)),
and the ratio by weight of the carboxylic acid to the alkaline
earth metal salt ranges from 0.2 to 15.
9. The composition of claim 1, wherein the ethylene-vinyl alcohol
copolymer (a) has an amount of phosphate compound ranging from 1 to
300 ppm (expressed as ppm by weight of the total amount of
phosphate groups in the ethylene-vinyl alcohol copolymer (a)).
10. The composition of claim 1, wherein the et hylene-vinyl alcohol
copolymer (a) is modified with a silicon-containing olefinic
unsaturated monomer, and the degree of modification of the
copolymer with the monomer ranges from 0.0002 and 0.5 mol % (based
on the moles of monomer from which the ethylene-vinyl alcohol
copolymer (a) was prepared).
11. The composition of claim 1, wherein the inorganic particles (B)
are silica and/or aluminum oxide.
12. The composition of claim 1, wherein the inorganic particles (B)
have a hydrophobic surface.
13. A powder coating composition comprising the composition of
claim 1.
14. A multi-layer structure comprising a substrate coated with at
least one layer of the powder coating composition of claim 13.
15. The multi-layer structure of claim 14, wherein the substrate
comprises a metal.
16. A method for preparing the composition of claim 1 comprising:
dry-blending 100 parts by weight of a powder (A) having a particle
size of 22 to 850 .mu.m, and 0.0001 to 2 parts by weight of
inorganic particles (B) having primary particles with a mean
particle size of from 1 to 100 nm, wherein powder (A) comprises an
ethylene-vinyl alcohol copolymer (a) having an ethylene content of
from 2 to 60 mol %, and a degree of saponification of more than
95%.
17. A method for preparing the composition of claim 1 comprising:
dry-blending 100 parts by weight of an ethylene-vinyl alcohol
copolymer (a) having an ethylene content of from 2 to 60 mol %, and
a degree of saponification of more than 95%, and 0.0001 to 2 parts
by weight of inorganic particles (B) having primary particles with
a mean particle size of from 1 to 100 nm, and grinding the
dry-blended ethylene-vinyl alcohol copolymer (a) and inorganic
particles (B).
18. The composition of claim 1, further comprising a thermoplastic
resin other than EVOH.
19. The composition of claim 1, further comprising an additive
selected from the group consisting of a plasticizer, an
antioxidant, a pigment, a UV absorbent, and antistatic agent, a
crosslinking agent, a filler, and a reinforcing agent.
20. The composition of claim 1, further comprising a thermosetting
resin.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an ethylene-vinyl alcohol
copolymer composition that comprises a powder of an ethylene-vinyl
alcohol copolymer and inorganic particles, and to a powder coating
composition comprising the ethylene-vinyl alcohol copolymer
composition. The invention also relates to a method for producing
such an ethylene-vinyl alcohol copolymer composition.
[0003] 2. Discussion of the Background
[0004] Polyethylene, polyamide or epoxy resin powders have been
used as resins for powder coatings to prevent metals or metal
substrates from becoming corroded, and to protect metals from
exposure to solvents. In particular, it is desirable to minimize
the use of solvent-type coating compositions in order to reduce the
load of solvents in the environment. Consequently, powder coating
compositions are considered to be useful in increasing productivity
and reducing costs.
[0005] However, acrylic, epoxy, polyamide or polyethylene resin
powders are principally used as powder coating resins for
preventing metals from becoming rusted or corroded. Since the
gas-barrier properties and/or the chemical resistance of these
resins are insufficient, films prepared from conventional resins
must be very thick. In addition, since the interlayer adhesion of
the resin film coating to the surface of metal is insufficient, the
metal surface must be pre-treated with a primer or the like before
being coated.
[0006] To solve these problems, Japanese Patent Laid-Open No.
115472/1991 discloses a method of using an ethylene-vinyl alcohol
copolymer (hereinafter abbreviated as EVOH) powder for a powder
coating resin.
[0007] In addition, Japanese Patent Laid-Open No. 241537/1997
discloses a powder coating resin composition that comprises 100
parts by weight of a saponified ethylene-vinyl acetate copolymer
having an ethylene content of from 15 to 70 mol % and a degree of
saponification of the vinyl acetate component of at least 80 mol %
and having a melt index of from 1 to 100 g/10 min, from 0.0001 to 1
part by weight of an acid compound, and from 0.1 to 1 part by
weight of a low-boiling-point compound having a boiling point of
not higher than 200.degree. C. This improves the uniformity of the
thickness of the resin-coating layer of articles coated with the
EVOH powder and improves the impact resistance of the surface of
the coating layer. Japanese Patent Laid-Open No. 241537/1997
indicates that water is a preferred low-boiling point compound
having a boiling point of not higher than 200.degree. C., because
it is safe and has a low environmental impact. Furthermore, when
the amount of the low-boiling point compound having a boiling point
of not higher than 200.degree. C. in the composition is greater
than 1 part by weight, and when the composition is applied to
substrates by means of a flame spray coating process, in which a
rapid temperature increase is inevitable, then the surface of the
coating layer formed is greatly roughened.
[0008] However, EVOH is a polymer of high hydrophilicity and it
absorbs water. In particular, compared with ordinary commercially
available EVOH pellets, EVOH powder having a particle size less
than 850 .mu.m has a large surface area per the unit volume, and
therefore it absorbs water readily. (EVOH powder having a particle
size of less than 850 .mu.m referred to herein is an EVOH powder
that contains at least 80% by weight of particles capable of
passing through a sieve having a nominal size of 850 .mu.m as
stipulated in JIS Z-8801.)
[0009] Therefore, when an EVOH powder having such a small particle
size is left in an open space for a long period of time, it will
absorb ambient water, and may contain at least 1 part by weight
(for example, from 1 to 3 parts by weight or so) of water relative
to 100 parts by weight of EVOH. Accordingly, if an EVOH powder
which has been left exposed to ambient moisture for a long period
of time is used for powder coating compositions, the powder is
preferably dried before use.
[0010] However, drying the EVOH powder involves additional cost and
is troublesome. In particular, when only a small amount of EVOH
powder is needed, the EVOH powder must be repeatedly dried whenever
it is used, which will cause thermal degradation of the EVOH
powder. In addition, when conventional EVOH powder is used for
coating substrates continuously over a long period of time in
high-humidity conditions, the water content of the EVOH powder
gradually increases, and, as a result, the uniformity of the
coating film formed is often poor (that is, the coating film
becomes less smooth and glossy).. Therefore, depending on the
working environment (especially in high-humidity conditions), it is
not always easy to continuously coat substrates with a coating
composition containing EVOH powder, over a long period of time.
Thus, it is desirable to develop a powder coating method in which a
powder composition comprising even an EVOH powder that contains one
or more parts by weight of water relative to 100 parts by weight of
EVOH, can form coatings having high uniformity.
SUMMARY OF THE INVENTION
[0011] The problems discussed above can be solved by an
ethylene-vinyl alcohol copolymer composition that comprises 100
parts by weight of a powder (A), having a particle size of from 22
to 850 .mu.m, of an ethylene-vinyl alcohol copolymer (a)
(hereinafter, EVOH (a)) which has an ethylene content of from 2 to
60 mol % and has a degree of saponification of higher than 95%, and
from 0.0001 to 2 parts by weight of inorganic particles (B) of
which the primary particles have a mean particle size of from 1 to
100 nm. In a preferred embodiment of the composition, the inorganic
particles (B) adhere to the surface of the powder (A).
[0012] In a second preferred embodiment of the composition of the
present invention, the EVOH (a) contains from 10 to 5000 ppm of a
carboxylic acid. In a more preferred embodiment thereof, the
carboxylic acid is at least one selected from a group consisting of
acetic acid, propionic acid and lactic acid.
[0013] In a third embodiment of the composition of the present
invention, the EVOH (a) contains from 5 to 500 ppm of an alkali
metal salt (expressed as ppm by weight of the elemental alkali
metal, relative to the weight of the EVOH (a)). In still another
embodiment thereof, the EVOH (a) contains from 10 to 5000 ppm of a
carboxylic acid and from 5 to 500 ppm of an alkali metal salt, and
the ratio by weight of the carboxylic acid to the alkali metal salt
(i.e., the weight of the carboxylic acid divided by the weight of
the alkali metal in the EVOH (a)) falls between 0.1 and 15.
[0014] In a fourth embodiment of the composition of the present
invention, the EVOH (a) contains from 5 to 250 ppm of an alkaline
earth metal salt (expressed as ppm by weight of the elemental
alkaline earth metal, relative to the weight of the EVOH (a)). In
still another embodiment thereof, the EVOH (a) contains from 10 to
5000 ppm of a carboxylic acid and from 5 to 250 ppm of an alkaline
earth metal salt, and the weight ratio of the carboxylic acid to
the alkaline earth metal salt (i.e., the weight of the carboxylic
acid divided by the weight of the alkaline earth metal in the EVOH
(a)) falls between 0.2 and 15.
[0015] In a fifth embodiment of the composition of the present
invention, the EVOH (a) contains from 1 to 300 ppm of a phosphate
compound (expressed as ppm by weight of phosphate groups, relative
to the weight of the EVOH (a); i.e., the total amount of
PO.sub.4.sup.3-, HPO.sub.4.sup.2-, and H.sub.2PO.sub.4.sup.-,
measured by ion chromatography analysis of the EVOH, as discussed
below).
[0016] In a sixth embodiment of the composition of the present
invention, the EVOH (a) is modified with a silicon-containing
olefinic unsaturated monomer, and the degree of modification of the
copolymer with the silicon-containing olefinic unsaturated monomer
falls between 0.0002 and 0.5 mol %.
[0017] In a seventh embodiment of the composition of the present
invention, the inorganic particles (B) comprise silica and/or
aluminum oxide. In still another embodiment thereof, the inorganic
particles (B) have hydrophobic surfaces.
[0018] The EVOH composition of the present invention may be used
for powder coating compositions. The powder coating composition may
also be applied to substrates to give multi-layer structures. In a
more preferred embodiment of the multi-layer structures, the
substrate is a metal.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The EVOH composition of the present invention is preferably
prepared by dry-blending 100 parts by weight of a powder (A) having
a particle size of from 22 to 850 .mu.m, and which comprises an
EVOH (a) that has an ethylene content of from 2 to 60 mol % and has
a degree of saponification of higher than 95%, with from 0.0001 to
2 parts by weight of inorganic particles (B), wherein the primary
particles have a mean particle size of from 1 to 100 nm.
[0020] The EVOH composition of the present invention may also be
prepared by dry-blending 100 parts by weight of an EVOH (a) that
has an ethylene content of from 2 to 60 mol % and has a degree of
saponification of higher than 95%, with from 0.0001 to 2 parts by
weight of inorganic particles (B), wherein the primary particles
have a mean particle size of from 1 to 100 nm, followed by grinding
the resulting mixture.
[0021] Preferably, the EVOH (a) of the present invention is
prepared by saponifying an ethylene-vinyl ester copolymer.
Ethylene-vinyl acetate copolymers are preferred as ethylene-vinyl
ester copolymers because the raw materials are inexpensive and
readily available. The ethylene content of the EVOH (a) of the
present invention falls between 2 and 60 mol %. If the EVOH has an
ethylene content greater than 60 mol %, the resulting coating does
not have acceptable gas-barrier properties and good chemical
resistance. The uppermost limit of the ethylene content of the EVOH
(a) is 60 mol %, preferably at most 57 mol %, more preferably at
most 54 mol %, most preferably at most 51 mol %. On the other hand,
if an EVOH having an ethylene content of less than 2 mol % is used
in the EVOH powder coating composition of the present invention,
the resulting coating film is too hard, and its impact resistance
is poor. In addition, EVOH having a lower ethylene content has a
higher melting point, and its decomposition point therefore tends
to be lower. Therefore, if EVOH having such a low ethylene content
is used in the EVOH powder coating composition of the present
invention, the processing latitude in coating substrates with the
powder coating of the present invention will be narrow. The
lowermost limit of the ethylene content of the EVOH (a) is 2 mol %,
preferably at least 5 mol %, more preferably at least 10 mol %,
even more preferably at least 15 ml %, most preferably at least 20
mol %.
[0022] The degree of saponification of the EVOH (a) of the present
invention must be higher than 95% (i.e., more than 95 mol % of the
ester groups of the precursor ethylene-vinyl ester copolymer have
been hydrolyzed). Powder coatings prepared from EVOH having a
degree of saponification of 95% or less do not provide satisfactory
gas-barrier properties and good chemical resistance. Thus, in order
to provide good gas-barrier properties and chemical resistance, the
degree of saponification of the EVOH (a) is at least 95%,
preferably at least 96%, more preferably at least 97%, even more
preferably at least 98%, still more preferably at least 99%.
[0023] Preferably, the MFR (melt flow rate; measured at 190.degree.
C., 2160 g load) of the EVOH (a) of the present invention falls
between 3 and 150 g/10 min. If an EVOH having an MFR of less than 3
g/10 min is used in the EVOH powder coating composition of the
present invention, the resin has poor flow properties, and the
surface of the coating film formed thereby will be rough. On the
other hand, if an EVOH having an MFR greater than 150 g/10 min is
used, the thickness of the coating film formed will be uneven. More
preferably, the MFR of the EVOH (a) falls between 5 and 120 g/10
min, even more preferably between 8 and 90 g/10 min, still more
preferably between 10 and 60 g/10 min (all MFR values measured at
190.degree. C., 2160 g load). If the glossiness of the coating film
formed from the powder coating composition of the present invention
is a matter of great importance, the MFR (190.degree. C., 2160 g
load) of the EVOH (a) preferably falls between 15 and 60 g/10 min,
most preferably between 20 and 60 g/10 min.
[0024] As discussed above, the vinyl ester monomer copolymerized
with ethylene is preferably vinyl acetate. However, the vinyl
acetate may be copolymerized with any other vinyl ester of a fatty
acid (e.g., vinyl propionate, vinyl pivalate, etc.).
[0025] If desired, the ethylene and vinyl ester monomers may be
copolymerized with a small amount of any other monomer capable of
copolymerizing with them. For example, such comonomers may include
propylene, isobutylene; .alpha.-olefins such as 1-octene,
1-dodecene; unsaturated acids such as acrylic acid, methacrylic
acid, crotonic acid, maleic acid, itaconic acid, and their
anhydrides, salts, and mono- or di-alkyl esters; nitriles such as
acrylonitrile, methacrylonitrile; amides such as acrylamide,
methacrylamide; olefinsulfonic acids such as ethylenesulfonic acid,
allylsulfonic acid, methallylsulfonic acid, and their salts; and
alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl
chloride, vinylidene chloride.
[0026] Preferably, the EVOH (a) of the present invention is
modified with a silicon-containing olefinic unsaturated monomer and
the degree of modification thereof with the monomer falls between
0.0002 and 0.5 mol %. When the powder coating composition
comprising the modified EVOH is applied onto substrates, the
interlayer adhesion between the coating film formed and the
substrate is improved. In particular, the interlayer adhesion
provided by the modified EVOH is more significantly improved when
the composition is applied to metallic substrates. However, when
the degree of modification of EVOH with the silicon-containing
olefinic unsaturated monomer is less than 0.0002 mol %, the
modified EVOH does not provide sufficiently improved interlayer
adhesion between the coating film and the substrate. On the other
hand, if the degree of modification of the modified EVOH is greater
than 0.5 mol %, the melt flowability of the resin decreases, and
the surface of the coating resin film formed thereby will be
rougher. More preferably, the degree of modification of the EVOH
(a) with the silicon-containing olefinic unsaturated monomer falls
between 0.001 and 0.1 mol %, even more preferably between 0.005 and
0.07 mol %, most preferably between 0.01 and 0.05 mol %.
[0027] Preferably, the silicon-containing olefinic unsaturated
monomer is one or more monomers selected from silicon-containing
olefinic unsaturated monomers of the following general formulae
(I), (II) and (III): ##STR1##
[0028] In these formulae, n is 0 or 1; m is an integer from 0-2,
inclusive; R.sup.1 represents a lower alkyl group having from 1 to
8 carbon atom, an allyl group, or an allyl-containing lower alkyl
group having from. 1 to 8 carbon atoms; R.sup.2 represents an
alkoxyl group having from 1 to 40 carbon atoms, which may have
oxygen-containing substituent(s); R.sup.3 represents a hydrogen
atom or a methyl group; R.sup.4 represents a hydrogen atom or a
lower alkyl group having from 1 to 8 carbon atoms; R.sup.5
represents an alkylene group, or a divalent organic residue with
carbon chains bonded to each other via an oxygen or nitrogen atom;
R.sup.6 represents a hydrogen atom, a halogen atom, a lower alkyl
group, an allyl group, or an allyl-containing lower alkyl group
having from 1 to 8 carbon atoms; R.sup.7 represents an alkoxyl
group or an acyloxyl group, which may have oxygen or
nitrogen-containing substituent(s); R.sup.8 represents a hydrogen
atom, a halogen atom, a lower alkyl group having from 1 to 8 carbon
atoms, an allyl group, or an allyl-containing lower alkyl group
having from 1 to 8 carbon atoms; and R.sup.9 represents a lower
alkyl group having from 1 to 8 carbon atoms.
[0029] Examples of the silicon-containing olefinic unsaturated
monomers of formula (I) are vinyltrimethoxysilane,
vinylmethyldimethoxysilane, vinyldimethylmethoxysilane,
vinyltriethoxysilane, vinylmethyldiethoxysilane,
vinyldimethylethoxysilane, allyltrimethoxysilane,
allylmethyldimethoxysilane, allyldimethylmethoxysilane,
allyltriethoxysilane, allyldimethylethoxysilane,
vinyltris(methoxyethoxy)silane, and
vinylisobutyldimethoxysilane.
[0030] Examples of the silicon-containing olefinic unsaturated
monomers of formula (II) are
3-(meth)acrylamidopropyltrimethoxysilane,
3-(meth)acrylamidopropyltriethoxysilane,
3-(meth)acrylamidopropyltri(-methoxyethoxy)silane,
3-(meth)acrylamidopropyltri(N-methylaminoethoxy)silane,
2-(meth)acrylamidoethyltrimethoxysilane, and
1-(meth)acrylamidomethyltrimethoxysilane.
[0031] Examples of the silicon-containing olefinic unsaturated
monomers of formula (III) are vinyltriacetoxysilane,
vinyltripropionyloxysilane, isopropenyltriacetoxysilane,
vinylisobutyldiacetoxysilane, vinylmethyldiacetoxysilane,
vinyldimethylacetoxysilane, vinylphenyldiacetoxysilane,
vinylmonochlorodiacetoxysilane, and
vinylmonohydrogendiacetoxysilane.
[0032] The preferred silicon-containing olefinic unsaturated
monomers of the silicon-containing olefinic unsaturated monomers of
formulae (I) to (III) are vinyltrimethoxysilane,
vinyltriethoxysilane and vinyltri(methoxyethoxy)silane.
Vinyltrimethoxysilane and vinyltriethoxysilane are especially
preferred.
[0033] The method for preparing the EVOH modified with such
silicon-containing olefinic unsaturated monomers is not
specifically defined. Preferably, for example, the modified EVOH
may be obtained by ternary copolymerization of ethylene and vinyl
acetate with a small amount of a silicon-containing olefinic
unsaturated monomer fed to the polymerization reactor; or by
dissolving EVOH in a suitable solvent such as dimethyl sulfoxide
followed by adding a silicon-containing olefinic unsaturated
monomer thereto along with a suitable catalyst to thereby graft the
EVOH with the silicon-containing olefinic unsaturated monomer; or
by adding a silicon-containing olefinic unsaturated monomer and a
suitable catalyst to EVOH via a plunger pump or the like while the
EVOH is kneaded as a melt in a twin-screw extruder or the like to
thereby graft the EVOH with the silicon-containing olefinic
unsaturated monomer. Ternary copolymerization of ethylene and vinyl
acetate with a small amount of a silicon-containing olefinic
unsaturated monomer fed to the polymerization reactor is especially
preferred, as it is an inexpensive method.
[0034] Preferably, the EVOH (a) of the present invention contains
from 10 to 5000 ppm of a carboxylic acid. When the EVOH (a)
contains a carboxylic acid in an amount falling within the
above-defined range, powder coatings formed therefrom have a
decreased tendency to thermally deteriorate during the coating
process, and therefore the coating film has a decreased tendency to
become yellowed. Preferably, the carboxylic acid has a pKa of at
least 3.5 at 25.degree. C. Carboxylic acids which have a pKa at
25.degree. C. which is smaller than 3.5 are not acceptable because
the pH of the VOH (a) containing such a carboxylic acid tends to be
difficult to control. In addition, EVOH powder compositions
containing such a carboxylic acid tends to gel then applied to
substrates, resulting in a coating film having an uneven
thickness.
[0035] Examples of the carboxylic acid usable in the present
invention are succinic acid, adipic acid, benzoic acid, caprylic
acid, lauric acid, glycolic acid, lactic acid, formic acid, acetic
acid and propionic acid. However, dicarboxylic acids such as
succinic acid and adipic acid are not as good as monocarboxylic
acids, since EVOH compositions containing such dicarboxylic acids
will more readily gel, and provide a coating film having an uneven
thickness. Thus, preferred carboxylic acids include acetic acid,
propionic acid and lactic acid. Acetic acid and propionic acid are
more preferred, since they are inexpensive and since their acidity
level is such that the pH of the EVOH (a) that contains such a
carboxylic acid is therefore easy to control.
[0036] If, however, the carboxylic acid content of the EVOH (a) is
greater than 5000 ppm, the EVOH powder coating composition will
tend to gel, and the thickness of the coating film formed therefrom
will be uneven. Thus, the uppermost limit of the carboxylic acid
content of the EVOH (a) is at most 5000 ppm, preferably at most
1000 ppm, more preferably at most 500 ppm. On the other hand, the
lowermost limit of the carboxylic acid content is preferably at
least 20 ppm, more preferably at least 30 ppm.
[0037] Also preferably, the EVOH (a) of the present invention
contains from 5 to 500 ppm of an alkali metal salt (expressed as
ppm by weight of the alkali metal, relative to the EVOH (a)). If
the coating composition contains an amount alkali metal salt within
the defined range, the interlayer adhesion between the coating film
formed from the EVOH powder composition and the substrate coated
with the film is improved. In particular, the improvement in the
interlayer adhesion between the substrate and the film is
significant when the coating composition is applied to metallic
substrates.
[0038] In order to provide good interlayer adhesion between the
EVOH coating film and the substrate, the lowermost limit of the
alkali metal salt content of the EVOH (a) is preferably at least 10
ppm, more preferably at least 20 ppm, even more preferably at least
50 ppm (expressed as ppm by weight of the alkali metal, relative to
the weight of the EVOH (a)). In order to prevent yellowing of the
EVOH coating film, and to provide a coating with a good appearance,
the uppermost limit of the alkali metal salt content of the EVOH
(a) is preferably at most 400 ppm, more preferably at most 300
ppm.
[0039] The alkali metal may include, for example, lithium, sodium
and potassium. For example, the alkali metal salt may be an
aliphatic carboxylate, aromatic carboxylate, phosphate, or a metal
complex of an alkali metal. Examples of alkali metal salts are
sodium acetate, potassium acetate, sodium propionate, potassium
propionate, sodium lactate, potassium lactate, sodium phosphate,
lithium phosphate, sodium stearate, potassium stearate, and sodium
salts of ethylenediaminetetraacetic acid. The preferred salts are
sodium acetate, potassium acetate, sodium propionate, potassium
propionate, sodium lactate and potassium lactate.
[0040] When the EVOH composition comprises an EVOH (a) which
contains both a carboxylic acid and an alkali metal salt, the ratio
by weight of the carboxylic acid to the alkali metal salt (i.e.,
the weight of the carboxylic acid divided by the weight of the
alkali metal) preferably falls between 0.1 and 15. The lowermost
limit of the ratio of carboxylic acid/alkali metal salt is
preferably at least 0.2, more preferably at least 0.3. On the other
hand, the uppermost limit of the ratio of carboxylic acid/alkali
metal salt is preferably at most 12, more preferably at most
10.
[0041] Also preferably, the EVOH (a) of the present invention
contains from 5 to 250 ppm of an alkaline earth metal salt
(expressed as ppm by weight of the alkaline earth metal element,
relative to the weight of the EVOH (a)). If the EVOH composition
contains an amount of alkaline earth metal salt within the defined
range, the interlayer adhesion between the coating film formed from
the EVOH powder composition and the substrate is improved. In
particular, the improvement in the interlayer adhesion between the
coating film and the substrate is remarkable when the coating
composition is applied to metallic substrates.
[0042] In order to provide satisfactory interlayer adhesion between
the EVOH coating film and the substrate, the lowermost limit of the
alkaline earth metal salt content of the EVOH (a) is preferably at
least 10 ppm, more preferably at least 20 ppm, even more preferably
at least 30 ppm. On the other hand, in order to prevent the EVOH
coating film from becoming yellowed, and to provide a film having a
good appearance, the uppermost limit of the alkaline earth metal
salt content of the EVOH (a) is preferably at most 200 ppm, more
preferably at most 150 ppm.
[0043] The alkaline earth metal may be for example, beryllium,
magnesium, calcium and barium. The alkaline earth metal salt may
be, for example, an aliphatic carboxylate, an aromatic carboxylate,
a phosphate, or a metal complex of an alkaline earth metal.
Examples of such alkaline earth metal salts are magnesium acetate,
calcium acetate, magnesium propionate, calcium propionate,
magnesium lactate, calcium lactate, magnesium stearate and calcium
stearate. The more preferred salts are magnesium acetate, calcium
acetate, magnesium propionate, calcium propionate, magnesium
lactate and calcium lactate.
[0044] If the EVOH copolymer (a) contains both a carboxylic acid
and an alkaline earth metal salt, the ratio by weight of the
carboxylic acid to the alkaline earth metal salt (i.e., the weight
of the carboxylic acid divided by the weight of the alkaline earth
metal in the EVOH (a)) preferably falls between 0.2 and 15, in
order to provide a suitable balance between preventing the
yellowing of the coating film, and improving the adhesion of the
coating film to the substrate. The lowermost limit of the ratio of
carboxylic acid/alkaline earth metal salt is preferably at least
0.4, more preferably at least 0.8. On the other hand, the uppermost
limit of the ratio of carboxylic acid/alkaline earth metal salt is
preferably at most 12, more preferably at most 10.
[0045] The EVOH (a) may contain both an alkali metal salt and an
alkaline earth metal salt. In this case, it is desirable that the
total amount of the alkali metal salt and the alkaline earth metal
salt added to the EVOH (a) falls between 10 and 400 ppm, expressed
as the combined weight of the alkali and alkaline earth metals
relative to the weight of the EVOH (a).
[0046] Also preferably, the EVOH (a) of the present invention
contains from I to 300 ppm of a phosphate compound (expressed as
ppm by weight of phosphate groups, relative to the weight of the
EVOH (a)). The EVOH composition of the present invention, in which
the EVOH (a) contains an amount of the phosphate compound within
the defined range, inhibits thermal deterioration during the
coating process and therefore effectively prevents yellowing of the
coating film formed. However, if the phosphate compound content of
the EVOH (a) is larger than 300 ppm, the EVOH powder composition
will gel when it is applied onto a substrate, and the thickness of
the coating film formed thereby will be uneven. Thus, the uppermost
limit of the phosphate compound content of the EVOH (a) is
preferably at most 250 ppm, more preferably at most 200 ppm. On the
other hand, the lowermost limit of the phosphate compound content
of the EVOH (a) is preferably at least 3 ppm, more preferably at
least 5 ppm, even more preferably at least 10 ppm.
[0047] The type of the phosphate compound added to the EVOH (a) is
not specifically defined. It may include various acids such as
phosphoric acid, phosphorous acid, and their salts. Any phosphate
of any type of primary phosphate, secondary phosphate and tertiary
phosphate may be used, and the associated cation is not
specifically defined. Alkali metal salts and alkaline earth metal
salts are preferred. Phosphoric acid, sodium dihydrogenphosphate,
potassium dihydrogenphosphate, disodium hydrogenphosphate and
dipotassium hydrogenphosphate are especially preferred; and
phosphoric acid, sodium dihydrogenphosphate and potassium
dihydrogenphosphate are more especially preferred.
[0048] A boron compound may also be added to the EVOH (a). The
boron compound may include, for example, boric acids, boric esters,
borate salts and boron hydrides. Specifically, the boric acids may
be orthoboric acid, metaboric acid and tetraboric acid; the boric
esters may be triethyl borate and trimethyl borate; and the borate
salts may be alkali metal salts and alkaline earth metal salts of
various boric acids such as those mentioned above, and borax.
Orthoboric acid is preferred. The amount of boron compound added to
the EVOH (a) is preferably controlled so that the boron compound
content of the EVOH (a) falls between 20 and 2000 ppm, more
preferably between 50 and 1000 ppm, expressed as ppm by weight of
boron, relative to the weight of the EVOH (a).
[0049] As mentioned above, the EVOH (a) of the composition of the
present invention may optionally contain at least one additive
component selected from a group consisting of carboxylic acids,
alkali metal salts, alkaline earth metal salts, phosphate compounds
and boron compounds. The method for preparing an EVOH (a) that
contains any of such components is not specifically defined. Some
preferred reparation methods are as follows: The EVOH (a) may be
dipped in a solution of an additive component; or the EVOH (a) may
be melted and mixed with an additive component; or the EVOH (a) may
be dissolved in a suitable solvent and then mixed with an additive
component.
[0050] The method of dipping the EVOH (a) in a solution of an
additive component in order to add the additive component to the
EVOH (a) may be carried out as a batch operation or a continuous
operation. The morphology of the EVOH so treated is not
specifically defined. For example, the EVOH may be in the form of a
powder, granules, spheres, or columnar pellets. The concentration
of the additive component in the solution is also not specifically
defined. The solvent for the solution is not also specifically
defined, but water is a preferred solvent since aqueous solutions
are easy to handle. The preferred range of the dipping time may
vary, depending on the morphology of the EVOH treated. Preferably,
for example, EVOH pellets having a size of from 1 to 10 mm or so
will be dipped in the solution for at least 1 hour, more preferably
for at least 2 hours.
[0051] The mode of dipping the EVOH in the solution of an additive
component is not specifically defined. For example, the EVOH may be
dipped in a plurality of different solutions separately containing
any of the additive components, or may be dipped in one solution
containing all of the additive components. In order to simplify the
processing operation, the EVOH is preferably dipped in one solution
containing all of the additive components. After dipping the EVOH
in the additive solution in the manner described above, the EVOH is
then dried. By means of this process, the treated EVOH contains at
least one additive selected from a group consisting of carboxylic
acids, alkali metal salts, alkaline earth metal salts and phosphate
compounds.
[0052] Two or more different types of EVOH (a) that differ in any
of the degree of polymerization, the ethylene content and/or the
degree of saponification may be combined for use in the composition
of the present invention. In addition, the EVOH (a) may also
contain any other suitable additives such as a plasticizer, an
antioxidant, a pigment, a UV absorbent, an antistatic agent, a
crosslinking agent, a filler and/or reinforcing agent such as any
of various fibers. In particular, when the EVOH composition of the
present invention is used in a powder coating composition, it is
desirable that the EVOH (a) contain at least one pigment. The
pigment may be kneaded in a melt of the EVOH (a) before the EVOH
(a) is ground; or the ground EVOH (a) may be subsequently
dry-blended with pigment. The former method of kneading the pigment
in a melt of the EVOH (a) before the EVOH (a) is ground is
preferred in order to uniformly disperse the pigment in the EVOH.
In order to enhance the dispersion of the additives in the EVOH
(a), a dispersant of, for example, higher fatty acids may be added
to the EVOH (a).
[0053] Any other thermoplastic resin other than EVOH may be added
to the EVOH (a) in the composition of the present invention. The
additional thermoplastic resin may include, for example, various
polyolefins (e.g., polyethylene, polypropylene, poly-1-butene,
poly-4-methyl-1-pentene, an ethylene-propylene copolymer, a
copolymer of ethylene with an .alpha.-olefin having at least 4
carbon atoms, a copolymer of a polyolefin with maleic anhydride, an
ethylene-vinyl ester copolymer, an ethylene-acrylate copolymer, and
modified polyolefins prepared by graft-modifying any of these
polymers with any of unsaturated carboxylic acids or their
derivatives, various nylons (e.g., nylon-6, nylon-6,6, nylon-6/6,6
copolymer), polyvinyl chlorides, polyvinylidene chlorides,
polyesters, polystyrenes, polyacrylonitriles, and modified
polyvinyl alcohol resins.
[0054] The EVOH (a) of the present invention may contain a
thermosetting resin. The thermosetting resin may include, for
example, various epoxy resins, acrylic resins, urethane resins,
polyester resins, and modifications thereof One or more such
thermosetting resins may be combined with a curing agent of, for
example, amines, acid anhydrides, dibasic acids or blocked
isocyanates, and may be added to the EVOH (a).
[0055] The EVOH resin prepared in the manner described above must
be processed into the intended EVOH powder (A) having a particle
size of from 22 to 850 .mu.m, except if the EVOH resin is already a
powder having a particle size of from 22 to 850 .mu.m. The method
of processing the EVOH is not specifically defined. For example,
the EVOH may be cryogenically ground; it may be mechanically ground
in a jet mill; or it may be dissolved in a mixed solvent of
water/alcohol and then precipitated and deposited as fine particles
in a poor solvent such as water or hexane.
[0056] The particle size of the EVOH powder (A) of the EVOH (a)
having an ethylene content of from 2 to 60 mol % and a degree of
saponification of higher than 95% of the present invention falls
between 22 and 850 .mu.m. Specifically, the EVOH powder (A)
comprises at least 80% by weight of particles capable of passing
through a standard sieve having a nominal size of 850 .mu.m but not
through a standard sieve having a nominal size of 22 .mu.m, as
stipulated in JIS Z-8801. The EVOH powder coating composition of
the present invention, containing an EVOH powder (A) having a
particle size range as described above, forms a good coating film
of high uniformity (that is, a smooth and glossy coating film) on
the shaped articles to which it has been applied. If the EVOH
powder (A) comprises more than 20% by weight of particles that pass
through the 22 .mu.m sieve, the particles of EVOH (a) will readily
aggregate together and the surface of the coating film will thereby
be rougher. On the other hand, if the EVOH powder (A) comprises
less than 80% by weight of particles that pass through the 850
.mu.m sieve, the surface of the coating film formed therefrom will
also be rougher. More preferably, the particle size of the EVOH
powder (A) of the power coating composition of the present
invention falls between 26 and 710 .mu.m, more preferably between
32 and 600 .mu.m, most preferably between 38 and 500 .mu.m.
[0057] The inorganic particles (B) of the composition of the
present invention have primary particles with a mean particle size
of from 1 to 100 nm. In a fine inorganic powder, in general, the
individual particles loosely aggregate together to form secondary
particles. In the present invention, the mean particle size of the
primary particles is defined as the particle size of the primary
particles which form the secondly particles. Specifically, the mean
particle size of the primary particles of (B) may be determined by
averaging the measured diameter of the primary particles of (B), as
determined by transmission electron microscopy.
[0058] Inorganic particles (B) having a mean particle size of less
than 1 nm are difficult to produce. In addition, it is difficult to
mix such particles with the EVOH powder (A) to give a homogeneous
EVOH composition, and therefore such a composition does not provide
a uniform coating film. On the other hand, if the inorganic
particles (B) have a mean particle size which is greater than 100
nm, the coating film formed from such a composition also tends to
be non-uniform.
[0059] The lowermost limit of the mean particle size of the
inorganic particles (B) is preferably at least 3 nm, more
preferably at least 5 nm, even more preferably at least 7 nm. On
the other hand, the uppermost limit of the mean particle size of
the inorganic particles (B) is preferably at most 85 nm, more
preferably at most 70 nm, even more preferably at most 55 nm.
[0060] The types of the inorganic particles (B) suitable for the
composition of the present invention are not specifically defined.
For example, the inorganic particles (B) may be silica, aluminum
oxide, talc, titanium oxide or calcium carbonate. Talc, titanium
oxide and calcium carbonate are intrinsically colored, and
therefore when these inorganic particles are used, the EVOH
composition of the present invention cannot readily be colored with
another pigment. When a transparent coating film is desired, it is
preferable that the inorganic particles (B) of the powder coating
composition of the present invention be transparent. Silica and
aluminum oxide of high transparency are especially preferred as the
inorganic particles (B) for transparent powder coating films.
[0061] The inorganic particles (B) of the present invention are
preferably rendered hydrophobic on their surfaces. Inorganic
particles (B) having a hydrophobic surface further enhances the
advantages of the present invention, although the reason for this
is not clear. Specifically, when the EVOH powder coating
composition has inorganic particles (B) with a hydrophobic surface,
the uniformity of the coating film formed is much improved compared
to otherwise identical compositions in which the inorganic
particles (B) have not been treated to have a hydrophobic surface.
Any known method for rendering the surfaces of the inorganic
particles (B) hydrophobic may be used. For example, the particles
may be treated with halogenosilanes, alkoxysilanes or
siloxanes.
[0062] The EVOH composition of the present invention may comprise
100 parts by weight of a powder (A) having a particle size of from
22 to 850 .mu.m of an EVOH (a) which has an ethylene content of
from 2 to 60 mol % and has a degree of saponification of higher
than 95%, and from 0.0001 to 2 parts by weight of inorganic
particles (B) of which the primary particles have a mean particle
size of from 1 to 100 nm. In one preferred embodiment of the EVOH
composition, the inorganic particles (B) adhere to the surface of
the EVOH powder (A). If the amount of inorganic particles (B) is
smaller than 0.0001 parts by weight relative to 100 parts by weight
of the EVOH powder (A), the EVOH powder coating composition does
not provide satisfactory uniformity in the coating film formed from
it. On the other hand, if the amount of the inorganic particles (B)
is larger than 2 parts by weight relative to 100 parts by weight of
the EVOH powder (A), the EVOH powder coating composition also does
not provide improved uniformity in the coating film formed from it.
In addition, the interlayer adhesion between the coating film and
the coated substrate significantly decreases. The lowermost limit
of the amount of the inorganic particles (B) in the composition of
the present invention is preferably at least 0.001 parts by weight,
more preferably at least 0.005 parts by weight, most preferably at
least 0.01 parts by weight relative to 100 parts by weight of the
EVOH powder (A) in the composition. On the other hand, the
uppermost limit of the amount of the inorganic particles (B) is
preferably at most 1.5 parts by weight, more preferably at most 1
part by weight, even more preferably at most 0.7 parts by weight,
most preferably at most 0.5 parts by weight relative to 100 parts
by weight of the EVOH powder (A) in the composition of the present
invention.
[0063] The method of producing the EVOH composition of the present
invention is not specifically defined. Preferably, for example, the
composition may be produced as described below. A powder (A)
comprising an EVOH (a) having a particle size of from 22 to 850
.mu.m, an ethylene content of from 2 to 60 mol %, and a degree of
saponification of higher than 95%, may be dry-blended with
inorganic particles (B) having primary particles with a mean
particle size of from 1 to 100 nm. In a second. method, pellets of
the EVOH (a) may be dry-blended with the inorganic particles (B)
and the resulting mixture ground. In a third method, the EVOH
powder (A) and the inorganic particles (B) may be suspended in a
liquid (e.g., water), fully stirred, then dewatered and dried. In a
fourth method, a suspension of the inorganic particles (B) in a
liquid (e.g., water) may be added to a dry EVOH powder (A) and
stirred in. The inorganic particles (B) and EVOH powder (A) are
well mixed and then dewatered and dried. The preferred methods are
the methods of dry-blending the EVOH powder (A) with the inorganic
particles (B), and dry-blending pellets of the EVOH (a) with the
inorganic particles (B) followed by grinding the resulting mixture.
These two methods are simple and have satisfactory productivity.
The method of dry-blending the EVOH powder (A) with the inorganic
particles (B) is especially preferred.
[0064] The methods of mixing the EVOH powder (A) with the inorganic
particles (B) discussed above have the advantages discussed below,
when compared to the different method of kneading (A) and (B)
together in a melt, followed by grinding the resulting mixture.
Specifically, in the former preferred methods, the inorganic
particles (B) can be deposited predominantly on the surface of the
EVOH powder (A) but not inside the EVOH particles. As a result, the
uniformity of the resulting coating film formed is good, even when
an extremely small amount of (B) is added to (A). That is, the
composition prepared in a preferred manner produces better and more
remarkable results.
[0065] The water content of the EVOH composition of the present
invention is not specifically defined. In order to provide a
coating film with good uniformity, it is desirable that the
uppermost limit of the water content of the EVOH composition of the
present invention is less than 6% by weight, more preferably at
most 4% by weight, even more preferably at most 3% by weight, still
more preferably at most 2.5% by weight. The uniformity of the
coating film provided by the EVOH powder coating composition of the
present invention is suitable even when the water content of the
EVOH composition is 1% by weight or less. The uniformity of the
coating film provided by the EVOH powder coating composition of the
present invention is better than that provided by an EVOH
composition having the EVOH (a) alone, but not the inorganic
particles (B). Thus, the EVOH composition of the present invention
may be dried so that there is essentially no water present.
However, an EVOH composition of the present invention, having a
water content of higher than 1% by weight, for example, having a
lowermost water content of at least 1.1% by weight or even at least
1.2% by weight, is significantly better than any other conventional
EVOH powders. Specifically, the advantage of an EVOH composition of
the present invention, having a water content of higher than 1% by
weight is that it can be directly used for powder coating
compositions, and does not require any complicated drying
treatment. Furthermore, the uniformity of a coating film formed
therefrom is very good. Thus, the EVOH composition of the present
invention is superior to conventional EVOH powder coating
compositions.
[0066] The EVOH composition of the invention is suitable for powder
coating compositions, and can be used in various powder coating
methods. For example, the EVOH composition of the present invention
may be used in fluidized bed coating methods, electrostatic coating
methods, or flame spray coating methods. The coating temperature of
the composition varies, depending on the coating method employed
and on the melting point of EVOH used. In general, it may fall
between approximately 150 and 300.degree. C.
[0067] The substrate to which the EVOH powder coating composition
of the present invention is applied is preferably metal, including,
for example, steel tubes and steel sheets. When the EVOH powder
coating composition of the invention is applied to such metallic
substrates, the substrates may be optionally pre-treated. For
example, they may be degreased, phosphorylated or plated for the
purpose of improving the adhesion of the coating film, the
corrosion resistance of the coating film, and the appearance of the
coated substrates. The EVOH composition of the present invention is
not limited to such metallic substrates, but may also be used for
coating earthenware, ceramics, glass, plastics, etc.
[0068] The EVOH powder coating composition of the present invention
may be applied in such a manner so as to provide substrates,
typically metallic substrates, with a multi-layer structure. During
the coating process, if desired, the substrate coated with coating
(or multiple coatings) of the composition of the present invention,
may be further layered with one or more additional resin layers in
any desired manner. For example, the multi-layer structures having
some additional resin layer may have the structure M/E/P1, M/P1/E
and M/P1/E/P2, in which M indicates a substrate, E indicates a
coating layer of the EVOH composition of the invention, and P1 and
P2 are each an additional resin layer. However, the invention is
not limited to these specific examples, but may also include other
multilayered film structures comprising one or more layers of the
EVOH composition of the present invention, and one or more layers
of additional resins.
[0069] The additional resin that may be laminated with the coating
layer of the EVOH composition of the present invention may include,
for example, olefin homopolymers and copolymers such as various
polyethylenes, polypropylenes, ethylene-vinyl acetate copolymers;
carboxylic acid-modified polyolefins; polyesters and polyester
elastomers such as polyethylene terephthalate; various polyamide
resins such as nylon-11, nylon-12; other thermoplastic resins such
as polyvinyl chlorides, polyvinylidene chlorides, acrylic resins,
polyurethane elastomers; as well as thermosetting epoxy resins,
thermosetting acrylic resins, thermosetting urethane resins,
thermosetting polyester resins, and modified derivatives of those
resins. Any of these resins may be laminated with the EVOH coating
layer, either as individual layers, or combinations of layers of
the various additional resins.
[0070] The method of combining the coating layer of the EVOH
composition of the present invention with any other resin layer on
a substrate is not specifically defined. For example, one substrate
may be coated sequentially with the individual powder coating
compositions, one after another; or a mixture of the EVOH
composition of the invention with one or more other resins may be
melted together, and subsequently phase separate in the resulting
melt owing to the affinity difference between the different resin,
and then applied to a substrate all at once to form two or more
resin layers on the substrate. The former method of sequentially
coating one substrate separately with the individual powder coating
compositions, one after another, is preferred as it does not
require any specific consideration for the affinity difference
between the resins used.
[0071] The surfaces of the coated multi-layer structures are not
roughened and their appearance is good. In addition, the adhesion
of the coating layers to the substrate is good. Therefore, the
coated multi-layer structures are suitable for use in water pipes
for potable water, metallic baskets, tanks for chemicals, etc. The
EVOH composition of the present invention is also suitable for use
in molding processes employing resin powders, such as rotational
molding and compression molding.
EXAMPLES
[0072] The present invention is described in more detail with
reference to the following examples, which, however, are not
intended to restrict the scope of the invention. Unless otherwise
specifically indicated, "%" and "parts" in the following Examples
are all by weight. The water used in the Examples is ion-exchanged
water.
Synthesis Example 1
[0073] 83.1 kg of vinyl acetate, 8.4 kg of methanol and 24.1 g of
vinyltrimethoxysilane were fed into a 200-liter polymerization
reactor, in which the oxygen was purged out with a stream of
ethylene gas. The temperature in the reactor was controlled at
60.degree. C., and ethylene gas was introduced into the reactor to
increase the pressure inside the reactor up to 6.18 MPa. After the
temperature and the pressure in the reactor were stabilized, a
solution of 150 g of a polymerization initiator,
azobisisovaleronitrile dissolved in 3 kg of methanol was introduced
into the reactor to initiate the polymerization of the monomers.
After 4 hours, the reactor was cooled to 20.degree. C., while at
the same time, a solution of 0.2 g of copper acetate dissolved in
20 kg of methanol was fed into the reactor to stop the
polymerization. At the end of the polymerization, the conversion of
vinyl acetate was 35%.
[0074] The ethylene gas was purged out of the reactor, and the
polymer solution was removed from the reactor and diluted with 20
liters of methanol. The resulting polymer solution was fed into the
top of a stripping column, while methanol vapor was fed through the
bottom, whereby the non-reacted monomer still remaining in the
polymer solution was evaporated away along with the methanol vapor,
thereby providing a methanol solution of an ethylene-vinyl acetate
copolymer. The ethylene content of the polymer was 47 mol %, and
the polymer concentration in the polymer solution was 43%.
[0075] The methanol solution of the vinyltrimethoxysilane-modified
ethylene-vinyl acetate copolymer thus obtained was fed into a
saponification reactor, to which was added 0.4 equivalents,
relative to amount of the vinyl ester groups in the copolymer, of a
solution of sodium hydroxide/methanol (80 g/liter). Additional
methanol was added to the mixture to provide a polymer mixture
having a polymer concentration of 20%. The solution was heated to
60.degree. C., and the polymer was saponified for about 4 hours,
during which nitrogen gas was introduced into the reactor. After 4
hours, the resulting solution was neutralized with acetic acid to
stop the reaction. The degree of saponification of the resulting
vinyltrimethoxysilane-modified ethylene-vinyl alcohol copolymer
(EVOH) was 99.4%.
[0076] The methanol solution of EVOH thus obtained was heated up to
80.degree. C., and the excess methanol was evaporated away to
provide a polymer solution with a polymer concentration of 43.3%.
To 100 parts by weight of the resulting methanol solution of EVOH,
was added 5.61 parts by weight of water to provide a methanol/water
solution of a polymer having a polymer concentration of 41%. The
methanol/water solvent ratio was 91/9 by weight. The aqueous
methanol solution of EVOH was extruded out through circular
orifices formed in a metal plate, into a coagulation bath of 10/90
by weight methanol/water at 5.degree. C. to form EVOH strands. The
resulting strands were cut into EVOH pellets each having a diameter
of about 3 mm and a length of about 5 mm. The EVOH pellets were
dewatered in a centrifuge, washed with a large quantity of water,
then again dewatered. This operation was repeated several times.
100 parts by weight of the resulting wet EVOH pellets (water
content of 55%, based on the weight of the wet EVOH pellets) were
dipped in 845 parts by weight of an aqueous solution containing 0.4
g/liter of acetic acid, 0.28 g/liter of calcium acetate and 0.075
g/liter of potassium dihydrogenphosphate, at 25.degree. C., for 6
hours. After dipping, the pellets were dewatered, and dried in a
hot air drier at 80.degree. C. for 3 hours, and then at 107.degree.
C. for 24 hours, thereby providing dry EVOH pellets. The carboxylic
acid content, the phosphate compound content, and the metal ion
content of the resulting dry EVOH pellets was then determined by
the methods discussed below.
(1) Determination of Carboxylic Acid Content of EVOH:
[0077] 20 g of a sample of the dry EVOH pellets was put into 100 ml
of ion-exchanged water, and thermally extracted at 95.degree. C.
for 6 hours. The resulting extract was titrated to the
neutralization point with 1/50 N NaOH, using phenolphthalein as an
indicator. The number of moles of acid determined in this manner
was multiplied by the molecular weight of the acid to calculate the
acid content of the EVOH. In addition, the extract was analyzed by
ion chromatography with an eluent of aqueous 0.1% phosphoric acid
solution, in a Yokogawa Electric SCS5-252 column in order to
identify the carboxyl anion of the acid.
(2) Determination of Alkali Metal Ion Content and Alkaline Earth
Metal Ion Content of EVOH:
[0078] 10 g of a sample of the dry EVOH pellets was placed in 50 ml
of aqueous 0.01 N HCl solution, and stirred at 95.degree. C. for 6
hours. The stirred aqueous solution was analyzed by ion
chromatography to quantify the metal ion concentration using a
Yokogawa Electric ICS-C25 column, using an aqueous solution
containing 5.0 mM tartaric acid and 1.0 mM 2,6-pyridinedicarboxylic
acid as an eluent. The metal ion concentration was calculated from
calibration curves, which were obtained by analyzing standard
aqueous solutions of various metal salts, such as aqueous sodium
chloride solutions, aqueous potassium chloride solutions, aqueous
magnesium chloride solutions and aqueous calcium chloride
solutions. Based on the amount of alkali metal ions and alkaline
earth metal ions measured by this method in the sample, the amount
of the alkali metal salt and the alkaline earth metal salt in the
dry pellets was calculated
(3) Determination of Phosphate Compound in EVOH:
[0079] 10 g of a sample of the dry EVOH pellets was put into 50 ml
of aqueous 0.01 N HCl solution, and stirred at 95.degree. C. for 6
hours. The stirred aqueous solution was analyzed by ion
chromatography in order to quantify the amount of phosphate ion,
using a Yokogawa Electric ICS-A23 column, and using an aqueous
solution containing 2.5 mM sodium carbonate and 1.0 mM sodium
hydrogencarbonate as an eluent. The amount of phosphate ion was
calculated based on a calibration curve derived from the analysis
of standard aqueous sodium dihydrogenphosphate solutions. The
amount of phosphate compound, expressed as the weight of phosphate
groups in the dry pellets, was calculated from the amount of
phosphate ions measured in the sample.
[0080] The carboxylic acid in the dry EVOH pellets was acetic acid,
and the acid content of the pellets was 320 ppm. The calcium salt
content of the EVOH pellets was 75 ppm (as Ca.sup.2+); the
potassium salt content was 35 ppm (as K.sup.+); and the phosphate
compound content was 50 ppm (as the total amount of
PO.sub.4.sup.3-, HPO.sub.4.sup.2.sup.-, and H.sub.2PO.sub.4.sup.-).
The MFR of the EVOH resin pellets, measured at 190.degree. C. under
a load of 2160 g, was 10 g/10 min. The ratio by weight of the
carboxylic acid to the alkali metal salt (i.e., the weight of the
carboxylic acid divided by the weight of the alkali metal) in the
EVOH was 9.1. The ratio by weight of the carboxylic acid to the
alkaline earth metal salt (i.e., the weight of the carboxylic acid
divided by the weight of the alkaline earth metal) in the EVOH was
4.3.
[0081] The degree of modification of the EVOH with the
silicon-containing olefinic unsaturated monomer and the intrinsic
viscosity of the modified EVOH were measured according to the
methods discussed below.
(4) Determination of Degree of Modification of EVOH with
Silicon-Containing Olefinic Unsaturated Monomer:
[0082] 10 g of a sample of the dry EVOH pellets was put into a
platinum crucible, to which was added a 1/1 mixture of concentrated
sulfuric acid/concentrated nitric acid. The crucible was then
heated and the sample was thereby carbonized. The carbonized sample
was ashed in an electric furnace at 600.degree. C., and then melted
in sodium carbonate at 900.degree. C. After cooling to room
temperature, distilled water was added thereto to provide an
aqueous solution having a volume of 50 ml. The silicon content of
the aqueous solution was measured by atomic absorption spectrometry
under the condition discussed below, from which was calculated the
degree of modification (Y) of the EVOH with the silicon-containing
olefinic unsaturated monomer.
[0083] Device: Perkin-Elmer Model 2380,
[0084] Measurement Wavelength: 251.6 nm,
[0085] Slit Width: 0.2 nm,
[0086] Lamp: Perkin-Elmer #303-6063,
[0087] Lamp current: 40 mA,
[0088] Frame: Acetylene-nitrous oxide frame.
(5) Intrinsic Viscosity of EVOH:
[0089] 0.20 g of a sample of the dry EVOH pellets was dissolved in
40 ml of aqueous phenol (water/phenol=15/85% by weight) and heated
at 60.degree. C. for 3 to 4 hours. The viscosity of the resulting
solution was measured at 30.degree. C. with an Ostwald viscometer
(t.sub.0=90 seconds). The intrinsic viscosity [.eta.] of EVOH was
calculated using the equation below.
[.eta.]=(2(.eta..sub.sp-1n.eta..sub.rel)).sup.1/2/C(liter/g) in
which;
[0090] .eta..sub.sp=t/t.sub.0-1 (specific viscosity),
[0091] .mu..sub.rel=t/t.sub.0 (relative viscosity),
[0092] C is the EVOH concentration in the sample (g/l),
[0093] t.sub.0 is the time taken by the blank (aqueous phenol) to
pass through the viscometer,
[0094] t indicates the time taken by the sample-containing aqueous
phenol solution to pass through the viscometer.
[0095] The vinyltrimethoxysilane content of the EVOH was 0.01 mol
%, and the intrinsic viscosity [.eta.] was 0.0856 liter/g.
Synthesis Example 2
[0096] EVOH having an ethylene content of 47 mol %, a degree of
saponification of 99.4%, and a degree of modification with a
silicon-containing olefinic unsaturated monomer of 0 mol % was
obtained in the same manner as in Synthesis Example 1, except that
vinyltrimethoxysilane was not added to the polymerization reaction.
The acetic acid content of the resulting EVOH obtained was 320 ppm;
the calcium salt content was 75 ppm; the potassium salt content was
35 ppm; and the phosphate compound content was 50 ppm. The MFR of
the EVOH, measured at 190.degree. C. under a load of 2160 g, was 16
g/10 min. The ratio by weight of the carboxylic acid to the alkali
metal salt in the EVOH was 9.1. The ratio by weight of the
carboxylic acid to the alkaline earth metal salt was 4.3.
Synthesis Example 3
[0097] 100 parts by weight of wet pellets (water content of 55%,
based on the weight of the wet pellets) of EVOH (a) having an
ethylene content of 47 mol %, a degree of saponification of 99.6%,
and a degree of modification with a silicon-containing olefinic
unsaturated monomer of 0 mol %, were dipped in 845 parts by weight
of an aqueous solution containing 0.25 g/liter of acetic acid and
0.483 g/liter of sodium acetate, at 25.degree. C. for 6 hours.
After dipping, the pellets were dewatered, and dried in a hot air
drier at 80.degree. C. for 3 hours and then at 107.degree. C. for
24 hours to provide dry pellets of EVOH (a). The acetic acid
content of the EVOH was 150 ppm, and the sodium salt content was
150 ppm. The MFR of the EVOH, measured at 190.degree. C. under a
load of 2160 g, was 46 g/10 min. The ratio by weight of the
carboxylic acid to the alkali metal salt in the EVOH was 1.
Example 1
[0098] The dry EVOH pellets obtained in Synthesis Example 1 were
used to prepare the EVOH (a). Specifically, the dry pellets of
Synthesis Example 1 were cooled with liquid nitrogen and milled in
a grinder to obtain an EVOH powder (A) having a particle size of
from 45 to 425 .mu.m of EVOH (a). (Thus, the EVOH powder (A) had at
least 80% by weight of particles of EVOH (a) that had passed
through a JIS standard sieve having a nominal size of 425 .mu.m but
not through a JIS standard sieve having a nominal size of 45
.mu.m.) To 100 parts of the EVOH powder (A), added were 0.1 parts
of inorganic particles (B), Nippon Aerosil AEROSIL R972 (a silica
powder having a mean particle size of the primary particles of 16
nm, and surface treated with a dimethylsilyl compound), and shaken
well to provide an ethylene-vinyl alcohol copolymer composition
comprising a mixture of (A) and (B). The water content of the EVOH
powder was 1.4%, measured according to the method discussed
below.
(6) Determination of Water Content of EVOH Composition:
[0099] Using a Mettler HR73-HALOGEN water content meter, about 2 g
of a sample of the EVOH composition was dried at 180.degree. C. for
20 minutes to determine the water content (X) of the EVOH
composition.
[0100] Next, the surface of an iron plate of dimensions 0.8 mm
thick.times.50 mm.times.100 mm was degreased by washing it with
detergent. The iron plate was coated with the EVOH powder
composition produced as described above, using a fluidized bed
coating method. Specifically, the fluidized bed coating method
comprises fluidizing the EVOH composition powder in a fluidizing
room by introducing air through a multi-holed plate and suspending
the iron plate substrate in the fluidized layer of the powder in
the room, thereby coating the substrate with the powder. The
fluidized bed coating conditions are discussed below.
[0101] Substrate pre-heating: 280.degree. C. for 10 minutes,
[0102] Dipping time: 5 seconds,
[0103] Post-heating: at 200.degree. C. for 5 minutes.
[0104] The iron plate thus coated with the EVOH powder was
evaluated for the uniformity of the coating film, the smoothness
and the glossiness of the coating film, using the criteria
discussed below. In addition, the degree of yellowing of the
coating film and the adhesion of the coating film to the substrate
were measured by the methods discussed below.
(7) Smoothness of Coating Film:
[0105] The smoothness of the coating film formed on the substrate
was visually evaluated according to the criteria below.
[0106] Rank: Condition
[0107] A (good): The coating film is smooth and good.
[0108] B (good): The coating film slightly roughened, but is of
commercially acceptable quality.
[0109] C (not good): The coating film exhibited significant
roughening, and is not of commercially acceptable quality.
(8) Glossiness of Coating Film:
[0110] The glossiness of the coating film formed on the substrate
was visually evaluated according to the criteria below:
[0111] Rank: Condition
[0112] A (good): The coating film is glossy and beautiful.
[0113] B (good): The coating film is not so glossy, but is of
commercially acceptable quality.
[0114] C (not good): The coating film is not glossy at all, (i.e.,
has the appearance of a frosted film), and is not of commercially
acceptable quality.
(9) Degree of Yellowing of Coating Film:
[0115] The color of the coating film formed on the substrate was
visually evaluated according to the criteria below.
[0116] Rank: Condition
[0117] A (good): The coating film is slightly yellowed.
[0118] B (good): The coating film is slightly yellowed, but is of
commercially acceptable quality.
[0119] C (not good): The coating film is significantly yellowed,
and does not have a commercially acceptable appearance.
(10) Adhesion of the Coating Film to the Substrate:
[0120] Using a knife, the EVOH coating film formed on the substrate
was partly cut, and then the coating was peeled from the substrate.
The adhesion of the coating film to the substrate was evaluated
according to the criteria below.
[0121] Rank: Condition
[0122] A (good): The coating film is difficult to peel off, and is
firmly adhered to the substrate.
[0123] B (good): When pulled slowly from the substrate, the coating
film peels off without tearing.
[0124] C (not good): The coating film is readily peeled off from
the substrate.
[0125] Based on the criteria mentioned above, the iron plate coated
with the EVOH powder in this Example (i.e., Example 1) was
evaluated in regard to the uniformity of the coating film (the
smoothness and the glossiness of the coating film), the degree of
yellowing of the coating film, and the adhesion of the coating film
to the substrate. The iron plate coated with the EVOH powder in
this Example ranked A in regard to the smoothness of the coating
film, the glossiness of the coating film, the degree of yellowing
of the coating film and the adhesion of the coating film to the
substrate, and ranked B in regard to the glossiness of the coating
film. The results are summarized in Table 1.
Example 2
[0126] An EVOH composition comprising EVOH powder (A) and inorganic
particles (B) was produced in the same manner as in Example 1,
except that the EVOH prepared in Synthesis Example 2 was used as
EVOH (a). An iron plate was coated with the EVOH powder composition
using a fluidized bed coating method, in the same manner as in
Example 1, and the coated plate was evaluated in regard to the
uniformity of the coating film (the smoothness and the glossiness
of the coating film), the degree of yellowing of the coating film,
and the adhesion of the coating film to the substrate. The test
results are summarized in Table 1.
Example 3
[0127] An EVOH composition comprising EVOH powder (A) and inorganic
particles (B) was produced in the same manner as in Example 2,
except that Nippon Aerosil AEROSIL R974 (a silica powder having a
mean particle size of 12 nm, and surface treated with a
dimethylsilyl compound) was used as the inorganic particles (B).
Also, an iron plate was coated with the EVOH powder composition
using the fluidized bed coating method of Example 2. The coated
plate was evaluated in regard to the uniformity of the coating film
(the smoothness and the glossiness of the coating film), the degree
of yellowing of the coating film, and the adhesion of the coating
film to the substrate. The test results are summarized in Table
1.
Example 4
[0128] An EVOH composition comprising EVOH powder (A) and inorganic
particles (B) was prepared in the same manner as in Example 2,
except that Nippon Aerosil AEROSIL RX200 (a silica powder having a
mean particle size of 12 nm, and surface treated with a
trimethylsilyl compound) was used as the inorganic particles (B).
Also, an iron plate was coated with the EVOH powder composition by
the fluidized bed coating method of Example 2. The coated plate was
evaluated in regard to the uniformity of the coating film (the
smoothness and the glossiness of the coating film), the degree of
yellowing of the coating film, and the adhesion of the coating film
to the substrate. The test results are summarized in Table 1.
Example 5
[0129] An EVOH composition comprising EVOH powder (A) and inorganic
particles (B) was prepared in the same manner as in Example 2,
except that Nippon Aerosil AEROSIL 200CF (a silica powder having a
mean particle size of 12 nm, but not surface treated) was used as
the inorganic particles (B). In the same manner as in Example 2, an
iron plate was coated with the EVOH powder composition by a
fluidized bed coating method, and the coated plate was evaluated in
regard to the uniformity of the coating film (the smoothness and
the glossiness of the coating film), the degree of yellowing of the
coating film, and the adhesion of the coating film to the
substrate. The test results are summarized in Table 1.
Example 6
[0130] An EVOH composition comprising EVOH powder (A) and inorganic
particles (B) was prepared in the same manner as in Example 2,
except that the EVOH (a) of Synthesis Example 3 was used. Also, in
the same manner as in Example 2, an iron plate was coated with the
EVOH powder composition by a fluidized bed coating method, and the
coated plate was evaluated in regard to the uniformity of the
coating film (the smoothness and the glossiness of the coating
film), the degree of yellowing of the coating film, and the
adhesion of the coating film to the substrate. The test results are
summarized in Table 1.
Comparative Example 1
[0131] A powder coating resin was produced in the same manner as in
Example 2, except that no inorganic particles (B) were added. The
composition instead comprised only an EVOH (a) having a particle
size of from 45 to 425 .mu.m. Also, in the same manner as in
Example 2, an iron plate was coated with the powder coating resin
by a fluidized bed coating method, and the coated plate was
evaluated in regard to the uniformity of the coating film (the
smoothness and the glossiness of the coating film), the degree of
yellowing of the coating film, and the adhesion of the coating film
to the substrate. The test results are summarized in Table 1.
Comparative Example 2
[0132] An EVOH composition comprising EVOH powder (A) and inorganic
particles (B) was produced in the same manner as in Example 2,
except that the amount of the inorganic particles (B) was 5 parts
by weight relative to 100 parts by weight of the EVOH powder (A).
Also, in the same manner as in Example 2, an iron plate was coated
with the EVOH powder composition by a fluidized bed coating method,
and the coated plate was evaluated in regard to the uniformity of
the coating film (the smoothness and the glossiness of the coating
film), the degree of yellowing of the coating film, and the
adhesion of the coating film to the substrate. The test results are
summarized in Table 1. TABLE-US-00001 TABLE 1 Water Content of
Smoothness Glossiness Degree of Adhesiveness of Powder of EVOH of
Coating of Coating Yellowing of Coating Film to Composition (wt. %)
Film Film Coating Film Substrate Example 1 1.4 A B A A Example 2
1.5 A B A B Example 3 1.3 A B A B Example 4 1.5 A B A B Example 5
1.3 B B A B Example 6 1.6 A A A B Comp. Example 1 1.4 C C A A Comp.
Example 2 1.6 C C A C
[0133] Even though the water contents of the compositions of Table
1 are higher than 51% by weight, the EVOH powder coating
compositions of Examples 1 to 6 of the present invention all formed
good coating films of high uniformity (that is, the coating films
formed were all smooth and glossy), when applied to substrates as a
powder coating. In particular, the coating film formed of the EVOH
composition of Example 1, in which the EVOH (a) was modified with a
silicon-containing olefinic unsaturated monomer to a degree of
modification of 0.01 mol %, had very good adhesion to the
substrate.
[0134] In contrast, the coating film formed from the powder coating
resin of Comparative Example 1, which did not contain any inorganic
particles (B), did not have good properties. Though the water
content of the powder coating resin of Comparative Example 1 was
almost the same as that of the EVOH composition of Example 2, the
coating film formed only from the powder coating resin comprising
EVOH (a) alone, was not uniform, glossy, and had a poor
appearance.
[0135] The coating film formed from the EVOH composition of
Comparative Example 2, in which the amount of the inorganic
particles (B) is greater than 2 parts by weight relative to 100
parts by weight of the EVOH powder (A), also was not uniform and
glossy, and its appearance was not good.
[0136] As discussed above, the EVOH powder coating composition of
the present invention forms a coating film having good uniformity
on substrates to which it has been applied. In particular, not only
dry but also wet EVOH powder compositions of the present invention,
having a water content of more than 1% by weight, provide a coating
film having good uniformity. Thus, the composition of the present
invention has superior properties compared to conventional powder
coating resin compositions.
[0137] The priority document of the present application, Japanese
application 2001-265944, filed Sep. 3, 2001, is incorporated herein
by reference.
[0138] Obviously, numerous modifications and variations on the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *