JPS5838306B2 - How to proceed - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of melt-kneading a molded resin material in a method for manufacturing a rigid polyvinyl chloride pipe joint, and more specifically, the present invention relates to a method of melt-kneading a molded resin material in a method for manufacturing a rigid polyvinyl chloride pipe fitting, and in particular, it relates to a method of melt-kneading a molded resin material in a method for manufacturing a rigid polyvinyl chloride pipe fitting, and in particular, it relates to a method of melt-kneading a molded resin material in a method for manufacturing a rigid polyvinyl chloride pipe joint, and in particular, it relates to a method of melt-kneading a molded resin material in a method for manufacturing a rigid polyvinyl chloride pipe joint. The present invention relates to a method for manufacturing vinyl chloride pipe joints by injection molding, using a polyvinyl chloride material having an average degree of polymerization of 1000 or more, and uniformly melting and kneading the material to a state suitable for injection molding.

Injection molding is a method for molding products with complex shapes with high dimensional accuracy and high efficiency, and is applied to a wide range of applications.

However, due to the overall 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. This constitutes an important bottleneck to expanding the application of injection molding methods.

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 (heat generation), and the latter's contribution is particularly large, 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. The temperature during storage must also be set quite high.

However, as described below, the temperature must be kept below the thermal decomposition starting temperature, and the need for temperature control has become even greater.Under the circumstances mentioned above, the operational management of injection moldings has become even more important. It has become difficult.

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, each stage of melting and kneading the material and filling the mold into the mold has its own problems, and as with the pressing or molding method, the melting and kneading of the material and the introduction into the mold are inseparable. You can't just think about it.

Furthermore, when looking at actual injection molding operations, the melt-kneading operation and the mold filling operation 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 the problem at the melt crosstalk stage.

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 However, the plasticizing temperature exceeds 180°C, and 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 no 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 thixotropic fluidity,
Semi-rigid polymers can be made by using low polymerization degree polymers (average polymerization degree 750-800) or low polymerization degree copolymers (average polymerization degree 600-SOO, containing 5-10% vinyl acetate), or by adding 2-3% plasticizer. 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 use a straight resin with a low polymerization degree (average degree of polymerization (hereinafter also referred to as P) SOO) to lower the flow temperature and melt viscosity, and to increase the flow resistance at the nozzle, pin gate 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 relatively small-sized products. .

However, impact resistance and fatigue fracture resistance have not been improved, and efforts have been made to improve stabilizers and reinforcing agents, improve gate balance, and improve 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. This inferiority has become a particularly noticeable problem in the field where extruded products are commonly used, particularly in the field of rigid polyvinyl chloride joints for water pipes.

In other words, hard polyvinyl chloride pipes are gradually being used in a wide range of fields with the development of extrusion forming technology, and are also being used in the water supply field to replace conventional cast iron pipes. Injection-molded products made of polyvinyl chloride have poor mechanical strength, so damage is gradually becoming apparent after long-term use.

For this reason, the reliability of injection molded joints made of hard polyvinyl chloride is reduced, and it is conceivable that use in joint fields other than water pipe joints may be discouraged.

The present invention was made with attention to the above circumstances, and the ultimate purpose is to manufacture an injection molded pipe joint made of hard polyvinyl chloride that has a strength comparable to that of an extrusion molded product. 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 improvements to the shape and dimensions of joints, but we have not yet found a fundamental solution. was not reached.

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 polyvinyl chloride with a number of 800 or less.'' P is the extruded pipe P (
I think that lower than P850 (normally 1000-1050) is an important factor, for example 9oO, 950, 1000, 1050, 1100, etc.
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 molten mixed wire resins that are suitable for injection molding if the melt-kneading conditions are devised. was found to be obtained.

As long as P is 850 or more, it will give a joint with higher strength than the conventional joint with F of 800 or less, but it is especially significant when using F of 1000 or more. The target is ↑1000 or more.

These facts are extremely surprising, and although they do not go beyond conventional technical common sense, they have led to the provision of a completely new injection molded joint made of high-profile materials.

That is, in the structure of the present invention, in the method of melting and kneading a hard polyvinyl chloride material when manufacturing a hard polyvinyl chloride pipe fitting using a single screw injection molding machine, the polyvinyl chloride resin material has an average polymerization of 1000 or more. A screw set injection molding machine with an L/D of 25 or more is used, and the temperature of the heating cylinder in the metering zone and combination zone of the injection molding machine is 175 to 175.
The gist is that the molding material is melted and kneaded at a temperature within the range of 185°C, and the melted and kneaded hard polyvinyl chloride material is stored at the tip of the cylinder.

As mentioned above, polyvinyl chloride with a high p value has a small difference between the thermal decomposition initiation temperature and the plastic flow temperature, and heating must be kept to the minimum necessary level.

In order to satisfy these conditions, it is necessary to suppress the amount of human heat from the heating cylinder as much as possible, and it is conventional wisdom that L/D should be made small for this purpose.
There is a common technical knowledge that if the L/D is made small, the kneading shear effect can be easily adjusted by adjusting the back pressure and the danger of thermal decomposition can be prevented. It had been.

However, even if L/D is reduced, the plastic flow temperature of polyvinyl chloride with a high P content, in other words, the final target temperature itself must be raised to some extent, so it is not possible to raise the temperature rapidly while passing through a short cylinder. Unavoidably, the difficulty of temperature control has become even more pronounced, with abnormal temperature rises caused by the internal heat generation mentioned above.

In particular, a high p value means that the polymerization degree is considerably higher than the average value, and because there is a considerable variation in the particle size of the raw material resin due to manufacturing circumstances, p = soo. It was found that the situation is completely different between the case where P≧1000 and the case where P≧1000.

Therefore, we dared to challenge the conventional technical common sense and tried using a screw with a high L/D, but by setting the L/D to 25 or more, the temperature rise rate, that is, the temperature rise gradient, could be made gentler. We have found that it is possible to substantially control the temperature of the heating cylinder in the metering zone and cone compression zone from 175 to 185.
It has been found that when the temperature is about ℃, polyvinyl chloride, which has a high rate of transport inside, becomes in an optimal plastic flow state due to the interaction of optimal external heat and optimal internal heat generation.

First, the use of a complete screw injection molding machine with L/D of 25 or more will be explained.

When manufacturing thermoplastic resin moldings, molding at high temperatures generally improves the viscosity, and conversely, the cooling time becomes longer, so the orientation that occurs during flow is relaxed during cooling, reducing residual strain. However, it is widely known that strength is improved 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 1,000 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;
Hard polyvinyl chloride resin with low thermal conductivity is difficult to heat uniformly, and high temperature areas due to external heat input and low temperature areas due to insufficient kneading are unevenly distributed, resulting in flash marks, weld marks, jetting marks, and silver marks. Poor precepts such as streaks are observed.

If an attempt was made to sufficiently heat the low-temperature section in order to eliminate the defective phenomenon, an overheating phenomenon would be observed as a whole, making it difficult to suppress the side phenomenon of polymer decomposition.

Therefore, even if a resin with p1000 or more was used, no significant quality improvement could be expected, and continuous molding was nearly impossible.

However, when L/D is set to 25 or more, it is possible to raise the temperature to a molding temperature that provides chicken-tropic viscoelasticity without thermal decomposition while maintaining a gradual temperature increase gradient, and to perform sufficient kneading, and when the temperature reaches the tip of the screw. In this case, almost completely uniform heating is performed, similar to those with F of 800 or higher.3 Therefore, overheating is suppressed, and it is possible to adjust to the optimal melting and kneading state that does not cause thermal decomposition. Favorable results are obtained in this layer.

In addition, when L/D is 25 or more, when using a twin-screw set injection molding machine, it is only necessary to adjust so that the value obtained by dividing the total length of each screw by the screw diameter becomes 25 or more.

As the one-screw injection molding machine used in the present invention, all known one-screw injection molding machines and improved machines thereof can be used, but a vent type injection molding machine is most preferred.

When using polyvinyl chloride resin with a p value of 1000 or more, 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. It is from.

Next, the conditions for human heat 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 high temperatures using hard polyvinyl chloride resin materials with a P800 or lower rating, which has poor thermal stability. It is common to adjust the temperature to 17Q°C, and it is rare to adjust the temperature above 17Q°C.

However, the molding material of piooo or higher used in the present invention has a high thermal decomposition temperature and can be heated to a relatively high temperature to melt it.

However, if the temperature is too high, thermal decomposition may occur and cooling within the mold will take a long time.On the other hand, if the temperature is set to a conventional level, a sufficient molten state cannot be obtained, which will cause difficulties in 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 not enough, and the heating cylinder in the meter link zone and compression zone The temperature is preferably 175 to 185°C, particularly preferably 178 to 182°C.
When the temperature was within this range, it was possible to obtain a melt-kneaded state suitable for producing an injection molded joint having physical properties and appearance comparable to extruded 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 inside the mold cavity will be longer after it is filled, so 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.

Thus, by using a complete screw injection molding machine with an L/D of 25 or more and adjusting the temperature of the heating cylinder in the metering zone and combination zone to a range of 175 to 185°C, PIOO, which was previously considered impossible, was achieved.
It is possible to melt and knead a hard polychlorinated beer resin material of O or more suitable for injection molding, and the first bottleneck in producing injection molded joints with favorable physical properties has been overcome. Ta.

The melt-kneaded resin obtained in this way is filled into a mold and formed into a joint of a predetermined shape.The technique for filling the mold is not particularly limited, and various techniques may be used in addition to the recommended method described below. may be applied.

Therefore, in this specification, although there is no need to specifically explain it, the filling technique employed in the examples described later will be explained.

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 tip of the screw, through the nozzle, part of the runner, and to 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.
This tendency is particularly strong in the case of hard polyvinyl chloride resin.

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

However, on the other hand, in order to ensure plastic fluidity and obtain optimal fluidity, 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 one, (the material at the beginning of driving) If the screw movement speed is made faster when the resin is filled into the cavity after being driven into the cavity (that is, while it is being filled into the cavity through the pin gate) The resin at the beginning of injection 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 is something big.

In order to carry out 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 the molding screw can be changed continuously or stepwise over the entire length of the metering stroke. An injection speed scale is attached to each stage, and the speed can be changed by adjusting the flow control valve etc. as 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, in the third and fourth stages, the screw moves forward at a medium to low speed scale, and the command is completed quietly while pressing 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.

The flow rate in the cavity portion is preferably adjusted to about 1.2 to 2.0 times the flow rate in a portion 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 a p value 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. It is.

Since the present invention is structured as described above, Y is 1000
The above-mentioned hard polyvinyl chloride resin material can be melt-kneaded successfully, and the physical properties of the joint obtained by injecting it can be comparable to that 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 QO, data for p850 is also shown for reference.

It should be noted that both the Example and the Comparative Example are compared using cases in which injection into the mold from an injection molding machine has been completed.

Example 1 When molding an elbow type pipe joint with a diameter of 751ILrIL, injection molding was performed using polychlorinated (vinyl resin) materials with p=soo, p=850, and 1050, respectively, according to the following conditions.

As an injection molding machine, use an inline screw 800 type molding machine when P=800, and use an inline screw 800 type molding machine when P=850 and 10
In the case of 50, 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 3 to 4 times the durability was obtained compared to the case where =soo.

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

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, the temperature of the screw tip, especially the nozzle, metering zone, combustion zone, etc., was raised. Good results were obtained.

Example 3 In the same manner as in Example 1, a socket-type pipe joint with a diameter of IQOm7fl was manufactured using a four-piece mold.

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

Claims (1)

[Scope of Claims] 1. In a method of melt-kneading a hard polyvinyl chloride material when manufacturing a hard polyvinyl chloride pipe fitting using a single-screw injection molding machine, the polyvinyl chloride resin material has an average degree of polymerization of 1000 or more. Use a screw set injection molding machine with an L/D of 25 or more, and set the heating cylinder temperature in the metering zone and combination zone of the injection molding machine to 175 to 1.
A method for melt-kneading a hard polyvinyl chloride material, which comprises melt-kneading the molding material at a temperature in the range of 85°C, and storing the melt-kneaded hard polyvinyl chloride material at the tip of a cylinder.