Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1999-06-18
2002-01-15
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S255000, C264S263000, C264S266000, C264S267000, C264S278000
Reexamination Certificate
active
06338812
ABSTRACT:
The present invention claims the benefit of the filing date of Japanese Patent Application Serial No. H10-357583, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for forming a helical antenna having an antenna element which is covered with, for example, an insulating layer, and more particularly, to a method for forming a helical antenna, in which the antenna element is integrated into the insulating layer by monolithically moulding the insulating layer around the antenna.
2. Description of the Related Art
In recent years, helical antennas having helical antenna elements (or aerial elements) are widely used in portable communication devices, such as cellular phones, because of their wide-band characteristics and the advantage of requiring less space.
An antenna element is generally attached to a portable communication device so that it projects from the case. Accordingly, the antenna element is covered with an insulating layer for purposes of preventing the antenna element from deforming due to external forces, and preventing the resonant frequency changing.
FIGS. 9 and 10
illustrate a conventional method for forming a helical antenna having an antenna element which is covered with a monolithically moulded insulating layer.
The conventional antenna element
101
is formed by helically coiling a conductive material. One end of the antenna element
101
is fixed to a metal fitting
102
. The antenna element
101
is electrically connected to the aerial coupled circuits and the transmitting/receiving circuit of a portable communication device (not shown) via the metal fitting
102
and the feeder
103
connected to the metal fitting
102
.
The coil pitch P of the antenna element
101
is determined based on the resonant frequency of the helical antenna. The coil pitch is almost the same over the entire length of the antenna along the longitudinal axis.
In order to cover the antenna element
101
with the monolithically moulded insulating layer
104
, a core pin
105
, which functions as a moulding die, is inserted from the free end of the antenna element along its longitudinal axis, as shown in FIG.
9
.
The antenna element
101
, in which the core pin
105
was inserted, is accommodated in the cavity
107
which is defined by the top and bottom dies
106
a
and
106
b,
as illustrated in FIG.
10
. The antenna element
101
is supported by the core pin
105
in the cavity
107
so that a prescribed gap is generated between the inner surface of the cavity
107
and the antenna element
101
.
Then, a molten resin, which is the material of the insulating layer
104
, is injected into the cavity
107
from the gate G to fill the gap between the antenna element
101
and the moulding dies
106
a
and
106
b.
When the moulding resin is cured, the antenna element
101
is integrated into the insulating cover
104
, whereby a helical antenna with an anternal element covered with the insulating layer is completed.
However, the conventional method has a problem that the injection pressure of the moulding resin, which forms the insulating layer, causes the coil pitch P of the antenna element
101
to change, and consequently, the electric parameters of the antenna deviate from the designed values.
For example, in
FIG. 9
, the pitches P
1
, P
2
, and P
3
measured at three different positions (i.e., near the base, in the middle, and near the tip) along the coil axis before the moulding of the insulating cover are 2.49 mm, 2.43 mm, and 2.464 mm, which are close to each other with the offsets within the acceptable error. However, with the injection gate located near the metal fitting
102
, as illustrated in
FIG. 10
, the pitches P
1
′, P
2
′, and P
3
′ of the antenna element
101
after the moulding become 3.18 mm, 2.68 mm, and 1.44 mm, and the end portion of the antenna element
101
is undesirably compressed. This pitch divergence inevitably occurs even if the gate position is adjusted. Thus, the resonant frequency of the helical antenna greatly deviates from the designed value depending on the moulding conditions, which results in a low product yield in mass production.
In order to overcome this problem, Japanese Patent Application Laid-open No. 8-894017 discloses a helical antenna, which can prevent the pitch divergence of the antenna element
111
by forming a helical guide groove
113
in the insulating cap
112
in accordance with the coil pitch P of the antenna element
111
, as shown in
FIG. 11
, and which can protect the antenna element
111
from external forces by bonding an insulating cover
114
, which was formed in advance, around the antenna element
111
by adhesive, or by fitting the antenna element
111
into the insulating cover
114
, as shown in FIG.
12
.
However, the helical antenna
110
disclosed in 8-894017 requires an assembling step or a bonding step for attaching the insulating cover to the helical antenna. In addition, the bonded or fitted insulating cover cannot sufficiently protect the anternal element. If the communication device is dropped, the insulating cover
114
is likely to break or to be disengaged from the antenna element
111
, and as a result, the antenna element is exposed.
SUMMARY OF THE INVENTION
The present invention was conceived in order to overcome these problems in the prior art, and it is an object of the invention to provide a method for forming a helical antenna with an antenna element covered with a monolithically formed insulating layer, which can reliably protect the antenna element from external forces, and can maintain the electric properties of the antenna element constant.
It is another object of the invention to provide a method for forming a helical antenna which does not require an extra assembling step for attaching an insulating cover to the antenna element, and which can prevent breakage or disengagement of the insulating cover, as well as undesirable exposure of the antenna element.
In order to achieve these objects, in one aspect of the invention, a helical antenna having a helical antenna element covered with an insulating layer is formed so that the antenna element and the insulating layer are monolithically moulded, and that the base of the antenna element is supported by a metal fitting. This method comprises the following steps:
(a) inserting the antenna element into an cylindrical cavity of an first moulding die, the inner diameter of the cylindrical cavity being equal to or slightly greater than the outer diameter of the antenna element;
(b) injecting an first insulating resin into the cylindrical cavity to produce a primary moulded product in which the antenna element is monolithically integrated into the first insulating resin;
(c) putting the primary moulded product in a cavity of a second moulding die so that a prescribed gap is formed between the outer surface of the primary moulded product and the inner surface of the second moulding die; and
(d) injecting a second insulating resin into the cavity of the second moulding die so that the cylindrical surface of the primary moulded product is monolithically covered with an insulating layer made of the second insulting resin, whereby the antenna element is completely covered with the monolithically formed insulating layer.
Because the inner diameter of the cylindrical cavity is equal to or slightly greater than the outer diameter of the antenna element, the antenna element is inserted into the cavity with its outer surface is in contact with the inner surface of the cylindrical cavity. When the first insulating resin is injected in the cylindrical cavity, the injection pressure causes the antenna element to expand outward in the radial direction, which further causes a friction force between the antenna element and the inner face of the moulding die. This friction force prevents the antenna element from moving along its longitudinal axis (or the coil axis). When the first insulating resin is set, the antenna element having a constant pitch
Ortiz Angela
SMK Corporation
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