JP3454474B2 - Injection molding method and mold for thermoplastic resin - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the width and length of a molded product.
Or for a molded product in which the ratio of diameter to length is larger
For more details on the injection molding method, refer to
By forming a shear orientation layer oriented in the longitudinal direction on the
To improve dimensional accuracy, warpage and strength of molded products
The present invention relates to an injection molding method.

[0002]

2. Description of the Related Art In conventional injection molding, a portion (hereinafter referred to as " skin layer " ) in which molten resin adheres to a wall surface of a mold and is solidified while the molten resin flows in a cavity.
And the orientation state of the resin or the filler is different in the portion where the molten resin which is flowing is not solidified (hereinafter referred to as “ core layer ” ). There are different orientation states in the same molded product,
Furthermore, since the distribution of orientation is partially different, different molding shrinkages exist on the same molded product, and unevenness in dimensional accuracy and warpage due to deformation are likely to occur. Regarding the uneven distribution of the alignment layer, various methods have been adopted, such as changing the gate position, the number of gate points and the shape, changing the shape of the molded product, the molding conditions, the resin used, etc. Was hard to get.

[0003] Further, in the conventional injection molding, filled with molten resin into the cavity (hereinafter, referred to as "filling process"), satisfies the molten resin into the cavity to complete the filling process at the same time, then, the resin Since resin shrinkage occurs in the process of cooling and solidification , the resin pressure is applied from the injection unit into the cavity to supply the resin for compensating for the shrinkage resin (hereinafter referred to as " pressure holding step " ). The molding method referred to as "calling" is used.

However, even if such a molding method is used,
A fountain flow phenomenon occurs at the flow end of the molten resin in the filling process. That is, the molten resin that has flowed the core layer, the fountain flow, in contact with the mold wall surface, rapidly cooled and solidified to form a skin layer, the molten resin that has flowed immediately thereafter, the freshly formed skin With a gap (hereinafter referred to as " shearing " ) between the layers, the fluid flows up to the end of the skin layer, contacts the mold wall surface, and forms a new skin layer. By repeating this shear occurs between the skin layer and the core layer. Shi
However, since the flow velocity of the resin in the cavity is slower near the wall surface of the mold and becomes faster as it approaches the center of flow of the molten resin, in the layer where shear occurs, the resin is stretched in the flow direction with respect to the molten resin. the behavior, such as shows, and as a result,
Resin molecules, fillers, fillers, etc. tend to be oriented in one direction. However, although this phenomenon is noticeable between the skin layer and the core layer where large shearing occurs, it does not occur inside the core layer, which holds most of the molded product,
The ratio of the orientation layer within the wall thickness is not large.

In addition, a skin layer is formed in the initial stage of the filling process and then shear is generated, and a skin layer is formed in the latter stage of the filling process, and the flow end side where shearing is hardly generated thereafter is obtained. A difference occurs in the alignment layer. That is, it is difficult to positively and uniformly form the alignment layer by a general molding method that shifts to the holding pressure immediately after the completion of filling.

[0006]

The object of the present invention is to achieve a dimensional precision by forming a uniform shear alignment layer in a molded article.
Molding of thermoplastic resin moldings with improved degree, warpage and strength
Is to provide a method.

[0007]

In order to achieve the above-mentioned object, in the invention described in claim 1, in the injection molding method of a thermoplastic resin, the ratio of the width to the length or the diameter to the length of the molded product is both the molded article molding cavity of larger length, at one end in the length direction of the cavity
Opposite from provided filling side gate after filled with the resin to a predetermined pressure in the cavity, or in the filling of the resin continues core layer of resin unsolidified state on the filling side gate
By flowing from and provided the discharge side gate outside the cavity, the shear is generated between the resin solidified in the core layer is in progress, and of continuing the flow of the resin
The Rukoto increasing toward the center in the core layer the shear layer while, is characterized in forming a shear orientation layer facing the same direction in the core layer.

Further, in the invention described in claim 2,
In the invention according to claim 1, the filling side gate is connected.
Fill the resin into the cavity from the filled injection unit
The discharge side injection unit connected to the discharge side gate.
The resin is collected from the cavity in the
Perform molding, after the injection molding of one product has been completed, the resin recovered in the discharge-side injection unit filled from the discharge-side gate into the cavity, the resin discharged from the case core layer is The second product is injection-molded by recovering it from the filling-side gate into the filling-side injection unit, and the waste of the resin is eliminated by repeating this molding cycle.

[0009]

When the molten resin is filled in the cavity from the filling side gate, the molten resin discharge side gate is provided in advance at the portion closest to the filling end. After filling the molten resin into the cavity, the resin so as to be pushed out from the discharge-side gate and Ru <br/> to continue the supply of molten resin key
It is discharged outside the cavity and the resin can continue to flow. By advancing the cooled and solidified while continuing the flow of the resin, at the same time cooling and solidifying progresses toward the core layer inside the central direction, a layer that generates a relatively large shear, cavitation
To shift toward from the layer close to the I wall in the center of the core layer.
Therefore, the alignment layer formed by shearing gradually
It increases from the layer near the cavity wall toward the center of the core layer. By this action, it is possible to obtain a molded product having the same orientation from the layer near the cavity wall surface to the vicinity of the center of the wall thickness.

Further, since the resin flow is continued even after the cavity is filled with the molten resin, the shearing effect generated between the filling side gate and the discharging side gate tends to be uniform. Therefore, it is possible to obtain a molded product in which the distribution of orientation is relatively uniform between the filling- side gate and the discharging- side gate.

[0011]

Example 1 Materials which can be used in the present invention will be described. General crystalline or amorphous thermoplastic resins, thermosetting resins, engineering plastics,
Materials mixed with anisotropic fillers such as glass fiber, carbon fiber, mica, various whiskers, and talc, as well as liquid crystal plastics can be mentioned. The effect of the molding is particularly remarkable when the length is larger than the width and the diameter. Further, the shape of the molded product is particularly effective when it is a cylinder, a cylinder or a prism.

An example of a method for molding a plate-shaped case using the injection molding method according to the present invention will be described with reference to FIG. First, the injection mold will be described. In FIG. 1, a cavity 2 is formed in a mold 20.
There are two gates, a molten resin filling side gate 3 and a molten resin discharge side gate 4.

The filling side gate 3 is filled through the runner 5.
It is connected to the side injection unit 9. Further, the discharge side gate 4 is connected to the discharge side injection unit 10 via the runner 6. In each injection unit 9 , 10 ,
There are flow channel opening / closing mechanisms 7 and 8 for molten resin, and these flow channel opening / closing mechanisms 7 and 8 can operate at different timings.

[0014] The following describes a procedure for molding using such a mold. First, the molten resin flow path opening / closing mechanism 7,
Open 8 In this state, the filling side injection unit 9
By advancing the screw 11 inside, the pre-measured molten resin 1 is injected, and the molten resin is filled in the cavity 2 through the runner 5 and the gate 3. This process is called a filling process.

The filling is continued even after the cavity 2 is filled with the molten resin 1. As a result, push from inside the cavity 2.
The discharged molten resin 1 is discharged side gate 4, runner 6
Through, it is discharged to the discharge side injection unit 10, by the pressure of the molten resin 1, the screw 12 on the discharge side injection unit 10 you retreat. This process is called a shearing process. During the shearing process, the resin pressure in the cavity 2 can be changed by applying a pressure to the screw 12 in the discharge side injection unit 10 to the extent that the screw retreat is not stopped. After continuing the resin movement in the shearing process for the required time and the required amount, the filling of the molten resin 1 is stopped.

After that, the gate opening / closing mechanism 8 is instantly closed, and a holding pressure is applied from the filling side injection unit 9. This process is called a pressure holding process. Then, after the molded product is sufficiently solidified, the mold 20 is opened and the molded product 21 is taken out. After that, the ejection side injection unit 10 used in the ejection step is used for filling, and the filling side injection unit 9 used for the filling is used for ejection, whereby repeated molding is possible.

The description in FIG. 1 is a molding example in a molding machine having two injection units, but this is an example performed for the purpose of reusing the discharged resin, and always two injection units are used. It does not require a molding machine with units. There is also a method of discharging the discharged resin to the outside of the mold, and a method of discharging it to the resin pool existing in the cavity is also effective. Furthermore, it is possible to control the resin pressure in the cavity by applying a pressure to the movable core existing in the resin reservoir.

Further, a flow passage opening / closing mechanism for molten resin in the drawing
7 and 8 show the flow path opening / closing mechanisms 7 and 8 in the form of a cold runner and a shut-off nozzle, but this is only an example, and the form is not limited. Both cold and hot runners can be fully effective. Further, the positions of the flow path opening / closing mechanisms 7 and 8 are also merely examples, and the positions are not limited and may exist in the section from the injection units 9 and 10 to the gates 3 and 4 .

[0019]

Example 2 Next, an example in which polypropylene containing 10% of glass fiber is used will be described. Width of molded product is 8
Use 0 mm, length 160 mm, on the cavity 2 and a thickness of 3.7 mm, it has a filling-side gate 3 in the center of the side width 80 mm, a cavity 2 having a discharge side gate 4 at the center of further opposite sides did. The mold and the injection mechanism used had the same structure as in Example 1. The molding conditions are the same as those shown in Example 1, and the time for each step is 0.4 seconds for the filling time and 4.0 for the shearing step.
Seconds, holding time 10.0 seconds, during the shearing process, 150
cm3 of resin was fed into the cavity.

The resulting molded product was measured for warpage in the longitudinal direction due to deformation and bending rupture strength of each part. The warpage in the longitudinal direction due to the deformation was 0.6 mm.
40m from the filling gate on the axis between the two gates
Bending rupture strength measurements (supporting pitch 60 mm) of m, 80 mm and 120 mm were performed. When the obtained values were averaged, it was 220 (N / cm 2) in the longitudinal direction and 230 (N / cm 2) in the lateral direction.

[0021]

Comparative Example 1 A molded article was obtained by molding under the same molding conditions as in Example 1 except that the shearing step was not performed after the filling step and the pressure holding step was immediately performed. The same measurement as in Example 1 was performed on the obtained molded product. The warp in the longitudinal direction due to the deformation was 4.3 mm. The bending rupture strength is 210 (N / cm2) in the longitudinal direction and 230 (N / c) in the lateral direction.
m2).

From a comparison between Example 2 and Comparative Example 1, it can be understood that the present invention is effective in warpage due to deformation and bending strength. In the above example, an example of numerical values when using polypropylene mixed with 10% of glass fiber is shown.
This is just an example and does not limit the type of resin or filler.

[0023]

Example 3 Next, AB mixed with 20% of glass fiber
An example of using S resin is shown below. Molded product has a diameter of 4.
A cavity 2 having a gate 3 on the filling side and a gate 4 on the discharge side was used at both ends of the cavity having a cylindrical shape of 0 mm and a length of 230 mm. The mold and injection mechanism are
The same structure as in Example 1 was used.

The molding conditions were the same as those in Example 1, and the time for each step was 0.24 seconds for filling time, 4.0 seconds for shearing step and 6.0 seconds for holding pressure. , Cavity 70cm3 of resin during the shearing process
It was supplied within 2 . About the obtained molded product, 45 mm, 115 m from the filling side gate 3 on the axis between the two gates.
Bending rupture strength measurement (supporting pitch 40 mm) was performed at a position of m and 185 mm. As a result, 840 (N / cm2) at the 45 mm position and 850 (N at the 115 mm position)
/ Cm2) and 850 (N / cm2) at the 185 mm position.

[0025]

Comparative Example 2 A molded article was obtained by molding under the same molding conditions as in Example 1, except that the shearing step was not performed after the filling step and the pressure holding step was immediately performed. The same measurement as in Example 1 was performed on the obtained molded product. As a result, 45m
840 (N / cm2) at m position, 84 at 115 mm position
0 (N / cm2), 760 at 185 mm position (N / cm2
It was 2). From a comparison between Example 3 and Comparative Example 2, it can be understood that the present invention is effective in making the bending strength distribution uniform.

[0026]

Example 4 Next, an example of using a POM resin is shown. As the mold and the cavity, those shown in Example 3 were used. The molding conditions are the same as those shown in Example 3, and the time for each step is 0.2 times the filling time.
4 seconds, shearing process time 4.5 seconds, pressure holding time 6.0 seconds,
90 cm3 of resin was fed into the cavity 2 during the shearing process. The same measurement as in Example 3 was performed on the obtained molded product. As a result, 540 (N /
cm2), 540 (N / cm2) at 115 mm position, 18
It was 500 (N / cm 2) at the 5 mm position.

[0027]

Comparative Example 2 A molded article was obtained by molding under the same molding conditions as in Example 4, except that the shearing step was not performed after the filling step and the pressure holding step was immediately performed. The same measurement as in Example 3 was performed on the obtained molded product. As a result, 45m
570 (N / cm2) at m position, 56 at 115 mm position
0 (N / cm2), 560 mm (N / cm2) at 185 mm position
It was 2). From a comparison between Example 3 and Comparative Example 2, it can be understood that the present invention is effective in improving bending strength and making the distribution uniform.

[0028]

EFFECTS OF THE INVENTION Since the molded product thus obtained has a uniform shear orientation in each part, the tensile strength, bending strength and impact strength are uniform in each part of the molded product between the filling side gate and the discharge side gate. And is excellent. In addition, since the difference in molding shrinkage between the filling- side gate and the discharge- side gate is small in each part of the molded product, the dimension of The accuracy is improved, and the warp and twist due to the deformation can be reduced.

[Brief description of drawings]

Illustration of a mold and an injection unit in FIG. 1 EXAMPLE 1

[Explanation of symbols]

1 molten resin 2 cavities Three and four gates 5, 6 runners 7, 8 Melt resin flow path opening / closing device 9,10 injection unit 11, 12 screws 20 mold

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-8-192444 (JP, A) JP-A-3-207625 (JP, A) JP-A-6-270218 (JP, A) JP-A-5- 337978 (JP, A) JP-A-1-299015 (JP, A) JP-A-61-179715 (JP, A) JP-A-5-337990 (JP, A) JP-A-6-31778 (JP, A) JP-A-3-274127 (JP, A) JP-A-6-155535 (JP, A) JP-A-60-242022 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B29C 45/13 B29C 45/23 B29C 45/26 B29C 45/46 B29C 45/77

Claims (2)

(57) [Claims] 1. A molding cavity for a molded product, wherein the width and the length of the molded product or the ratio of the diameter to the length of the molded product are both larger, and the molding cavity is provided at one end side in the length direction of the cavity. br /> set opposite from the filling side gate after filled with the resin to a predetermined pressure in the cavity, or the resin of the unsolidified state filling of the resin continues in the core layer on the filling side gate
By flowing from the discharge gate to the outside of the cavity , shear is generated between the solidified resin in the core layer and the resin does not flow continuously.
The Rukoto increasing <br/> toward the center of al the shear layer in the core layer, a thermoplastic injection molding process of the resin molded article to form a shear orientation layer facing the same direction in the core layer. 2. When the resin is filled into the cavity from the filling side injection unit connected to the filling side gate , the cavity is placed in the discharging side injection unit connected to the discharging side gate.
Resin is collected from the inside to mold one product, and after the injection molding of this one product is completed, the resin collected in the discharge side injection unit is discharged from the discharge side gate into the cavity. was filled in the resin discharged from the case core layer performs injection molding of a product of the two eyes by recovering the filling side injection unit from the filling side gate,
The method for injection molding of a thermoplastic resin molded article according to claim 1, wherein waste of resin is eliminated by repeating this molding cycle.