JP2858182B2 - Method and apparatus for controlling compression pressure in injection compression molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection compression molding for injection molding of a thermoplastic resin, which can always mold a fixed quality product even if the temperature of a mold or the temperature of a molten resin fluctuates. The present invention relates to a compression pressure control method and apparatus.

[0002]

2. Description of the Related Art Conventionally, in the injection compression molding of a thick molded product having a large thickness, when the molten resin filled in a cavity is cooled and solidified, a large shrinkage rate occurs between the surface portion and the central portion of the molded product. Due to the difference, there is a problem that sinks, voids or warpages occur in the molded product. In order to solve this problem, a method has been proposed in which the compression step is gradually cooled over a long period of time.

[0003]

However, according to the above-mentioned conventional technology, the formation of sink marks, voids or warpage can be prevented to some extent, but the physical properties of the molded product change with the mold temperature and the molten resin temperature every molding cycle. There is a problem that the optical characteristics change due to the change, and in particular, in the case of molding an optical element, the optical characteristics change every molding cycle.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and does not cause sink marks, voids, or warpage when molding a thick molded product. It is an object of the present invention to realize a compression pressure control method and apparatus in injection compression molding capable of molding a thick molded product having constant physical properties.

[0005]

In order to achieve the above object, a method of controlling a compression pressure in injection compression molding according to the present invention comprises, following a filling step of injecting a molten resin into a cavity of a clamped mold, A compression step of applying a predetermined compression pressure to the mold by a compression cylinder, wherein the cavity is divided into a plurality of cross-sectional positions at equal intervals from the wall surface toward the center of the cavity. Wherein the pressure of the pressurized fluid supplied to the compression cylinder during the compression stage is controlled so that the compression pressure at which the molten resin reaches the solidification temperature is constant in each molding cycle. It is.

A compression pressure control device in injection compression molding according to the present invention is an injection device for injecting and injecting a molten resin into a cavity of a mold clamped by a mold clamping device, and applying a compression pressure to the mold. A control device for an injection compression molding machine, comprising: a compression cylinder for supplying a pressurized fluid to the compression cylinder via a servo valve; a resin temperature detector for detecting a temperature of a molten resin injected and injected into the cavity; A mold temperature detector for detecting a mold temperature; and a compression pressure detector for detecting a compression pressure in the compression cylinder. An arithmetic processing unit that divides into a plurality of cross-sectional positions at equal intervals toward each other, and calculates a compression pressure target value when the molten resin reaches a solidification temperature at each cross-sectional position; A control device comprising a compression pressure control unit for storing a target value, comparing the target value with a detection value of the compression pressure detector, and controlling the servo valve so that the two coincide with each other. It is.

[0007]

When the molten thermoplastic resin is cooled and solidified, the pressure at which the solidification temperature is reached has been found to greatly affect the shrinkage ratio, optical characteristics, and the like. From this, when the molten resin filled in the cavity is cooled and solidified, if the pressure at which the molten resin reaches the solidification temperature is controlled to be constant in each molding cycle, the shrinkage ratio, optical characteristics, etc. It has been found that it is possible to make the molded article constant, that is, to mold a molded article having constant physical properties in each molding cycle.

According to the present invention, based on the above findings, a plurality of cross-sectional positions are determined in advance at equal intervals from the surface to the center of a thick molded product, using the molten resin temperature and the mold temperature at the time of molding a good product as reference values. The compression pressure target value when the resin temperature at each cross-sectional position reaches the solidification temperature is calculated and stored.

The compression pressure in the compression stage is controlled so that the compression pressure matches the compression pressure target value for each molding cycle.

[0010]

An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view showing one embodiment of a compression pressure control device in injection compression molding of the present invention.

The injection device 1 is of a so-called in-line screw type, and includes a heating cylinder 1a having a nozzle 3 at a tip end thereof, and a screw 1b disposed in the heating cylinder 1a so as to advance and retreat and rotate freely. Screw 1b
Moves forward and backward by the driving force of the fluid pressure cylinder 1c provided at the rear end of the heating cylinder 1a, and the motor 1e
It is configured to be rotated by the driving force of. On the other hand, the mold 2 having the cavity 2a is configured so that the mold is clamped and opened by a mold clamping device (not shown), and a compression pressure is applied to the mold 2 by the compression cylinder 11 in a compression stage.

A sensor 4a of a resin temperature detector 4 for detecting a resin temperature is provided at an appropriate portion of the nozzle 3, and a mold temperature detector 5 for detecting a mold temperature is provided at an appropriate portion of the mold 2.
And a sensor 6a of a compression pressure detector 6 for detecting a compression pressure is mounted on an appropriate wall surface of the compression cylinder 11.

The control device 7 includes an A / D converter 7 for converting output signals of the resin temperature detector 4, the mold temperature detector 5, and the compression pressure detector 6 into digital signals.
c, 7d, 7e, and an arithmetic processing unit 7 which receives signals from the A / D converters 7c, 7d, 7e and performs arithmetic processing described later.
and a compression pressure control unit 7b that outputs a signal for controlling the compression pressure based on the output signal of the arithmetic processing unit 7a and the output signal of the compression pressure detector 6.
The output signal of the compression pressure control unit 7b is sent to the servo valve 9 via the servo valve amplifier 8, and controls the pressure of the pressurized fluid supplied from the pressurized fluid supply source 10 to the compression cylinder 11.

Next, a method of controlling the compression pressure in the injection compression molding of the present invention will be described with reference to FIGS.

First, as shown in FIG. 5, a compression pressure target value Pj ^* when the molten resin reaches the solidification temperature in the cavity is obtained by an arithmetic expression described later, and this is stored in the compression pressure control section 7b. (Steps S1 to S
6).

Next, as shown in FIG. 6, similarly to the known injection compression molding method, the molten resin is charged into the cavity 2a of the mold 2 which has been clamped, and then the process proceeds to the compression stage (step S11).

During the compression stage, compression pressure control as described below is performed.

The molten resin temperature, mold temperature and compression pressure detected by the resin temperature detector 4, the mold temperature detector 5 and the compression pressure detector 6, respectively, are the amplifiers 4b to 6b and the A / D converters 7c to 7c. 7e, each digital signal T _R ,
It is converted into T _W and P and sent to the arithmetic processing unit 7a (step S12). The arithmetic processing unit 7a calculates a compression pressure target value Pj ^* based on the digital signals T _R , T _W and P and outputs it to the compression pressure control unit 7b (step S1).
3, S14, S15, S16, S17). The compression pressure detected by the compression pressure detector 6 is also sent to the compression pressure control unit 7b, where it is compared with the compression pressure target value Pj ^*, and the compression pressure is compared with the compression pressure target value Pj ^*. And outputs a signal to control the servo valve 9 via the servo valve amplifier 8. As a result, the pressure of the pressurized fluid supplied from the pressurized fluid supply source 10 to the compression cylinder 11 is controlled, and the compression pressure is adjusted to the compression pressure target value Pj ^* .

Here, the compression pressure target value Pj ^* is calculated by the following method.

The molten resin is filled into the cavity 2a of the mold 2 clamped by the mold clamping device by injection injection through the sprue 2c and the gate 2b by the injection device 1. In the compression stage, the charged molten resin is exposed to heat from the mold wall surfaces 2a-1 and 2a-2, as shown in FIG. After being lowered and cooled to a temperature close to the mold temperature T _W through a solidification temperature Tg (flow stop temperature, glass transition temperature, crystallization temperature, etc.) specific to the resin A, the resin A is removed from the mold 2. At the same time, the resin A shrinks, and pressurization by the compression cylinder 11 is performed to compensate for the shrinkage.
The resin temperature of the cavity 2a in the compression stage can be regarded as a one-dimensional infinite flat plate, and is expressed by the unsteady heat conduction equation of the equation (1).

[0022]

(Equation 1) The solution of equation (1) of equation (1) becomes equation (2) of equation (2).

[0023]

(Equation 2) According to equation (2) of equation 2, the resin temperature T of the cavity 2a
(T, x) is with the passage of time t, as shown in FIG. 3, it decreases exponentially towards the mold temperature T _W from the molten resin temperature T _R.

For example, a mold temperature and a molten resin temperature in the reference cycle are defined as T _WS and T _RS, and a resin temperature of the cavity 2 a at the time t and the cross-sectional position x is defined based on a specific molding cycle such as when molding non-defective products. Expressed as T _S (t, x). Further, the resin temperature T _S (t,
The time tgj when x) becomes the solidification temperature Tg is defined by the following equation (3).

T _s (tgj, xj) = Tg (3) where j represents the division number of the sectional position of the molded product, and takes a value from 1 to N. N indicates the number of divisions.

Next, the resin temperature of the cavity 2a when the mold temperature is T _W 'and the molten resin temperature is T _R ' is T '(t,
x). Further, in T _W ′ and T _R ′, T ′
Time t′g when (t, x) reaches the solidification temperature Tg
j is defined by the following equation.

[0027] T '(tgj', xj) = Tg ......... (4) cross-sectional position xj, temperature difference at xk, at any time t, the mold temperature T _W, a change of the molten resin temperature T _R (5)

{T ′ (t, xk) −T ′ (t, xj)} / {T _S (t, xk) −T _S (t, xj)} = (T ′ _R −T ′ _W ) / ( to _{T RS -T WS) ............ (5} ) formula in _{general, T R '> T W'} , because it is T _RS> T _WS,
Equation (5) has a positive sign.

Therefore, T _s (t, xk)> T _s
If (t, xj), T '(t, xk)> T (t, xj)
Thus, even if the mold temperature T _W and the molten resin temperature T _R change, the magnitude relationship between the resin temperatures T (t, x) of the cavities 2a at different cross-sectional positions does not change. From the above, time change and mold temperature T _W of the resin temperature T of the cavity 2a (t, x), the change in resin temperature T of the cavity 2a due to a change of the molten resin temperature T _R (t, x) is Third
FIG. 4 and FIG.

Next, at the cross-sectional position xj, when the mold temperature and the molten resin temperature are T _WS and T _RS , T _s (tgj, x
j) = Tg, and when T _W ′ and T _R ′, T ′ (t ′
gj, xj) = Tg, T _{S at} tgj ′
(Tgj ', xj) is expressed by Expression (6) of Expression 3.

[0031]

(Equation 3) From equation (6), at the mold temperature T _W ′ and the molten resin temperature T _R ′, the time tg at which the resin temperature T ′ (t, x) becomes Tg.
In j ′, the reference mold temperature T _WS and molten resin temperature T _RS
Resin temperature T _S (t, x) in is independent of the cross-sectional position xj, a constant temperature represented by the equation (6). Therefore, when the mold temperature changes from T _WS to T ′ _W and the molten resin temperature changes from T _RS to T _R ′, the resin temperature T ′ (t, x) of the cavity 2a at the cross-sectional position xj solidifies. Temperature Tg
In order to determine the time tgj 'at which the resin temperature T _S (t, x) at T _WS and T _RS reaches the temperature calculated by the equation (6), it is sufficient to obtain the time tgj ′. T _S (t,
FIG. 4 shows the relationship between x) and T '(t, x), and the relationship between tgj and tgj'.

Next, the compression pressure at the mold temperature T _WS and the molten resin temperature T _{RS is} represented by P _S (t), and the compression pressure at the T _W 'and T _R ' is represented by P '(t). In T _WS and T _RS ,
The resin temperature T _S (t, xj) at the cross-sectional position xj is the solidification temperature T
The pressure at which g is reached is represented by P _S (tgj) from T _S (tgj, xj) = Tg. Also, T _W ′, T
_R ′, the resin temperature T ′ (t, t,
The pressure when x) reaches the solidification temperature Tg is T '(tg
j ′, xj) = Tg and is represented by P ′ (tgj ′). Even when T _WS changes to T _W ′ and T _RS changes to T _R ′, the resin temperature T at each cross-sectional position xj of the cavity 2 a is changed.
In order for the compression pressures when (t, x) reaches the solidification temperature Tg to be equal, the equation (7) of Expression 4 needs to be satisfied.

[0033]

(Equation 4) However, Pj ^* in number 4 (7), mold temperature T _WS, the molding cycle as a reference of the molten resin temperature T _RS, the pressure Ps (TGj when the temperature of the cross-sectional position xj greets solidification temperature Tg ) Is defined again as the target value Pj ^* .

From the above, even if the mold temperature T _W and the molten resin temperature T _R change, it is necessary to control the compression pressure when the molten resin reaches the solidification temperature Tg so as to be constant at each molding cycle. It is necessary to change the pressure waveform as shown in FIG. 4 according to the temperature change. Then, these pressure waveforms correspond to the resin temperature T _S (t,
x) is calculated by the equations (2) and (6), and the compression pressure P _S (t) in the compression cylinder 11 at T _WS and T _RS of the reference molding cycle is measured, and the equation (7) is obtained. Can be calculated.

In T _WS and T _RS , T _S (tgj, x
j) = Tg become time TGj, placing the cooling temperature at the cross-sectional position xj C _S (tgj, xj) and (℃ / sec).
Then, at T _W ′ and T _R ′, T ′ (tgj ′, x
j) = Tg T at the time tgj 'to be _S (tg
j ′, xj) and Tg, the difference δT between
Expression (5) is expressed by Expressions (8) and (9).

[0036]

(Equation 5) δΤ does not depend on the sectional position xj, but tgj, C _S
(Tgj, xj) depends on the sectional position xj and the time tgj.

[0037]

Since the present invention is configured as described above, the following effects can be obtained.

In each molding cycle, the inside of the cavity is divided into a plurality of cross-sectional positions at regular intervals from the wall surface to the center, and the compression pressure when the molten resin at each of the divided cross-sectional positions reaches the solidification temperature is kept constant. Since control is performed, sinks, voids or warpage do not occur in the thick molded product, and in addition, the physical properties of the portion corresponding to each of the cross-sectional positions of the thick molded product are constant, and the thick molded product is molded in each molding cycle. Product reproducibility is improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a compression pressure control device in an injection compression molding machine of the present invention.

FIG. 2 is an explanatory diagram showing a heat flow in a cavity according to the present invention.

FIG. 3 is a graph showing a temporal change of a resin temperature in a cavity.

FIG. 4 is a graph illustrating a temporal change at a plurality of cross-sectional positions in a cavity and a method for calculating a compression pressure target value.

FIG. 5 is a flowchart showing a procedure for calculating data required in a subsequent molding cycle in a reference molding cycle.

FIG. 6 is a flowchart showing a process of controlling a compression pressure in a normal molding cycle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection apparatus 1a Heating cylinder 1b Screw 1c Fluid pressure cylinder 1d Piston 1e Motor 2 Mold 2a Cavity 2b Gate 3 Nozzle 4 Resin temperature detector 5 Mold temperature detector 6 Compression pressure detector 7 Controller 7a Arithmetic processing unit 7b Compression Pressure controller 7c, 7d, 7e A / D converter 8 Servo valve amplifier 9 Servo valve 10 Pressurized fluid supply source 11 Compression cylinder

Claims (2)

(57) [Claims] 1. A method for injection compression molding, comprising: a filling step of injecting and injecting a molten resin into a cavity of a clamped mold, and a compression step of applying a predetermined compression pressure to the mold by a compression cylinder. The inside of the cavity is divided into a plurality of cross-sectional positions at equal intervals from the wall surface to the center, and the compression pressure when the molten resin reaches the solidification temperature at each cross-sectional position is constant in each molding cycle. Controlling the pressure of the pressurized fluid supplied to the compression cylinder during the compression step. 2. An injection device for injecting and injecting a molten resin into a cavity of a mold clamped by a mold clamping device, and a compression cylinder for applying a compression pressure to the mold, wherein a pressurized fluid is supplied to a servo valve. A control device for an injection compression molding machine that supplies the compression cylinder with the compression cylinder via a resin temperature detector that detects a temperature of a molten resin injected into the cavity, a mold temperature detector that detects a mold temperature, and the compression. A compression pressure detector for detecting a compression pressure in the cylinder is provided, and the inside of the cavity is divided into a plurality of cross-sectional positions at equal intervals from the wall to the center based on the detection value of each of the detectors. An arithmetic processing unit that calculates a compression pressure target value when the molten resin reaches the solidification temperature at each cross-sectional position, stores the compression pressure target value, and detects the compression pressure target value and the detection value of the compression pressure detector. Compared to compressing pressure control system in the injection compression molding, characterized in that it comprises a control device comprising a compression pressure control unit for controlling said servo valve so they match.