Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Utility Patent
1999-06-16
2001-01-02
Dawson, Robert (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...
C525S089000, C525S097000, C525S098000, C524S451000, C524S425000
Utility Patent
active
06169144
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an injection-molded product of a propylene based resin composition. The injection-molded product is satisfactory in its weld appearance and flow mark appearance and therefore may be suitably used for a car part, an electronic and electric instrument part and a machinery part.
BACKGROUND OF THE INVENTION
Propylene based resin compositions have been extensively used for molding car parts, electronic and electric instrument parts and machinery parts by an injection molding method. In recent years, these kinds of parts have been required to be higher in their level of weld appearance and flow mark appearance as well as in their impact resistance, rigidity and resistance to heat deformation.
In molding a part by an injection molding method, it is generally known that at least two confluent portions at which flows of molten resin run together are found in a mold, and weld marks appear at the confluent portions in products molded therewith. Thus, conventional propylene based resin compositions are satisfactory in their mechanical properties such as impact resistance and rigidity, but are not satisfactory in their weld appearance.
In order to improve the weld appearance of molded products, for example, the following methods 1 to 4 have been previously proposed.
1. A method wherein a composition comprising (i)a propylene based resin, (ii)a fibrous reinforcing agent having a specific form, (iii)talc and (iv)calcium carbonate is used (JP-A-62-91545).
2. A method wherein a composition comprising (i) a resin such as a polypropylene resin or a polystyrene resin and (ii)a specific pigment is used (JP-A-9-183918).
3. A method wherein a confluent portion in a mold is improved (JP-A-4-156322).
4. A method wherein a composition comprising (i)a propylene based resin containing a polymer component derived from ethylene monomer, (ii)a propylene based resin obtained by further treating the above-mentioned propylene based resin with an organic peroxide, and (iii)an inorganic filler is used (JP-A-62-45638).
Although the above methods 1 to 4 exhibit an effect of improving the weld appearance, they leave following problems 1 to 3.
1. They are limited in their effects of improving the physical properties of the molded product.
2. Molds and injection molding machines to be used are restricted to specific ones in kind.
3. They are too high in costs to be used extensively.
In addition, in order to improve an undesirable appearance of “heaping” on the weldline, it has been proposed that a propylene based resin composition having a specific proportion of a swelling ratio measured at a higher shear rate and at a specific high temperature to a swelling ratio measured at a lower shear rate and at that temperature be used (JP-A-6-339944).
However, the method proposed in JP-A-6-33944 also leaves problems such that when the confluent portion is located near a gate of a mold, or when the injection molding is completed within a relatively short period of time, or when the injection molding is carried out using a propylene based resin composition having a high fluidity, not heaping but instead “grooving” on the weldline appears frequently, and such a weld cannot be improved to a proper degree of satisfaction.
Each of the references referred to above is incorporated herein by reference in its entirety.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an injection-molded product of a propylene based resin composition, which product is satisfactory in its weld appearance and flow mark appearance.
The present inventors have undertaken extensive studies to develop an injection-molded product containing a propylene based resin composition, which product is satisfactory particularly in its weld appearance and flow mark appearance. As a result, it has been found that a propylene based resin composition having a specific melt viscosity and swelling ratio can give an injection-molded product satisfactory in its weld appearance and flow mark appearance, and thereby the present invention has been obtained.
The present invention provides an injection-molded product containing a propylene based resin composition having a melt viscosity of not more than about 32 Pa·s measured at a shear rate of 2,432 s
−1
and at a temperature of 240° C. and a swelling ratio of from about 1.3 to 2.0 measured at a shear rate of 2,432 s
−1
and at a temperature of 240° C., which composition comprises:
(i) about 50 to 70% by weight of a propylene based resin;
(ii)about 15 to 30% by weight of a thermoplastic elastomer; and
(iii) about 10 to 30% by weight of an inorganic filler.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5624991 (1997-04-01), Harada et al.
patent: 5824759 (1998-10-01), Watanabe et al.
patent: 62-45638 (1987-02-01), None
patent: 62-91545 (1987-04-01), None
patent: 4-156322 (1992-05-01), None
patent: 6-339944 (1994-12-01), None
patent: 9-183918 (1997-07-01), None
Higashi Kenichi
Kanzaki Susumu
Toyoda Masao
Birch & Stewart Kolasch & Birch, LLP
Dawson Robert
Peng Kuo-Liang
Sumitomo Chemical Company Limited
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