JPH08267493A - Gas injection compression molding method - Google Patents

Abstract

PURPOSE: To mold a molding having a large side without defect such as shrink or warpage by compressing a resin in a mold in which reinforcing rib can be formed at the side while injecting the resin in a mold semi-opened state, and then pouring a pressurized gas under lower pressure than the internal pressure of a cavity of a pressing surface. CONSTITUTION: A resin is injected from an injection nozzle in the state that a mold is semi-opened, the mold is compressed during continuing the injection of the resin, and clamped. The resin in the mold is oriented by the clamping, fluidizing to the side 4 by a reinforcing rib 2 is expedited, spread to the corners of the mold and brought into close contact with the entire inner surface of the mold. After the compression, pressurized gas is injected from a gas injection mold 1 provided at one or more positions at the side 4, the corner or the pressing surface 3 near the corner. The gas is press injected after the charging of the resin in the cavity is substantially completed, and the pressure is set to lower than the resin pressure of the surface 3. After the predetermined pressure is held and cooling time is elapsed, the pressurized gas is exhausted, and a molding is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas injection compression molding method capable of easily providing a molded product having a large side surface without product defects such as sink marks and warpage.

[0002]

2. Description of the Related Art In the injection compression molding disclosed in, for example, Japanese Patent Laid-Open No. 61-283520, a resin is supplied with a low injection pressure by injecting the resin in a mold half-open state and compressing the resin by a mold clamping force. In addition to enabling, the orientation of the resin is relaxed because the resin is stretched in all directions by compression,
There is an advantage that a molded product having a thickness of about 2 to 3 mm and having no sink mark can be obtained.

However, in the case where the molded product has a shape having a partially thick portion such as a reinforcing rib, shrinkage after releasing may cause sink marks or warpage.

On the other hand, in injection molding, pressurized gas is injected into the resin injected into the mold cavity to form a hollow portion in the thick portion of the molded product, thereby preventing sinking or warpage of the molded product. Gas injection is known.

Therefore, in the injection compression molding, there has been proposed gas injection compression molding in which pressurization of a pressurized gas in the gas injection is applied.

Conventionally, the following methods have been known as gas injection compression molding methods.

(1) A method of injecting a resin in a mold half-opened state and clamping the resin to compress the resin, and then pressurizing a pressurized gas into the resin in the compressed state (JP-A-4-37516).

(2) In a half-open state of the mold, an amount of resin insufficient to fill the mold is injected (short shot), and pressurized gas is injected into the injected resin to form a balloon-shaped parison. After that, the mold is clamped and compressed (Japanese Patent Publication No. 6-351
No. 38).

(3) After a short shot in the mold half-open state, pressurizing gas is pressed into the resin, the mold is slightly pushed open by the pressure of the pressurizing gas pressurized, and then the mold is clamped and compressed. Method (JP-A-4-59211).

[0010]

However, when molding a molded product having a side surface by the above-mentioned conventional technique, a pressure is directly applied to the pressing surface of the molded product, that is, the plane orthogonal to the pressing direction of the mold. The side surface, that is, the plane having an angle θ with the pressing surface as shown in FIG.
There is a problem that only the pressure of sθ is applied and the improvement effect of injection compression molding cannot be obtained in the side surface portion. Also,
When the side surface area of the molded product is significantly larger than the area of the pressed surface, that is, when the molded product is in the shape of a deep box, there is a problem that the resin flow to the side surface becomes difficult.
Therefore, it is very difficult to obtain a molded product having a deep box shape by the above-mentioned conventional technique.

The present invention has been made in view of the above conventional problems, and in gas injection compression molding in which pressurization of pressurized gas is applied to injection compression molding, side walls are provided with reinforcing ribs. In addition to promoting resin flow to the side parts, gas is pressed into the reinforcing ribs from the side parts or near the corners to compensate for the pressure applied to the side parts, and large molded products on the side parts are not damaged or warped. The purpose is to be able to provide.

[0012]

SUMMARY OF THE INVENTION According to the present invention, when injection-molding a molded article having a side surface portion, a resin is injected in a mold half-open state into a mold in which a reinforcing rib can be formed on the side surface portion. Provided is a gas injection compression molding method which comprises pressurizing a pressurized gas at a gas pressure lower than a cavity internal pressure of a press surface from a gas injection hole provided in a side surface portion or near a corner portion after being compressed. It is a thing.

The injection compression molding referred to in the present invention is a so-called mold stamping method in which a molten resin is injected into a mold of a press molding machine after or during injection, and in injection molding, clamping is performed with a clamping force lower than an injection pressure. A method of injecting resin into the mold to open the mold and then compressing by increasing the mold clamping force, injection press molding capable of synchronous control of resin injection and press (for example, Komatsu injection press machine, etc. )including. All of these methods obtain a low injection pressure by increasing the cavity thickness at the resin injection stage,
Further, this is a method in which the mold clamping pressure is applied to the resin even during cooling while promoting the flow of the resin in the compression stage. As a result, thin injection molded products (large L (flow length) / t with low injection pressure)
It is known that (thickness) can be achieved).

However, in injection compression molding, a large L /
Only the pressing surface that is directly compressed can realize t. At the side surface that forms an angle θ with the press surface, only cos θ pressure is applied in the thickness direction, so θ
Becomes smaller, the pressure becomes smaller. Particularly when θ is 30 degrees or more, a significant pressure difference from the press surface occurs, and when θ is 90 degrees, almost no pressure is applied in the thickness direction. Therefore, it is not always possible to realize a large L / t even by injection compression molding on the side surface portion. The method of the present invention is particularly effective for molding a molded product having a side surface portion having a θ of 30 degrees or more that causes a significant pressure difference from the pressing surface.

In the present invention, the side surface portion means a flat surface having an angle θ with the press surface, and does not necessarily have to be a flat surface connected to the end portion of the press surface, and exists in a rib shape at an arbitrary position on the press surface. It may be flat.

The molding method of the present invention will be described in detail below, taking as an example the case of molding a molded product in which reinforcing ribs are formed only on the side surfaces as shown in FIGS. 1 and 2.

First, in the gas injection compression molding method according to the present invention, the resin is injected from the injection nozzle in a state where the mold is half-opened or half-opened by the injection pressure.

Next, while the resin injection is continued, the mold is compressed and is in a mold clamped state. Although the resin in the mold is stretched by this mold clamping, the reinforcing rib also promotes the flow to the side surface portion, and the resin spreads to every corner of the mold and is closely adhered to the entire inner surface of the mold. At the time of injection, as with ordinary injection compression molding, more resin than the cavity volume when the mold is completely closed so that pressure is applied to the pressing surface even in the cooling stage,
Generally, an excess resin of about 0.1 to 0.3 mm may be injected in a gap between mold surfaces.

Clamping the resin while injecting the resin prevents the appearance of defects such as so-called hesitation marks by clamping the resin from the resin without stopping the flow of the resin in the mold. This is because. On the other hand, if the mold is clamped after the completion of the injection of the resin, the flow of the resin in the mold stops once between the completion of the injection and the start of the mold clamping, and at this time, the resin contacting the inner surface of the mold A poor appearance such as a so-called hesitation mark occurs near the boundary of the resin that is not in contact with the resin.

As the resin used in the present invention, thermoplastic resins used in general injection molding and extrusion molding can be widely used. Further, a thermosetting resin can be used if necessary. Furthermore, fillers such as feelers and various additives can be added to these resins as needed.

The degree of compression of the resin may be determined according to the thickness of the molded product to be molded.

After the compression, the pressurized gas is injected through the gas injection holes provided at one or more places on the side surface, the corner portion or the press surface near the corner portion. As the pressurized gas, for example, air, carbon dioxide gas or the like can be used,
An inert gas such as nitrogen is preferred. A known method can be used for gas injection, and a gas nozzle incorporated in the injection nozzle may be used to press into the mold through the same flow path as the resin, or a gas nozzle may be provided in the mold to directly apply the gas into the mold. Pressurized gas may be injected, and which method should be adopted may be appropriately determined depending on the shape of the molded product and the mold structure.

The pressurization of the pressurized gas must be started after the completion of filling the resin into the cavity. More specifically, the resin should fill the gas injection hole portion, and after the gas is injected, the gas injection should be started at a timing when there is no large flow of the resin in the cavity due to compression. If the gas injection is too fast, the gas will break through the resin in the cavity, the gas will be trapped by the flow of the resin, and the resin pressure on the press surface will not rise enough, causing gas invasion into the press surface. There is a risk.

It is essential that the pressure of the press-fit gas is lower than the resin pressure on the pressing surface. However, it is preferable that the gas pressure is high in order to promote the invasion of the gas into the side surface portion. This optimum condition may be appropriately determined depending on the shape of the molded product and the mold structure.

The reinforcing ribs should be arranged so as to support the flow of the resin on the side surface, and should be provided along the direction of the resin flow due to compression. In addition, a reinforcing rib should be arranged at a corner which is a boundary between the side surface portion and the pressing surface in order to guide the gas to the reinforcing rib far from the gas injection hole. The shape and height of the reinforcing rib are not particularly limited, but as shown in FIG. 4, the root width T of the rib is preferably T = 1.0t to 3.0t with respect to the plate thickness t of the side surface portion.

Although the volume of the reinforcing rib is not particularly limited,
Since the cooling contraction of the resin is compensated for by the invasion of gas, it is preferably 3 to 20% with respect to the volume of the side surface portion. Within this range, the product weight is not increased and the gas reaching distance is not shortened, which is preferable.

After the predetermined gas pressure is maintained and the cooling time has passed through the above steps, the pressurized gas in the resin is discharged, the mold is opened, and the molded product is taken out.

Although the molded product in which the reinforcing ribs are provided only on the side surface portions has been described above, it goes without saying that a thick portion such as the reinforcing ribs may be provided on the pressing surface to introduce the gas. In this case, when pressurizing the pressurizing gas, the mold is opened for a moment and the resin is immediately compressed. preferable.

That is, when pressurizing the pressurized gas, the movable die is slightly retracted to instantly open the die. By setting this mold open state, the resin pressure in the mold can be lowered, and the pressurized gas can be injected into the resin even if the pressurized gas is not so high. In addition, since the mold open state is instantaneously formed by a slight movement of the movable mold, the pressurized gas that has been press-fitted does not unnecessarily spread and is selectively press-fitted into the thick wall portion with low flow resistance. It

The amount of movement of the movable die to the mold open state is defined by the thickness of the press surface portion in the mold open state, and the thickness of the press surface portion in the mold clamping state immediately before (hereinafter referred to as the "first mold clamping state"). It is preferable that the movement amount is 1.1 to 1.5 times.

If the moving amount of the movable die is too small, the resin pressure drop in the die is insufficient, and unless a high pressure gas is used, the pressure gas is sufficiently injected to the end of the thick part of the press surface. Hard to do. On the other hand, if the amount of movement of the movable die is too large, the pressurization gas is in a state close to that in the short shot state, and it becomes difficult to selectively pressurize the pressurization gas into a necessary thick portion.

Further, the mold open state needs to be instantaneous, and immediately after the mold open state, the mold clamp state (hereinafter,
"Second mold clamping state"), and the resin in the mold is compressed again. Specifically, it is preferable that the mold open state is held for 10 seconds or less. If the holding time in the mold open state is too long, the pressurized gas tends to stick out from the thick portion and be easily press-fitted.

The start of the supply of the pressurized gas and the start of the transition to the mold open state may be started at the same time, but in order to reliably pressurize the pressurized gas during the short mold open state time. The workability is better when the supply of the pressurized gas is slightly advanced. Further, the gas pressure may be lowered by stopping the supply of the pressurized gas at the same time as the transition to the second mold clamping state.

The second mold clamping state is a state in which the resin is compressed again by the mold clamping from the mold open state, and the resin compression by the second mold clamping state should form the thickness of the press surface portion. It is performed by compressing the molded product to a predetermined wall thickness. Due to the second mold clamping state, the resin pressure in the mold is increased to prevent excessive pressurization of the pressurized gas and improve the mold reproducibility of the molded product.

The resin is compressed in the second mold clamping state until the thickness of the press surface portion in the second mold clamping state becomes less than the thickness of the press surface portion in the first mold clamping state. It may be stopped within a range that does not reach the thickness of the pressing surface portion in the mold clamping state. However, if the compression in the second mold clamping state is too weak, the mold reproducibility of the obtained molded product is lowered, and sink marks and warpage are likely to occur. On the other hand, if the compression in the second mold clamping state is too strong, the pressurized gas pressed into the thick portion escapes to the periphery and is trapped, and the surface of the molded product tends to swell.

The compression in the second mold clamping state is such that the thickness of the press surface portion in the second mold clamping state is 0.90 to 1.2 times the thickness of the press surface portion in the first mold clamping state. It is preferable to perform it so that the thickness of the pressing surface portion in the second mold clamping state is substantially equal to the thickness of the pressing surface portion in the first mold clamping state.

After the second mold clamping state, the state is maintained until the required cooling is completed, after which the pressurized gas in the resin is discharged, and then the mold is opened to take out the molded product.

The molded product molded in this manner has hollow portions formed not only on the side surface portions but also along thick portions such as reinforcing ribs that are partially present on the pressing surface.

Further, the practical implementation of the above-mentioned method is carried out as in the conventional injection compression blow molding apparatus, which is generally used.
It does not have a simple mold opening / closing control mechanism that only performs mold clamping from the mold half-open state to the required mold clamping state, and further mold opening / closing control during the transition from the mold half-open state to the mold clamping state. This is possible only by using an injection compression blow molding apparatus having a control mechanism that can be performed.

That is, during the mold clamping operation from the mold half-open state to the mold clamping state, an injection compression hollow molding apparatus having a mold opening / closing control mechanism capable of setting the above-mentioned momentary mold open state after the mold is once clamped. Results in a practical implementation.

Examples of the effective molded product of the present invention include, for example, a box-shaped chassis, a deep tray, and a cabinet. For example, it has a relatively thin wall thickness of 2.0 to 3.0 mm and partially has a reinforcing rib with a width of 1.0 to 3.0 mm, and has a large side surface portion, for example, a side surface portion having a height of 30 mm or more. It is possible to easily mold a molded product having the above-mentioned condition without causing sink marks or warpage.

[0042]

The present invention will be described in more detail with reference to the following examples.

Example 1 A Komatsu IP1050 injection press machine was used as a molding machine, and an ABS resin (“Stylac-ABS.120” manufactured by Asahi Kasei Kogyo Co., Ltd.) was used as the resin, and the conditions shown below were used to obtain the results shown in FIGS. 1 and 2. Box-shaped product with such reinforcing ribs (Minimum product thickness (press surface) 1.0 mm)
Was molded.

From the gas injection hole 1, the gas pressure is 50 kg / c
When gas was press-fitted at m ² , 150 kg / cm ² , 200 kg / cm ² , the gas was introduced along the reinforcing ribs 2,
A good molded product without shrinkage of the reinforcing rib portion 2 and warp deformation of the molded product was obtained.

(Injection conditions) Resin temperature: 250 ° C. Mold temperature: 60 ° C. Injection speed: 45 mm / sec Injection pressure: 96 kgf / cm ² G

(Press conditions) Mold clamping start position: 70% (mold clamping starts when the resin injection amount is 70%) Initial mold opening amount: 5.0 mm Press speed: 10 mm / sec Press pressure: 200 kg / cm ²

(Gas injection condition) Pressurized gas injection delay time (time from completion of mold clamping to pressurization gas injection start): 0.1 sec Pressing time (pressurization gas press-in time): 3.0 sec Holding time (addition Holding time from the completion of the pressurization of the pressurized gas to the start of the recovery of the pressurized gas that has been pressurized): 10 sec Recovery time (the time for recovering the pressurized gas that has been pressurized from the hollow portion): 10 sec

Example 2 Under the same injection conditions as in Example 1 and the following press and gas press-fitting conditions, a box-shaped molded article with reinforcing ribs as shown in FIG. 3 was molded.

From the gas injection hole 1, the gas pressure is 50 kg / c
When gas was press-fitted at m ² , 150 kg / cm ² , 200 kg / cm ² , the gas was introduced along the reinforcing ribs 2,
A good molded product without shrinkage of the reinforcing rib portion 2 and warp deformation of the molded product was obtained.

(Press condition) First mold clamping condition Mold clamping start position: 70% (mold clamping starts when the resin injection amount is 70%) Initial mold opening amount: 5.0 mm Press speed: 10 mm / sec Press Pressure: 200kg / cm ² Press surface thickness at completion of pressing: 2.0mm

Mold open condition Mold moving speed: 1.0 mm / sec Dimension open amount: 0.4 mm Dimension hold time: 3.0 sec Dimension hold pressure: 200 kg / cm ²

Second mold clamping condition Press speed: 5.0 mm / sec Press pressure: 200 kg / cm ² Press surface thickness after pressing: 2.0 mm

(Gas injection condition) Pressurized gas injection delay time (time from completion of first mold clamping to initiation of pressurization gas injection): 0.1 sec Press injection time (pressurization gas injection time): 3.0 sec Hold Time (holding time from completion of pressurization of pressurization gas to start of recovery of pressurization gas pressurization): 10 sec Recovery time (time to recover pressurization gas pressurization from hollow part): 10 sec

Comparative Example 1 Under the same injection and pressing conditions as in Example 1, a box-shaped molded product as shown in FIGS. 5 and 6 was molded. When the thickness of the press surface 3 was 1.5 mm, the side surface 4 was not filled with the resin even when the injection pressure and the injection speed were maximized. Only a molded product with large warp deformation was obtained.

Comparative Example 2 Under the same injection and pressing conditions as in Example 1, a box-shaped molded article with reinforcing ribs as shown in FIGS. 7 and 8 was molded.
By providing the reinforcing ribs 2, the resin flow to the side surface 4 was promoted, and the resin could be filled up to the side surface 4 even if the press surface 3 had a wall thickness of 1.0 mm. Moreover, the warp deformation was further increased as compared with Comparative Example 1.

[0056]

According to the molding method of the present invention, it is possible not only to mold a molded product having a large side surface at low pressure in the injection compression molding method, but also to press the reinforcing rib provided on the side surface from the side surface or near the corner. By press-fitting the gas, a molded product having a large and deep side surface with respect to the pressed surface without warping, deformation or sinking can be obtained.

[Brief description of drawings]

FIG. 1 is a back view of a molded product molded in Example 1.

FIG. 2 is a sectional view taken along line AA in FIG.

3 is a back view of a molded product molded in Example 2. FIG.

FIG. 4 is a diagram showing an example of the shape of a reinforcing rib.

5 is a back view of a molded product molded in Comparative Example 1. FIG.

6 is a cross-sectional view taken along the line AA in FIG.

7 is a back view of a molded product molded in Comparative Example 2. FIG.

8 is a cross-sectional view taken along the line AA in FIG.

[Explanation of symbols]

 1 Gas injection hole 2 Reinforcing rib 3 Press surface 4 Side surface 5 Gate

Claims (2)

[Claims] 1. When injection-molding a molded article having a side surface portion, after the resin is injected and compressed in a mold half-open state in a mold in which a reinforcing rib can be formed on the side surface portion, the side surface portion or a corner portion is formed. A gas injection compression molding method characterized in that a pressurized gas is injected at a gas pressure lower than the internal pressure of the cavity of the press surface from a gas injection hole provided in the vicinity. 2. The gas injection compression molding method according to claim 1, wherein the volume of the reinforcing rib is 3 to 20% of the volume of the side surface cavity.