JPH09262883A - Injection compression molding method of thin large-sized molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a larger areal thin molding by a method wherein resin is spread at a single heat with molds during the condition that the fluidity of the resin is maintained. SOLUTION: This molding has a flat shape with the thickness of 0.8-3.0mm, the length of 100cm and the width of 40-100cm. Molds are so oriented as for the cavity surface for forming the flat face of the molding to set perpendicular. A receding distance is 0.5-4 times as much as the thickness of a cavity at mold clamping. The travelling of the receding distance L(in mm) or from the receded position to the mold clamping finishing position is performed in the time represented by the formula τ(in sec)=0.2+L/10. Further, the duration from the start of injection of melted thermoplastic resin to the finish of mold clamping is performed in the limiting time θ calculated by the formula, in which θ is in sec, D is the thickness (in cm) of a molding, ln is the natural logarithmic function, Tf is the flowing temperature (in deg.C) of resin, Tc is the temperature (in deg.C) of molds, TG is the resin injection temperature (in deg.C) in a gate α is the thermal diffusion coefficient are represented by the formula α=k/ρ×Cp , in which (k) is the thermal conductivity, (ρ) is the density and Cp is the specific heat.

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 method, and more particularly to a method for injection compression molding a molded article having excellent smoothness, a small birefringence, a uniform thickness, and a wide thin area. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, in injection compression molding, a cavity space is slightly expanded by slightly retracting a movable mold before injection, and a molten resin is compressed into the cavity after or during injection. Is known as a molding method for obtaining a molded product having a predetermined wall thickness. Since this method has good transferability and little distortion, it is used for molding small flat molded articles such as optical disks. However, in the case of a much larger thin-walled molded product, such as a molded product having a thickness of 40 cm x 40 cm and a thickness of 1.5 mm, the resin is practically evenly distributed to every corner of the molded product, A uniform molded product with less distortion and uneven thickness could not be obtained, and it could not be manufactured by conventional injection compression molding. For this reason, conventionally, it has been impossible to obtain such a large-sized thin-walled molded product by injection compression molding. Moreover, even if such a large-sized thin-walled molded product is to be molded by injection molding, it is extremely difficult to inject the resin into the thin cavity and spread the resin to every corner of the wide cavity before the resin solidifies. Not only is it economically unacceptable because it requires a theoretically extremely large molding machine and mold clamping mechanism because it requires a large injection rate (and therefore a large injection pressure) and a high injection resin temperature, and in fact, the resin burns. However, problems such as the above have occurred, and molding was virtually impossible. Under such circumstances, such a large-sized thin-walled molded article has been conventionally molded as an extruded sheet.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for molding such a large-sized thin-walled molded product by injection compression molding. The present inventor has set a specific combination of molding conditions, that is, retracts the movable mold by a predetermined amount more than in the past, and the molten resin is injected into the increased cavity space at a predetermined rate or more immediately after high-speed injection. By performing mold clamping at high speed and performing them within a fixed time determined by the physical characteristics of the resin, the temperature of the resin, the mold temperature, and the wall thickness of the molded product, large-scale thin-wall molding that was previously impossible It has been found that production of goods can be carried out.

[0004]

That is, according to the present invention, a molten thermoplastic resin is injected into a cavity in a state where the movable mold is retracted from a mold clamping position by a predetermined distance, and then the movable mold is moved to clamp the mold. An injection compression molding method, in which (1) the molded product has a thickness of 0.8 to 3.0.
mm, width 40 cm × 40 cm to 100 cm × 100 cm in a flat shape, and (2) the mold is oriented so that the cavity surface forming the flat surface of the molded product is vertical, (3) The retreat distance is 0.5 to 4 times as large as the thickness of the cavity at the time of mold clamping. (4) When the retreat distance is L [mm], the time from the retracted position to the completion of the mold clamping is τ.
(Sec) = 0.2 + L / 10 within the time calculated, and (4) moving the movable mold for mold clamping from the retracted position at a speed of 10 mm / sec or more. And (5) a formula from the start of injection of the molten thermoplastic resin into the cavity to the completion of mold clamping,

[0005]

[Equation 2]

[Wherein the unit of θ is seconds, D is the thickness of the molded product (cm), ln is the natural logarithmic function, T _F is the flow temperature of the resin (° C.), T _C is the mold temperature (° C.), T _G is the resin injection temperature (° C.) at the gate, α is the thermal diffusivity of the resin, and α = K
/ Ρ × C _P , where K, ρ, and C _P are respectively K: thermal conductivity [cal / cm · sec · ° C.] ρ: density [g / cm ³ ] C _P : specific heat [cal / g・ ℃] ] The method is characterized in that it is carried out within a time (hereinafter referred to as "extreme time") calculated by the above.

Description will be made with reference to the drawings. FIG. 1 is a conceptual diagram showing a state in which a movable die 2 is located at a die clamping position with respect to a fixed die 1. For the sake of convenience, the wall thickness of the molded product is much larger than the vertical dimension (corresponding to the flat surface of the molded product) in the figure, but in reality, the wall thickness is extremely thin compared to the vertical dimension. The cavity between the fixed mold 1 and the movable mold 2 is
As shown in FIG. 1, the cavity surfaces forming the flat surface of the molded product are arranged vertically.

FIG. 2 is a conceptual view showing the movable die 2 retracted from the die clamping position by a predetermined distance. This receding distance is in the range of 0.5 to 4 times the cavity thickness at the time of mold clamping, so that the cavity thickness is temporarily
The size is 1.5 to 5 times the thickness when the mold is clamped.

FIG. 3 is a conceptual diagram showing a state where the molten thermoplastic resin is injected into the cavity with the movable die 2 retracted. During this time, the movable mold 2 is stopped.

FIG. 4 is a conceptual diagram showing a state where the movable mold 2 is moved toward the fixed mold 1 and the mold is clamped after the injection of the resin is completed. The moving speed of the movable mold 2 at this time is 10 mm
/ Sec or more. The injection of FIG. 3 and the completion of the mold clamping of FIG. 4 are performed within the limit time defined above.

1 to 4 are diagrams for a one-point gate, whereas FIGS. 5 to 8 are diagrams for a two-point gate, the number and position of gates and injection into the cavity are shown. The directions are not limited to the positions shown in these figures.

As used herein, the "flow temperature" of a resin refers to the lowest temperature at which a given resin can maintain its fluid state. The flow temperature of each resin is indicated in the instructions issued by the resin manufacturer. It has been found by the present inventor that completing the injection to the mold clamping within the above-mentioned limit time is advantageous for maintaining the fluidity of the resin until the mold clamping of the resin is completed.

For example, K = 5 × 10 ⁻⁴ [cal / cm · second · ° C.], ρ = 1.19 [g / cm ³ ], C _p = 0.35 [cal]
/ G · ° C.], θ [sec] is the value in the rightmost column of the table with respect to the values of D, T _F , T _C , and T _G in Table 1 below.

[0014]

[Table 1]

In the method of the present invention, the mold is oriented so that the flat surface of its cavity is vertical. The movable mold is configured to slide horizontally with respect to the fixed mold, and a horizontal mold can be used as the injection molding device. In this mold orientation, the molten resin can be injected into any part of the cavity. For example, it may be injected into the central portion of the cavity, or may be injected through one or more side gates, fan gates, etc. provided in the peripheral portion of the cavity. In the present specification, the term "vertical" as to the flat surface of the cavity is not necessarily vertical in a strict sense, but may be any vertical direction.

When the resin is injected, the movable mold is retracted by a distance of 0.5 to 4 times the thickness of the cavity when the mold is clamped, and the thickness of the cavity at the time of injection is enlarged as compared with the conventional case. Therefore, the flow resistance of the resin in the cavity is greatly reduced, and as a result, the injection pressure can be set low and the resin can be injected at a high injection rate.
Furthermore, the resin is less likely to be spread thinly during injection, which is advantageous in maintaining sufficient resin temperature and fluidity from the start of injection to the completion of mold clamping.

The process from the start of injection to the completion of mold clamping is performed within the "extreme time" as described above.

It is preferable to move the movable mold for clamping the mold at a speed of 10 mm / sec or more. For example, if the wall thickness of the molded product is 0.8 mm, the retreat distance of the movable mold is 3 times (2.4 mm) the wall thickness of the molded product, and the moving speed of the movable mold is 12.5 mm / sec, the mold from the retracted position is The time required to move the movable type to the tightening position is calculated as 2.4 ÷ 12.5 = 0.192 seconds.
However, because it is necessary to avoid collision between both molds, deceleration time is required just before the molds are closed, and it is difficult to avoid a total time loss of about 0.2 seconds including the time required for the mold clamping mechanism to respond. As a result, the time required from the start of moving the movable mold to the completion of mold clamping is about 0.39 seconds. Considering the time loss of about 0.2 seconds, the retreat distance is L [m
m], τ (seconds) from the retracted position to the completion of mold clamping
= 0.2 + L / 10, the moving speed of the movable mold falls within a preferable range of 10 mm / sec or more if it is carried out within the time.

The time θ _I (second) required from the start of resin injection into the cavity to the end of injection and the time θ _M (second) required from the start of movement of the movable mold to the completion of mold clamping are θ ≧ θ _I
It may be set appropriately within a range that satisfies + θ _M. For example, if you set the moving speed of the movable mold, because theta _M is the formula, obtained from theta _M = steerable retreat distance / movable die movement speed + deceleration time (0.2 seconds), theta _I formula, theta _I ≦ The range is calculated by θ−θ _M. Therefore, if an appropriate value of θ _I that satisfies this is set, the required resin injection rate r (cc / sec)
Is the equation where the cavity volume is V (cc), r = V / θ
It can be calculated from _I. As a result, it is possible to select a device having an appropriate injection rate. When setting the value, it is desirable to have an appropriate margin.

For example, the retreat distance of the movable mold is three times the cavity thickness (D) when the mold is clamped, and the moving speed of the movable mold is 12.5 m.
Table 2 below shows the time (θ _M ) required from the start of movement of the movable mold to the mold clamping when m / sec and the deceleration time are 0.2 sec.

[0021]

[Table 2]

By comparing Tables 1 and 2 above, the time that can be used for resin injection under each condition θ-θ _M (θ within this range
_(I can be set) and θ _I = θ−θ _M is set, a circle with a diameter of 50 cm, a circle with a diameter of 70 cm, and 1
Cavities (volumes 157 cc, 308 cc, 800 c, respectively) for molded articles of thickness D with a square shape of 100 cm on each side.
The injection rates r ₁ , r ₂ and r ₃ (cc / sec) required for injecting the resin into each c _I second in c) are illustrated in the following Table 3.

[0023]

[Table 3]

As described above, the required injection rate and thus the required injection functional force are determined. θ _I should be less than θ-θ _M , so if θ-θ _M is relatively long and there is a margin in the injection rate, then θ _I should be shortened accordingly to maximize the performance of the injector. Meanwhile, the molding time can be shortened. Further, when the calculated θ is sufficiently long and there is a margin in the capacity of the molding apparatus, it is naturally preferable from the viewpoint of molding efficiency to perform from the start of injection to the completion of mold clamping in the shortest possible time. In this respect, the period from the start of injection to the completion of mold clamping is preferably performed within 5 seconds, more preferably within 3 seconds, and particularly preferably within 2 seconds.

Only by combining the predetermined retreat distance of the movable mold, the operation completion within the limit time, and the predetermined moving speed of the movable mold, it is possible to perform injection compression molding of a thin and large molded product as defined in the present specification. There was found. As a result, the mold clamping is completed while maintaining the temperature of the resin, that is, the fluidity. Therefore, the resin has a uniform thickness in the range of 0.8 to 3.0 mm, a size of 40 cm square to 100 cm square, which was impossible in the past. It is possible to spread widely to
It is possible to mold extremely thin and large molded products without warping, distortion or uneven thickness. In addition, preferably, the pressure is 60 kg / cm ² or more from the start to the completion of the movement of the movable die for clamping, and the movement is smoothly performed. Here, “smoothly” means that the change of the moving speed of the movable type is continuous, for example, it is a constant speed, or that the increase / decrease of the speed is continuous. Such a smooth movement ensures a particularly homogeneous molding. Such smooth movement of the mold under such high speed and constant sufficient pressure can be carried out by choosing a hydraulic or electric clamping mechanism with corresponding capacity.

In the above mold orientation, since the resin injected into the cavity receives gravity in the direction parallel to the cavity surface (vertical surface), the resin of the cavity is compared with the case where the cavity surface is oriented horizontally. Although it is necessary to perform the injection and the mold clamping particularly quickly, it has been found that the adverse effect of gravity on the final product can be avoided by rapidly performing the process from the injection start of the molten resin to the completion of the mold clamping within the above limit time.

In carrying out the present invention, T _C (mold temperature)
And T _G (resin injection temperature at the gate) may be appropriately selected so that θ in the above equation is a convenient time length for operation. For example, it is generally advantageous for the mold temperature to be in the range of 50 to 80 ° C. in terms of the entire molding operation including cooling and taking out of the product.

The method of the present invention can be effectively applied to highly viscous thermoplastic resins such as polymethylmethacrylate and polycarbonate or resins containing these, which have been particularly difficult to produce thin-walled molded articles. .

For example, in the case of a polymethylmethacrylate resin having a standard cylinder temperature of 220 to 280 ° C. in injection molding, for example, a gate injection resin temperature of 220 to 280 ° C. and a mold temperature of 50 to 80 ° C. according to the method of the present invention, a large thin wall The board can be easily obtained.

In consideration of the presence of some variations in the physical property data of the raw material resin and the measurement error such as the temperature of the injection resin, the limit from the start of the injection of the resin into the cavity to the completion of the mold clamping is calculated. Instead of time θ
It may be performed within 0.9 times or 0.8 times. In these cases, the certainty of the molding method of the present invention is assured in accordance with the small multiplication coefficient.

According to the method of the present invention, as described above, it is possible to mold a large-sized thin-walled molded article which has not been successful in the conventional injection compression molding, though it is a simple process. The wall thickness is 0.8-3.0 mm, for example 0.8 mm, 1.
0 mm, 1.2 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.
It can be set arbitrarily such as 0 mm. Similarly, the size of the molded product can be arbitrarily set within the range of 40 cm × 40 cm to 100 cm × 100 cm, and for example, 40, 50, 60, 70,
It may be 80, 90 or 100 cm square. Further, the shape may be an arbitrary contour such as a polygon such as a square, a circle, and an ellipse. Further, in the present specification, the "flat shape" of the molded product does not necessarily have to be a plate-like shape, and a bent shape is included as long as it is a substantially flat shape as a whole, and some irregularities may be included. Including those that include.

In the method of the present invention, a small injection molding apparatus and a mold with low rigidity can be used because the injection pressure and the mold clamping pressure can be small even though the molded product is large. Since the installation area is small and complicated control is not required and it can be easily performed with a simple device, molding at low cost is possible. Further, it can be performed by using a horizontal injection molding apparatus of the type which has been widely used in the past and which is highly versatile, which is extremely economically advantageous.

[0033]

EXAMPLES The present invention will be described in more detail with reference to some typical examples. [Example 1] Polymethylmethacrylate resin (Acrypet MF: Mitsubishi Rayon Co., Ltd.) was used for injection compression molding of the present invention. The physical properties of the resin, the shape and shape of the molded product, and the operating conditions were as follows. (1) Thermal conductivity of resin (K) = 5 × 10 ⁻⁴ cal / cm ·
hr · ° C (2) Resin density (ρ) = 1.19 g / cm ³ (3) Resin specific heat (C _P ) = 0.35 cal / g · ° C. (4) Resin flow temperature ( _TF ) = 140 ° C. 5) molded article thickness (D) = 1.5 mm (6) molded article shape: diameter 70cm, discoid (7) retreat distance of the mobile = 4.5 mm (8) temperature _{(T C) = 70 ℃ (} 9 ) Resin injection temperature at gate ( _TG ) = 260 ℃ (10) Number of gates: 1 point gate (11) Gate position: molded product center (12) Injection direction: Horizontal (13) Time from injection start to injection completion = 0.84 seconds (14) Time from completion of injection to completion of mold clamping = 0.65 seconds (15) Mold clamping pressure (from movement start to final mold clamping): 10
0 kg / cm ²

Example 2 The same resin as in Example 1 was used for injection compression molding of the present invention. The physical properties of the resin,
The shape and dimensions of the molded product and the operating conditions were as follows. (1) Thermal conductivity of resin (K) = 5 × 10 ⁻⁴ cal / cm ·
hr · ° C (2) Resin density (ρ) = 1.19 g / cm ³ (3) Resin specific heat (C _P ) = 0.35 cal / g · ° C. (4) Resin flow temperature ( _TF ) = 140 ° C. 5) molded article thickness (D) = 1.5 mm (6) molded article shape: diameter 70cm, discoid (7) retreat distance of the mobile = 4.5 mm (8) temperature _{(T C) = 70 ℃ (} 9 ) Resin injection temperature at gate ( _TG ) = 260 ℃ (10) Number of gates: 2 points gate (11) Gate position: Top and bottom of molded product (12) Injection direction: Vertical (13) From injection start to injection completion Time = 0.84 seconds (14) Time from injection completion to mold clamping completion = 0.65 seconds (15) Mold clamping pressure (from movement start to final mold clamping): 10
0 kg / cm ²

Example 3 The same resin as in Example 1 was used for injection compression molding of the present invention. The physical properties of the resin,
The shape and dimensions of the molded product and the operating conditions were as follows. (1) Thermal conductivity of resin (K) = 5 × 10 ⁻⁴ cal / cm ·
hr · ° C (2) Resin density (ρ) = 1.19 g / cm ³ (3) Resin specific heat (C _P ) = 0.35 cal / g · ° C. (4) Resin flow temperature ( _TF ) = 140 ° C. 5) Molded product thickness (D) = 0.8 mm (6) Molded product shape: 50 cm x 50 cm, square plate shape (7) Moving mold receding distance = 2.4 mm (8) Mold temperature (T _C ) = 70 ° C ( 9) Resin injection temperature at gate ( _TG ) = 260 ℃ (10) Number of gates: 1 point gate (11) Gate position: Molded product center (12) Injection direction: Horizontal (13) Time from injection start to injection completion = 0.30 seconds (14) Time from injection completion to mold clamping completion = 0.44 seconds (15) Mold clamping pressure (from start of movement to final mold clamping): 10
0 kg / cm ²

Example 4 The same resin as in Example 1 was used for injection compression molding of the present invention. The physical properties of the resin,
The shape and dimensions of the molded product and the operating conditions were as follows. (1) Thermal conductivity of resin (K) = 5 × 10 ⁻⁴ cal / cm ·
hr · ° C (2) Resin density (ρ) = 1.19 g / cm ³ (3) Resin specific heat (C _P ) = 0.35 cal / g · ° C. (4) Resin flow temperature ( _TF ) = 140 ° C. 5) Molded product thickness (D) = 0.8 mm (6) Molded product shape: 50 cm x 50 cm, square plate shape (7) Moving mold receding distance = 2.4 mm (8) Mold temperature (T _C ) = 70 ° C ( 9) Resin injection temperature at gate ( _TG ) = 260 ℃ (10) Number of gates: 2 points gate (11) Gate position: Top and bottom of molded product (12) Injection direction: Vertical (13) From injection start to injection completion Time = 0.30 seconds (14) Time from injection completion to mold clamping completion = 0.44 seconds (15) Mold clamping pressure (from movement start to final mold clamping): 10
0 kg / cm ²

The thin plates obtained in Examples 1 to 4 had no warp or shrinkage and had a very uniform thickness variation of ± several%. Virtually no variation was observed in the radius and the side direction of the square.

[0038]

According to the molding method of the present invention, since the resin can be spread at a stretch while maintaining the fluidity of the resin, the resin can be stretched over a long distance on the mold surface with a low shearing force, and thus the conventional method can be used. It is possible to obtain a large-area thin-walled molded product that could be molded only as an extruded sheet. Also,
1/5 to 1 of theoretically predicted pressure in injection molding method
Molding can be performed at a low pressure of / 6 or less,
Therefore, the cost of the molding device can be significantly reduced. Also,
It is homogeneous, has little birefringence, has good optical properties, and has little residual stress so that warpage does not occur and a molded product with excellent impact resistance can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual side view (one-point gate) when the mold is first closed.

FIG. 2 is a conceptual diagram (one-point gate) when the movable mold is retracted.

FIG. 3 is a conceptual diagram (one-point gate) after the resin has been injected.

FIG. 4 is a conceptual diagram (one-point gate) when the mold is clamped.

FIG. 5 is a conceptual side view (two-point gate) when the mold is first closed.

FIG. 6 is a conceptual diagram (two-point gate) when the movable mold is retracted.

FIG. 7 is a conceptual diagram (two-point gate) where the resin has been injected.

FIG. 8 is a conceptual diagram (two-point gate) where the mold is clamped.

[Explanation of symbols]

 1,11 = fixed type, 2,12 = movable type

Claims (10)

[Claims] 1. An injection compression molding in which a movable mold is retracted from a mold clamping position by a fixed distance, a molten thermoplastic resin is injected into the cavity, and then the movable mold is moved to perform mold clamping. (1) The molded product has a thickness of 0.8 to 3.0 mm and an area of 40 cm × 40 cm to 100 c
It has a flat shape in the range of m × 100 cm, (2) the mold is oriented so that the cavity surface forming the flat surface of the molded product is vertical, and (3) the retreat distance is 0.5 to 4 times the thickness of the cavity,
(4) When the retracted distance is L [mm], the retracted position to the completion of mold clamping is performed within the time calculated by τ (second) = 0.2 + L / 10, and (5) the cavity. From the start of injection of the molten thermoplastic resin to the completion of mold clamping, [Here, the unit of θ is seconds, D is the wall thickness (cm) of the molded product,
ln is a natural logarithmic function, T _F is a resin flow temperature (° C.), T _C
Is the mold temperature (° C.), T _G is the resin injection temperature (° C.) at the gate, α is the thermal diffusivity of the resin, and α = K / ρ × C _P
Where K, ρ, and C _P are respectively K: thermal conductivity [cal / cm · sec · ° C.] ρ: density [g / cm ³ ] C _P : specific heat [cal / g · ° C.] . ] It is what is performed within the limit time (theta) calculated by these. 2. The method according to claim 1, wherein the molded article has a thickness of 0.8 to 1.5 mm. 3. The molded product has an area of 70 cm × 70 cm to 100 cm.
The method of claim 1 or 2 in the range of cm x 100 cm. 4. The mold temperature is 50 to 80 ° C., and the mold temperature is 50 to 80 ° C.
Either method. 5. The method according to claim 1, wherein the movable die for clamping the die from the retracted position is smoothly moved with a pressing force of 60 kg / cm ² or more during movement. . 6. The method according to claim 1, wherein movement of the movable mold for clamping the mold from the retracted position is performed by a hydraulic or electric mold clamping mechanism. 7. The method according to claim 1, wherein the thermoplastic resin contains polymethylmethacrylate and polycarbonate. 8. The method according to claim 1, wherein the polymethylmethacrylate resin is molded at an injection resin temperature of 220 to 280 ° C. and a mold temperature of 50 to 80 ° C. 9. A limit time θ × 0.9 from the start of injection of the molten thermoplastic resin into the cavity to the completion of mold clamping.
The method according to any one of claims 1 to 8, wherein the method is performed within the period of time. 10. The method according to claim 1, wherein the process from the start of injection of the molten thermoplastic resin into the cavity to the completion of mold clamping is performed within 5 seconds.