JPH06210659A - Synthetic resin injection molded piece and molding method and device therefor - Google Patents

Abstract

PURPOSE:To mold with low clamping pressure a large-sized molded piece having excellent dimensional precision and smooth surface without sink mark and warp by forming, on a thick part to be substantially connected to a gate, an injection pressure transfer channel. out of a foamed injection pressure transfer member consisting of foaming low molecular weight polymer having specific viscosity and softening temperature. CONSTITUTION:In a molded piece 2, for example, an injection pressure transfer channel 3 expanding from a gate 1 to the neighborhood of a resin fluid end 4 is formed in the inside of a thick part 5, which is provided as a wall core contained in a synthetic resin. The channel 3 is filled with a foamed injection pressure transfer member. For the injection pressure transfer member, a low molecular weight polymer containing a foaming agent is used and the quantity of it is 1/10 or less of the synthetic resin in volumetric ratio. The viscosity of the low molecular weight polymer at injection is 1/50 or less of the viscosity of the synthetic resin at injection and 0.5 poise or more. As for the low molecular polymer, (viscosity at 120 deg.C)/(viscosity at 220 deg.C) is 100 or more, and Vicat softening point is 60 deg.C or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin injection-molded article, a molding method and a molding apparatus therefor, and more particularly to a large-sized molded article having excellent dimensional accuracy and having a smooth surface and no sink or warp.

[0002]

2. Description of the Related Art Generally, a synthetic resin injection-molded article is obtained by injecting a heat-plasticized synthetic resin into a mold cavity for molding. In order to obtain a good injection-molded product, it is necessary to inject a synthetic resin at a high pressure into a mold clamped with a sufficient mold clamping force. It is said that the mold clamping force is generally required to be 300 to 500 kg / cm ² per projected area of a molded product. Therefore, the mold clamping force of the injection molding machine becomes very large,
Generally, a mold clamping force of several thousand tons is required to mold a large-sized molded product. If a large molded product can be molded with a small clamping force, its economic effect will be great.

The thinner and larger the injection molded product, the more difficult it is for the injection pressure of the injection cylinder to be transmitted to the end of the mold cavity. That is, since the injection pressure applied to the synthetic resin by the injection cylinder is transmitted to the synthetic resin at the end of the mold cavity through the synthetic resin of the injected mold cavity, a large pressure loss occurs during this period, which causes a large molding machine. In many cases, the injection pressure at the end of the mold cavity is reduced to about one tenth of the gate pressure. In general injection molding, even if the injection pressure is 1000 kg / cm ² , the pressure at the end of the mold cavity often drops to about 100 kg / cm ² . The average pressure per projected area of the molded product is 300 to 500 kg / cm ² , and the required mold clamping force is 300 to 500 kg / cm ² .

Since the pressure loss is large and the pressure transmission is insufficient as described above, it is necessary to use an injection molding machine having a high injection pressure and a high mold clamping force in order to make a large-sized molded product. Due to the large pressure difference near the end of the mold cavity, there have been problems such as warpage of the molded product and inaccuracies in the size of the molded product.

On the other hand, it is generally difficult to apply sufficient pressure to the entire molded product to prevent the occurrence of sink marks. Therefore, the type of design has been limited because the molded product is designed so that sink marks or the like are less likely to occur. For example, a molded product having a thin rib and a small boss diameter and a molded product in which the thickness (width) of the rib is smaller than the thickness of the surface portion of the molded product have been generally designed. It has heretofore been difficult to reduce the weight of the molded product as a whole by providing thick and strong ribs only to the molded product where strength is required and making the molded product surface thin. It is also difficult to attach a large boss to reduce the number of parts in the assembly.

Conventionally, as a method for solving these problems, a foaming injection molding method in which a foaming agent is mixed with a synthetic resin to perform injection molding, or a synthetic resin is injected, and then a gas body is injected. A gas assisted injection molding method has been proposed.

USP 4 for gas-assisted injection molding
824732, USP 4923666, etc.

In US Pat. No. 4,923,666, a gas body forms a gas channel in a thick portion such as a root of a rib of a molded product to prevent sink marks which are likely to occur in the thick portion, and to control injection pressure at the end of the molded product. To communicate to.

In US Pat. No. 4,824,732, it is shown that a non-plastic fluid is used to form a hollow body, and the non-plastic fluid is discharged out of the mold after molding. Therefore, the fluid described here is a gas or a gas-like substance having a very low viscosity.

On the other hand, a molding method generally known as sandwich injection molding at present, that is, a first synthetic resin is injected into a mold cavity and then a second synthetic resin is injected to fill the mold cavity. However, there is a molding method for molding a sandwich structure having a so-called skin-core structure, but in this molding method, it is generally difficult for the second synthetic resin to be injected to form an injection pressure transmission channel such as a gas channel. Yes, not known.

[0011]

[Problems to be Solved by the Invention] USP 5149482
Discloses a method of reducing the mold clamping force in sandwich injection molding by forming a mold cavity shape in which a thick flow passage is provided in a part of the mold cavity of a thin portion. In this case, in order to selectively flow the second synthetic resin into the thick flow passage, it is necessary to extremely increase the difference in wall thickness between the thin portion and the thick portion. The amount of will also increase. That is, USP 5149482 does not describe any difference in viscosity between the first synthetic resin and the second synthetic resin (corresponding to the low molecular weight polymer of the present invention), which is the greatest feature of the present invention described later, and USP 5149482 does not describe at all.
It is difficult to reduce the mold clamping force by making the amount of the second synthetic resin as small as the amount of the low molecular weight polymer of the present invention.

US Pat. No. 4,140,672 shows a method of injecting a synthetic resin into a mold cavity, then injecting a low-viscosity fluid to fill the mold cavity, and discharging the low-viscosity fluid out of the die after molding. However, it is shown here that the molding process also forms a sandwich structure having a skin-core structure similar to the sandwich injection molding, and it is shown that the low-viscosity fluid also forms the injection pressure transmission channel in this molding method. Not not.

Heretofore, it has been considered that the injection pressure transmission channel is formed by a gas body or a gas-like substance.
Gas-assisted injection molding is a very excellent molding method, but this method also has various problems. Eg 2
Equipment costs are high due to the use of high pressure gas such as nitrogen gas of 0 to 300 kg / cm ² , special safety measures are required, and various measures are required to comply with the High Pressure Gas Control Law in Japan. I have a problem. In order to further increase the gas pressure and improve the mold surface reproducibility of the molded product, the equipment cost is further increased. The present invention has been made to solve these problems. That is, according to the present invention, it is possible to provide a large-sized molded product that can be injection-molded with a low mold clamping force, has a smooth surface and is free from sink marks and warpage.

[0014]

Means and Actions for Solving the Problems First of the Invention
Is a synthetic resin injection molded product in which the foamed injection pressure transmitting material remains in the injection pressure transmitting channel in the molded product, (1)
A thick portion substantially connected to the gate, and (2) an injection pressure transmission channel is formed inside the thick portion,
(3) The injection pressure transmitting channel is filled with a foamed injection pressure transmitting material, (4) the injection pressure transmitting material is made of a foamable low molecular weight polymer, and (5) the amount of the injection pressure transmitting material is a synthetic resin amount. 1/10 or less (volume ratio), and (6) the viscosity of the low molecular weight polymer at the time of injection is 1 of the synthetic resin viscosity at the time of injection.
/ 50 or less and 0.5 poise or more, (7) low molecular weight polymer (viscosity at 120 ° C) / (viscosity at 220 ° C) ratio of 100 or more, (8) low molecular weight polymer Vicat softening The temperature is 60 ° C. or higher, which is a synthetic resin injection molded product.

A second aspect of the present invention is a molding method suitable for molding the above-mentioned molded article. That is, the injection pressure transmitting material (low molecular weight polymer) satisfying the conditions (4) to (8) in which the synthetic resin is thermoplasticized in the main injection cylinder and the chemical blowing agent is contained in the auxiliary injection cylinder is used as the chemical blowing agent. Of the molded product, which is plasticized by heating at a temperature below the decomposition temperature of, the synthetic resin is first injected into the mold cavity, and then the low molecular weight polymer is injected above the decomposition temperature of the blowing agent near the nozzle and / or inside the mold. It is a molding method.

A third aspect of the present invention is a synthetic resin injection-molded article characterized in that a main injection cylinder for synthetic resin and a sub-injection cylinder having a capacity of ⅕ or less of the main injection cylinder are connected to the same nozzle. Molding equipment.

The synthetic resin injection-molded article of the present invention is a synthetic resin injection-molded article in which a foamed injection pressure transmitting material remains in the injection pressure transmitting channel in the molded article, and (1) is substantially connected to the gate. It has a meat part.

As the synthetic resin described in the present invention, all synthetic resins generally used for injection molding can be used. For example,
Polyolefin such as polyethylene and polypropylene, polystyrene, styrene-acrylonitrile copolymer, A
Styrene resin such as BS resin, nylon 6, nylon 6
Polyamides such as 6 and the like, polyacetals, polyesters, polyphenylene ether resins, polyvinyl chloride resins and the like.

The foamed injection pressure transmitting material is a material capable of foaming to transmit an injection pressure, and in the present invention, a low molecular weight polymer containing a foaming agent is used.

The foamed injection pressure transmitting material, after forming the injection pressure transmitting channel, is not discharged to the outside of the mold but remains in the injection pressure transmitting channel.

The thick portion preferably has a ratio of (diameter of virtual circle of cross section of molded product of thick portion) / (diameter of virtual circle of cross section of molded product of general portion) of 1.5 to 3.5, more preferably Is 1.8-
It is 3.0. This ratio is calculated from the thick part and the general part in the same plane. The diameter of the imaginary circle of the cross section of the molded product described here is the diameter of the largest sphere that does not protrude from the molded product in the molded product. Looking at the cross section of the molded product, the diameter of the largest circle that fits in the cross section is obtained. If this diameter is small,
The injection pressure transmitting material becomes difficult to flow, and if it is too large, the cooling time becomes long, which is not preferable.

In the present specification, the general part of a molded product is a part that occupies the main part of each part of the molded product. For example, in the case of a box-shaped molded product, it is the surface that forms the bottom of the box, and It is a surface forming a side surface. The thickness of the bottom surface may be different from the thickness of the side surface. In this case, the thickness of the bottom surface is the thickness of the bottom portion and the thickness of the side surface is the thickness of the general portion.

The thick portion is substantially connected to the gate,
It continues in the direction of the resin flow end. The fact that the thick portion is substantially connected to the gate means that there is a thick portion necessary for forming the injection pressure transmission channel from the gate to the flow end. Therefore, the distance between the gate and the thick portion where the injection pressure transmission channel is continuous, or the break in the middle of the thick portion is included in the scope of the present invention. Generally, if the distance between the gate and the thick portion is 20 mm or less, and if the cut in the middle of the thick portion is 5 mm or less, the injection pressure transmission channels are sufficiently connected. Here, the resin flow end portion is a portion farthest from the gate of the molded product, and is a portion to which the injection pressure is most difficult to be transmitted when there is no special injection pressure transmission channel.

In the synthetic resin injection-molded product of the present invention, (2) the injection pressure transmission channel is formed inside the thick portion.

The injection pressure transmitting channel being formed inside the thick portion described in the present invention means that most of the injection pressure transmitting material is inside the injection pressure transmitting channel portion inside the thick portion. The present invention also includes the case where some injection pressure transmitting material is shown inside the general portion. Particularly, a part of the injection pressure transmitting material easily enters inside the general portion near the gate, which is also included in the present invention.

In order to sufficiently transmit the injection pressure to the resin flow end, it is preferable that the injection pressure transmission channel reaches near the resin flow end, and the distance is 70% or more of the resin flow end. It is more preferable to reach it, and it is most preferable to reach the resin flow end. The vicinity of the resin flow end means a distance of 60% or more of the distance to the end.

The present invention also includes a case where the injection pressure transmission channel does not reach near the resin flow end. That is,
The injection pressure transmission channel is intended to suppress the occurrence of sink marks on the thick ribs and thick bosses in addition to the injection pressure transmission.When the thick ribs and thick bosses are near the gate, or even to the resin flow end. When the distance is about half of the distance, the injection pressure transmission channel should reach the vicinity thereof.

The injection pressure transmitting material can be put inside the desired position by forming the molded product into a shape in which channels are formed in advance. That is, the low molecular weight polymer that is the injection transmission material of the present invention has the property of selectively advancing through the thick wall portion of the molded product, and the thick wall passage that extends from the gate to the resin flow end portion in advance in the molded product. The object of the present invention can be achieved by attaching.

In the synthetic resin injection-molded article of the present invention,
(3) The injection pressure transmitting channel is filled with a foamed injection pressure transmitting material, and (4) the injection pressure transmitting material is made of a foamable low molecular weight polymer.

The injection pressure transmitting material in the present invention is an expandable low molecular weight polymer which is a low molecular weight polymer containing a foaming agent. Since the injection pressure transmission channel is formed in the thick part of the molded product, a dent generally called a sink caused by cooling shrinkage is likely to occur on the surface of the molded product in that part. In order to prevent the occurrence of sink marks, the injection pressure transmitting material is made of a foamable low molecular weight polymer to which a foaming agent is added. As the foaming agent, both a physical foaming agent and a chemical foaming agent generally used for injection molding can be used. For example, pentane, hexane,
Examples include propane, carbon dioxide gas, azodicarboxylic acid amide, dinitrosopentamethylenetetramine, sodium bicarbonate and the like. The amount of the foaming agent added is preferably 0.1% by weight to 5% by weight. By containing a foaming agent, the foamed gas in the pressurized state compensates for the fact that the injection molded synthetic resin cools and shrinks in volume, causing the pressure in the mold to drop rapidly. Work. That is, the foaming agent-containing low molecular weight polymer that has entered the thick portion foams to compensate for the volume shrinkage of the synthetic resin and the low molecular weight polymer. The degree of foaming varies depending on the shape of the molded product, and is generally about 1% by volume to 50% by volume of the volume of the low molecular weight polymer, and includes minutely foamed ones.

In the synthetic resin injection-molded article of the present invention,
(5) The amount of injection pressure transmitting material is 1/10 or less of the synthetic resin amount (capacity ratio). The injection pressure transmitting material functions as an injection pressure transmitting material in a low-viscosity fluid state at the time of injection, and it is preferable that the injection pressure transmitting material be as small as possible within a range that does not deteriorate the performance such as mechanical strength of the molded product, and the volume ratio is 1 / 200 ~
1/10 is preferable, and more preferably 1/100 to 1 /
It is 15 or less.

In the synthetic resin molded product of the present invention, (6)
The viscosity of the low molecular weight polymer at the time of injection is 1/50 or less of the viscosity of the synthetic resin at the time of injection, and 0.5 poises or more.

Viscosity generally depends on shear rate. The viscosity in the present invention is the viscosity at the time of injection. Specifically, it is the viscosity when a low molecular weight polymer or synthetic resin is ejected from a nozzle. Therefore, although the temperature is equal to the temperature of the nozzle, the shear rate is often uncertain, so the shear rate is about 1000 at the general injection molding temperature when the fluid flows in the mold.
The viscosity value measured at (1 / sec) is used. Specifically, it can be measured directly or indirectly using a capyrograph (manufactured by Toyo Seiki Seisakusho) or the like.

The viscosity of the low molecular weight polymer is 1/5 of that of the synthetic resin.
When it exceeds 0, the effect of injection pressure transmission becomes low, and the injection pressure transmission channel forming property deteriorates. In order to obtain a high injection pressure transmission effect, it is preferably 1/100 or less. or,
If the viscosity is less than 0.5 poise, there will be a problem in safety during injection molding, and it will be difficult to give the necessary Vicat softening temperature value to the low molecular weight polymer. It is preferably 1 poise or more.

The viscosity of the polymer increases with the degree of polymerization,
The relationship between the viscosity and the degree of polymerization varies depending on the type of polymer,
It is expressed by the following two equations with the molecular weight called the critical molecular weight as the boundary.

When the molecular weight is below the critical molecular weight, it is represented by the following formula.

Log η = aLog Mw + K (T) 1 <a <1.8 K (T): constant determined by substance and temperature Mw: weight average molecular weight η: viscosity

However, when the molecular weight of the polymer exceeds a certain molecular weight, a phenomenon in which the viscosity η rapidly increases in proportion to the 3.4th power of the molecular weight Mw is observed, which is expressed by the following equation. It is famous as “Flory-Fox 3.4 power law” Log η = 3.4 Log Mw + K (T). It is explained that when the molecular weight is higher than the critical molecular weight, long molecules are entangled with each other, and when one molecule moves, other molecules are also dragged and move together, so that the viscosity suddenly increases. The critical molecular weight is approximately 10,000 to 40,000 in terms of weight average molecular weight, although there is some difference depending on the type of molecule.

Generally, a polymer which greatly exceeds the critical molecular weight is used for synthetic resins, synthetic fibers and the like, and a polymer near the critical molecular weight or smaller than the critical molecular weight is not generally used as the synthetic resin. The physical properties and chemical properties of the synthetic resin appear only when the molecules have a high molecular weight that greatly exceeds the critical molecular weight and the molecules are sufficiently entangled with each other.

The low molecular weight polymer of the present invention preferably has a molecular weight around the critical molecular weight, and a low molecular weight polymer which greatly exceeds or greatly falls below the critical molecular weight is not preferred.

When the synthetic resin is a difficult-to-process resin, or has a very high molecular weight and a high viscosity, the low molecular weight polymer is effective even if the viscosity is 100 poise or more, and general synthetic resins are also low molecular weight polymers. In some cases, a polymer having a molecular weight exceeding the critical molecular weight is also used in the present invention as a low molecular weight polymer because it has a relatively small molecular weight as compared with a synthetic resin.

Generally, when the fluid is a Newtonian fluid, the pressure loss of the fluid flowing between the parallel plates is expressed by the following equation. That is, the pressure loss is proportional to the viscosity.

ΔP = β · l ηQ / H ² ΔP: Pressure loss η: Viscosity Q: Flow rate H: Distance between parallel plates β: Constant l: Flow distance

At the time of injection, if the injection pressure transmission channel filled with the low molecular weight polymer having a viscosity of 1/50 or less of the viscosity of the synthetic resin reaches near the resin flow end, the injection pressure loss is the injection of the synthetic resin. 1/50 or less of pressure loss,
The injection pressure will be well transferred to the resin flow end. As a result, the injection pressure and mold clamping force of the injection molding machine can be reduced. Further, the pressure near the gate and near the end of the molded product acts in a uniform direction, the warp of the molded product is reduced, and the dimensional accuracy of the molded product is improved.

When a gas body is used as the injection pressure transmitting material,
Since the viscosity of the gas body is about 1/10 ⁶ of synthetic resin,
The pressure loss ΔP becomes 1/10 ⁶ of the injection pressure loss of the synthetic resin (the method using a gas body as the injection pressure transmitting material is gas assist injection molding). It is not necessary to reduce the pressure loss ΔP so much, and if it is set to 1/50 or less, the injection pressure can be effectively transmitted to the resin flow end in good condition.
When it is set to 1/100 or less, or 1/1000 or less, the pressure loss ΔP does not substantially affect the transmission of injection stress.

A molding method generally called sandwich injection molding, that is, a molding method of injecting a first synthetic resin into a mold cavity and then a second synthetic resin to fill the mold cavity is well known. Although it is a molding method, it is a completely new concept to use a low molecular weight polymer in place of the second synthetic resin to act as a gas body for gas-assisted injection molding. That is, 100 of a gas body that is 0.0001 poise
It is a surprising finding that a low molecular weight polymer having a viscosity close to 00 times can selectively advance through the thick wall portion of a molded article like a gas body and form an injection pressure transmission channel. That is,
Until now, it has been considered that only the gas body can form the injection pressure transmission channel.

In the synthetic resin injection-molded article of the present invention,
(7) Low molecular weight polymer (viscosity at 120 ° C.) /
The (viscosity at 220 ° C.) ratio is 100 or more.

It is preferable that the low molecular weight polymer has a small viscosity in the molding temperature range (200 ° C. to 280 ° C.) of a general synthetic resin and rapidly increases in viscosity when cooled. The low molecular weight polymer used in the present invention has a (viscosity at 120 ° C.)
/ (Viscosity at 220 ° C.) ratio is 100 or more, preferably 500 to 20000.

This is quite the opposite of USP 4140672, which indicates a molding method using mucus, that "a mucus whose viscosity does not change rapidly with temperature is preferable". That is, in USP 4140672, since the mucus is released outside the mold after molding, the mucus that does not change rapidly with temperature is more likely to be released, and the non-plastic fluid generally used in gas-assisted injection molding is most preferable.

A soft polymer such as atactic polypropylene, which has a relatively large molecular weight but is non-crystalline or low in crystallinity and has many side chains, has a small viscosity change with temperature. In contrast, a low molecular weight linear polymer having a relatively high crystallization temperature rapidly increases in viscosity when cooled. The former polymer is preferred for USP 4140672 and the latter polymer is preferred for the present invention.
A low molecular weight polymer whose viscosity changes little with temperature generally has a low Vicat softening temperature, and when a molded product having the polymer in the inner core of a thick portion is molded, the cooling time required in the mold becomes long and the productivity decreases. Then there is a problem.

The synthetic resin and the low molecular weight polymer are preferably compatible with each other when melted. This is important when considering recycling of molded products, and also when reusing sprues, runners, etc. generated during molding.
It is preferable that the synthetic resin and the low molecular weight polymer are polymers of the same system but different molecular weights.

FIG. 1 shows the viscosity versus temperature of some polymers. In FIG. 1, the viscosity is 1000 at a shear rate.
It is a value at the time of (1 / second). Details of some of the polymers of FIG. 1 are shown in Table 1. PS SB150, PS of FIG.
Like ST120, HD-PE 800P, PP 550P, the ratio of (viscosity at 120 ° C) / (viscosity at 220 ° C) is 100 or more, preferably 500 to 20,000.
In the present invention, low molecular weight polymers which rapidly increase in viscosity when the temperature is lowered are used.

[0053]

[Table 1]

In the synthetic resin injection-molded article of the present invention, the low molecular weight polymer (8) has a Vicat softening temperature of 60 ° C. or higher.

In injection molding, a synthetic resin that has been plasticized by heating is injected into a mold cavity, cooled and solidified and taken out of the mold to obtain a molded product. The time for cooling and solidification in the mold is the largest in the molding cycle time. Influence. The lower the solidification temperature of the synthetic resin or the low molecular weight polymer, the longer the required cooling time in the mold. Therefore, the low-molecular weight polymer is a low-viscosity fluid having a viscosity of 1/50 or less of the synthetic resin at the time of molding, but the solidification temperature is preferably close to the solidification temperature of the synthetic resin.

The solidification temperature is the temperature at which it is solidified to the extent that it can be taken out of the mold, and in the present invention, it is indicated by the Vicat softening temperature. The Vicat softening temperature is measured by the method described in ASTM-D1525.

In the present invention, the low molecular weight polymer has a Vicat softening temperature of 60 ° C. or higher, preferably 70 ° C. or higher, more preferably 75 ° C. or higher. Further, the upper limit of the Vicat softening temperature of the low molecular weight polymer is not preferable because the low molecular weight polymer solidifies significantly faster than the synthetic resin during molding,
Vicat softening temperature of synthetic resin + 10 ° C. is preferable.

To obtain a Vicat softening point of 60 ° C. or higher, it cannot be obtained if the molecular weight of the low molecular weight polymer is too small, and even if the molecular weight is increased, a Vicat softening point of 60 ° C. or higher cannot be obtained. Polymers of composition cannot be used.

Unlike the gas-assisted injection molding method, in which the fluid injected into the molded article (the fluid is a gas body in gas-assisted injection molding) is discharged to form a molded article, the present invention is different. Most of the fluid injected into the molded product, that is, the low molecular weight polymer, remains inside the molded product. Therefore, in the present invention, it is economically very important that the solidification temperature of the fluid is high. On the other hand, when the fluid is discharged out of the mold, the solidification temperature of the fluid is preferably low. Some known literature on gas-assisted injection molding (eg USP 4,
824, 732) shows a non-plastic fluid as the fluid, and the Vicat softening point described in the present invention is 60 ° C.
The above fluids are not shown.

The molded product of the present invention will be described with reference to FIGS.

FIG. 2 shows the molded product of the present invention. Figure 2
In (1), in the molded product 2 of the present invention that is molded by being injected from the gate 1, the injection pressure transmission channel 3 reaching from the gate 1 to the vicinity of the resin flow end 4 is contained in the synthetic resin. Is provided as. The cross section AA ′ of FIG. 2 (1) is shown in FIG. 2 (2). The injection pressure transmission channel 3 is formed inside the thick portion 5 of the molded product 2.

FIGS. 3 (1) and 3 (2) similarly show the molded product 6 of the present invention. In FIG. 3 (1), the molded product 6 is provided with a rib 9 from the gate 7 toward the vicinity of the resin flow end portion 8. At the root of the rib 9, the injection pressure transmitting material filled with the injection pressure transmitting material is injected. Channel 10 has entered as a core. A cross section taken along the line BB ′ of the molded product of FIG. 3 (1) is shown in FIG. 3 (2). 2 (1), (2), and FIG.
Although the case where there is one gate has been described in (1) and (2), the same applies to a multipoint gate.

FIGS. 4 (1) and 4 (2) are sectional views of the thick portion and the general portion of the molded product of the present invention. FIG. 4 (1) shows a molded product having a rib 12 in a general part 11 of the molded product. A thick wall part is provided in a root part 13 of the rib, and an injection pressure transmitting material is flowed therein. FIG. 4 (2) shows a case where a thick portion 16 is specially provided in the molded product to prevent warpage and reduce the mold clamping force.
Reference numerals 14 and 15 are virtual circle diameters in the cross section of the thick portion and the general portion of the molded product, respectively.

FIGS. 5 (1) and 5 (2) are cross sections of a conventional injection-molded product, showing the relationship between the thickness 11 of the general portion and the thickness of the rib 12. 5 (1) and 5 (2) are both the general part 11 of the molded product.
A rib 12 and a boss 17 are attached to the. In FIG. 5 (1), the thickness of the rib 12 is smaller than that of the general portion 11 of the molded product, and a small boss is provided to prevent the occurrence of sink marks. Figure 5
(2) shows that the general portion 11 of the molded product is thin and the thick rib 1
2 is a molded product having a large boss 17, and a sink mark 18 is generated on the surface in this shape.

FIG. 6 (1) shows a molded product formed by the molding method shown in the present invention using the mold having the shape shown in FIG. 5 (2). The injection pressure transmitting channel 19 is formed inside, and the use of the injection pressure transmitting material of the present invention containing the foaming agent can prevent the occurrence of sink marks. In the molded product of FIG. 6 (1), in order to reduce the weight of the molded product, the surface of the molded product is made thin, and the portion requiring strength is reinforced with thick ribs. FIG. 6 (2) is a perspective view of a molded product similar to FIG. 6 (1).

The injection pressure transmission channel described in the present invention is shown in FIGS. 2 (1), (2), 3 (1), (2), and FIG.
As shown in (1) and (2), this is a path that leads from the gate to the resin flow direction through almost the center of the thick portion of the molded product.

The present invention also provides an injection molding apparatus capable of favorably molding the synthetic resin molded product described above. That is, the injection molding apparatus is characterized in that a main injection cylinder for a synthetic resin and a sub injection cylinder for a low molecular weight polymer having a capacity of ⅕ or less of the main injection cylinder are connected to the same nozzle. The capacity of the sub-injection cylinder is preferably 1/8 to 1/15 of the capacity of the main injection cylinder.

FIG. 8 shows only the characteristic parts of the molding machine of the present invention. As shown in FIG. 8, the present molding apparatus comprises a main injection cylinder 24 for injecting a synthetic resin and a main injection cylinder 25 for injecting a low molecular weight polymer. It is connected to the nozzle 26. The synthetic resin can be injected from the main injection cylinder 24, and then the low-molecular weight polymer can be injected from the auxiliary injection cylinder 25 to fill the mold cavity to form the molded product of the present invention.

If necessary, the low molecular weight polymer is injected at the same time as the synthetic resin, or a small amount of the synthetic resin is injected after the low molecular weight polymer is injected.

The molding apparatus of the present invention can be manufactured by installing the sub-injection cylinder 25 next to the main injection cylinder 24, which is the injection cylinder of a general injection molding machine, and manufacturing and connecting the special nozzle 26. Sub injection cylinder 2
5 may be an in-line screw type or a plunger type. Since the low-molecular weight polymer injected from the sub-injection cylinder 25 has a low viscosity and contains a foaming agent, a nozzle having an opening / closing valve such as a needle opening / closing valve 27 at the tip of the nozzle is preferable.

As a typical molding method for molding the molded article of the present invention, a method of first injecting an amount of synthetic resin insufficient to fill the mold cavity and then injecting a low molecular weight polymer to fill the mold cavity is used. Can be mentioned.

At this time, it is necessary that the amount of the low molecular weight polymer is 1/10 or less of the amount of the synthetic resin and the mold cavity shape (molded product shape) is formed so that the injection pressure transmission channel described in the present invention can be formed. . The low-viscosity fluid has the property of selectively flowing through the thick part of the molded product, and the molded product of the present invention can be obtained by thickening the part where the injection pressure transmission channel is desired to be formed. Since the low-viscosity fluid easily flows at the roots of the thick ribs and serves as an injection pressure transmission channel, it is most preferable to form the molded product in which the thick ribs are connected from the gate. The injection amount of low molecular weight polymer is approximately equal to the amount required to form the injection pressure transmission channel.

Further, a synthetic resin in an amount substantially filling the mold cavity was injected, and then a low molecular weight polymer was continuously pressed in, and the synthetic resin was cooled and shrunk in the mold cavity to produce a volume of the low molecular weight polymer in a thick portion. A method of press-fitting inside to form an injection pressure transmission channel can also be used favorably.

A chemical foaming agent is blended with the low molecular weight polymer which is the injection pressure transmission channel, and this is added to the auxiliary injection cylinder 2
It can be used favorably by heat-plasticizing at 5 and then injecting the synthetic resin. At this time, it is preferable that the low molecular weight polymer is heated and plasticized in the sub-injection cylinder 25 at a temperature lower than the decomposition temperature of the chemical foaming agent, and is injected while being foamed in the vicinity of the nozzle 26 and / or in the mold at the decomposition temperature or higher. . The low-molecular weight polymer has a smaller viscosity when heated and plasticized than a synthetic resin, so that the foaming gas is less likely to move forward.
Therefore, the most preferable method is to decompose the chemical foaming agent after reaching the vicinity of the nozzle 26. A method of injecting a synthetic resin and then a low molecular weight polymer, or a method of injecting a synthetic resin, simultaneously injecting some synthetic resin and a low molecular weight polymer, and then injecting a low molecular weight polymer, etc. Can be used accordingly.

[0075]

【Example】

(Example 1) A mold cavity having a shape of the molded product 21 shown in FIGS. 7 (1) and 7 (2), having a size of 380 mm × 70 mm × 3 mm and having ribs of 5 × 5 mm in the longitudinal direction was formed. The mold used was used. A synthetic resin was injected from the gate 20 at the end in the longitudinal direction in an amount that substantially fills the mold cavity, and then a low molecular weight polymer was injected to fill the mold cavity and injection molding was performed.

High-impact polystyrene (“HIPS # 492” manufactured by Asahi Kasei) as a synthetic resin, and 0.5 weight of a chemical blowing agent (“Celmic CE” azodicarbonamide manufactured by Sankyo Kasei: decomposition temperature 208 ° C.) as a low molecular weight polymer. %
And 2.5% by weight talc of low molecular weight polystyrene (“HYMER ST-120” manufactured by Sanyo Chemical Co., Ltd.) are used, and the main injection cylinder 24 and the nozzle 26 are sub-injected to 230 ° C. by the injection molding apparatus shown in FIG. 190 cylinder 25
Molded by setting the temperature to ℃.

The synthetic resin used has a Vicat softening temperature of 1
The low molecular weight polymer has a Vicat softening temperature of 73 ° C., and the low molecular weight polymer has a viscosity of (120 ° C.) / (220 ° C.).
The viscosity) ratio was 700. Temperature at injection 2
The viscosity of the synthetic resin at 30 ° C. was 2300 poises, and the viscosity of the low molecular weight polymer was 6.6 poises. (Diameter of imaginary circle of cross section of molded product in thick portion) / (Diameter of imaginary circle of cross section of molded product in general part) was 1.9.

Injection molding was carried out by variously changing the injection amount ratio of the synthetic resin and the low molecular weight polymer into the mold cavity, and the (low molecular weight polymer) / (synthetic resin) ratio was 3/97 (volume ratio).
At this time, the injection pressure transmission channel is formed in the thick wall portion and the molded product reaching the vicinity of the resin flow end is molded, and as a result,
A molded article of the present invention having a good surface without sink marks, good releasability, and no cracking or warping was obtained. The required minimum mold clamping force of the injection molding machine, which enables good molding, was measured.
Molding was possible with a low mold clamping force of ton. On the other hand, when injection molding was performed using only synthetic resin, a mold clamping force of 72 tons was required.

(Examples 2 and 3) Molding was carried out in the same manner as in Example 1 using the synthetic resins of Examples 2 and 3 in Table 2 and the low molecular weight polymer. Low molecular weight polymer (viscosity at 120 ° C)
/ (Viscosity at 220 ° C) ratio is 2 for PP 550P
It was 000.

All of Examples 2 and 3 could be molded in the same manner as in Example 1, and a good molded article of the present invention in which the injection pressure transmission channel made of a low molecular weight polymer was formed in the thick portion was obtained. The required mold clamping force could be reduced by 40% as compared with the case where only the resin was used.

[0081]

[Table 2]

(Comparative Examples 1 and 2) Using the mold used in Example 1, the first polymer shown in Table 3 and then the second polymer shown in Table 3 were injected into the cavity in that order to obtain a mold cavity. Satisfied. That is, in order to compare with the low molecular weight polymer of the present invention shown in Examples, the case where a high molecular weight polymer was used as the second polymer and the case where polyethylene glycol having a low softening temperature was used was shown. The weight ratio of the second polymer and the first polymer injected into the mold cavity was 3/97 (volume ratio).

In Comparative Example 1, the second polymer was filled only in the vicinity of the gate, and the channel having the second polymer in the thick portion was not formed in the molded product. Therefore, a sink mark was generated at the base of the rib, and the required mold clamping force could not be reduced.

In the case of Comparative Example 2, although the injection pressure transmitting channel was formed by the second polymer, sink marks were generated at the roots of the ribs, and it took a long time for the second polymer to solidify in the mold. (2 minutes or more) was required, and economical molding could not be performed. That is, PEG6000 (viscosity at 120 ° C)
/ (Viscosity at 220 ° C.) was 1.4, and the Vicat softening temperature was also 50 ° C. or less, and it could not be used in the present invention.

[0085]

[Table 3]

[0086]

According to the present invention, injection molding can be performed with a low mold clamping force, and the dimensional accuracy of a molded product can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between temperature and viscosity of synthetic resins and low molecular weight polymers.

FIG. 2 is a diagram showing an example of a molded product of the present invention.

FIG. 3 is a view showing another example of the molded product of the present invention.

FIG. 4 is a view showing a cross section of a molded product of the present invention, showing a cross section of the molded product of a thick portion and a general portion.

FIG. 5 is a diagram showing an example of a conventional molded product.

FIG. 6 is a diagram showing an example of a molded product of the present invention.

FIG. 7 is a diagram showing an example of a molded product of the present invention.

FIG. 8 is a cross-sectional view of an injection molding device of the present invention.

[Explanation of symbols]

 1 Gate 2 Molded Product 3 Injection Pressure Transmission Channel 4 Resin Flow End 5 Thick Part 6 Molded Product 7 Gate 8 Resin Flow End 9 Rib 10 Injection Pressure Transmission Channel 11 Molded Product General Part 12 Rib 13 Base of Rib 14 Thickness Diameter of imaginary circle of cross section of molded product of meat part 15 Diameter of imaginary circle of cross section of molded product of general part 16 Thick wall part 17 Boss 18 Mark 19 Injection pressure transmission channel 20 Gate 21 Molded product 22 Injection pressure transmission channel 23 Thick part 24 Main injection cylinder 25 Sub injection cylinder 26 Nozzle 27 Needle valve

Claims (8)

[Claims] 1. A synthetic resin injection molded product in which a foamed injection pressure transmitting material remains in an injection pressure transmitting channel in a molded product, and (1) has a thick portion substantially connected to a gate,
(2) An injection pressure transmission channel is formed inside the thick portion, (3) the injection pressure transmission channel is filled with a foamed injection pressure transmission material, and (4) the injection pressure transmission material has a low foaming property. It is composed of a molecular weight polymer, and (5) the amount of injection pressure transmitting material is 1/10 or less of the amount of synthetic resin (volume ratio),
(6) The viscosity of the low molecular weight polymer at the time of injection is 1/50 or less of the viscosity of the synthetic resin at the time of injection and 0.5 poises or more,
(7) Low molecular weight polymer (viscosity at 120 ° C.) /
(Viscosity at 220 ° C.) ratio is 100 or more,
(8) A synthetic resin injection-molded article characterized in that the low molecular weight polymer has a Vicat softening temperature of 60 ° C. or higher. 2. The thickness of the thick portion is 1.5 to 3.5 in terms of (diameter of virtual circle of cross section of molded product of thick portion) / (diameter of virtual circle of cross section of molded product of general portion). The synthetic resin injection-molded article according to claim 1. 3. The synthetic resin injection-molded article according to claim 1, wherein the amount of the injection pressure transmitting material is 1/200 to 1/10 of the synthetic resin amount in terms of volume ratio. 4. The synthetic resin injection-molded article according to claim 1, wherein the injection pressure transmission channel is up to 60% or more of the resin flow end portion. 5. The synthetic resin injection-molded article according to claim 1, wherein the viscosity of the low molecular weight polymer at the time of injection is 1/100 or less and 1 poise or more of the viscosity of the synthetic resin at the time of injection. 6. The (viscosity at 120 ° C.) / (Viscosity at 220 ° C.) ratio of the low molecular weight polymer is 500 to 2000.
The synthetic resin injection-molded article according to claim 1, which has a value of 0. 7. The Vicat softening temperature of the low molecular weight polymer is 7.
The temperature is 0 ° C to the Vicat temperature of the synthetic resin + 10 ° C.
The synthetic resin injection-molded product described. 8. An injection pressure transmitting material (low molecular weight polymer) satisfying the conditions (4) to (8), wherein a synthetic resin is thermoplasticized in a main injection cylinder and a chemical foaming agent is contained in a sub injection cylinder. Thermoplasticization is performed at a temperature below the decomposition temperature of the chemical foaming agent, first, the synthetic resin is injected into the mold cavity, and then or at the same time, the low-molecular weight polymer is heated to above the foaming agent decomposition temperature near the nozzle or / and in the mold. Molding method for injection molding.