Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
1999-06-01
2001-05-08
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S50200C, C528S503000, C528S902000
Reexamination Certificate
active
06228981
ABSTRACT:
The present invention relates to a process for preparing an aqueous dispersion coating material and a process for preparing a powder coating material. More particularly, the present invention relates to a process for producing an aqueous dispersion coating material and a process for producing a powder coating material, wherein various materials which will be coating film-constituting components, are blended, melted and kneaded, then cooled and solidified, and crushed to obtain coarse particles, and then, the coarse particles are wet-pulverized in an aqueous dispersant to form fine particles and be dispersed.
Heretofore, as an aqueous dispersion coating material, a slurry coating material prepared by a phase transition method for an aqueous dispersion coating material obtained by wetting in an aqueous medium fine particles obtained by finely pulverizing a powder coating material, has been known.
As disclosed in JP-A-8-311369, preparation of a slurry coating material by a phase transition method, is a technique wherein from a solvent type coating material employing a water-soluble organic solvent, the organic solvent is removed to form coating resin particles, and then the coating resin particles are dispersed in water to prepare a slurry coating material. By this technique, it is necessary to prepare a solvent type coating material, forcibly emulsify the solvent type coating material in water in order to remove the organic solvent, remove the organic solvent to prepare solid coating resin particles and disperse the coating resin particles in water. Namely, many steps are required, and further, it has been necessary to recover the organic solvent from water.
Further, in the method for removing the organic solvent directly from the solvent type coating material by heating and reduced pressure, the concentration of non-volatile contents and the concentration of the resin component tend to be high towards the end point of the removal, and the viscosity tends to be high due to the resin component having a high concentration. Accordingly, a large quantity of energy has been required to completely remove the organic solvent. As an additional problem, the coating resin obtained by removing the organic solvent tends to be bulky, and in order to disperse it stably in water, it has been necessary to finely pulverize the resin.
A problem resulting from this fine pulverization is such that as the particle size of the fine resin powder becomes small, the efficiency of energy required for fine pulverization tends to be poor, and a special technique will be required for capturing the fine powder, in the same manner as for the preparation of a fine powder to be used as a powder coating material.
It is an object of the present invention to provide a process for producing an aqueous dispersion coating material, which is free from the above mentioned various problems. Namely, it is an object of the present invention to provide a process for producing a powder coating material at a low cost with a relatively simple operation without necessity to use an organic solvent or without necessity of a trouble of capturing a fine powder.
The present inventors have conducted an extensive research to accomplish the above object and as a result, have found that an aqueous dispersion coating material having good stability, wherein the average particle size of fine particles of coating resin is at most 10 &mgr;m, can be obtained in good yield with good energy efficiency, by blending various starting materials which will be coating film-constituting components, melt-kneading the blend material, cooling and solidifying it, followed by crushing to obtain coarse particles, then wet-pulverizing the coarse particles in an aqueous dispersant, for example, by introducing coarse particles to a wet system pulverizer wherein an aqueous medium for dispersion is circulated, to pulverize the desired coating resin particles to fine particles and directly dispersing them in water, i.e. by carrying out pulverization into fine particles, stabilization of the dispersion and capturing fine particles at the same time, and that a powder coating material can be obtained very well by subjecting the aqueous dispersion coating material to dehydration treatment. The present invention has been accomplished on the basis of these discoveries.
Namely, the present invention provides a process for preparing an aqueous dispersion coating material containing a resin component having a softening temperature of from 10 to 250° C., which comprises:
(1) a step of mixing various starting materials which will be coating film-constituting components, to obtain a blend material,
(2) a step of melting and kneading the blend material at a temperature of at least the softening temperature of said resin component, to obtain a homogenized material,
(3) a step of cooling and solidifying the homogenized material, followed by crushing, to obtain coarse particles, and
(4) a step of wet-pulverizing the coarse particles in an aqueous dispersant, to obtain an aqueous dispersion coating material containing fine particles having an average particle size of at most 10 &mgr;m.
Further, the present invention provides a process for preparing a powder coating material containing a resin component having a softening temperature of from 10 to 250° C., which comprises:
(1) a step of mixing various starting materials which will be coating film-constituting components, to obtain a blend material,
(2) a step of melting and kneading the blend material at a temperature of at least the softening temperature of said resin component, to obtain a homogenized material,
(3) a step of cooling and solidifying the homogenized material, followed by crushing, to obtain coarse particles,
(4) a step of wet-pulverizing the coarse particles in an aqueous dispersant, to obtain an aqueous dispersion containing fine particles having an average particle size of at most 10 &mgr;m and
(5) a step of subjecting the aqueous dispersion to dehydration treatment, to obtain a powder coating material.
Now, the present invention will be described in detail with reference to the preferred embodiments.
In order for the aqueous dispersion coating material or the powder coating material obtained by the process of the present invention to form a coating film, it is necessary that after it is coated, the resin component will be softened or melted by heating to form a uniform coating film.
For this purpose, the softening temperature of the resin component which will be a coating film-constituting component, is required to be from 10 to 250° C. More preferably, the softening temperature is from 30 to 200° C.
If the softening temperature of the resin component is lower than 10° C., the coating resin particles in the aqueous dispersion coating material are likely to agglomerate even during the storage at room temperature, because as compared with an emulsion coating material, the particle sizes of the coating resin particles are larger by 100 times to 1,000 times. By reducing the average particle size of the coating resin particles in the aqueous dispersion coating material, it is possible to maintain the aqueous dispersion coating material stably even with coating resin particles of a resin component having a low softening temperature. However, in such a case, the total surface area of coating resin particles in the aqueous dispersion coating material increases, whereby a wetting agent such as a surfactant is required to be present in a large amount in order to disperse the coating resin particles stably in the aqueous medium. Accordingly, in such a case, the resulting coating film tends to be poor in such a performance as water resistance or gloss.
Further, if the softening temperature of the resin component exceeds 250° C., a temperature exceeding 250° C. will be required for heat curing to form a coating film, and at such a high temperature, the coating film is likely to undergo yellowing, or the coating film is likely to be oxidized by air and tends to loose flexibility. As a method for preventing such a phenomeno
Okazaki Haruhiko
Tagami Akiko
Dai Nippon Toryo Co., Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Teskin Fred
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