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
1998-10-14
2001-05-29
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S176000, C525S439000, C241S023000
Reexamination Certificate
active
06239234
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to PET resin powder capable of forming a coating film or paint film by close adhesion to the surface of a metal, or the like, and to a process of preparation. The present invention permits the use of small broken pieces of recovered containers such as PET bottles as raw PET resin material.
PET (polyethylene terephthalate) resin exhibits low adhesivity to the surface of metal. Moreover, even when a baked coated film is formed from the material, crystallization of the coated film progresses which results in the development of the tendency to craze or peel. Accordingly, the resin is normally not utilized as a powder coating (powder paint). In addition, PET resins and other thermoplastic resins generally have low heat resistance and are elastic. Consequently, when machine grinding is performed at ordinary temperatures, ground particles have strand-like or whisker-like projections exceeding 1 mm in length, making it impossible to handle the polymer as a so-called powder. Generally, the particle size of powder for electrostatic coating is required to be 5-150 &mgr;m (average particle diameter 40 &mgr;m) and that of powder for fluidization dip, 60-350 &mgr;m (average particle diameter 150 &mgr;m). Accordingly, it is very difficult to prepare a fine powder (5-350 &mgr;m) suitable for powder coating, or the like, by means of ordinary machine grinding. Grinding is presently performed by refrigeration grinding method using liquid nitrogen. Refrigeration grinding requires a large quantity of liquid nitrogen, and it is also necessary to adapt grinding machines and other peripheral devices to specific applications which are capable of enduring low temperature environments. This necessitates the provision of large scale equipment with a resulting increase in grinding costs.
SUMMARY OF THE INVENTION
It Accordingly, one object of the present invention is to impart close adherence to PET resin with poor metal adhesion and provides a powder coating which is applicable to electrostatic coating and fluidization dip processes.
Another object of the invention is provide a powder coating which can utilize, as a raw material recovered food containers such as PET bottles, disposal of which has recently become a serious social problem.
Briefly, these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by a composition for powder coating, which comprises a melt blend of 100 weight parts of PET resin pellets or small pieces obtained from recovered PET resin molded products with (i) 5-40 weight parts of a polyester resin (excluding PET) or a modified polyester resin, (ii) 3-30 weight parts of modified polyolefin resin or ethylene unsaturated carboxylic acid copolymer resin, or (iii) 3-30 weight parts of polycarbonate resin, the powder material exhibiting an improved ability to adhere to metal surfaces.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the present process PET resin pellets or flakes obtained by “machine grinding” of recovered PET products or pellets obtained by further melt-kneading of the above flakes by means of an extruder are mixed with modifiers which improve metal adhesion and molten film forming properties. The resulting mixture is melt-kneaded by means of an extruder to provide composite pellets, and then the pellets are heated at 170° C. for a predetermined time to achieve a degree of crystallinity of 35% or higher. The pellets are then machine ground or dissolved in a common solvent to provide chemically fine powder.
Suitable examples of modifiers include polyester resins excluding PET, e.g. polybutylene terephthalate, polyethylene naphthalate, modified polyester resins, polyolefine resins acid-modified with unsaturated carboxylic acids or anhydrides thereof, e.g. acrylic, methacrylic, maleic, fumaric, and itaconic acids; maleic anhydride, itaconic anhydride, and the like, and further copolymer resins of the acids with olefins, or polycarbonate resins.
The baking temperatures of the modified polyester resins can be lowered by converting the resin to a kneaded mixture of e.g. 40 wt. % PET resin, 40 wt. % PBT resin, and 20 wt. % low molecular olefin wax with adhesive properties. The compounding amounts of the respective modifiers are 5-40 weight parts, preferably 20 weight parts or thereabout, based on 100 weight parts of raw PET resin. Concerning the polyolelfins acid-modified with unsaturated carboxylic acid or anhydrides thereof, maleic anhydride-modified polyolefins are preferred with respect to the property of close adherence. The maleic anhydride-modified polyolefins are prepared by kneading 100 weight parts of low molecular olefin resins with 10-40 weight parts of maleic anhydride, preferably 30 weight parts of the latter for close adherence. The compounding amount of the maleic anhydride-modified olefin resin is in the range of 3-30 weight parts, preferably 5-20 weight parts, of the maleic anhydride per 100 weight parts of PET resin. Also in the case of using, as modifier, a copolymer resin of acrylic acid, or the like, with olefins, or a polycarbonate resin, its compounding amount is 3-30 weight parts. Since the present invention has as one of the objects utilization of recovered PET resin, it is desired from this viewpoint that the amount of the modifier blended be held as small as possible. However, since small added amounts cause lesser improvements in metal adherence, increases in the hardness of the coating film, tendencies to reduce anti-impact strength, the added amount is adjusted according to the coated film performance desired.
The modifier can be used either singly or in combination. The degree of crystallinity of the composition pellets containing the respective modifiers is in the range of 20-30%, and machine grinding of the pellets as such by normal method will produce whisker-like projections on the surface of ground particles, which renders their utilization as a powder coating impossible. However, heating the pellets to 166±10° C., which is the range of crystallization temperature of PET resin, which is the base material, or heating to 170° C. for several hours, which is applicable for industrial purposes, can increase the degree of crystallinity (to be sought by DSC analysis). When machine grinding is effected after the degree of crystallinity of 35% or more is achieved, whisker projections are no longer produced and spherical particles dominate. Moreover, the grinding time tends to be shortened in proportion to the degree of crystallinity.
REFERENCES:
patent: 3382295 (1968-05-01), Taylor
patent: 3435093 (1969-03-01), Cope
patent: 3956229 (1976-05-01), Bollen
patent: 4243712 (1981-01-01), Hoheisel
patent: 4357385 (1982-11-01), Kuroda
patent: 4670508 (1987-06-01), Ohdaira
patent: 042747 (1976-04-01), None
Buttner David J.
K. K. Seishin Kigyo
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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