JPH0716941A - Production of dielectric lens - Google Patents

Abstract

PURPOSE:To form a surface radom layer in necessary thickness without deforming the same in the production of a dielectric lens for an antenna and to shorten a foam molding cycle. CONSTITUTION:A mold 10 is filled with a foamable material based on a resin and a radom layer 3 is formed on the surface part of the resin by foam molding so as to be thinly solidified. Next, a foamed molded object 1 is taken out of a mold 10 and received in a retaining mold 20 to be naturally cooled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a dielectric lens, and more particularly to a method for manufacturing a dielectric lens used as an antenna element for receiving microwaves for communication and broadcasting.

[0002]

2. Description of the Related Art Conventionally, as an antenna element for receiving microwaves of 50 GHz or more, a mixture of a resin material such as polypropylene, polyethylene, polystyrene and a foaming agent, and a ceramic powder as a dielectric constant adjusting agent is foamed into a dome shape. Molded dielectric lenses are known. In this type of dielectric lens, the surface portion is solidified during foam molding to form a radome layer. The radome layer functions as a protective layer for reinforcing the weather resistance and strength of the foam body.

However, if the radome layer is not sufficiently solidified or is taken out from the mold in a thin state, the radome layer will be deformed by the foaming pressure inside. On the other hand, when the mold is rapidly cooled or the cooling time in the mold is set to be long, the radome layer grows thick to impair the lens efficiency, or the molding cycle becomes long and the production efficiency decreases.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a dielectric material having a required thickness for a radome layer without deformation and capable of shortening a foam molding cycle. It is to provide a manufacturing method of a lens. In order to achieve the above object, a method for manufacturing a dielectric lens according to the present invention is such that a molding die is filled with a foam material containing a resin as a main component, and the radome layer is thin in a substantially dome shape and a surface portion. It comprises a step of foam-molding so as to solidify, and a step of taking out the foam-molded article from the molding die and storing it in a shape-retaining die having a cavity having a shape substantially the same as the outer shape of the foam-molded article. . The foamed material in a molten state starts foaming immediately after being filled in the molding die, and a radome layer is formed on the surface portion of the foamed body. When the radome layer is thinly solidified, the foamed molded product is taken out of the molding die and housed in the shape retaining die.

According to the present invention, since the foamed molded product is taken out from the molding die while the radome layer is thin, the foaming molding cycle can be short and the molding die can be used efficiently. Moreover, while the foamed molded body continues to foam while being housed in the shape-holding mold, the surface shape is regulated by applying an appropriate pressure in the cavity of the shape-holding mold, and the radome layer is kept inside. It is not deformed by foaming pressure. Further, the radome layer stops growing almost at the thickness formed in the molding die and solidifies at a thickness of about 2 mm or less that does not impair the lens efficiency in practical use.

[0006]

Embodiments of the method for manufacturing a dielectric lens according to the present invention will be described below with reference to the accompanying drawings. The manufacturing method is performed in the order of the foam molding step shown in FIG. 1 (A) and the shape retention step shown in FIG. 1 (B).

The foam material used in the foam molding process has a composition of 98 wt% polypropylene as the resin material and 2 wt% azodicarbonamide as the foaming agent. Further, CaTiO ₃ or the like may be used as the dielectric constant adjusting agent. This foam material is molded from a cylinder into a mold 10.
Is injected into the cavity 13. Molding die 10 is fixed side 1
1a and the movable side 11b, which are made of a metal material (copper, iron or the like) having a good thermal conductivity, and have a temperature adjusting hole 12 for circulating a cooling liquid. The cavity 13 has a hemispherical shape with a radius of 90 mm, and the foamed molded body 1 having this shape is obtained. The conditions for injection foam molding are as follows.

Cylinder temperature: 220 ° C. Mold temperature: 80 ° C. Injection pressure: 1448 kg / cm ² Holding pressure: 1267 kg / cm ² Injection speed: 114 cm ³ / sec Cooling time: 180 sec

The cooling time is the time until the radome layer 3 is thinly solidified on the surface of the foam main body 2 after the foam material is injected and the mold temperature is maintained at 80 ° C. to wait for the internal foam. . After a lapse of a predetermined cooling time, the foamed molded body 1 is taken out from the molding die 10 and the shape retention step is performed.

The shape-retaining mold 20 is composed of a main body 21 having a cavity 22 and a movable plate 25 supported by a guide rod 23 so as to be vertically movable. The movable plate 25 is elastically urged downward by the spring force of the coil spring 24 attached to the guide rod 23. Further, the cavity 22 has the same shape as the outer shape of the foam molding 1. Both the main body 21 and the movable plate 25 are formed of a material having a low thermal conductivity, for example, wood powder hardened with ABS resin, or ceramic. The thermal conductivity of resin is 5 × 1
0 ^-4 cal / cm · S · ° C, that of alumina is 4 × 10
^-3 cal / cm · S · ° C.

The foamed molded body 1 taken out from the molding die 10 is immediately accommodated in the shape-retaining die 20, and the movable plate 25 applies a pressure of 5.75 kg / cm ² and holds it for about 1 hour. The foamed molded body 1 is naturally cooled in the shape retention mold 20. The foam main body 2 of the foam molded body 1 continues to foam a little even in this state, but the radome layer 3 formed on the surface portion is regulated by the shape-holding mold 20 and solidifies without being deformed by the foaming pressure. To do. The radome layer 3 has already been thinly solidified in the molding die 10, and the shape-retaining die 20
Finally solidified within. The shape-holding die 20 is naturally cooled in the shape-holding die 20, and the shape-holding die 20 is made of a material having a low thermal conductivity (which means that the shaping die 10 has a lower thermal conductivity than the metal material of the shaping die 10). Because it is formed, the radome layer 3
Do not grow thick.

The dielectric lens manufactured by the above steps has a foaming ratio of 1.15, a relative dielectric constant of 2.1, a radome layer 3 thickness of about 1 mm, and a hemispherical shape accuracy of ± 0.5.
Since it is less than or equal to mm, there is no sink mark, swirl mark, or void.

The manufacturing method according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the gist thereof. In particular, polyethylene, polystyrene or the like can be used as the resin material, and p, p-oxybenzenesulfonyl hydrazide or the like can be used as the foaming agent. Further, as a dielectric constant adjusting agent, BaTiO ₃ , CaTi
O ₃ , MgTiO ₃ or the like can be used. Also, the mold 1
The configuration of 0 and 20 is arbitrary.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, (A) shows a foam molding step, and (B) shows a shape retention step.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Foaming molding (dielectric lens) 2 ... Foaming main body 3 ... Radome layer 10 ... Molding die 20 ... Shape retaining die

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Claims (1)

[Claims] 1. A step of filling a foaming material containing a resin as a main component in a molding die, and foaming the foaming material in a substantially dome shape so that a radome layer is thinly solidified on a surface portion, and a foamed molded article. A method of manufacturing a dielectric lens, comprising the steps of: taking out from the molding die and accommodating it in a shape-retaining die having a cavity having substantially the same shape as the outer shape of the foam molding.