JPS5838305B2 - How to do it - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing a rigid polyvinyl chloride pipe joint,
In detail, in order to manufacture a hard polyvinyl chloride pipe joint with strength comparable to hard polyvinyl chloride extrusion pipe by injection molding, a polyvinyl chloride material with an average degree of polymerization of 1000 or more is used and the joint is uniformly molded. The present invention relates to a method of manufacturing the pipe fitting by combining the steps of melting and kneading the material into a state suitable for injection molding, and then filling it into a mold.

The injection forming method is a method for forming 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 certain shaped products are surprisingly low. , which constitutes an important bottleneck to expanding the application of injection molding methods.

This is thought to be due to the uniqueness of the ejection kaigata method, and that there are many points that cannot be discussed in the same way as the oshidetsu iogata 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). L・ku.

Therefore, in the case of an extrusion type, the resistance inside the cylinder is low, temperature control is easy, and thermal decomposition is difficult to occur, but in the case of an injection type, the molten resin material is temporarily stored at one end of the cylinder. Therefore, the screw itself must be gradually retracted within the cylinder while transferring the molten and kneaded resin to the reservoir of the nozzle.

Therefore, the subsequent melt-kneaded resin receives extrusion force from the screw and at the same time receives large back pressure from the tip of the cylinder, and the melt-kneaded resin receives not only frictional heat with the channel wall but also contact frictional heat between the resins (i.e. (internal heat generation), and the latter's contribution 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 the extrusion method, so the fluidity of the molten resin needs to be considerably higher than in the case of extrusion molding. The temperature during storage at the tip must also be set quite high.

However, as described below, the temperature must be below the thermal decomposition initiation temperature, and the need for temperature control has become even greater.Under the penalty that temperature control is difficult, injection or other operational management has become 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, and since the nozzle part and the mold cavity part are connected by L-shaped passages called spools, runners, gates, etc., no liquid is injected from the nozzle part. The molten resin 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.

The present invention has succeeded in solving these two problems and combining them to produce a pipe joint with good physical properties.

The general problems in injection molding are as explained above, but especially when considering the case where hard polyvinyl 1,1'4 vinylide is used as the material, the thermal decomposition onset temperature of the resin is 20.
The temperature is around 0°C (however, as the degree of polymerization increases, the temperature rises to around 207-208°C), but 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 chickentropic 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 use a straight resin with a low polymerization degree (average degree of polymerization (hereinafter also referred to as p)) below SOO to lower the flow temperature and melt viscosity, increase the flow resistance at the nozzle, the pin gate of the mold, etc., and prevent thermal decomposition. By applying a very large injection pressure to produce as much frictional heat and shear mixing effect as possible, we were able to produce a relatively small shaped product.・It was only a matter of time.

However, it was not possible to improve impact resistance or fatigue fracture resistance, and further efforts were made to improve stabilizers and reinforcing agents.
・Efforts have been made to improve balance, wall thickness, and corner shape.

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 of joints used with extruded products, 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 molding technology, and are also being used in the waterworks field to replace conventional cast iron pipes. Injection molded products made of vinyl chloride have poor mechanical strength, so 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 has been made with attention to these eight circumstances, and its purpose is to manufacture an injection molded pipe joint made of hard polyvinyl chloride that has strength comparable to extrusion molded products. In order to achieve this, research has been carried out from various perspectives such as selection and formulation of molding materials, selection of molding conditions, mold design, and devising the shape and dimensions of joints, but it is still difficult to find the essential solution. It didn't work out.

However, during this research process, I began to question the technical common sense in the field that says, ``When obtaining injection molded joints made of rigid polyvinyl chloride, use a material with a diameter of 800 or less.'' The P of the injection molded joint is the P of the extruded pipe.
(usually 1000-1050) I thought that the important factor was lower than P850, for example 900, 950, 1000, 1050, 11oo,
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 make injection molded joints by devising melt-kneading conditions. It was discovered that a melt-kneaded resin in a suitable state could be obtained, and that the filling operation could be carried out safely by adjusting the conditions for filling the mold, thereby perfecting the present invention.

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 the case where p is 1000 or more that shows great significance, so the present invention The target group was set as 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 material.

That is, the structure of the present invention is as follows: In a method for manufacturing a hard polyvinyl chloride pipe joint using a screw set injection molding machine, a material having an average degree of polymerization of 1000 or more is used as the polyvinyl chloride resin material. In the kneading process, a screw injection molding machine with L/D of 25 or more is used, and the temperature of the heating cylinder in the metering zone and compression zone of the injection molding machine is kept in the range of 175 to 185 ° C. In the filling process where the molten and kneaded material is adjusted and kneaded and the molten and kneaded material is driven into a pipe joint or mold, the molten and kneaded material at the beginning of the injection process is carried out until it reaches the cavity. The gist is that when the screw moving speed is set to 1, the screw moving speed when the cavity is filled with the melt-kneaded material is set to 12 to 2.0.

As mentioned above, polyvinyl chloride with a high P content has a slight difference between the thermal decomposition initiation temperature and the plastic flow temperature, so 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 common technical knowledge that if the L/D is made small, the cross-wire shearing effect can be easily adjusted by adjusting the back pressure and the risk of thermal decomposition can be prevented, and it is generally recommended to keep the L/D at about 16 to 20. 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 higher than the average value, and that the particle size of the raw resin varies considerably due to manufacturing circumstances, so P = 80 It was found that the situation is completely different when p is about 0 and when 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 practically possible to control the temperature of the heating cylinder in the K meter IJ zone and cone compression zone from 175 to 18.
It has been found that when the temperature is set to about 5°C, the high-P polyvinyl chloride transported inside the polyvinyl chloride reaches an optimal plastic flow state due to the interaction of optimal external human heat and optimal internal heat generation.

First, use a complete screw injection molding machine with L/D of 25 or more.
・Explain about things.

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

However, as mentioned 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 especially common 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 with a p1000 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, resulting in uneven distribution of high-temperature areas due to external heat input and low-temperature areas due to crosstalk, resulting in flash marks, weld marks, and jetting marks. , silver streaks and other disfiguring phenomena 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 a p1000 or higher was used, no significant quality improvement could be expected, and it was almost impossible to achieve continuous shape.

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, and when the temperature reaches the tip of the screw. Almost completely uniform heating is performed in the case where p is 800 or more.

Therefore, overheating is suppressed, the melting and kneading state can be adjusted to an optimum state that does not cause thermal decomposition, and more favorable L results can be obtained.

In addition, when L/D is 25°C or more, when using a twin-screw injection molding machine, adjust the total length of each screw divided by the screw diameter to be 25 or more. good.

As the screw set injection molding machine used in the present invention, all known screw set 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 an F value of 1000 or more, this is to prevent air, moisture, and other volatile components accompanying the raw materials from evaporating and expanding and appearing in the injection molded product. Because it is desirable.

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 rating of P800 or less, which has poor thermal stability. It was common practice to adjust the temperature above 170°C, and it was rare for the temperature to exceed 170°C.

However, the thermal decomposition temperature of the preformed material of PIOOO or higher used in the present invention is high, and it has become possible to melt the material by heating it to a relatively high temperature.

However, if the temperature is too high, thermal decomposition may occur or 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, causing problems in injection molding. It turns out.

After conducting various studies to find the optimal value for the temperature of the heating cylinder from this point of view, we found that simply adjusting the temperature of the heating cylinder uniformly was insufficient, and that the temperature of the heating cylinder in the metering zone and combustion zone The temperature is preferably 175-185°C, particularly preferably 178-182°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 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.

Thus, by using a complete screw injection molding machine with 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, we were able to achieve a temperature that was previously impossible. PIO that was
It is possible to melt and knead a hard polyvinyl chloride resin material of OO or higher and make it suitable for injection molding, and the first bottleneck in producing injection molded joints having desirable physical properties is overcome. became.

The thus obtained molten gauze resin is filled into a mold to form a joint of a predetermined shape. Next, the filling technique into the mold 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 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 portion at high speed, and a desire to avoid abnormal temperature rise due to friction with the pin gate wall, two clearly contradictory demands that must be satisfied. I had to.

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 moving speed of the screw is increased when the resin is subsequently filled into the cavity (that is, while the resin 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, allowing high-speed filling into the cavity. It becomes possible.

In other words, the orientation due to low-speed flow is not frozen, and good results can be obtained such as thinning or eliminating the orientation layer, and it also contributes to increasing fracture energy, reducing residual strain, and eliminating weld marks and jetting marks. There is something very thick.

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

This type of injection molding machine with a variable speed mechanism is configured so that the moving speed of the molding screw can be changed continuously or in steps over the entire length of the metering stroke, and usually in several steps. For example, a five-stage injection speed scale is attached, and the speed can be changed by adjusting a flow control valve or the like when the screw moves forward.

Therefore, for example, in the first stage of the injection molding, the entire part of the runner up to the bin gate is filled with 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 a 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 is advanced at intermediate to low speed scales, and a certain shape is quietly completed with careful pressure.

If you use an injection molding machine that does not have such a transmission 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.

Note that the flow velocity in the cavity portion is preferably adjusted to about 12 to 2.0 times the flow velocity in a portion of the runner.

If the flow velocity ratio exceeds 2.0, thermal decomposition may occur.

Regarding the resin material used in the present invention, a hard polyvinyl chloride resin material with a P of 1000 or more is used, 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 constructed as follows, P is 100
The hard polyvinyl chloride resin material of about 0 or more must be melted and kneaded well, and the physical properties of the joint obtained by injection of the same can be comparable to those of injection-molded pipes.

It has improved tensile strength, elongation, pressure resistance, pulsating water pressure resistance, and impact resistance, making it more reliable when used, for example, as a water pipe joint, and exhibiting extremely high resistance to fatigue fracture.

In addition, there are certain things that contribute to the eradication of molding defect phenomena such as flash marks, weld marks, sheet ink marks, and silver marks, which tend to appear more prominently as F 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, and as a comparative example p=s
In addition to showing the data for o and o, data for p850 is also shown for reference.

Example 1 When molding into an elbow type pipe joint with a diameter of 75 mm, P = 8
00 and P=1050 polyvinyl chloride resin materials were used, and injection molding was carried out according to the following conditions, respectively.

As the injection molding machine, an in-line screw 800 type molding machine was used when P=800, and an inline screw 1250 type molding machine was used when P=1050.

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
= 800, approximately 2.5 to 4 times the durability was obtained.

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

In addition, in the conventional general-purpose L・RUP800, L/D is 2.
8, no particular effect has been observed.

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 conditions were varied, as shown in Table 2, favorable results were obtained in all cases where L/D was approximately 25 or more.

In the case of P=850, an in-line screw 1250 type machine was used.

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

The precept conditions and precept results are shown in Table 3.

Particularly remarkable effects were obtained regarding pulsating water pressure durability and tensile strength.

Claims (1)

[Claims] 1. A method of manufacturing a hard polyvinyl chloride pipe joint using a screw injection or molding machine, using a polyvinyl chloride resin material having an average degree of polymerization of 1000 or more, and in a kneading step using a screw. In this case, a screw set injection molding machine with 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 adjusted to be in the range of 175 to 185°C. In the filling process, in which the molten and kneaded material is poured into a pipe fitting mold, the screw moves until the molten and kneaded material reaches the cavity at the beginning of the injection. When the speed is 1, the screw moving speed when filling the cavity with the melt-kneaded material is 1.2 to 20. A method for manufacturing a rigid polyvinyl chloride pipe joint using injection molding, characterized by: