JPS5856504B2 - annular die - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an annular die used for inflation molding of thermoplastic resin.

The present invention provides an annular die with a relatively small diameter that is easy to perform high-output molding without impairing the quality of the molded thermoplastic resin film, is easy to manufacture, and is inexpensive. It is something.

In a conventional spiral die, resin is supplied from the center of the bottom of the die, passes through several resin supply ports provided inside the mandrel, reaches the outer periphery of the mandrel, and gradually decreases the depth of the groove along the outer periphery of the mandrel. The liquid flows along several spiral grooves provided in the direction of the discharge port, merges in the middle, becomes uniform, and is discharged from the die discharge port.

However, in order not to impair the quality of the molded product, such as by preventing thickness unevenness and joining lines, it is necessary to reduce the diameter of the helical flow path, make it longer, narrow the gap between the mandrel and the outer ring, and improve the resin flow path. The resistance of the clamping die was increased, increasing the back pressure.

For this reason, it is difficult to perform high-output molding with small-diameter dies.
Furthermore, due to the large back pressure, there is also the problem that the pressure strength of the die must be increased, which inevitably leads to troublesome manufacturing and an increase in price.

In addition, when increasing the amount of resin discharged with such a die, the discharge pressure increases due to the back pressure of the die, which has the effect of increasing the suppressing strength of the extrusion equipment including the die and increasing the extruder motor. In addition, due to the large resistance of the die, the temperature of the extruded resin increases significantly due to self-heating, and as a result, the cooling capacity of the extrusion equipment is generally exceeded, making it impossible to control the temperature, and the temperature of the resin increases. This causes the problem that stable molding becomes extremely poor.

Such problems naturally become larger as the diameter of the die outlet is smaller, and is one of the reasons why productivity cannot be increased, especially in dies with a diameter of 100 mm or less.

Common methods for reducing back pressure in spiral dies and the like include widening the gap between the resin discharge ports and widening the gap between the mandrel and the outer ring.

However, although these methods can simply lower the resin pressure and increase the discharge amount, they have the following problems.

The method of widening the gap between the resin discharge ports is such that as the gap is widened, the formed film is stretched more in the longitudinal direction, which upsets the balance between the longitudinal and circumferential orientations of the resulting molded product and reduces impact. strength, tear strength, tensile strength,
This results in a significant decrease in film properties such as strength such as tensile elongation, appearance such as transparency and gloss, and increased thickness unevenness, as well as an increase in the processing limit of the molded product.
There are drawbacks such as difficulty in obtaining thin molded products, and there is a natural limit to not impairing film quality, processability, etc.

The method of widening the gap between the mandrel and the outer ring is the least preferable method because it impairs the uniform distribution of the resin and deteriorates the film quality, such as the tendency for resin joining lines to appear on the molded product.

The present inventors have conducted extensive research to obtain a die with low back pressure that enables high-output molding without deteriorating the quality of the molded product, and as a result, formed the spiral resin flow path portion 5. We have found that it is extremely effective to combine the diameter of the part with the diameter C of the starting point of the spiral resin flow path 5 connected to the resin supply section 4 of the mandrel 1, and have arrived at this invention. be.

That is, the features of the annular die of the present invention are as follows: 1) The diameter of the helical resin flow path of the mandrel 1 is at least 1.5 times the diameter a of the resin discharge port 2) The spiral resin is connected to the resin supply section inside the mandrel 3) Set the diameter C of the starting point of the flow path 5 to 0.2 times or more the resin discharge port diameter a.3) Set the depth of the groove of the spiral resin flow path 5 to the spiral resin flow path 5.
The groove gradually decreases from the starting point 4> after passing at least the upper part of the starting point 4 that it first encounters, the groove becomes the ending point and merges into the circular tubular resin flow path.

The effects of the present invention are achieved by the combination of the above features, which allows the resin to be distributed uniformly in the circumferential direction, and by widening the gap between the discharge ports without the formation of bond lines, the back pressure can be reduced without deteriorating the quality of the molded product or processability. This lowers the resin temperature and enables high discharge molding.

In addition, even if b/a is 1.5 or more, the effect of lowering back pressure is small if c/a is 0.2 or less, and if b/a is 1.5 or less, the effect of lowering back pressure is small. c.
If /a is 0.2 or more, there are still problems such as the formation of resin bonding lines, which is undesirable.

The die of the present invention will be explained in detail with reference to FIG.

In the die of the present invention, the diameter of the helical resin flow path portion of the mandrel 1 is made larger than 1.5 times the diameter a of the resin discharge port, and at the same time, the diameter of the helical resin flow path portion 5 of the mandrel 1 connected to the resin supply portion 4 is increased. The diameter C of the starting point is made larger than 0.2 times the diameter a of the resin discharge port, and the depth of the groove of the spiral resin flow path 5 is gradually decreased from the starting point of the spiral resin flow path 5, so that the starting point 4 that first meets After passing through the upper part of the pipe, the pipe ends at the groove and merges into the circular tubular flow channel.

By increasing the diameter of the helical resin flow path of the mandrel 1, the circular tubular resin flow path 6 formed by the mandrel 1 and the outer ring 2 is enlarged without widening the gap. This makes it possible to lower the resistance caused by the passageway, and also to reduce the pitch angle α of the spiral resin flow passage 5, which significantly improves uniformity in the circumferential direction and creates a resin bond line. This produces the effect of lowering back pressure without causing any damage.

Increasing the diameter of the starting point 4 of the spiral resin flow path 5 means that
This enlarges the resin flow path, reduces the resistance in the flow path, and has the effect of lowering the back pressure of the die.

This method leads to quality deterioration such as uniformity in the circumferential direction and generation of resin bonding lines, but by combining it with increasing the diameter of the spiral resin flow path, it is possible to This made it possible to prevent quality deterioration.

In order to obtain these effects, the diameter of the helical resin flow path portion of the mandrel 1 is made to be at least 1.5 times the resin discharge port diameter a, and the diameter of the starting point 4 of the helical resin flow path 5 is C
must be at least 0.2 times the diameter a of the resin discharge port.

The larger the ratio b/a of the diameter of the resin flow path section to the diameter of the discharge port a, the more advantageous it is to make the back pressure uniform in the circumferential direction.

However, making the die unnecessarily large will increase the weight of the die, making it difficult to handle, and will be uneconomical as it will require an increase in the heater capacity, and there is little need to make the die more than three times the size due to the effect of reducing back pressure. .

The larger the diameter C of the starting point 4 of the spiral resin flow path 5 is, the more the resin flow path is enlarged, which has the effect of lowering the back pressure.

However, if the diameter is to be increased, the diameter of the spiral resin flow path must also be increased.

The effect of lowering the back pressure requires a ratio of at least 0.2 times, preferably at least 0.3 times, the diameter of the discharge port, and it is more effective to increase the ratio for a die with a small diameter of the discharge port.

The number of threads in the spiral resin flow path 5 may be single, but although a plurality of threads is more effective in reducing back pressure, distributing resin, and making it more uniform, unnecessarily increasing the number of threads may cause the spiral resin to become The pitch angle α of the flow path 5 becomes large, which is undesirable for distribution and uniformity, and two threads* are sufficient for a small-diameter die applied to the die of the present invention.

The number of turns of the helical resin flow path 5 around the mandrel must be gradually reduced so that it merges into the circular tubular flow path 6 after passing through the upper part of the starting point 4 of the helical resin flow path 5 that first encounters it. In the die of the present invention, since the effect of distribution and uniformity is significantly improved, it is sufficient that the number of turns is one turn or less after passing the upper part of the starting point 4 where the spiral resin flow path 5 first meets.

Therefore, the length of the mandrel 1 can be made shorter than before, and the resistance of the die can also be made smaller.

Example Judgment Criteria Formability ◎: The increase in the amount of extrusion that can be molded without losing quality is 100% or more compared to the conventional die (AI)01 The increase in the amount of extrusion that can be molded without losing quality is more than 100% compared to conventional die (AI) Film quality ◎: Excellent overall, with no bonding lines observed.

○: Something that looks like a bond line is slightly observed, but there is no quality abnormality (passed product) △: A bond line is clearly observed.

(Rejected product) ×: There is a joining line and it is more likely to be damaged than that part.

Regarding the annular die of the present invention and the conventional die having the dimensions shown in Table 1, the melt index was 2.5 g/10 min density 0.9 using an extruder with a diameter of 507W7W at a set temperature of 130°C.
The relationship between the extrusion amount, resin pressure, resin temperature, and range in which stable inflation molding was possible when discharging low-density polyethylene No. 22 was investigated.

The results are shown in Table 1 and Figure 2. The resistance of the die is measured as resin pressure by a Bourdon tube pressure gauge inserted into the short tube connecting the die and the presser, and the resin temperature is detected by a thermistor thermometer inserted into the resin discharge port of the die. It is.

The inflation molding range was 250 m/m during folding and a film with a thickness of 0.020 mm, and a fluctuation during folding of 2 degrees or less was set as the limit for stable film formation.

As shown in Figure 2, in order to increase the extrusion rate to the limit that allows stable film formation, lower the resin temperature (165°C in this example).
The following) is required, and the resin temperature drop is achieved by lowering the resin pressure (back pressure of the die), and the discharge rate that allows stable molding is achieved for the first time with the die of the present invention without sacrificing quality. It is.

By increasing the diameter of the spiral resin flow path independently, it is possible to increase the diameter of the spiral resin flow path without deteriorating the quality of the molded product such as the formation of resin bond lines.
Although it is possible to lower the resistance of the die, the effect is slight as in the comparative example, die A5.48.410.

If the diameter of the starting point of the spiral resin flow path 5 connected to the resin supply section 4 is increased independently, it is possible to lower the resistance of the die, but the distribution effect in the circumferential direction is significantly reduced, and the joining line of the resin is increased. The quality of the molded product deteriorates, such as the occurrence of
Its effectiveness is limited as in I61, 42, and Kuzu3.

However, in the die of the present invention, in which the diameter of the helical resin flow path portion is expanded by combining the diameter C of the starting point of the helical resin flow path 5, due to the synergistic effect, when the resistance of the die and the resin temperature are increased individually. In addition to a larger drop, the die does not impair the distribution effect in the circumferential direction and does not cause deterioration in molded product quality such as the occurrence of resin bonding lines (~1.5 times that of conventional dies).
This method was found to have the characteristic of achieving 2.0 times higher productivity.

As shown in the examples, the effect of improving productivity without impairing film quality is when b/a is 1.5 or more and c
/ It is noticeable in those with a of 0.2 or more.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the annular die for molding thermoplastic resin of the present invention. FIG. 2 is a graph showing the relationship between discharge amount, resin pressure, and resin temperature stable film formation range for the conventional die and the die of the present invention. 1... Mandrel, 2, 3... Outer m,
4...Resin supply path, 5, 6...Resin flow path in mandrel, 7...Resin discharge port, 8...
...Internal gas filling hole.

Claims (1)

[Claims] 1. In an annular die for molding a thermoplastic resin film having a small-diameter resin discharge port, the diameter of the spiral resin channel portion of the mandrel 1 is at least 1.5 times the diameter a of the resin discharge port of the mandrel 1. In addition, the diameter C of the starting point 4 of the spiral resin flow path 5 connected to the resin supply path inside the mandrel is 0.2 times or more the diameter a of the resin discharge port of the mandrel 1, and the spiral shape While the depth of the groove of the resin flow path 5 is gradually decreased from the starting point 4 of the spiral resin flow path 5, after passing at least the upper part of the starting point 4 where it first meets, that groove becomes the end point, and the circular tubular resin flow path 6 is formed. An annular die for molding a thermoplastic resin film, characterized by having a structure that allows the two to merge together.