BACKGROUND ART Fig. 5 hereof shows a conventional hot runner mold 101 having a nozzle body 102 disposed therein. The nozzle body 102 has flow passageways 104,105 centrally positioned relative to a lateral direction thereof and formed to extend longitudinally therethrough. <BR> <P>Theseflowpassageways104, 105guidemoltenresin103therethrough.

The nozzle body 102 has a heating means 107 mounted around an outer peripheral surface 106 thereof. The heating means 107 maintains the resin 103 at a predetermined temperature and prevents the resin 103 from solidifying within the flow passageway 104.

For the thus arranged runner mold 101, however, when removed from the mold 101, a molded article 108 can cause a stringiness as will be next described in relation to Fig. 6.

In Fig. 6, when removed from the mold 101 as indicated by an arrow, the article 108 produces a stringiness portion 111 leading to a runner portion 109 thereof. At the same time, the resin 103 causes a stringiness portion 113 leading to at a distal end 112 thereof. Such stringiness is developed by stretching of resin from the distal end 112 in the form of a string, which results in failed

moldings.

In order to prevent production of unwanted stringiness, one may propose to precisely control temperature of the resin 103 or provide the hot runner mold with an additional valve for regulating or controlling the flow of resin 103. With this arrangement, however, the mold is inevitably complicated in construction. Such a compli- cated hot runner mold is undesirably costly to produce.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide an injection nozzle for a hot runner mold. The nozzle is less costly to manufacture, and is arranged such that the hot runner mold produces molded products without causing stringiness.

According to an aspect of the present invention, there is provided an injection nozzle for use in a hot runner mold having a cavity and a space formed therein, the space communicating with the cavity, said nozzle being positioned within the space and having an outer peripheral surface having a heating means disposed thereon for heating said nozzle, characterized in that the outer peripheral surface of said nozzle has a heat transmitting ring disposed thereon for releasing heat of a distal end portion of said nozzle to the hot runner mold, and has a heat-insulating groove formed thereon for preventing heat generated by the heating means from being transferred to the distal end portion.

Preferably, the heating means, said heat-insulating groove, and said heat transmitting ring are disposed in order along a direction of flow of resin within the hot runner mold.

The heat-insulating groove and the heat transmitting ring

are provided on the outer peripheral surface of the nozzle and are disposed in order along the direction of the flow of resin.

The groove serves to prevent heat generated by the heating means from being transferred to the distal end portion of the nozzle while the ring serves to release heat of the distal end portion to the hot runner mold. The resin lying in the distal end portion can thus be cooled with efficiency. With this arrangement, there is developed no stringiness between a molded product and the distal end portion when the molded product is removed from the mold.

The heating means, the groove, and the heat transmitting ring are provided in such a manner as to provide simplified construction of the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a side elevation view of a hot runner mold, showing a stationary mold in cross-section, according to the present invention; Fig. 2 is a view showing on large scale a portion of the stationary mold encircled with an oval 2 of Fig. 1; Fig. 3 is a cross-sectional view taken along line 3-3 of Fig. 2; Fig. 4 is a view showing how an injection nozzle disposed within the stationary mold is operated in accordance with the present invention; Fig. 5 is a view showing a conventional nozzle of a hot runner

mold ; and Fig. 6 is a view showing unwanted stringiness caused by the use of the nozzle of Fig. 5.

BEST MODE FOR CARRYING OUT THE INVENTION Referring to Fig. 1, a hot runner mold 10 includes a stationary mold 12 and a movable mold 13 disposed to engage the stationary mold 12. The mold 10 is mounted in an injection molding machine 14 for the purpose of producing a resin molded product 18.

The machine 14 includes a carrier 16, an injection device 17 positioned on the carrier 16, and a mold clamping mechanism 18.

The mechanism 18 includes a stationary platen 21, tie bars 2 2 mounted to the platen 21, and a movable platen 23 slidablymounted to the tie bars 22. The movable platen 23 is slidable in a direction as shown by an arrow al, to move the movable mold 13 mounted to the platen 23 to a closed position as shown by a double-dot-and-dash line. In the closed position, the mold 13 is clamped to the stationary mold 12 with a predetermined pressure exerted thereon.

The movable platen 23 is also slidable in a direction as shown by an arrow a2, to move the mold 13 back to an opened position as indicated by a solid line.

The stationary mold 12 includes a body 24, a runner member 25 provided in the body 24 and connected to the injection device 17, and an injection nozzle 26 connected to the runner member 25.

The body 24 has a runner 27 formed therein. The runner 27 leads to the nozzle 26. The body 24 also has a parting surface 28 to which the runner 27 leads through a gate (not shown). The parting

surface 28 defines a cavity 29 in cooperation with the mold 13.

Turning to Fig. 2, the nozzle 26 includes a nozzle body 31.

The nozzle 26 has a heating means 36 and a heat transmitting ring (hereinafter referred to as"heat releasing ring") 38 both disposed on an outer peripheral surface 35 thereof. The nozzle 26 has a flange portion 32 formed at a proximal end portion 43b thereof.

The flange portion 32 is connected to the runner member 25. The nozzle 26 has a flow passageway 33 and a runner 34 positioned centrally relative to a lateral direction thereof. The passageway 33 and the runner 34 communicate with each other. More specifically, the nozzle body 31 has the passageway 33 formed therethrough and extending longitudinally thereof. The outer peripheral surface 35 has a heat-insulating groove 37 formed thereon. The heating means 36, the groove 37, and the ring 38 are disposed in order along a direction as shown by an arrow a3. As described hereinafter, resin 51 (see Fig. 4) flows in the direction of the arrow a3. The flange portion 32 has a seat surface 41 held in contact with the runner member 25. The nozzle 26 has a distal end portion 43a positioned opposite from the proximal end portion 43b. The distal <BR> <BR> end portion 43b has a seat surface 42 formed thereat. Thestationary mold 12 has a nozzle mounting hole (space) 44 formed therein. The nozzle 26 is mounted within the hole 44.

The nozzle 26 is made from carbon steel such as S45C.

The flow passageway 33 has its diameter D. The passageway 33 has a reduced portion 45 of diameter Ds formed distally thereof.

The diameter Ds is smaller than the diameter D. The runner 34 communicates with the flowpassageway 33 through the reduced portion

45.

The runner 34 is tapered providing an angle 0 between planes in which upper and lower inner surfaces of the runner 34 lie. The runner 34 is continuous with the reduced portion 45. Forming the tapered runner 34 and the reduced portion 45 enables moldings to be removed from the reduced portion 45 when the hot runner mold 10 is in an opened position.

The heating means 36 is a band heater providing a power (a heat capacity) Q. The heating means 36 heats a portion of the nozzle body 31 having the flow passageway 33 formed therein.

The heat-insulating groove 37 is formed on the outer peripheral surface 35 of the nozzle 26. More specifically, the nozzle 26 has an intermediate portion 47 provided between the distal end portion 43a and the nozzle body 31. The distal end portion 43a and the intermediate portion 47 have the runner 34 formed to extend therethrough. The intermediate portion 47 has the groove 37 formed on an outer peripheral surface 35b thereof. In other words, the groove 37 extends circumferentially of the outer peripheral surface 35b of the intermediate portion 47. The distal end portion 43a, the intermediate portion 47, the nozzle body 31, and the flange portion 32 are integral with each other. The distal end portion 43a has the heat releasing ring 38 mounted around an outer peripheral surface 35a thereof. Namely, the ring 38 extends circumferentially of the outer peripheral surface 35a of the distal end portion 43a. The nozzle body 31 has the heating means 36 mounted around an outer peripheral surface 35c thereof located adjacent or in the proximity of the groove 37. That is, the heating means

36 extends circumferentially of the outer peripheral surface 35c of the nozzle body 31. The groove 37 is disposed in the vicinity of the reduced portion 45. The groove 37 is of depth M and width B. The groove 37 is disposed forwardly of the heating means 36.

The ring 38 is disposed forwardly of the groove 37.

The nozzle 26 has an external thread formed throughout the length of the outer peripheral surface 35. The ring 38 has an internal thread formed on an inner peripheral surface thereof.

The internal thread of the ring 38 is formed to threadedly engage the external thread. The ring 38 has a fitting surface 46 formed on an outer peripheral surface thereof. The surface 46 is designed to tightly or intimately contact an inner peripheral surface 24a of the body 24 defining the hole 44.

The ring 38 is made from, for example, aluminum, aluminum alloy, copper or copper alloys.

The nozzle body 31 has a temperature Tn. The stationary mold 12 has a temperature Tf. The distal end 43a has a temperature Tt. The heat releasing ring 38 has a temperature Tr. A relation between the temperatures Tn, Tf, Tt, and Tr can be shown by a mathematical expression Tf < Tr < Tt < Tn.

The nozzle 26 is mounted within the hole 44 as follows.

First, the heating means 36 is mounted around the outer peripheral surface 35c of the nozzle body 31. The ring 38 is then threaded onto the distal end portion 43a. Second, the nozzle 26 having the ring 38 mounted on the distal end portion 43a is fitted into the nozzle mounting hole 44 of the mold 12. Finally, the runner member 25 is mounted within the mold 12 into tight contact

with the seat surface 41. This causes the seat surface 42 to be pressed against an inner wall surface 48 of the body 24 exposed or facing to the a space defined within the hole 44.

With respect to Fig. 3, the ring 38 is shown as being fitted within the hole 44. During molding operation, the heat releasing ring 38 increases in size or produces thermal expansion to bring the surface 46 into tight contact with the inner peripheral surface 2 4 a of the body 24. Thus, no gap can be formed between the surface 46 and the inner peripheral surface 24a of the body 24.

Discussion will be made in relation to Fig. 4 as to how the injection nozzle 26 disposed within the hot runner mold 10 is operated according to the present invention.

During the molding operation, the resin 51 is injected from the injection nozzle 26 into the cavity 29 (see Fig. 1). More specifically, the resin 51 flows through the flow passageway 33 and the runners 34,27 into the cavity 29, as shown by an arrow a4, to then fill the cavity 29. The resin 51 lying within the runners 34,27 and the cavity 29 starts to solidify. At this time, the heating means 36 provided around the outer peripheral surface 35c of the nozzle body 31 heats a leading end portion 31a of the nozzle body 31 located adjacent the groove 37 or in the vicinity of the reduced portion 45, as shown by arrows a5, a5, to thereby transmit heat to the resin 51. The resin 51 lying within the flow passageway 33 can thus be maintained at a predetermined temperature.

It thus becomes possible to prevent the resin 51 from decreasing in temperature. The resin 51 is no longer solidified.

Providing the groove 37 increases surface area of the

intermediate portion 47 positioned between the heating means 36 and the distal end portion 43a. This makes it possible to prevent the heat generated by the heating means 36 from being transferred from the leading end portion 31a to the distal end portion 43a.

Consequently, the distal end portion 43a does not increase in temperature.

Because the ring 38 provided around the outer peripheral surface 35a of the distal end portion 43a is held in tight contact with the inner peripheral surface 24a of the body 24, the distal end portion 43a is united with the stationary mold 12 by means of the ring 38. With this arrangement, heat of the distal end portion 43a is transmitted or released to the stationary mold 12, as indicated by arrows a6, a6. As a result, the temperature Tt can be made lower than the temperature Tn. The resin 51 melted within the runner 34 can thus be cooledwith efficiency. The resin 51 thus cooled can produce no stringiness.

The nozzle 26 including the heating means 36, the groove 37, and the ring 38 as shown in Fig. 4 is simple in construction.

This results in reduced cost for producing the mold 10.

As described hereinbefore, the heat releasing ring 38 is made from aluminum, aluminum alloy, copper, or copper alloy all of which provide greater thermal conductivity than material from which the nozzle 26 is made. Using such a ring 38 achieves improved thermal conduction. More specifically, the ring 38 can release or transmit heat of the distal end portion 43a to the body 24 of the stationary mold 12 with improved efficiency.

The hot runner mold 10 has been described as having the runner

27 leading to the nozzle 26, however, it may be altered depending upon configuration of resin moldings. For example, the mold 10 is modified to provide a gate leading directly to the nozzle 26.

The groove 37 may take on any configuration.

The ring 38, which has been described as being threaded onto the distal end portion 43a, may not be threaded as long as it is mounted around the outer peripheral surface 35a of the distal end portion 43a.

Coolant may be provided in the vicinity of the ring 38 so as to cool the mold 12.

INDUSTRIAL APPLICABLITY With the arrangements as explained above, the inventive nozzle effectively cools the resin within the distal end thereof, thereby enabling removal of the molded product from the distal end without producing stringiness. Further, the nozzle is simple in construction and this leads to reduction in the cost of manufacture of the hot runner mold. Thus, the nozzle is useful particularly in resin molding using a hot runner mold.