Coating processes – Immersion or partial immersion – Running lengths
Reexamination Certificate
2000-08-11
2002-05-28
Barr, Michael (Department: 1762)
Coating processes
Immersion or partial immersion
Running lengths
C427S434600, C427S289000, C264S103000, C264S171230, C264S172110
Reexamination Certificate
active
06395342
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process of preparing pellets of a synthetic organic fiber reinforced polyolefin, more particularly, to a process of the same which will provide a molded product having superior impact resistance and recyclability when used as raw materials for injection molding, injection-compression molding, extrusion, blow molding and a like molding process. The pellets obtained by the process of the invention can be effectively utilized as molding materials for interior and exterior automotive parts such as a bumper fascia, side maul, battery tray, fan shroud, engine cover, instrument panel, console box, shift lever base, wheel cover and an air spoiler; civil engineering and construction materials such as a concrete panel and a sound barrier; transportation instruments such as a pallet and a container; and furniture items such as a chair and a desk.
2. Description of the Related Art
Polyolefins reinforced with an inorganic filler such as glass fiber or talc for improving heat resistance and rigidity, have the poor impact resistance, particularly at low temperatures. To overcome this disadvantage, there have been proposed a number of molding materials incorporated with a synthetic organic fiber as disclosed in Japanese Examined Patent Publication No.6-25288 and Japanese Unexamined Patent Publications Nos.62-146945, 3-290453, 4-202545 and 6-306216.
In the process of preparing such molding materials, pelletization is carried out by mixing raw materials of a matrix resin and a reinforcing fiber while heating and agitation using a mixer, or melt-mixing, blending or kneading the raw materials using rolls, extruder or a Ko-kneader. The disadvantage of this process is that the reinforcing fiber tends to fracture due to the mechanical mixing, resulting in the poor reinforcing effect.
Another disadvantage of this process is that the synthetic organic fiber used as the reinforcing fiber is deteriorated by heat when the mechanical melt-mixing is carried out at 200° C. or higher. Therefore the resulting molded products exhibit poor impact resistance, particularly at low temperatures.
It is desired to carry out the melt-mixing at relatively low temperature to avoid the heat deterioration. According to an example of Japanese Unexamined Patent Publication No. 3-290453, melt-mixing was carried out at 190° C. Also, Japanese Unexamined Patent Publication No.62-146945 has described that melt-mixing is carried out preferably at 170°-230° C., more preferably at 180-200° C., and in an example thereof the melt-mixing was carried out at 180° C. However, if the melt-mixing is carried out at such a low temperature, the matrix resin still has a high viscosity. Because of the high viscosity, the reinforcing fiber receives a larger load during the melt-mixing process and hence may be undesirably stretched or broken into fiber pieces having shorter lengths. As a result, the sufficient reinforcing effect cannot be obtained.
Japanese Unexamined Patent Publication No.4-202545 discloses a method of providing pellets of a synthetic organic fiber formulated molding materials. In this process, the continuous reinforcing fibers are impregnated with a molten matrix resin and pulled out. The resulting strand therefrom is cut to form pellets. This publication does not describe the retention time of impregnation and only describes the temperature of the molten matrix resin.
In general, the viscosity of a matrix resin needs to be lower for a reinforcing fiber to be sufficiently impregnated with the matrix resin, and for this reason, a process of heating the matrix resin up to a considerably high temperature is typically employed so as to decrease the viscosity thereof. However, a composite material having a mass ratio of an organic fiber to glass fiber mass ratio over 1.9 exhibits remarkably poor impact resistance. Presumably, this is because the organic fiber is exposed to such a high temperature for a prolonged time (i.e., the retention time in the molten matrix resin is long) and hence deteriorated by heat. If the temperature of the molten matrix resin is lowered to avoid such heat deterioration of the organic fiber, the viscosity of the molten resin increase, leading to the decreased productivity and may result in an insufficient impregnation of the fibers with the molten resin. Further, fibers may easily falling off from a pellet thus obtained to form fuzz, which may cause a bridge problem at a hopper in injection molding.
Additionally, Japanese Unexamined Patent Publications Nos.3-7307 and 50-67350 describe methods in which a reinforcing fiber woven fabric is impregnated with a resin to form a sheet and the sheet is cut into pellets. Such methods are economically disadvantageous because numerous steps are required as well as a substantial loss occurs in the cutting process.
There is also known a method of improving the impact resistance by using a long glass fiber as a reinforcing fiber. Though this method somewhat improves the impact resistance at low temperatures, satisfactory improvements cannot obtained as well as a synthetic organic fiber. This is because a glass fiber tends to fracture than a synthetic organic fiber. In the case of recycling the molded product, breaking the glass fiber is inevitable in a re-molding process, hence a fiber length enough for the sufficient reinforcement cannot maintained. Therefore, the resulting recycled products will show the poor impact resistance.
In addition, the recycling process requires cutting or breaking of the molded products into pellets, and such a cutting or breaking operation causes glass fiber to fracture and scatter into the working atmosphere thereby making the working environment worse, for example, operators come to feel prickled.
The invention has been made in view of the foregoing problems residing in the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to a process for preparing pellets of a synthetic organic fiber reinforced polyolefin, comprising:
heating a polyolefin at the temperature which is higher than the melting point thereof by 40° C. or more to lower than the melting point of a synthetic organic fiber to form a molten polyolefin;
passing a reinforcing fiber comprising the synthetic organic fiber continuously through the molten polyolefin within six seconds to form a polyolefin impregnated fiber; and
cutting the polyolefin impregnated fiber into the pellets. wherein the synthetic organic fiber has the melting point in the range of over 200° C. to 265° C.
The foregoing and other objects, features and attendant advantages of the present invention will be more fully appreciated from the reading of the following detailed description.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the present invention, pellets of a synthetic organic fiber reinforced polyolefin are prepared from a reinforcing fiber comprising a synthetic organic fiber and a polyolefin as a matrix resin by the process of melt pultrusion process. In this process, the reinforcing fiber is impregnated with the molten polyolefin while the reinforcing fiber is passing continuously through the molten polyolefin and then the resulting polyolefin impregnated fiber is cut into the pellets.
First of all, raw materials used in the invention is described.
I. Reinforcing Fiber
The reinforcing fiber preferably has the form of a roving (a bundle of long filaments). It is recommended that each filament should have a diameter ranging between 0.5 &mgr;m and 100 &mgr;m, more preferably between 1.0 &mgr;m and 50 &mgr;m. For improvements in impact resistance, it is effective to use a fiber having a strength of not less than 3.55 cN/dtex (4 g/denier), preferably not less than 5.33 cN/dtex (6 g/denier).
The reinforcing fiber is preferably used in a pellet in an amount of 10 mass % to 50 mass %, preferably 15 mass % to 40 mass %. When the amount is smaller than 10 mass %, the resulting impact resistance is not sufficient. When the amount is larger than 50 mass %, the reinforcing fiber is poorly impregnated with the p
Asai Toshihiro
Hirano Yasuo
Kadowaki Ryosaku
Barr Michael
Kabushiki Kaisha Kobe Seiko Sho
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