Stock material or miscellaneous articles – Structurally defined web or sheet – Including variation in thickness
Reexamination Certificate
1999-07-13
2001-04-10
Loney, Donald (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including variation in thickness
C428S043000, C428S213000, C264S328100, C264S328120, C280S728300
Reexamination Certificate
active
06214442
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin molded product and a method for producing the same. Particularly, it relates to a method of preventing external appearance failure such as uneven luster, or the like, from occurring in wall-thickness changed portions of an injection-molded product.
The present application is based on Japanese Patent Application No. Hei. 10-197431, which is incorporated herein by reference.
2. Description of the Related Art
Injection molding is a typical molding method with resin material. In the injection molding, molten resin is injected into a cavity through a gate of a die so that the cavity is filled with the resin. After the resin is cooled, die release is effected to take out the resin molded product.
In the background-art injection molding method, however, uneven luster and sinking may occur in surfaces of wall-thickness changed portions
911
in a case where a resin molded product
9
having a wall changed in thickness as shown in
FIG. 7A
is formed. That is, when a groove
910
extending in the direction crossing the resin flow direction
95
is provided in the resin molded product
9
, uneven luster stripes
914
occur in the surfaces of the wall-thickness changed portions
911
on opposite sides of the groove
910
. Also in a case where a step-like wall-thickness changed portion
911
is provided in the resin molded product
9
as shown in
FIG. 7B
, an uneven luster stripe
914
occurs in a surface of the wall-thickness changed portion
911
.
SUMMARY OF THE INVENTION
In consideration of the background-art problem, it is an object of the present invention to provide a resin molded product in which uneven luster and sinking is prevented from occurring in a wall-thickness changed portion to provide good external appearance, and a method for producing such a resin molded product.
According to the present invention, provided is a resin molded product made of a thermoplastic resin composition and having at least one thick-walled portion, at least one thin-walled portion, and at least one wall-thickness changed portion provided between the thick-walled portion and the thin-walled portion. The thermoplastic resin composition exhibits a melting viscosity of not larger than 1500 poise and a die swell ratio of not lower than 1.0 when measured by using a capillary rheometer (temperature of 200° C. and die L/D=10 mm/1 mm) at a shear rate of not lower than 1200/sec.
The present invention uses a thermoplastic resin composition having a predetermined melting viscosity and a predetermined die swell ratio to thereby prevent uneven luster and sinking from occurring in a wall-thickness changed portion of an injection-molded product.
It is estimated that uneven luster is caused in a wall-thickness changed portion by grain displacement in a flow path-reducing portion due to residual stress of molten resin in the flow path reducing portion at the die-releasing time or by shortage of transfer due to generation of negative pressure in a flow path enlarging portion, in the case where the thermoplastic resin composition is injected in the direction crossing the wall-thickness portions.
In the present invention, therefore, the melting viscosity of a thermoplastic resin composition
50
is set to be not higher than 1500 poise as shown in FIG.
1
. As a result, uneven luster in the wall-thickness changed portions
3
can be prevented. That is, residual stress in the flow path reducing portion
12
just after injection is relaxed to thereby prevent both the grain displacement and the swelling of the flow path reducing portion
12
from occurring at the time of die-releasing. Accordingly, the occurrence of uneven luster in the flow path reducing portion
12
can be prevented.
Further, the die swell ratio of the thermoplastic resin composition
50
is set to be not smaller than 1.0. As a result, negative pressure in the flow path enlarging portion
13
at the time of injection is suppressed so that both the die-facing characteristic and the die-transferring characteristic for resin can be improved. Accordingly, the occurrence of uneven luster and sinking in the flow path enlarging portion
13
can be suppressed.
Incidentally, the die swell ratio is preferably set to be not smaller than 1.2.
Because the resin molded product according to the present invention is formed from the thermoplastic resin composition having the aforementioned physical property values, no uneven luster and sinking are produced in either case whether the resin molded product has an embossed (delustered) surface or a mirror surface. Accordingly, the resin molded product according to the present invention is excellent in external appearance characteristic.
The present invention will be described below in detail.
The resin molded product according to the present invention has a thick-walled portion, a thin-walled portion and a wall-thickness changed portion provided between the thick-walled portion and the thin-walled portion. Specific examples of the shape of the resin molded product are shown in
FIGS. 2A
to
2
E.
As shown in
FIG. 2A
, a thin-walled portion
1
forms the bottom portion of a groove
10
formed between thick-walled portions
2
and
2
and in the direction crossing a resin flow direction
5
, and wall-thickness changed portions
3
are formed on the opposite sides of the thin-walled portion
1
.
As shown in
FIG. 2B
, a thick-walled portion
2
constitutes a rib
20
formed between thin-walled portions
1
, and wall-thickness changed portions
3
are formed on the opposite sides of each of the thin-walled portions
1
so as to extend in the direction crossing the resin flow direction
5
.
As shown in
FIG. 2C
, a thick-walled portion
2
and a thin-walled portion
1
are formed on the upstream and downstream sides, respectively, of the resin flow direction
5
in an injection die, and a step-like wall-thickness changed portion
3
is formed between the thick-walled portion
2
and the thin-walled portion
1
.
As shown in
FIG. 2D
, a thin-walled portion
1
and a thick-walled portion
2
are formed on the upstream and downstream sides, respectively, of the resin flow direction
5
in an injection die, and a step-like wall-thickness changed portion
3
is formed between the thick-walled portion
2
and the thin-walled portion
1
.
As shown in
FIG. 2E
, a thin-walled portion
1
constitutes the bottom portion of a triangular groove
100
formed between thick-walled portions
2
and
2
so as to extend in the direction crossing the resin flow direction
5
, and wall-thickness changed portions
3
are formed on the opposite sides of the thin-walled portion
1
.
Incidentally, the wall-thickness changed portion means a portion in which the wall thickness changes gradually from a thick state to a thin state or a portion in which the wall thickness changes like a perpendicular step between a thick-walled portion and a thin-walled portion.
The melting viscosity and the die swell ratio of the thermoplastic resin composition used in the resin molded product are measured by using a capillary rheometer. The melting viscosity used herein is defined as apparent viscosity (JIS K 7199).
The aforementioned physical property values of the thermoplastic resin composition are measured by using the capillary rheometer under the following conditions. The die has a length (L) of 10 mm and a diameter (D) of 1 mm. Further, the temperature of the thermoplastic resin composition at the time of the measurement is 200° C. The shear rate is not lower than 243-6080/sec.
When the melting viscosity of the thermoplastic resin composition used in the resin molded product according to the present invention is measured by using the capillary rheometer under the aforementioned measurement conditions, the melting viscosity is low so as to be not higher than 1500 poise at the shear rate of 1200/sec. Accordingly, residual stress in the flow path reducing portion can be relaxed so that swelling of the molded product at the time of die-releasing can be prevented and
Mizutani Haruyasu
Tanaka Yasuaki
LandOfFree
Resin molded product and method for producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Resin molded product and method for producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Resin molded product and method for producing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2536618