JP3415866B2 - Synthetic resin foam manufacturing equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a synthetic resin foam. [0002] A synthetic resin is melted in an extruder, and a gaseous foaming agent (N ₂ gas or CO ₂ gas for high foaming degree, etc.) is added to the synthetic resin from outside the extruder. There is known an apparatus for producing a synthetic resin foam by injecting / containing a resin, extruding from an extruder, and causing physical foaming. [0003] If the injection amount of the gaseous foaming agent is not always constant, the degree of foaming of the synthetic resin foam becomes unstable and a high-quality synthetic resin foam cannot be produced stably. A flow control valve element is provided in the extruder as the injection nozzle itself, and the downstream pressure P of the injection nozzle is set.
₂ (that is, the pressure in the extruder) and the ratio P ₂ / P ₁ of the pressure P ₁ on the upstream side of the injection nozzle are set to be equal to or less than the critical pressure ratio, and gaseous foaming from the injection nozzle into the extruder is performed. The injection amount (flow rate) of the agent was kept constant. However, from the viewpoint of practical production speed and the like, if the hole diameter of the injection nozzle is not less than 10 μm,
In some cases, the pressure ratio P ₂ / P ₁ cannot be obtained below the critical pressure ratio.
It is difficult to manufacture, and it is very difficult to perform maintenance such as removal of clogging of the injection nozzle. Therefore, according to the present invention, the injection nozzle has a hole diameter of 10 μm.
In the case where the state below the critical pressure ratio cannot be obtained unless the diameter is not more than about m or less, the nozzle inlet / outlet pressure ratio P /
Even if P ₀ is larger than the critical pressure ratio S (that is, even if the injection nozzle hole diameter D is not made fine), the injection amount of the gaseous foaming agent into the extruder can always be kept constant. It is an object of the present invention to provide a synthetic resin foam manufacturing apparatus capable of stably obtaining a degree of foaming. [0006] In order to achieve the above object, the present invention provides an injection nozzle for injecting a gaseous foaming agent into an extruder, the outlet pressure of the injection nozzle and the injection nozzle. Nozzle inlet / outlet pressure ratio corresponding to the ratio of the inlet side pressure of the nozzle, the injection nozzle hole diameter is set so as to be larger than the critical pressure ratio, a flow control valve for flowing the gaseous foaming agent at a constant flow rate to the injection nozzle. A temperature for controlling the temperature between the outlet of the flow control valve and the injection nozzle and controlling the pressure at the nozzle inlet side so that the gas flow rate at the nozzle is constant with respect to the fluctuation of the outlet side pressure. A control means is provided. [0007] The gaseous foaming agent is adjusted to a constant flow rate by the flow rate regulating valve and sent to the injection nozzle. However, since the nozzle inlet / outlet pressure ratio is set to be larger than the critical pressure ratio, the outlet is set. When the side pressure fluctuates, the injection amount (flow rate) of the gaseous foaming agent injected into the extruder from the injection nozzle tends to fluctuate accordingly. In this case, the temperature control means calculates a nozzle inlet side pressure such that the nozzle inlet / outlet pressure ratio becomes constant with respect to the outlet side pressure fluctuation, and adjusts the flow rate adjusting valve so that the inlet side pressure becomes the same. To control the temperature between the injection nozzles.
Thereby, the injection amount of the gaseous foaming agent from the injection nozzle into the extruder can always be kept constant. The present invention will be described below in detail with reference to the drawings showing embodiments. FIG. 1 shows an example of an apparatus for producing a synthetic resin foam according to the present invention. The apparatus is provided with an extruder 1 and, in the illustrated example, is used to coat a long body 7 such as a cable. An example is shown. The extruder 1 includes a hopper 2, a cylinder 3, a screw 4, and a crosshead 5. Cylinder 3
Is provided with an injection nozzle 6 for injecting a gaseous foaming agent such as N ₂ gas or CO ₂ gas into the cylinder 3. Thus, the synthetic resin is supplied from the hopper 2 into the cylinder 3 and sent to the crosshead 5 by the screw 4 while being heated and melted. At the same time, a gaseous foaming agent is injected (press-fitted) into the cylinder 3 from the injection nozzle 6 to be contained in the molten synthetic resin, and the molten synthetic resin containing the foaming agent is extruded from the crosshead 5. Physical foaming is performed to produce a synthetic resin foam. In the illustrated example, the elongated body 7 passing through the inside of the crosshead 5 is extrusion-coated with a synthetic resin foam to form a coated elongated body 8. On the other hand, as shown in FIG. 1 and FIG.
The injection nozzle 6 having the first pipe 10, the flow control valve 11,
The second pipe 12, the filter 13, and the third pipe 14 are connected to and connected to a high-pressure gas generator 15. The high-pressure gas generator 15 supplies a gaseous foaming agent having a pressure sufficiently higher than the pressure P on the outlet side of the injection nozzle 6 (that is, the pressure in the cylinder 3). The first pipe 10 has an inside 6 a of the injection nozzle 6.
An inlet-side pressure detector 16 for detecting an inlet-side pressure P ₀ of the injection nozzle 6 is provided, and an outlet-side pressure detector 17 for detecting an outlet-side pressure P of the injection nozzle 6 is provided for the cylinder 3. The extruder 1 is provided with a rotation detector 21 for detecting the number of rotations of the screw 4. In FIGS. 1 and 3, reference numeral 18 denotes a temperature control means.
The temperature between the flow control valve 11 and the injection nozzle 6 can be controlled using a heat medium 22 such as oil whose temperature can be adjusted. That is, the inlet side temperature T ₀ of the inside 6a (see FIG. 2) of the injection nozzle 6 can be controlled. Reference numeral 19 denotes a temperature detector for detecting a temperature between the flow control valve 11 and the injection nozzle 6. The temperature control means 18 has a comparison operation controller 20, and based on data (pressure, temperature, etc.) detected by the pressure detectors 16, 17 and the temperature detector 19, etc.
A predetermined comparison operation is performed at 20, the temperature of the heat medium 22 is adjusted according to the result (temperature instruction), and the temperature between the flow control valve 11 and the injection nozzle 6 is controlled. The flow rate of the gaseous foaming agent flowing from the flow control valve 11 to the injection nozzle 6 is set by a flow rate setting device 23, and the comparison operation controller 20 controls the flow control valve 11 so that the flow rate is always constant. . The reference inlet pressure P ₀ , inlet temperature T _{0, and the} like are set by a pressure / temperature setting unit 24. [0023] Then, as shown in FIGS. 1 and 2, the injection nozzle hole diameter D of the injection nozzle 6, and the outlet side pressure P, the ratio P / P ₀ (hereinafter this nozzle entrance pressure ratio of inlet pressure P ₀ P / P ₀ ) is set to be larger than the critical pressure ratio S. If the nozzle inlet / outlet pressure ratio P / P ₀ is larger than the critical pressure ratio S, the injection nozzle 6
The injection amount (flow rate) G of the gaseous foaming agent injected into the inside is determined by the inlet pressure P ₀ , the outlet pressure P, the inlet temperature T _{0, and the} like. Specifically, assuming that the critical pressure ratio S is an isentropic flow from the flow characteristics of the tapered injection nozzle 6,
It is represented by equation (1). ## EQU1 ## Where κ is constant pressure specific heat / constant volume specific heat,
For example, in the case of N ₂ gas, κ is about 1.4, and the critical pressure ratio S is about 0.53. The injection amount G is given by equation (2). Here, A is the cross-sectional area of the injection nozzle 6, g is the gravitational acceleration, and v ₀ is the specific volume on the inlet side of the injection nozzle 6. ## EQU2 ## From the equations (3) and (4), the injection amount G in the equation (2) becomes the equation (5). Where R in equation (4)
Is the gas constant. [Equation 3] (Equation 4) [Equation 5] FIG. 4 shows the relationship between ψ in the equation (3) and the nozzle inlet / outlet pressure ratio P / P ₀ . As is clear from FIG. 4, when the nozzle inlet / outlet pressure ratio P / P ₀ is larger than the critical pressure ratio S, ψ (that is, the injection amount G) changes with the change of the outlet side pressure P. Here, by changing the inlet side temperature T _0, and changing the gas pressure at which the flow rate is made constant by the flow control valve, the flow is not an isentropic flow, but the nozzle injection amount G is kept constant. Can be done. That is, from the above equations (3) and (5), when the outlet side pressure P fluctuates, the nozzle inlet / outlet pressure ratio P / P ₀ becomes constant in accordance with the change of the outlet side pressure P. If the inlet pressure P ₀ is changed, the increase / decrease of ψ and the increase / decrease of P ₀ show the opposite tendency. Further, the inlet side pressure P _{0 is changed} to the inlet side temperature T
If control is performed by changing ₀ (see equation (4)), the above equation (5) can be used to calculate the increase / decrease of 、 and the following equation (6)
It can be seen that there are P ₀ , T ₀ that can cancel out the increase / decrease of the value of, and make the injection amount G constant. Of course, P ₀ and T ₀ are in a proportional relationship. (Equation 6) Thus, the nozzle inlet / outlet pressure ratio P / P ₀
Is larger than the critical pressure ratio S, if the nozzle inlet pressure P ₀ is controlled at the inlet side temperature T ₀ so that the gas flow rate at the nozzle becomes constant with respect to the fluctuation of the outlet side pressure P, G can be kept constant at all times. Thus, as shown in FIGS. 1, 2 and 3, the gaseous blowing agent supplied from the high-pressure gas generator 15
After passing through the third pipe 14, the filter 13 and the second pipe 12, the flow rate is adjusted to a constant flow rate by the flow control valve 11, and is sent to the injection nozzle 6 through the first pipe 10. At this time, since the nozzle inlet / outlet pressure ratio P / P ₀ is set to be larger than the critical pressure ratio S, when the outlet side pressure P fluctuates, the injection nozzle 6 flows into the cylinder 3 accordingly. The injection amount G of the gaseous blowing agent to be injected also tends to fluctuate. However, the comparison operation controller 20 calculates the inlet pressure P ₀ so that the injection amount G becomes constant with respect to the fluctuation of the outlet pressure P, and calculates the inlet pressure P ₀ so that the inlet pressure P ₀ is obtained. Since the inlet-side temperature T ₀ is controlled by adjusting the temperature of the heat medium 22, the injection amount G from the injection nozzle 6 into the cylinder 3 can be always kept constant. For example, when N ₂ gas is used as the gaseous foaming agent, the injection amount G is 2 N l / min, the injection nozzle hole diameter is 0.03 mm, and the nozzle inlet / outlet pressure ratio P / P ₀ is 0.60.
When the critical pressure ratio S is 0.53, the outlet pressure P is 159 kg /
When the pressure fluctuates from cm ² to 173 kg / cm ² , the inlet side temperature T ₀ becomes 30
By setting the temperature from 41 ° C. to 41 ° C., the injection amount G can be controlled to be constant. At this time, the nozzle inlet / outlet pressure ratio P / P ₀ ≒ 0.63. Further, when the injection amount G is 0.5 N l / min, the injection nozzle hole diameter is 0.02 mm, and the nozzle inlet / outlet pressure ratio P / P ₀ is 0.60 (critical pressure ratio S is 0.53) with N ₂ gas, the outlet side When the pressure P changes from 90 kg / cm ² to 98 kg / cm ² , the injection amount G is increased by changing the inlet side temperature T ₀ from 30 ° C. to 41 ° C.
Can be controlled to be constant. At this time, the nozzle inlet / outlet pressure ratio P / P
₀ ≒ 0.64. Since the present invention is configured as described above, the following significant effects can be obtained. If the injection nozzle hole diameter D is not less than 10 μm,
In the case where the pressure ratio P / P _{0 at} the nozzle inlet / outlet cannot be obtained below the critical pressure ratio S, the pressure ratio P / P at the nozzle inlet / outlet cannot be obtained.
₀ is larger than the critical pressure ratio S, and the injection nozzle hole diameter D is
By making it larger than 10 μm, the injection amount (flow rate) G of the gaseous blowing agent injected from the injection nozzle 6 into the extruder 1 can be surely and always kept constant. Accordingly, the foaming degree can be stably obtained, and a high-quality synthetic resin foam can be manufactured. In addition, the production of the injection nozzle 6 is facilitated, and maintenance such as removal of clogging of the injection nozzle 6 can be easily performed. The present invention is particularly suitable for those having a high foaming degree using a gaseous foaming agent such as N ₂ gas or CO ₂ gas.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall simplified configuration diagram showing one embodiment of the present invention. FIG. 2 is a sectional view of a main part of an injection nozzle. FIG. 3 is a block diagram. FIG. 4 is a graph showing the relationship between ψ and P / P ₀ . [Description of Signs] 1 Extruder 6 Injection nozzle 11 Flow control valve 18 Temperature control means P ₀ Inlet pressure P Outlet pressure S Critical pressure ratio D Injection nozzle hole diameter

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-198698 (JP, A) JP-B-57-59056 (JP, B2) JP-B-58-10221 (JP, B2) JP-B-59- 28170 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 45/00-45/84 B29C 47/00-47/96

Claims (1)

(57) [Claim 1] An injection nozzle for injecting a gaseous foaming agent into an extruder is provided, and corresponds to a ratio of an outlet pressure of the injection nozzle to an inlet pressure of the injection nozzle. The inlet / outlet pressure ratio is set to be larger than the critical pressure ratio, the injection nozzle hole diameter is set, and the injection nozzle is provided with a flow control valve for flowing the gaseous foaming agent at a constant flow rate. Temperature control means for controlling the temperature between the nozzles and controlling the pressure at the inlet of the nozzle so that the gas flow rate at the nozzle becomes constant with respect to the fluctuation of the pressure at the outlet. Equipment for manufacturing resin foam.