JPS5838307B2 - How to proceed - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of filling a mold with a molten resin material in the production of rigid polyvinyl chloride pipe joints, and more specifically, the present invention relates to a method for filling a mold with a molten resin material in the production of rigid polyvinyl chloride pipe fittings, and more particularly, the present invention relates to a method for filling a mold with a molten resin material in the production of rigid polyvinyl chloride pipe fittings, and in particular, the present invention relates to a method for filling a mold with a molten resin material in the production of rigid polyvinyl chloride pipe fittings. In order to manufacture a hard polyvinyl chloride pipe joint using the injection molding method, the pipe joint is manufactured by safely filling a mold with a uniformly melted and kneaded polyvinyl chloride material having an average degree of polymerization of 1000 or more. It's about how to do it.

The injection molding method is a method for molding complex-shaped products with high dimensional accuracy and high efficiency, and has been applied to a wide range of applications.

However, due to the comprehensive influence of residual orientation during molding, uneven cooling rate, polymer decomposition, residual strain during mold release, etc., the impact resistance and fatigue fracture resistance of molded products are surprisingly low. , we will look at the important bottlenecks in expanding the use of the ejaculation precept method.

This is thought to be due to the uniqueness of the injection molding method, and there are many points that cannot be discussed in the same way as the extrusion molding method.

In other words, in the extrusion molding method, the resin material put into the cylinder is heated from outside the cylinder and kneaded by the screw, reaching the tip of the screw while being melted and kneaded, passing through the mold as it is and being released into the atmosphere. Since the molten and kneaded resin is discharged into the cylinder, it does not stay at the tip of the cylinder and is continuously discharged from the mold with almost no resistance (substantially only due to frictional resistance with the channel wall). go.

Therefore, in the case of extrusion molding, the resistance inside the cylinder is low, temperature control is easy, and it is difficult to thermally decompose, but in the case of injection molding, it is necessary to temporarily store the molten resin material at the tip of the cylinder. Therefore, the screw itself must gradually move back inside the cylinder while transferring the molten and kneaded resin to the storage section of the nozzle.

Therefore, the subsequent melt-kneaded resin receives a pressing force from the screw and at the same time receives a large back pressure from the tip of the cylinder, and the melt-kneaded resin receives not only frictional heat from the channel wall but also contact frictional heat between the resins (i.e., internal The latter is particularly important, causing the temperature of the molten resin to rise rapidly.
Controlling temperature becomes difficult.

Moreover, the flow rate of the molten resin into the mold in injection molding is not as high as that in extrusion molding, so the fluidity of the molten resin needs to be considerably higher than in extrusion molding, which means that it accumulates at the tip of the cylinder. The temperature inside must also be set quite high.

However, as described below, the temperature must be kept below the pyrolysis initiation temperature, and the need for temperature control has become even greater.Under the circumstances described above, the operational management of injection molding is even more difficult. It has become a thing.

The above are the problems related to melt-kneading, but the stored resin melt-kneaded in this way must be flowed into the mold all at once in the next step.

This is the filling process into the mold, but since the nozzle part and the mold cavity part are connected by passages called spools, runners, gates, etc., the molten resin injected from the nozzle part is filled into the cavity through these passages.

However, it is necessary to prevent the fluidity from being adversely affected even if the temperature of the molten resin decreases while passing through these passages, and it is necessary to melt the melted and kneaded resin more uniformly. In order to reduce the volume ratio, the diameter is generally small.

Therefore, there is a risk that excessive frictional resistance is applied to the flow of the molten resin, and the temperature of the passing resin is increased too much, leading to decomposition.

As outlined above, in the case of injection molding, there are problems unique to each stage of melting and kneading the material and injecting it into the mold. It is not possible to think of them as inseparable.

Furthermore, in actual injection molding operations, the melt-kneading operation and the injection operation into the mold are clearly separated, and the problems that exist in each stage must be solved independently. This is considered to be extremely significant when considering the actual situation in this field.

The present invention is particularly aimed at solving problems at the stage of filling a mold.

The general issues with injection molding are as explained above, but especially when considering the case where hard polyvinyl chloride is used as a material, the temperature at which the thermal decomposition of the resin starts is around 200℃ (however, the degree of polymerization increases ), but the plasticizing temperature exceeds 180°C,
The difference is extremely small.

Moreover, if the plastic flow temperature is to be high enough to obtain fluidity suitable for high-speed filling into molds, a high temperature close to 200°C is required, so it is necessary to control the temperature extremely carefully. There is a risk that thermal decomposition may occur while it remains at the tip of the screw.

For this reason, stabilizers with excellent stabilizing ability are added,
Even with such stabilizers, it is difficult to suppress thermal decomposition, and polyvinyl chloride melted at such high temperatures has the disadvantage that it does not have viscoelasticity and does not exhibit thixotropic fluidity.

Furthermore, polyvinyl chloride has a characteristic of low thermal conductivity, making it difficult to uniformly heat the same product and making it impossible to avoid variations in strength.

For this reason, in order to lower the melting temperature of hard polyvinyl chloride, that is, the molding temperature, and to give it chicken-tropic fluidity,
By using low polymerization degree polymer (average polymerization degree 750-800) or low polymerization degree copolymer (average polymerization degree 600-800, blending 5-10% vinyl acetate), or by adding 2-3% plasticizer, it can be made semi-rigid. Sometimes it is finished into a product.

However, the latter method does not provide an essential solution for hard polyvinyl chloride products, and is in no way applicable to water supply fittings, for example, where the softening temperature based on penetration strength is strictly regulated.

Therefore, we used a low polymerization degree straight resin with an average degree of polymerization (hereinafter also referred to as P) of 800 or less to lower the flow temperature and melt viscosity, and to increase the flow resistance in the nozzle, the hysogates of the mold, etc., and to prevent thermal decomposition. By devising ways to prevent this from occurring, and by applying extremely high injection pressure to generate as much frictional heat and shear mixing effect as possible, they were only able to barely succeed in producing molded products with relatively small dimensions.

However, impact resistance and fatigue fracture resistance have not been improved, and efforts have been made to improve stabilizers and reinforcing agents, gate balance, and wall thickness and corner shape. There is.

Although some improvement has been achieved through such efforts, it is far from a fundamental solution to the inferiority of strength compared to extruded products.

Such inferiority has become a particularly noticeable problem in the field where extrusion molded products are commonly used, particularly in the field of hard polyvinyl chloride joints for water pipes.

In other words, hard polyvinyl chloride pipes are gradually being used in a wide range of fields as extrusion molding technology develops, and they are also being used in the water supply field to replace conventional cast iron pipes. Since vinyl injection molded products have poor mechanical strength, damage is gradually becoming apparent after long-term use.

As a result, the reliability of injection-molded joints made of hard polyvinyl chloride is reduced, and it is conceivable that they will be discouraged from being used in joint fields other than water pipe joints.

The present invention was made with attention to these circumstances, and the ultimate purpose is to manufacture an injection molded pipe fitting made of hard polyvinyl chloride that has a strength comparable to that of extruded pipe fittings. In order to achieve this, we have conducted repeated research from various perspectives, including the selection and formulation of molding materials, selection of molding conditions, mold design, and devising the shape and dimensions of joints, but we have not found the essential solution. I couldn't find it.

However, in the course of this research, I began to question the technical common sense in the field that says, ``When obtaining injection molded joints made of rigid polyvinyl chloride, use materials with P of 800 or less.'' P of the extruded tube is P of the extruded tube (
I think that p850 or higher is an important factor, such as 900, 950, 1000, 10501, 11001,
After repeated research on obtaining injection molded joints for ......, we found that even when these high polymerization degree resins are used, it is possible to create a state suitable for injection molding by devising melt-kneading conditions. They discovered that a melt-kneaded resin could be obtained and filed a separate patent application.

Furthermore, the present invention was completed by discovering that a safe filling operation can be accomplished by adjusting the conditions for filling the mold.

As long as P is 850 or more, it will give a joint with higher strength than the conventional joint with P of 800 or less, but it is especially significant when using P of 1000 or more, so the present invention The target audience is piooo and above.

These facts are extremely surprising and do not go beyond conventional technical common sense, but together they have led to the provision of a completely new injection molded joint using a specified molding material.

That is, the configuration of the present invention is such that, when manufacturing a hard polyvinyl chloride pipe fitting using a screw injection molding machine, a molten mixture of hard polyvinyl chloride resin material stored at the tip of the injection molding machine is put into an injection mold. In the filling method, a polyvinyl chloride resin material having an average degree of polymerization of 1000 or more is used, and when the screw movement speed until the melt-kneaded material reaches the cavity part at the beginning of implantation is set to 1, the melt-kneaded material is then melted and mixed. The screw movement speed when filling the cavity with material is set to 12 to 2.0.

There is a gist in the points.

In order to improve physical properties in a general injection molding method, it is desirable to fill the cavity at high speed by high-speed injection.

However, with a normal injection mechanism, the injection speed cannot be adjusted, so if you try to fill the cavity at high speed, the resin material will pass through at high speed from the screw tip, through the nozzle, a part of the runner, and the pin gate. do.

However, the nozzle, part of the runner, etc. have narrow flow paths, and if the fluid passes through these gaps at high speed, thermal decomposition due to frictional heat is likely to occur.
Hard polyvinyl chloride resin has a particularly strong tendency to stiffen.

Furthermore, in the case of polyvinyl chloride with a high P content, the above-mentioned danger is particularly strong because the difference between the plastic flow temperature and the thermal decomposition temperature is small.

However, on the other hand, it is desired to ensure plastic fluidity and further obtain optimal fluidity, and it is recommended to instantaneously slightly raise the temperature when passing through the pin gate.

In other words, there is a desire to raise the temperature to a certain extent by passing through the pin gate part at high speed, and a desire to avoid abnormal temperature rise due to friction with the pin gate wall, and it is necessary to satisfy two clearly contradictory demands. did not become.

Therefore, when the screw movement speed until the melted and kneaded material at the beginning of driving reaches the cavity part (that is, from the tip of the screw through the nozzle to the part of the runner and reaching the pin gate) is set as one, the material at the beginning of driving is If the screw moving speed is made faster when the resin is subsequently filled into the cavity (that is, while the resin is being filled into the cavity through the pin gate) (expressed as "increasing the flow velocity in the cavity part"), the resin at the beginning of implantation reaches the cavity without experiencing excessive frictional resistance between it and the pin gate, making it possible to fill the cavity at high speed.

In other words, the orientation due to low-speed flow is not frozen, and good results are obtained in thinning or eliminating the orientation layer, and it also significantly contributes to increasing fracture energy, reducing residual strain, and eliminating weld marks and jetting marks. There are some thick ones.

In order to perform such variable speed filling, it is preferable to use an injection molding machine with a variable speed mechanism.

Such an injection molding machine with a variable speed mechanism is configured so that the moving speed of a certain forming screw can be changed continuously or stepwise over the entire length of the measuring screw, and is usually is equipped with an injection speed scale of several steps, for example, five steps, so that the speed can be changed by adjusting a flow control valve etc. when the screw moves forward.

Therefore, for example, in the first stage of injection molding, the entire part of the runner up to the pin gate is filled with the resin material, and in this stage the screw advances at a speed on the intermediate scale.

When the filling of the material into a part of the runner is completed, the speed is changed to the high speed scale and the screw is advanced, so that the resin speed when the cavity is filled is higher than that when the runner is partially filled.

When the filling of the cavity is almost completed, the screw is advanced at intermediate to low speed scales in the third and fourth stages, and the molding is completed quietly while being pressed carefully.

If you use an injection molding machine that does not have such a speed change mechanism,
If the process leading to the nozzle, a part of the runner, and the pin gate is made high-speed, there is a high possibility that thermal decomposition will occur, and as a result, high-speed filling into the cavity will not be possible.

It is desirable to adjust the flow rate in the cavity to about 12 to 2.0 times the flow rate in a part of the runner.

If the flow velocity ratio exceeds 20, thermal decomposition may occur.

The resin material used in the present invention is a hard polyvinyl chloride resin material with P of 1000 or more, but if necessary, it is also possible to add an auxiliary agent to increase heat resistance, an auxiliary agent to increase impact resistance, etc. be.

If the mold is filled as described above, P>1
Pipe fittings with good physical properties can be manufactured by safely filling a molten material containing polyvinyl chloride with a polyvinyl chloride content of 000 or more, but there are no particular restrictions on the manufacturing procedure for the melt-kneaded resin used as the filling material. Various techniques are applied in addition to the law.

Therefore, in this specification, although there is no need to specifically explain it, the melt-kneading technique employed in the Examples described later will be explained.

When manufacturing thermoplastic resin moldings, shaping at high temperatures generally improves the viscosity state, and conversely, the cooling time becomes longer, so the orientation that occurs during flow is relaxed during cooling, and residual strain is reduced. It is widely known that this decreases the strength of the steel and improves the strength as a result.

However, as described above, if the set temperature of the heating cylinder is set high as described below, there is a risk of thermal decomposition, and this risk is particularly high in the case of hard polyvinyl chloride.

In order to resolve this bottleneck, the inventors of the present invention took into consideration the fact that before adjusting the temperature of a part of the heating cylinder, the L/D was made large and the rate of temperature rise, that is, the temperature rise gradient, was made gentler. As a result, it has been found that optimum conditions can be obtained for melt-kneading polyvinyl chloride of PIOOO or higher.

In other words, in the conventional one-screw injection molding machine where L/D is less than 20, the time to reach the plasticizing temperature is short;
It is difficult to uniformly heat hard polyvinyl chloride resin with low thermal conductivity, resulting in uneven distribution of high-temperature areas due to external heat input and low-temperature areas due to insufficient kneading, resulting in flash marks, weld marks, and jetting marks. , Silvers 1, molding defects such as leakage are observed.

If an attempt was made to sufficiently heat the low-temperature part in order to eliminate the defective phenomenon, an overheating phenomenon would be observed overall, making it difficult to suppress the secondary phenomenon of decomposition of the polymer.

Therefore, even if a resin with a p1000 or higher was used, no significant quality improvement could be expected, and continuous molding was close to the impractical performance.

However, when L/D is set to 25 or more, it is possible to raise the temperature to a temperature that provides thixotropic viscoelasticity without thermal decomposition while maintaining a gentle temperature increase gradient, and to perform sufficient kneading. At the point when the temperature is reached, almost completely uniform heating is performed as in the case where P is 800 or more.

Therefore, overheating is suppressed, and the optimum melting and kneading state can be adjusted to prevent thermal decomposition, and more favorable results can be obtained.

When L/D is 25 or more, when using a twin-screw injection molding machine, the total length of each screw divided by the screw diameter may be adjusted to be 25 or more.

Although all known screw set injection molding machines and improved machines thereof can be used as the screw set injection molding machine used in the present invention, the Benn 1 type injection molding machine is particularly preferred.

This is a polyvinyl chloride resin with P of 1. O O O
This is because when using the above materials, it is desirable to prevent air, moisture, and other volatile components accompanying the raw materials from evaporating and expanding and appearing in the injection molded product.

Next, the conditions for heat input from the heating cylinder will be explained.

It is impossible to raise the temperature in the metering zone and conflation zone of the heating cylinder to a high temperature using hard polyvinyl chloride resin material with a P800 or less, which has poor thermal stability. It was common practice to do so, and it was rare for the temperature to exceed 170°C.

However, the molding material with Pi 000 or more used in the present invention has a high thermal decomposition temperature, and it has become possible to melt it by heating to a relatively high temperature.

However, if the temperature is set too high, thermal decomposition may occur or cooling in the mold will take a long time, while if the temperature is set to the conventional level, a sufficient molten state cannot be obtained, causing problems before injection molding. It turns out.

After conducting various studies to find the optimal value for the temperature of the heating cylinder from this perspective, we found that simply adjusting the temperature of the heating cylinder uniformly was insufficient, and the temperature of the heating cylinder in the metering zone and combination zone was insufficient. The temperature is preferably 175 to 185°C, particularly preferably 178 to 182°C.
When the temperature was within the range of °C, it was possible to obtain a melt-kneaded state suitable for producing an injection molded joint having physical properties and appearance comparable to extruded molded pipes.

The reason why the temperature range was set this way is that a sufficient melting state cannot be obtained below 175°C, so 185°C
If the value exceeds 100, the cooling time in the mold cavity after being filled will be longer, so that the resin material for the next filling, which is waiting to be melted at the screw tip in preparation for the next injection, will melt during the waiting period. This is because it may undergo thermal decomposition.

The temperature of other parts of the heating cylinder was not particularly subject to any substantial restrictions.

Since the present invention is configured as described above, P is 1000
The molten mixture of hard polyvinyl chloride resin material as described above is safely filled into the mold, and the physical properties of the resulting joint are comparable to those of an extruded pipe.

That is, the tensile strength, elongation, pressure resistance, pulsating water pressure resistance, and impact resistance values have been improved, and the reliability when used as a water pipe joint, for example, has increased, and the resistance to fatigue fracture has become extremely high.

In addition, there are certain things that are extremely helpful in eliminating molding defects such as flash marks, weld marks, jetting marks, and silver streaks, which tend to appear more prominently as P increases.

Therefore, desired physical properties can be obtained without significantly increasing the thickness of the product, making it possible to apply it to a wide range of fields as an alternative to castings.

Examples of the present invention will be described below, but as a comparative example, P=8
In addition to showing data for P850, data for P850 is also shown for reference.

In addition, both the Examples and Comparative Examples are compared with those in which melting and kneading in an injection molding machine was followed by injection into a mold.

Example 1 When shaping elbow type pipe joints in order of diameter 75, P = 8
Using polyvinyl chloride resin materials of 00, P=850, and 1050, injection molding was performed according to the following conditions.

As an injection molding machine, in the case of P-800, an in-line screw 800 type or molding machine is used, and p=850 and 1
In the case of 050, an in-line screw 1250 molding machine was used.

In this example, the mold for four pipe joints was used.

The composite stabilizer in Table 1 consists of tribasic lead sulfate, dibasic lead stearate, barium stearate, white titanium, and carbon.

The test results of the molded product obtained are shown in Table 1.

As is clear from the results in Table 1, the pulsating water pressure time is longer than that of the conventional P
Approximately four times the durability was obtained compared to -800.

Furthermore, the tensile strength was significantly improved, and it was able to fully meet the requirements for pipe joints for waterworks.

It should be noted that even with the conventionally widely used one with P=850, no particular effect has been observed unless the injection speed ratio is changed.

Example 2 In the same manner as in Example 1, an elbow type pipe joint and a cheese type pipe joint were injection molded.

When various molding conditions were varied, as shown in Table 2, favorable results were obtained in all moldings in which the flow velocity in the cavity was increased.

Example 3 In the same manner as in Example 1, a socket-type pipe joint with a diameter of 100 was manufactured using a four-piece mold.

The molding conditions and molding results are shown in Table 3, and particularly remarkable effects were obtained in terms of pulsating water pressure durability and tensile strength.

Claims (1)

[Scope of Claims] 1. When manufacturing a hard polyvinyl chloride pipe joint using a screw injection molding machine, a molten mixture of hard polyvinyl chloride resin material stored at the tip of the injection molding machine is put into an injection molding mold. In the method of filling a polyvinyl chloride resin material with an average degree of polymerization of 1000 or more, the screw moving speed until the melt-kneaded material reaches the cavity at the beginning of pouring is set to 1, and then the melt-kneaded material is melt-kneaded. A method for filling an injection mold with a melt-kneaded material of a hard polyvinyl chloride resin material, characterized in that the screw movement speed when the material is filled into a cavity part is set to 1.2 to 2.0.