JPH04348926A - Resin changing method of injection molder - Google Patents

Abstract

PURPOSE:To carry out quick color change by a method wherein feed ratio and stroke ratio are specified. CONSTITUTION:In order to perform quick color change and stock feeding for normal running in an alternative way, a stock resin feeding selecting means 21, the detecting means 30 of the start of color changing resin feeding, the detecting means 40 of the completion of discharging and the detecting means 50 of the completion of color change. In this case, let X1 be a feed ratio and X3 be a stroke ratio, then conditions: 0.7<=X1<=1.8 and 1<=X3<=1.7 are satisfied when the amount of resin consumed for resin change is minimum, where X1=P1 V1/(PCV1+PFVF), X3=stroke/screw diameter, V1 represents intermittent feed (m<3>), VF represents the volume (m3) of a feeding section, VC represents the volume (m<3>) of a compression section, VM represents the volume (m<3>) of a metering section, VO represents the volume (m<3>) per one shot of injection and P1, PF and PC represent the densities at the respective sections.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for changing resin in an injection molding machine.

0002

[Prior Art] One example of a raw material supply device that improves the color changing performance of injection molding machines and extrusion molding machines is
This device is disclosed in Japanese Patent No. 41450, and as shown in FIG. 12, a shutter 12 is provided in the middle of a raw material passage 9 of a raw material supply device 11, and raw resin is intermittently supplied by controlling opening and closing of the shutter 12. . In the figure, 1 is a screw, 2 is a cylinder, 3 is an end cap, 4 is an injection nozzle, 5 is a hydraulic motor for rotating the screw, 6 is a hopper for supplying raw resin, and 7 is an injection cylinder. A shutter 8 is provided in the middle of the raw material passage 9 to open and close the raw material passage 9 in accordance with the timing by a control device (not shown). In addition, 10 in the figure is a torpedo.

[0003] The screw 1 constitutes a feed section a, a compression section b, and a metering section c in order from its base end side. The areas where old resin is most likely to remain when changing colors are:
These are the outer peripheral surface d of the torpedo, the inner wall surface e of the end cap 3, and the inner wall surface f of the nozzle 4. The raw material supply device herein means a portion including the hopper 6, the shutter 8, the raw material passage 9, and a shutter opening/closing mechanism (not shown). However, the raw material passage 9 includes not only the cylinder 2 side but also the cylindrical outlet portion of the hopper 6.

Now, as shown in the figure, the raw material passage 9 of the raw material supply device 11 is closed by the shutter 12 to stop the supply of the old raw material, and in this state, the rotation and injection of the screw 1 are repeated, and at least the feed section a of the screw 1 and the compression The part b is brought into a hollow state (this is also called a starvation state), and the raw material in the hopper 6 is replaced with a new raw material. Next, the shutter 12 is opened and the screw 1 is rotated. At this time, the cavity is filled with new unmelted resin. When the screw 1 continues to rotate in this state, molten resin with a higher viscosity than in the steady operating state is supplied to the resin retention parts d, e, and f at the tip of the screw 1, and the resin pressure increases, causing the screw to 1 retreats.

When the screw 1 is retracted to the metered stroke, the rotation of the screw 1 is stopped, hydraulic pressure is supplied to the back pressure side of the cylinder 7, and the screw 1 moves forward to proceed to the injection process. At this time, the highly viscous molten resin flows through the resin retention parts d, e, and f, and a large shearing force acts on the wall surface of the resin flow path, producing an effect of scraping off the old resin adhering to the wall surface. By repeating this screw rotation and injection, the upstream part of the resin flow with the check ring 11 as a border is mainly affected by the scraping action due to shearing by the solid bed, and the downstream part is affected by the high shearing force caused by the flow of high-viscosity molten resin. The scraping action works, and the removal of the old resin adhering to the resin flow path, that is, the color change progresses, and eventually a steady state is reached.

However, in this steady state, the temperature of each part increases and the viscosity of the resin decreases, so the shearing force acting on the wall becomes smaller and the above-mentioned effect becomes smaller, so the shutter 12 is closed. Then, perform each of the above operations again, and then repeat this process again. In this way, the effect of color change by temporarily stopping the supply of raw resin in the hopper and feeding unmolten resin into the place where the molten resin in the cylinder has been extracted is simply to change the resin and then turn the screw and inject it. Compared to the conventional method of changing colors repeatedly,
An exceptional effect has been achieved, with a 60% reduction in resin consumption.

However, the color changing method described above leaves room for improvement in that the time required for color changing is not much different from the conventional method. The main reason for this is that the amount of resin filled per cycle of the resin change operation described above is excessive, and after reaching a steady state, a cavity is created to fill the unmolten resin, that is, the amount required for resin discharge is The reason is that time is not shortened. In order to solve this problem, the inventors of the present invention developed a raw resin supply device that aims to shorten the color change time by reducing the resin filling amount to the minimum amount that maximizes the scraping effect. was previously proposed in Japanese Patent Application No. 1-254865.

That is, the raw resin supply device of the prior application is a raw resin supply device used for an injection molding machine or an extruder, and when performing a color change operation using the raw material to be color changed, the resin passage is In a raw material supply device that opens and closes intermittently to intermittently supply raw resin to the feed section, it is installed in the middle of the resin passage and selectively supplies a specific amount of raw resin to the feed section between intermittent supply and continuous supply. A raw material resin supply selection means to select, a color change resin supply start detection means for detecting the supply start time of the specified amount, a discharge completion detection means for detecting completion of discharge corresponding to the specified amount of raw resin, and a color change completion detection means. The apparatus is equipped with a detection means, and is configured to selectively perform a quick color change and supply raw materials for normal operation.

The specific resin filling amount can be controlled by controlling the opening time of one opening/closing means for opening and closing the raw material passage, or by providing two opening/closing means at a distance and opening and closing them alternately. This can be done by weighing a certain volume of raw material, ensuring that the minimum amount is filled to maximize the scraping effect. In short, a small amount of unmelted resin is filled into the screw cavity many times, and the color change operation is performed while maintaining a high scraping effect, reducing the loss of resin and shortening the time required for color change. It is to be.

In the raw material resin supply device, when a color change command is issued from the main cycle of the control device, it is compared in the judgment section of the color change completion detection means, and since the color change has not yet been performed, it is natural that the color change completion is detected. Since the initial value from the means is 0, a NO signal is output, and the raw material resin supply selection means stops supplying the raw material. However, even after the feedstock supply is stopped, the injection cycle continues until the cavity within the cylinder reaches a predetermined length. It is determined by the color change resin supply start detection means that the length of the cavity has reached a predetermined length, and the first color change raw material resin is supplied in a specific amount and injection is repeated.
Drain the resin inside the cylinder. The specific filling amount discharge detection means determines whether or not this discharge amount has reached the specified amount supplied, and this discharge cycle continues until the condition is satisfied.

[0011] The above-mentioned ejection completion is determined based on, for example, whether the number of injections has reached a predetermined set number. Each time this discharge cycle is completed, the input values for the color change condition and completion condition increase by 1, and the cycle continues until the values reach the set values, that is, until the specified amount of raw resin is filled and discharged a predetermined number of times. continues. When the input value reaches the set value, the color change is completed, and thereafter the normal operating state is reset and the normal molding cycle is resumed.

[0012] The raw resin supply device of the prior application will be explained with reference to Fig. 6. 1 is a screw, 2 is a cylinder, 3 is an end cap, 4 is an injection nozzle, 5 is a hydraulic motor for rotating the screw, and 6 is for supplying raw resin. Hopper, 7 is a hydraulic cylinder for injection, 9 is a raw material passage, 10 is a torpedo, and 11 is a check ring. Further, 20 is a raw resin supply device, which includes the following parts (
21, 30, 40, 50). That is,
Reference numeral 21 denotes a raw material resin selective supply means, which is provided in the middle of the raw material passage 9 that communicates the raw material resin supplying hopper 6 and the inside of the cylinder 2 . For example, it includes a shutter that opens and closes the raw material passage 9 based on commands from the control device 60.

Further, 30 is a color change resin supply start detection means for determining whether the cavity length has reached a predetermined amount. It detects that the specified screw rotation speed has been reached and outputs it to the control device 60. 40
is an ejection completion detection means that detects whether a specific amount of filled resin has been ejected through repeated injections. For example, the number of strokes of the screw 1 is measured with a measuring device, and when the number of strokes set in advance is reached, the control is performed. This is what is output to the device. Further, 50 is a color change completion detection means, which outputs an output to the control device when the number of times of filling a specific amount of raw material resin reaches a preset number of times, and switches to normal operation or the like.

FIG. 7 shows an operation flowchart of an injection molding machine having the raw resin supply device. In Fig. 7, N1 is the screw rotation speed, N2 is the number of injections, and N3 is the number of injections.
indicates the number of times the specified filling amount of raw resin is supplied, N1S, N2
S and N3S are preset values corresponding to each, and have the following meanings. N1S: Criteria for determining the time to start supplying color change resin, which is a set time or a set value for the total number of rotations of the screw. N2S: A criterion for determining the completion of discharging a specific filling amount of raw material resin, and a set value for the number of injections. N3S: This is a reference value for detecting and judging the completion of color change, and is a set value for the number of times a specific filling amount of raw resin is supplied.

Next, the operation of the conventional device will be explained. First, when a color change operation signal is output from the main cycle of the control device 60, the raw resin supply selection means 21 of the raw resin supply device 20 stops supplying the old raw material. Generally, when the injection operation is continued with the supply of raw materials stopped, the resin in the raw resin transfer groove space h' formed by the thread groove m of the screw 1 and the inner wall surface of the cylinder 2 is transferred from the base of the screw 1 to the tip. It decreases over time, forms a cavity h (or starvation region), and gradually develops to the tip.

The flow of the molten resin is dammed by the check ring 11 provided at the tip of the screw 1 (on the torpedo 10 side), and the effective pushing force of the screw thread of the screw 1 acting on this and the inner part of the check ring 11 are The cavity develops to a position where the flow resistance of the molten resin flowing through the gap g formed between the wall surface and the outer wall surface of the screw 1 is balanced. The growth of the cavity is stopped at the point 1), and the so-called residual resin 1 is formed. Contact surfaces with the molten resin on the downstream side of the resin flow flowing toward the nozzle 4 after the residual resin l, for example, the outer peripheral surface d of the torpedo 10, the inner wall surface e of the head cover 3, the inner wall surface f of the nozzle 4, and the surface of the check ring gap g Molten resin remains.

Furthermore, since the compression portion b of the screw 1 is inclined at an angle where the bottom surface of the thread groove opens toward the tip, a lot of resin is observed to adhere to the wall surface of the groove in the same portion. The maximum growth state of the cavity that develops in the thread groove of the screw 1 after the raw material supply is stopped, or a state close to it, can be determined by determining the time or the total number of screw rotations by experiment or simulation. This is set by the time limit setting means or screw rotation speed counting means, and detected by the color change resin supply start detection means 30. Further, based on the output of the color change resin supply start detection means 30, the control device 60 issues a raw material supply command to the raw material resin supply selection means 21, and after the raw material resin supply selection means 21 supplies a specific amount of new raw material resin,
Stop raw material supply.

An insufficient amount of unmelted resin to fill the length of the cavity is fed into the hollow groove h of the screw 1 from the raw material passage 9 toward the residual resin portion, forming a solid bed. The screw moves within the screw groove as shown in FIG. 9, and an extremely large shearing force acts on the surface of the screw groove as shown in FIG. 10, thereby scraping off the resin film on the compression part b of the screw where a large amount of old molten resin adheres. Then, if the screw continues to rotate, the residual resin l at the tip of screw 1
is pushed out to the nozzle 4 side via the check ring 11, and the raw material resin sent in the form of a solid bed is also melted and pushed out through the gap g of the check ring 11, and at the same time, the screw 1 is retracted by the back pressure. do.

When the screw 1 is retracted to the injection position, the control device 60 stops the rotation of the screw 1, commands injection, and moves the screw 1 forward to perform injection. Thereafter, this process is repeated while the raw material supply is stopped. When the injection discharge of the old resin filled earlier is completed and a specific amount of new molten resin is filled and injected, the resin temperature is lower than that during continuous injection operation, so the high viscosity The resin is injected, and a high shearing force due to the high viscosity molten resin acts on the surfaces of the resin retention parts d, e, f, and g as shown in FIG. 11, and the removal of the used resin film progresses due to the scraping effect. .

[0020] The stage at which the cavity growth of the screw 1 reaches saturation due to the discharge of the resin filled in a specific amount is determined in advance by setting the number of injections corresponding to the specific filling amount, and when the number of injections reaches this set number. This is detected by a specific filling amount discharge detection means 40 such as a counter, and it is detected that the specific amount of filling has been discharged. Thereafter, the above operation is repeated, and the color change completion detection means 50 such as a counter detects that the number of repetitions has reached the set value, and a color change completion signal is sent to the control device 60, and the process then proceeds to the normal molding cycle of the main cycle. . Note that η in the figure indicates viscosity.

Next, a method of measuring a specific amount of supplied resin for the color change will be specifically explained using FIG. 8 as an example. This is carried out by means of raw resin selective supply means 21 consisting of two shutters 21-1 and 21-2 provided at an interval. First, the lower shutter 21-
2 is closed, and then the upper shutter 21-1 is opened, the amount of raw resin falling from the hopper 6 down the raw material passage 9 is always kept at a constant height, and the upper shutter 21-1 is closed. If you close both shutters 21-1, 21-
The amount j of the raw material resin trapped between the two is a specific amount. When a raw resin supply command is received in this state, the lower shutter 21-2 is opened, and a specific amount of raw resin is supplied to the feed section a of the screw 1.

When the supply of raw materials is completed (this detection may be performed using a photoelectric switch, etc.), the lower shutter 21-2 is closed, and then the upper shutter 21-1 is opened.
As long as the number of times of supply is within a predetermined number, it may stand by in the metering state, and after a supply command is issued from the control device 60, the closing operation is performed, and then the supply operation of the specified amount is performed. On the other hand, in response to a continuous supply command, both shutters 21-1 and 21-1
Both 1 and 2 are kept open.

In an injection molding machine, if a specific supply amount is determined to be equivalent to the discharge amount for one injection, and an injection cycle is performed each time a specific amount is supplied, the color change operation will proceed at the limit, and the color change will Both the amount of resin lost and the time lost are minimal. Of course, this specific amount may be determined as an amount corresponding to the amount of multiple injections. In addition, the start of screw injection is determined by the potentiometer output as a backward position detection means, or by starting time measurement when the screw is injected and reaches the forward end, and after a predetermined time, the output is
A time limit means for outputting an N signal is also used, and injection is performed by one of the signals. If the specific amount is set to be ejected in one injection, the specific amount and time should be selected so that the viscosity at the time of injection will be within the appropriate range, although there will be variations from injection to injection. The color change operation progresses without any mechanical damage caused by the color change operation, and the completion of the color change is detected by counting the number of injections or the number of times a specific amount is supplied and comparing this with a set value.

[0024]

The advantages of the conventional apparatus described above are supported by the results of sensitivity analysis of color change time shown in FIG. That is,

[Formula 2] ln(t×γW)=−a×ηR/ηW +b
(1) However, a, b: positive constant t: color change time (number of color change shots multiplied by average cycle) [sec] γW: apparent shear rate (wall surface) [sec-1] η
R: Resin viscosity (value calculated from the viscosity curve at the intersection of resin temperature and shear rate) [Pa. s] ηW: Resin viscosity on the wall (value calculated from the viscosity curve at the intersection of the wall surface temperature setting and shear rate) [Pa. s] The following conclusion can be obtained from the above equation. [Conclusion for speeding up color change] Lowering the resin temperature (increasing ηR), increasing the wall surface temperature (reducing ηW), and flowing the resin at a higher speed (increasing γW) will lead to faster color change. .

However, equation (1) is based on the main specifications of the injection molding machine: VI, VF, VC, VO, D, L(
(The meanings of the symbols will be explained later), etc., and it was necessary to clarify the relationship between them.

The present invention has been proposed to solve the above-mentioned conventional problems.

[0027]

[Means for Solving the Problems] Therefore, the present invention provides a method for supplying raw resin for use in an injection molding machine or an extruder, in which a resin passage is connected when performing a color change operation using a raw material to be changed. In a raw material supply method in which raw resin is intermittently supplied to the feed section by opening and closing intermittently, a valve is installed in the middle of the resin passage and selectively supplies a specific amount of raw resin to the feed section between intermittent supply and continuous supply. A raw material resin supply selection means to select, a color change resin supply start detection means for detecting the supply start time of the specified amount, a discharge completion detection means for detecting completion of discharge corresponding to the specified amount of raw resin, and a color change completion detection means. It is equipped with a detection means to selectively supply raw materials for quick color change and normal operation, and to detect the minimum amount of resin consumed for resin change when the feed rate ratio is X1 and the stroke ratio is X3. It is designed to satisfy the following conditions: 0.7≦X1≦1.8 and 1≦X3≦1.7, and is used as a means to solve the problem.

[Equation 3] VI: Intermittent supply amount (m3) VF: Feed section volume (m3) VC: Compression section volume (m3) VM: Metering section volume (m3) VO: Injection 1
Shot volume (m3) ρI, ρF, ρC: Density of each part (kg/m3)

[0028]

[Effect] I. Conditions for minimizing the required resin amount
When Y1 is the dependent variable, the characteristic of the required resin amount Y1 with the metering ratio X3 as a parameter is expressed as shown in FIG. From this, (1) When determining X3, Y1 is the minimum X
1 exists. (2) If X3 is set from about 1 to 1.7, X1 becomes 0.
Even if it varies over a wide range of 7 to 1.8, Y1 is still the same as the conventional 7.
It can be set to a range of about 0% or less. (3) When X3 is about 0.5, set X1 to 0.6 to 1.5
If selected, Y1 can be reduced to 70% or less of the conventional value. (4) Especially when 0.8≦X1≦1.7 and 1≦X≦1.
If 5 is selected, Y≦0.6 can be satisfied. II. Conditions for shortest time required

The characteristic of the required time ratio Y2, which will be described later, with respect to X1 with X3 as a parameter is expressed as shown in FIG. Y2 also has a minimum value. From this, (1) If you choose X3 to be approximately 1 to 1.5, then X1 will be 1.2
Even if it changes to a wide range of ~1.8, Y2 remains the same as the conventional 70
% or less. (2) By setting 1.0≦X1≦1.7 for X3≧0.5, Y2≦0.7 can be achieved. (3) Especially for 1.0≦X3≦1.5, 1.3≦X
If 1≦1.7, then Y2≦0.6. III. Condition 1≦X where both resin amount and predetermined time are 70% or less
3 ≦1.5, if you choose 1.2≦X1≦1.8, Y
1 and Y2 can be similarly reduced to 70% or less of the conventional values.

The reason why the minimum value exists is explained as follows based on the test results (FIG. 3) conducted under the condition that X3 = 1 and varying the intermittent feed amount X1 x VI. In FIG. 3, the value of X1 when Y1 and Y2 show minimum values is
= 1.0, and at this time, the peak value of the resin pressure in the cylinder is at its maximum, and it is considered that the scraping effect has increased. This is because if the intermittent supply amount is less than the optimum value, when the solid bed is compressed in the compression section, it will be compressed slowly (
Since the apparent specific gravity is small, the effective pressure applied to the solid bed is small and the cleaning effect is considered to be small. Moreover, if the intermittent supply amount is too large, it approaches a state of continuous supply, which promotes melting and reduces the shear stress on the screw wall surface, which reduces the cleaning effect. Furthermore, the reason why the value of X1 that gives the minimum value of Y1 and Y2 changes when X3 is changed is not fully understood at present, but the facts show that there is a value of X1 that gives the minimum value.

[0031]

[Example] The present invention will be described below with reference to the embodiments shown in the drawings. In order to examine the optimal amount of intermittent supply, the following dimensionless number is defined, and this dimensionless number is colored as an explanatory variable. Multiple regression analysis was performed using the resin amount ratio Y1 as a characteristic value.

[Math 4] However, n×ρO VO ≒ρI VI

[Equation 5] Here, the meaning of each symbol is as follows. VI: Intermittent supply amount (m3) VF: Feed section volume (m3) VC: Compression section volume (m3) VO: Injection 1 shot volume (m3) ρI, ρF
, ρC: Density of each part (kg/m3) q: Injection rate (m
3/s) L: Injection stroke (m) D: Screw outer diameter (m) n: Number of shots per intermittent supply Also, by changing X1 with X3 as a parameter, Y1,
The results of multiple regression analysis of Y2 are shown in FIGS. 1, 2, and 3.

[0032]

As described in detail above, according to the present invention, the relationship between the optimum feed rate ratio X1 and the optimum stroke ratio X3 is clarified with respect to the specifications of the machine, and
3, Y≦0.7, Y2≦0.
7, and furthermore, a significant improvement such as Y1≦0.6 can be achieved.

[Brief explanation of drawings]

FIG. 1 is a required resin amount characteristic diagram according to an example of the present invention.

FIG. 2 is a required time ratio characteristic diagram according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram of Y1, Y2 and cylinder internal pressure when X3=1.

FIG. 4 is a diagram showing the relationship between the volume of each part of the screw and the resin temperature.

FIG. 5 is a color change sensitivity characteristic diagram showing an example of the present invention.

FIG. 6 is a system diagram of a raw resin supply device for a conventional molding machine.

FIG. 7 is a control flow diagram in FIG. 6;

FIG. 8 is a system diagram of a raw resin control device of the molding machine, which is different from FIG. 6;

FIG. 9 is an explanatory diagram showing the flow of a conventional solid bed.

FIG. 10 is an explanatory diagram showing the shear stress distribution of the solid bed.

FIG. 11 is an explanatory diagram showing the shear stress distribution of the molten resin.

FIG. 12 is a side sectional view showing an example of a conventional injection molding machine.

[Explanation of symbols]

1 Screw 2 Cylinder 4 Injection nozzle 5 Hydraulic motor for screw rotation 6 Raw resin supply hopper 20 Raw resin supply device 21 Raw resin supply selection means 30 Color change resin supply start detection means 40 Ejection completion detection means 50 Color change completion detection means 60 Control device

Claims (1)

[Claims] Claim 1: A raw material resin supply method used in an injection molding machine or an extrusion machine, which comprises intermittently opening and closing a resin passage to supply raw resin to a feed section when performing a color change operation using a raw material to be changed. In an intermittent raw material supply method,
A raw resin supply selection means is provided in the middle of the resin passage and selectively selects between intermittent supply and continuous supply of a specific amount of raw resin to the feed section, and detects the timing at which the supply of the specific amount starts. The system is equipped with a color change resin supply start detection means for detecting the start of supply of color change resin, a discharge completion detection means for detecting the completion of discharge corresponding to a specific amount of raw material resin, and a color change completion detection means. When supplying is performed selectively, and the feed rate ratio is X1 and the stroke ratio is X3, the minimum amount of resin consumed for resin replacement is 0.7≦X1≦1.8, 1
A method for changing resin in an injection molding machine, characterized in that the condition of ≦X3≦1.7 is satisfied. However, [Equation 1] VI: Intermittent supply amount (m3) VF: Feed section volume (m3) VC: Compression section volume (m3) VM: Metering section volume (m3) VO: Injection 1
Shot volume (m3) ρI, ρF, ρC: Density of each part (kg/m3)