Coating processes – Particles – flakes – or granules coated or encapsulated – Applying superposed diverse coatings or coating a coated base
Reexamination Certificate
2000-03-01
2003-12-30
Le, H. Thi (Department: 1773)
Coating processes
Particles, flakes, or granules coated or encapsulated
Applying superposed diverse coatings or coating a coated base
C264S143000, C264S173160, C425S097000, C425S114000, C425S133100, C425S464000, C425S468000, C428S403000, C428S407000
Reexamination Certificate
active
06669986
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for manufacturing multilayer pellets and a die equipment for manufacturing multilayer pellets. In more detail, the present invention relates to a process for manufacturing multilayer pellets served as a molding material for various plastic products and having a core-sheath structure comprising a plurality of molding materials and a die equipment used for manufacturing multilayer pellets with the extrusion molding technique.
The present invention also relates to masterbatch resin pellets with improved brittleness and a process for manufacturing thereof using a multilayer pellet.
The present invention further relates to a process for drying and manufacturing thermoplastic polyester resin with good drying acceleration using a multilayer pellet.
Pellets for plastic molding are obtained by heating and melting plastic materials previously blended and extrusion-molding the melted materials into strand forms, and then cutting the obtained plastic strands into small tablet forms, so-called pellets.
When various plastic products are molded, preparing the pellets as described above has many advantages. For example, blending and adjusting materials are not required every time when plastic products are molded; stable operation of plastic molding can be performed; stabilized product quality can be obtained; and raw materials can be easily supplied to the molding machine and other handling becomes easier.
Plastic pellets entirely molded from one plastic material are common. However, double-layer pellets or multilayer pellets comprising a plurality of plastic materials and a process for manufacturing such pellets have also been proposed.
JP-A-7-171828 (“JP-A-” indicates Japanese Unexamined Patent Publication) discloses multilayer pellets of a core-sheath structure in which a material with rich adhesiveness is used as the core and a crystalline polyolefin resin with less adhesiveness is used as the sheath in order to solve the problem of likeliness to cause blocking of pellets manufactured from materials with rich adhesiveness.
JP-A-59-81121 discloses a process for manufacturing pellets from an olefin-vinyl alcohol copolymer which is unable to form strands for manufacturing pellets due to its too small melt tension. In the process, multilayer pellets of a core-sheath structure is manufactured by cutting multilayer strands having a core with resin having small melt tension, i.e, the olefin-vinyl alcohol copolymer, outer circumference of which is covered with resin having large melt tension. JP-A-59-81121 also shows a manufacturing equipment having a dice-head for pellet molding equipped with a structure for feeding sheath material to the circumference of core material.
PROBLEMS TO BE SOLVED BY THE INVENTION
With the conventional multilayer pellet manufacturing technique, the molding speed of multilayer strands must be set to a comparatively low level in order to successively cover the sheath material around the outer circumference of the core material when the multilayer strand is molded.
Consequently, the productivity of the multilayer strand and multilayer pellets is poor and manufacturing cost of multilayer pellets is high.
In order to solve this problem, a method of using a strand molding machine equipped with a plurality of dice heads, that is, extrusion ports, and manufacturing a plurality of multilayer strands simultaneously could be proposed.
However, it is difficult to adjust in such a manner as to successfully cover the outer circumference of the core material with the sheath material of a specified thickness at each of a plurality of extrusion ports. It is also difficult to feed the molten resin materials to a plurality of extrusion ports in a uniform quantity and at uniform flow rate and to control uniformly the flow of core material and sheath material throughout the full circumference of the flow.
One object of the present invention is to solve the above-mentioned problem and to provide a process for manufacturing multilayer pellets of a high quality and having a stable core-sheath structure at a high productivity.
As mentioned above, the present invention also relates to masterbatch resin pellets with improved brittleness and a process for manufacturing thereof using a multilayer pellet.
As methods for blending pigments; low molecular weight polymer such as wax, additives such as plasticizer, antioxidant, ultraviolet absorbent, light stabilizer, etc. (hereinafter called the “pigments, etc.”) in a thermoplastic resin such as polystyrene, polyester and polypropylene, a method for adding these pigments, etc. at the time of polymerization reaction; a method for adding masterbatch, in which pigments, etc. are dispersed in or stuck to a polymer at a high concentration, to natural resin; a method for adding, directly to polymer, the pigments, etc. or processed pigments or the like which comprises the pigments, etc. and dispersant such as low-molecular weight polyethylene or a metallic soap; and other methods are known. Of these, the method for adding masterbatch is most popularly used in various fields because of its handiness at the time of addition and excellent performance, for example, non-contamination, suitability to automatic weighing, and suitability to transportation.
The masterbatch comprises base resin as a main component, to which pigments, etc. are mixed, and in general, the masterbatch is used by diluting 2 to 150 times by a resin, so-called natural resin, at the time of its application. In general, for the base resin of the masterbatch, a resin identical to or similar to the natural resin is used because of the relation in properties to the natural resin or fluidity of the masterbatch. For the masterbatch manufacturing method, it is common practice to extrude the melt containing the base resin and pigments, etc. into a form of strand, and then, to cool the strand, and to cut it into pellets.
Since the masterbatch is diluted with natural resin at the time of application, it is desirable to contain pigments, etc. at a high concentration. However, manufacturing such a masterbatch containing a high concentration of pigments by a conventional method, strand breakage at the time of melting-extrusion and generation of chips at the time of cutting are caused due to the brittleness of the composition. In addition, since compatibility of the additives with the base resin is generally low, if a masterbatch containing a high concentration of additives is manufactured by a conventional method, the additives tend to be localized and the portions where the additives-localized becomes brittle, also causing problems of strand breakage at the time of melting-extrusion and generation of chips at the time of cutting.
Another object of the present invention is to provide a process for manufacturing master-batch resin pellets containing a high concentration of pigments, etc. free of strand breakage at the time of melting-extrusion and chip generation at the time of cutting. It is also an object of the present invention to provide masterbatch resin pellets obtained by the process.
The inventors have found that these objects of the present invention can be accomplished by using specific multilayer pellets manufactured by a process such as those mentioned above.
As mentioned above, the present invention further relates to a process for drying and manufacturing thermoplastic polyester resin with good drying acceleration using a multilayer pellet.
Thermoplastic polyester resin such as polyethylene terephthalate, etc. is composed with repetitive units having ester bonds. However, when it is heated in the presence of moisture, esteric bonds are hydrolyzed to change resin quality, and to cause problems of poor moldability, etc. Consequently, before molding, the moisture in the thermoplastic polyester resin must be removed, and from the industrial viewpoint, it is generally preferable to dry at sufficiently higher temperature than the glass transition point. If the resin is highly crystalline like polyethylene terephthalate or poly
Hamada Sumio
Itou Tuyoshi
Kodama Kenji
Komai Jun
Mori Hiroyuki
Birch & Stewart Kolasch & Birch, LLP
Le H. Thi
Sumika Color Company, Limited
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