JPH04344215A - Die for molding thermoplastic resin multilayer pipe - Google Patents

Abstract

PURPOSE:To provide the title die capable of molding a thermoplastic resin multilayer pipe reduced in wall thickness irregularity and having good appearance. CONSTITUTION:In a multilayer pipe molding die equipped with an outer mandrel 2 and an inner mandrel 3 and also equipped with an annular nozzle part 17 being the distributing part of the resin guided by both mandrels 2, 3 to be extruded to a cylindrical resin meeting passage 16, spiral grooves 18, 19 are respectively provided to both mandrels 2, 3 and the outer diameter of the leading end of the annular nozzle part 17 is set to 0.7-1.3 times that of a multilayer pipe ready to obtain and the width thereof is set to 1.0-1.6 times the thickness of the multilayer pipe.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a die for molding a multilayer pipe made of thermoplastic resin.

0002

2. Description of the Related Art FIG. 4 is a cross-sectional view of an example of a conventional two-layer pipe forming die. In the figure, 31 is a die body, 32 is an outer layer mandrel attached to the die body 31, 33 is a feed block, and 34 is a spider (support leg) for holding an inner layer mandrel 35, which will be described later, in a predetermined position. The spider 34 is an outer layer mandrel 32
It is coaxially attached to the outer layer mandrel 32 by being sandwiched between the outer layer mandrel 32 and the feed block 33. 35 is an inner layer mandrel attached to the spider 34, 36 is a thickness unevenness adjustment ring attached to the die body 31, and 37 is a bolt for adjusting the position of the thickness unevenness adjustment ring. The outer layer mandrel 32 and the inner layer mandrel 35 are straight mandrels that do not have resin guide grooves such as spiral grooves on their outer peripheral surfaces. 38 is an outer layer resin extruder attached to the die body 31, and the center line of the cylinder is aligned with the outer layer mandrel 32.
It is installed at right angles to that of the

A resin supply channel 39 is provided in the die body 31 and is supplied with the outer layer resin extruded from the extruder 38 . Reference numeral 40 denotes a resin distribution path provided in an annular shape on the circumferential outer peripheral surface of the outer layer mandrel 32. This resin distribution path 40 is for distributing the outer layer resin extruded from the extruder 38 and coming out through the resin supply path 39 in the circumferential direction of the outer layer mandrel 32.

Reference numeral 41 denotes an inner layer resin extruder attached to the feed block 33 so that the center line of the cylinder and that of the inner layer mandrel 35 coincide with each other. 42 is a resin supply path provided in the feed block 33;
The inner layer resin extruded from the extruder 41 is supplied. 4
3 is a resin distribution path formed between the conical portion 34a of the spider 34 and the conical recess 33a of the feed block 33, and 44 is a resin distribution path provided in the feed block 33. As shown in FIG. 5, the latter resin distribution path 44 has four
It is divided into four sections by two bridges 34b. Both resin distribution channels 43 and 44 are for distributing the inner layer resin fed to the resin supply channel 42 in the circumferential direction of the inner layer mandrel 35. 45 is an inner layer resin flow path, 46 is an outer layer resin flow path,
47 is a resin confluence channel, and 48 is a nozzle portion.

Since the conventional pipe forming die has the above-mentioned configuration, the inner layer resin n is fed from the extruder 41 to the resin supply path 42, and the outer layer resin g is fed from the extruder 38 to the resin feed path 39. By extruding each layer, a two-layered pipe is created using the following process.

That is, the inner layer resin n is
, 44 in the circumferential direction of the inner layer mandrel 35 and extruded into the inner layer resin channel 45 in a cylindrical shape. on the other hand,
The outer layer resin g is distributed in the circumferential direction of the outer layer mandrel 32 by the resin distribution path 40 and extruded into the outer layer resin flow path 46 in a cylindrical shape. The inner and outer layer resins n and g pushed out into the inner and outer layer resin channels 45 and 46 merge in a resin merging channel 47 and are pushed out from the nozzle part 48, forming a two-layer pipe consisting of both resins n and g. Become.

[0007]

[Problems to be Solved by the Invention] However, conventional pipe forming dies have the following problems. (1) When the inner layer resin n passes through the resin distribution path 44 of the spider 34, as shown in FIG. 6, the flow of the inner layer resin n is separated by the bridge 34b, and the flow velocity distribution of the resin n is A valley forms. In this valley part, four weld lines called spider marks appear on the cylindrical inner layer resin n. And this weld line is
Since the inner layer mandrel 35 is a straight mandrel, the information from the resin confluence channel 47 to the nozzle portion 48 is stored as is. As a result, as shown in FIG. 8, four thin-walled portions t are formed in the inner layer N of the obtained pipe product, the thickness of the inner layer N becomes uneven, and the strength of the pipe is reduced. In addition, G
is the outer layer.

(2) Conventionally, therefore, in order to eliminate this weld line, the withdrawal rate (resin take-off speed/resin extrusion speed) was increased. However, in order to increase the drawing rate (drawing speed), for example, the outer diameter of the nozzle portion 48 must be 1.5 mm larger than the outer diameter of the pipe from which the nozzle portion 48 is obtained.
Since the width of the nozzle portion 48 is 10 to 20 times greater than the thickness of the resulting pipe, vertical wrinkles are generated on the outer surface of the pipe, and the quality of the appearance is rather deteriorated.

The present invention has been made to solve these conventional problems, and provides a die for molding a thermoplastic resin multilayer pipe that can produce a multilayer pipe with less uneven thickness and a good appearance. The purpose is to

0010

[Means for Solving the Problems] The thermoplastic resin multilayer pipe forming die provided by the present invention includes a plurality of mandrels, and rectifies resin guided by each mandrel and extruded into a cylindrical resin confluence channel. The die for forming a multilayer pipe is provided with an annular nozzle portion that is a part, and each of the mandrels is provided with a spiral groove, and the outer diameter of the tip of the annular nozzle portion is set to 0 of the outer diameter of the multilayer pipe to be obtained. .7-1.3
The width of the annular nozzle tip is 1.0 to 1.6 times the thickness of the multilayer pipe to be obtained.

It is essential that the outer diameter of the tip of the nozzle is 0.7 to 1.3 times the outer diameter of the pipe to be obtained.
The preferred range is 0.9 to 1.1 times. If it is less than 0.7 times, the pipe shape of the molten resin becomes unstable, resulting in poor roundness of the pipe and uneven thickness. 1.
If it exceeds 3 times, there will be inconveniences such as having to change the dimensions of the cooling tank inlet depending on the extrusion speed, and troubles are likely to occur near this inlet.

[0012] The width of the tip of the nozzle is 1.0 of the thickness of the pipe.
It is essential to make it ~1.6 times, and the preferable range is 1.1 to 1.4 times. If it is less than 1.0 times, wrinkles etc. are likely to occur on the surface of the molten pipe, resulting in poor appearance. If it exceeds 1.6 times, the molten resin is likely to break, making the molding unstable and causing uneven thickness.

[0013] The thermoplastic resin used for molding the multilayer pipe includes polyolefin resins such as low density polyethylene, high density polyethylene, polypropylene, ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer, and blends of combinations thereof. Compositions are preferred. Furthermore, these resins have a melt index of 0.01 g/10 min to 4.0 g/10 min, measured based on JIS K6760.
A range of 0 g/10 minutes is preferred. Various auxiliary agents such as plasticizers, colorants, fillers, and carbon can be added to the thermoplastic resin as necessary.

[0014]

[Operation] (1) The outer diameter of the annular nozzle tip is set to 0.7 to 1.3 times the outer diameter of the multilayer pipe to be obtained, and the width of the annular nozzle tip is set to 0.7 to 1.3 times the outer diameter of the multilayer pipe to be obtained. 1.0 to 1.6 times the thickness of the pipe, resin withdrawal rate (take-up speed)
Since the pipe can be made small, there is no risk of vertical wrinkles forming on the outer surface of the pipe.

(2) By the way, if the resin withdrawal rate (take-up speed) is reduced in this way, uneven thickness of the pipe will occur due to uneven flow of the supplied resin, and weld lines caused by spiders will remain in the pipe. However, in the present invention, since each mandrel is provided with a spiral groove, the resin extruded into the spiral groove of each mandrel is uniformly dispersed in the circumferential direction of each mandrel by the spiral groove. Therefore, the thickness of each layer of the pipe extruded from the die is uniform, and therefore the overall thickness is also uniform. Furthermore, there is no possibility that weld lines will be formed in each layer of the pipe that will impair the appearance quality of the pipe.

[0016]

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to FIGS. 1 to 3. The die in this example is a two-layer pipe molding die, and is suitable for manufacturing pipes with an outer diameter of 20 to 100 mmφ and a thickness of 3 to 12 mm, and is particularly suitable for manufacturing polyethylene pipes among thermoplastic resins. It is something that

In FIG. 1, 1 is a die body, 2 is an outer layer mandrel, 3 is an inner layer mandrel, and 4 is a feed block. These are coaxially assembled together. 5 is a die mandrel coaxially attached to the inner layer mandrel 2; 6 is a thickness unevenness adjustment ring attached to the die body 1; 7
is an uneven thickness adjustment bolt. The die mandrel 5 and the uneven thickness adjustment ring 6 are available in various sizes as interchangeable unit parts.

8 is an extruder for the outer layer resin. This extruder 8 is disposed coaxially with the inner layer mandrel 3 and attached to the feed block 4 at respective flanges 8a, 4a. Reference numeral 9 denotes an extruder for the inner layer resin, which is attached to the side of the feed block 4.

Reference numeral 10 denotes a resin supply path through which the outer layer resin extruded from the extruder 8 is supplied, and is provided at the axial center of the feed block 4. Reference numeral 11 designates resin distribution channels, which are four resin flow channels that branch from the resin supply channel 10 and pass through the feed block 4 and the inner and outer layer mandrels 3 and 2, and have openings 11a on the outer peripheral surface of the outer layer mandrel 2. It becomes more.

The four resin flow paths referred to herein are provided symmetrically at 90 degree intervals around the center line of the resin supply path 10, and the openings 11a thereof are located at the circumference of the outer peripheral surface of the outer layer mandrel 2. Openings are made at 90 degree intervals in the direction. This resin distribution path 11 is for uniformly distributing the resin extruded into the resin supply path 10 in the circumferential direction of the outer layer mandrel 2.

Reference numeral 12 denotes a resin supply channel through which the inner layer resin extruded from the extruder 9 is supplied, and the inner layer mandrel 3 side thereof is provided at the central axis of the feed block 4 and the inner layer mandrel 3. 13 is a resin distribution path, which is connected to the resin supply path 1
It consists of four resin channels that branch from 2 and pass through the inner layer mandrel 3, and have openings 13a on the outer peripheral surface of the mandrel 3.

The four resin flow paths referred to herein are provided radially in the radial direction at 90 degree intervals around the center line of the resin supply path 13, and the openings 13a thereof are located on the outer peripheral surface of the inner layer mandrel 3. The holes are opened at 90 degree intervals in the circumferential direction.

Reference numeral 14 denotes an outer layer resin flow path formed between the die body 1 and the outer layer mandrel 2, 15 an inner layer resin flow path formed between the outer layer mandrel 2 and the inner layer mandrel 3, and 16
is a resin confluence channel formed between the die body 1 and the inner layer mandrel 3 and between the thickness unevenness adjusting ring 6 and the die mandrel 5, where the inner and outer layer resins merge. 17 is a nozzle portion formed between the die body 1 and the die mandrel 5.

FIG. 2 shows the cross-sectional shape of the tip of the nozzle portion 17, and its outer diameter D and width W are determined by appropriately combining the die mandrel 5 of various dimensions and the thickness unevenness adjusting ring 6 described above. be able to. For example, outer diameter 19m
When the die mandrel 5 of m and the uneven thickness adjustment ring 6 of 30 mm inside diameter are installed, the outside diameter D is 30 mm and the width W is 5.5 m.
m of nozzle portions 17 can be provided. In this embodiment, the outer diameter D of the tip of the nozzle part 17 is 0.7 to 1.3 times the outer diameter of the pipe to be obtained, and the nozzle part 1
7 The width W of the tip is 1.0 to 1 of the desired pipe thickness.
．． Die mandrels 5 and thickness unevenness adjusting rings 6 of various sizes are prepared so that the thickness becomes 6 times larger.

Reference numeral 18 designates a spiral groove provided on the outer circumferential surface of the outer layer mandrel 2 facing the outer resin flow path 14, and 19 represents a spiral groove provided on the outer circumferential surface of the inner layer mandrel 3 facing the inner layer resin flow path 15. . FIG. 3 shows the detailed configuration of the spiral groove 19 provided in the inner layer mandrel 3, and shows the four openings 1 of the resin distribution channel 13 of the inner layer mandrel 3.
This is a groove extending spirally from 3a to the outer circumferential surface of the inner layer mandrel 3.

Next, the operation of the die according to the embodiment when forming a two-layer pipe will be explained. The outer layer resin extruded into the resin supply path 10 is divided into four equal parts and distributed in the circumferential direction of the outer layer mandrel 2 by the four resin distribution paths 11,
It is pushed out into the spiral groove 18. On the other hand, resin supply path 1
The inner layer resin extruded into the inner layer mandrel is distributed in the circumferential direction of the inner layer mandrel through four radially branched resin distribution channels 13.
It is equally divided and distributed and extruded into the spiral groove 19.

The inner and outer layer resins extruded into the spiral grooves 19 and 18 are
The fluid is uniformly distributed in the circumferential direction of the outer layer mandrels 3 and 2. Then, they merge in the resin confluence channel 16 and are extruded from the nozzle part 17, forming a two-layered pipe.

As mentioned above, in the die of the embodiment,
Since the resin is supplied to the resin supply channels 12 and 10 provided at the core of the die and extruded from there to the four resin distribution channels 13 and 11, the resin in the resin supply channels 12 and 10 is It is evenly distributed in the resin distribution channels 13 and 11, and is not unevenly distributed in the inner and outer layer resin flow channels 15 and 14.

Then, the resin pushed out into the inner and outer layer resin channels 15 and 14 is transported by the spiral grooves 19 and 18.
More evenly distributed circumferentially. Therefore, the thickness of each layer of the obtained two-layer pipe becomes uniform, and therefore the thickness of the entire pipe becomes uniform. Furthermore, no weld lines occur in each layer that impair the quality of the pipe's appearance.

Furthermore, since the size of the tip of the nozzle portion 17 is set within the above-mentioned range so that the drawing-off rate (take-up speed) of the resin can be made small, there is no possibility that vertical wrinkles will be formed on the outer surface of the pipe.

In order to confirm the above effects, the following experiment was conducted using the above two-layer pipe forming die.

(Experiment example) For the inner layer, linear low-density polyethylene (melt index 0.65 g/10 min, density 0.922 g/cm3) was used, and for the outer layer, carbon black was added to the same resin as for the inner layer. A pipe containing 2.2 wt% was used, and these were melt-extruded at a temperature of 210°C to form a two-layered pipe with an outer diameter of 42 mm, a wall thickness of 5.5 mm, and an inner layer thickness and an outer layer thickness of 3.5 mm and 2.0 mm, respectively. The pipe was formed. For molding, the die structure and the size of the tip of the nozzle part 17 were determined according to Experimental Examples 1 to 7 and Comparative Examples 1 to 5 shown in Table 1.
It was changed as follows.

When the appearance of the obtained pipe was observed and the thickness of the entire layer and inner layer of the pipe were measured, the results shown in Table 1 were obtained. Incidentally, the thickness deviation (%) was determined using the following formula.

[0034]

[Math 1]

[0035]

[Table 1]

[0036]

As explained above, according to the present invention, the resin extruded onto the outer peripheral surface of each mandrel is uniformly flowed and dispersed in the circumferential direction of each mandrel by the spiral groove provided on the outer peripheral surface of each mandrel. As a result, uneven thickness due to uneven flow of the supplied resin does not occur in the pipe, and weld lines caused by spiders do not remain in the pipe. Therefore, it is possible to obtain a multilayer pipe with uniform thicknesses in each layer and the entire thickness, and with excellent appearance quality.

Further, according to the present invention, the outer diameter of the annular nozzle tip is 0.7 of the outer diameter of the multilayer pipe to be obtained.
~1.3 times, and the width of the annular nozzle tip is 1.0 to 1.6 times the thickness of the multilayer pipe to be obtained, so that the drawing rate (drawing speed) of the resin can be reduced. Therefore, there is no risk of vertical wrinkles forming on the outer surface of the pipe.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a die for forming a two-layer pipe according to an embodiment.

FIG. 2 is an enlarged sectional view taken along line II-II in FIG. 1.

FIG. 3 is a perspective view of essential parts of the inner layer mandrel in FIG. 1.

FIG. 4 is a cross-sectional view of a conventional two-layer pipe forming die.

FIG. 5 is a sectional view taken along line V-V in FIG. 4.

FIG. 6 is a sectional view taken along VI-VI in FIG. 5.

FIG. 7 is a cross-sectional view taken along VII-VII in FIG. 4.

FIG. 8 is a cross-sectional view of a two-layer pipe formed by a conventional two-layer pipe forming die.

[Explanation of symbols]

1 Die body 2 Outer layer mandrel 3 Inner layer mandrel 4 Feed block 5 Dimandrel 6　Thickness unevenness adjustment ring 8,9 Extruder 10, 12 Resin supply path 11, 13 Resin distribution path 11a, 13a opening 14 Outer layer resin flow path 15 Inner layer resin flow path 16 Resin confluence channel 17 Nozzle part 18, 19 Spiral groove

Claims (1)

[Claims] 1. A die for forming a multilayer pipe, comprising a plurality of mandrels and an annular nozzle portion serving as a rectifying portion for resin guided by each mandrel and extruded into a cylindrical resin confluence channel, the die comprising: A spiral groove is provided in each mandrel, the outer diameter of the tip of the annular nozzle portion is set to 0.7 to 1.3 times the outer diameter of the multilayer pipe to be obtained, and the width of the tip of the annular nozzle portion is set to 1 of the thickness of the multilayer pipe to be
．． A die for molding a thermoplastic resin multilayer pipe, characterized in that the die is 0 to 1.6 times larger.