Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-04-06
2003-01-14
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S208000, C525S221000, C525S222000, C525S232000, C525S238000, C525S241000
Reexamination Certificate
active
06506843
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a thermosetting powder coating composition comprising a vinylidene fluoride polymer and methyl methacrylate polymer as resin components.
BACKGROUND ART
With respect to a fluorine-containing resin powder coating composition, various proposals have been made hitherto.
For example, with respect to a thermoplastic powder coating composition containing no curing agent, JP-A-4-227743 discloses a powder coating composition comprising a vinylidene fluoride (VdF)/hexafluoropropylene (HFP) copolymer and thermoplastic acrylic resin as resin components, and JP-A-6-108103 discloses a powder coating composition comprising polyvinylidene fluoride (PVdF), thermoplastic resin and VdF/tetrafluoroethylene (TFE)/HFP terpolymer as resin components. However since the thermoplastic powder coating composition is not subjected to curing (crosslinking), a hardness of an obtained coating film does not become high. Also the resin mixtures described in the above-mentioned patent publications cannot be finely pulverized at room temperature, and it is necessary to pulverize at a very low temperature, i.e. at a temperature of a liquid nitrogen, etc.
Also a thermosetting powder coating composition of fluorine-containing resin has been proposed.
For example, JP-A-1-103670 discloses a powder coating composition comprising a fluorine-containing copolymer as a sole resin component. However the fluorine-containing copolymers disclosed therein are only copolymers comprising chlorotrifluoroethylene (CTFE) and/or TFE as main components. Those fluorine-containing copolymers are difficult to be finely pulverized at room temperature and it is necessary to make them into powders by a method of pulverizing at very low temperature as mentioned above. Also a combination use with a thermoplastic resin is not disclosed therein.
JP-A-6-279549 discloses a thermosetting powder coating composition comprising a copolymer of VdF and allyl derivative as a resin component. According to a technique described in that patent publication, the above-mentioned copolymer is used solely as a resin component and though it can be pulverized at room temperature, an appearance such as a gloss of an obtained coating film is not always sufficient.
It is an object of the present invention to provide a thermosetting powder coating composition of VdF polymer which can be finely pulverized at room temperature and gives a coating film having excellent characteristics.
The present inventors have made intensive studies and found that the above-mentioned problems can be solved when a composite resin prepared by introducing crosslinkable functional group in a VdF polymer and further combining the VdF polymer with a methyl methacrylate (MMA) polymer has a specific melt flow rate, and thus have completed the present invention.
DISCLOSURE OF INVENTION
Namely the present invention relates to the thermosetting powder coating composition comprising a powder of composite resin which comprises a VdF polymer having crosslinkable functional group and a MMA polymer and has a melt flow rate (MFR) of 1 to 1,000 g/10 minutes when measuring at 130° C. at a load of 2.1 kg.
It is preferable that the above-mentioned composite resin powder is a powder pulverized at room temperature and having an average particle size of 1 to 100 &mgr;m.
It is further preferable that the MMA polymer also has crosslinkable functional group.
The present invention further relates to the thermosetting powder coating composition comprising the above-mentioned composite resin powder and a curing agent.
Particularly it is preferable that the crosslinkable functional group of the resin is at least one selected from carboxyl, hydroxyl and epoxy, and the curing agent has reaction sites having a reactivity with the respective crosslinkable functional groups.
Further the present invention relates to the coated article obtained by applying the above-mentioned thermosetting powder coating composition to a substrate and then baking for curing.
Preferred substrates are those having electric conductivity such as metal plates of stainless steel, aluminum, steel and galvanized steel, metal plates thereof subjected to chemical conversion treatment and resins endowed with electric conductivity by dispersing conductive carbon therein from the point that electrostatic coating can be carried out.
BEST MODE FOR CARRYING OUT THE INVENTION
In the thermosetting powder coating composition of the present invention, essential resin components thereof are a VdF polymer having crosslinkable functional group and MMA polymer.
The VdF polymer having crosslinkable functional group comprises a VdF unit, a unit having crosslinkable functional group and if necessary, a unit of other monomer copolymerizable therewith.
It is preferable that the VdF unit is contained in the VdF polymer in an amount of not less than 60% by mole, especially from 70 to 99% by mole based on the VdF polymer from the viewpoint of excellent compatibility with the MMA polymer.
Examples of the other copolymerizable monomer are, for instance, one or two of more of fluoroolefin monomers such as tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), monofluoroethylene (VF), and the like. Use of those comonomers can produce such excellent effects that melt kneading with MMA polymer, pigment and additives for coating can be conducted at relatively low temperature, melt-leveling of the powder coating occurs at relatively low temperature to give a coating film having good appearance, and cracking can be prevented at post-fabrication of a coated metal plate. Those effects cannot be obtained when only VdF unit is used. A content of those comonomer units is preferably from 0 to 40% by mole, especially from 1 to 30% by mole.
Examples of the crosslinkable functional group of VdF polymer are, for instance,
wherein R is alkyl having 1 to 3 carbon atoms.
Among those functional groups,
are preferred.
Examples of the monomer being capable of introducing such crosslinkable functional group are, for instance, perfluorobutenoic acid (PFBA), fluorine-containing monomer having ether unit described in JP-A-8-67795 and non-fluorine-containing monomers having carboxylic acid group such as maleic anhydride (MAL), vinyl acetate (VA), undecylenic acid (UA) and allyloxypropionic acid; hydroxyl-containing monomers such as hydroxybutyl vinyl ether (HBVE) and allyl alcohol; epoxy-containing monomers such as glycidyl vinyl ether (GVE) and allyl glycidylether (AGE); allyl derivatives described in JP-A-6-279549; and the like.
Among them, from the viewpoint of reactivity in a baking temperature range in case of a combination with a known curing agent, PFBA, carboxyl-containing monomers such as maleic anhydride, hydroxyl-containing monomers such as HBVE and epoxy (glycidyl)-containing monomers such as GVE are preferred.
The crosslinkable functional group forms a curing site. An amount thereof varies depending on a reactivity of the functional group, kind of a curing agent and whether or not the crosslinkable functional group is introduced in the MMA polymer. When a composite resin is prepared in combination of the MMA polymer, the amount is not particularly limited as far as in the whole composite resin, an acid value is from 1 to 300 mgKOH/g, a hydroxyl value is from 1 to 200 mgKOH/g or an epoxy equivalent is in the range of from 5 to 15,000 equivalents. From the point that compatibility with the VdF polymer is lowered when too many functional groups are introduced, it is preferable to carry out the copolymerization so that the MMA unit is contained in an amount of not less than 70% by mole, more preferably not less than 80% by mole. For example, in case where the MMA polymer has no crosslinkable functional group, it is preferable that the crosslinkable functional groups are contained in the VdF polymer so that an acid value is from 1 to 300 mgKOH/g, a hydroxyl value is from 1 to 200 mgKOH/g or an epoxy equivalent is in the range of from 5 to 15,000 equivalents.
From the viewpoint mention
Fukagawa Ryoichi
Iwakiri Miyuki
Iwakiri Ryuji
Kitahara Takahiro
Nagai Go
Dajkin Industries, Ltd.
Iwakiri Miyuki
Nutter Nathan M.
Sughrue & Mion, PLLC
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