JPH03132328A - Molding method for resin pipe - Google Patents

Abstract

PURPOSE:To improve smoothness of the inner surface of a pipe of wall thickness of 3 mm or more by blending a specified quantity of a metal soap having specified melting point, and subjecting to an outer diameter sizing molding a straight- chain ethylene polymer having the MFR value and melting tension value within a specified range. CONSTITUTION:0.01 - 1wt. % of metal soap having the 100 - 130 deg.C melting point is blended with a straight-chain ethylene polymer having 0.05 - 2 g/10 minutes MFR value measured at JIS-6760 and 2.16 g load and melting tension of 3 g or more at 190 deg.C, and the blending is kneaded with a kneader, a Henschel mixer or the like to mold pellets of a resin composition. The outer diameter sizing molding method is applied to said pellets for molding pipe having wall thickness of 3 mm or more. As for said ethylene polymer, a straight-chain ethylene polymer or an ethylene and alpha-olefin copolymer obtained by using a chrome oxide based Phillips type catalyst is suitable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background of the Invention] <Industrial Field of Application> The present invention relates to a method for forming a pipe by an outer diameter sizing method that provides excellent smoothness of the inner surface of a thick-walled pipe.

<Conventional technology> Traditionally, polyethylene pipes have been formed by using the outer diameter sizing method, as the outer diameter is more important than the inner diameter when constructing joint connections, and the outer diameter is more important than the inner diameter. From the viewpoint of extrusion moldability, it has been common to use general-purpose high-density polyethylene and low-density polyethylene for extrusion molding, which have a relatively wide molecular weight distribution.

Polyethylene pipes have excellent long-term performance and chemical resistance, are inexpensive, and are easy to process, so they have been used primarily for water supply and drainage pipes since ancient times, taking advantage of these characteristics. In particular, low-density ethylene/α-olefin copolymer (linear low-density polyethylene) has excellent characteristics such as flexibility and chlorine water resistance, so it was designated as a class 6762 pipe (
In recent years, it has also begun to be used for soft pipes.

In addition, in the case of a tape molded by the outer diameter sizing method, the resin is once extruded from the extruder die in a molten state and then guided to an external cooling sizing device, so the shape retention in the molten state, i.e. Ethylene homopolymer or ethylene-α with a relatively wide molecular weight distribution is required to have excellent drawdown properties.
-Olefin copolymers have been used.

<Problems to be Solved by the Invention> However, it has not been attempted to form a thick-walled pipe using the above-mentioned linear ethylene polymer with a relatively wide molecular weight distribution and good extrusion processability by the outer diameter sizing method. As a result, it has been found that random streak-like wrinkles occur on the inner surface (inner wall) of the pipe, impairing its commercial value in terms of appearance, and at the same time causing an increase in flow resistance within the pipe, which poses a serious problem in practice.

The detailed mechanism for the occurrence of such wrinkles is unknown, but it is due to the unstable flow state of the molten resin (a kind of pulsation), the fact that the molten resin is squeezed by a sizing die smaller than its outer diameter, and the fact that the pipe This is thought to be due to the fact that when the wall thickness of the product increases, the outer surface is cooled first, and as a result, the inner surface shrinks toward the outer surface.

On the other hand, if molding is performed using a resin with a relatively narrow molecular weight distribution, wrinkles will not occur, but the drawdown properties will be reduced due to insufficient melt tension of the resin, and as a result, the molten resin will not only sag, making molding difficult. It is known that, especially under conditions of low temperature and high speed extrusion molding, rough skin phenomenon (commonly known as sharkskin) occurs on the inner and outer surfaces of the pipe, which is also a major problem.

[Summary of the invention]

Summary> In order to solve the above-mentioned problems, the present inventors have conducted intensive research to prevent the occurrence of wrinkles on the inner surface of thick-walled pipes due to the outer diameter sizing molding method, and as a result, they have found that a specific ethylene resin The present invention was completed by discovering that by blending specific additives, a resin composition for pipes that has excellent drawdown properties and does not generate wrinkles can be obtained.

That is, the resin pipe molding method of the present invention is a method of molding a pipe with a wall thickness of 3■■ or more by subjecting the resin to an outer diameter sizing molding method, and the MFR of the resin is 0.05 to 0.05.
A linear ethylene polymer having a melt tension of 3 g or more at 2 K/10 minutes and 190°C has a melting point of 100 to 13
It is characterized by using a composition containing 0.01 to 1% by weight of metal soap at 0°C.

<Effects of the Invention> According to the resin pipe molding method of the present invention, the problem of wrinkles occurring on the inner surface of the pipe in the prior art described above when a specific additive is blended with a specific ethylene polymer is solved. be done.

Furthermore, among the metal soaps that have traditionally been mainly used as neutralizing agents or dispersants, only those with a specific melting point have no practical problems, have excellent drawdown properties, and are effective in preventing wrinkles. That was completely unexpected.

Therefore, the resin pipe molding method of the present invention can be utilized as a highly practical molding method in fields where thick-walled pipes are required.

[Detailed description of the invention]

(1) Composition (1) Constituent component (a) Ethylene polymer The ethylene polymer used in the resin pipe molding method of the present invention is a linear polymer produced using an ionic polymerization catalyst, and is produced by a gas phase method. It can be applied to any manufacturing method such as solution method, slurry method, high pressure method, etc., and is obtained by copolymerizing ethylene homopolymer or the main component ethylene and one or more comonomers other than ethylene. It is a copolymer.

This ethylene polymer has MFR (J
Is-6760, load 2.16kg) is 0.05~
2g/10 minutes can be applied, especially 0.1 to 1 [/1
0 minutes is preferable. Among these, polymers with lower MFH have excellent drawdown properties, strength, etc., but those with excessively low MFH, for example, less than 0.05, have poor moldability such as fluidity during molding. Also, those with an MFR of more than 2 are inferior in drawdown properties, strength, etc.

In addition, the melt tension of this ethylene polymer is determined by JIS
- A cylinder extrusion rod is extruded at a speed of 10 mm/min at a temperature of 190°C from the furnace and nozzle used in the MFR measurement method of 6760, and the melt tension is 3 g or more when pulled at a speed of 4 m/min. It is applicable, and in particular, from the viewpoint of drawdown property, 4 g or more is preferable.

As an ethylene polymer, chromium oxide supported on an inorganic carrier such as silica or alumina, that is, a chromium oxide Phillips type catalyst, is used by a gas phase method, a solution method, a slurry method, or a pressure of 500 kg/cd or more and a temperature of 10
Products obtained by polymerizing ethylene alone or copolymerizing the main component ethylene and a-olefin by applying a production process such as bird pressure ion polymerization under conditions of 0 to 350°C are particularly suitable for this invention. The effects of the invention are greatly achieved.

The α-olefin to be copolymerized with ethylene includes α-olefins having about 3 to 12 carbon atoms, such as propylene, butene-1, pentene-11, hexene-1,4
Examples include methylpentene-1 and octene-1. Particularly preferred α-olefins are those having 4 to 8 carbon atoms, especially 1-butene, 1,4 hexene-1, methylpentene-1 and 1-octene. Two or more of these α-olefins can be used in combination. The α-olefin content in the copolymer is 0. 5-20% by weight, preferably 1-1
It is 5% by weight.

Among them, the density of ethylene/α-olefin copolymer (J
Is-6760 test method) is 0.915 to 0
．． 930g/C! 1, especially 0.920-0.925+r
/cd is preferable in terms of compressive strength and long unrollability. The density of these copolymers varies depending on the type and/or content of the copolymerized α-olefin.

This polymer also has FR (MFR at a load of 10 kg and MFR at a load of 2.16 kg mentioned above), which is a guideline for molecular weight distribution.
Those with a ratio of 13 to 25, especially those with a ratio of 14 to 20,
is preferred. A polymer with a lower FR has excellent impact strength, etc., but tends to have lower moldability such as fluidity during molding. Furthermore, the higher the FR, the lower the impact strength and the like tend to be.

Such ethylene polymers can be appropriately selected from commercially available products.

(b) Metallic soap The metal soap used in the resin pipe molding method of the present invention is a metal salt of a higher fatty acid with a melting point of 100 to 130°C, preferably 110 to 125°C, and is designed in consideration of dispersibility in the resin. It is preferable to use a powder having a relatively small particle size.

Such metal soaps include organic acids such as fatty acids, resin acids, and naphthenic acids, and metal salts such as zinc, magnesium, calcium, cadmium, barium, and lead. Salt is preferred. Specifically, zinc stearate (melting point 117~
125℃), zinc laurate (melting point 110-120℃)
, magnesium stearate (melting point 108-115°C)
Among them, zinc stearate is the most preferred.

High melting point types such as calcium stearate may have a small wrinkle prevention effect, depending on the usage conditions.
Or it may even get worse.

In addition, low-melting point types cause stickiness (bleed-out phenomenon) on the surface of the pipe product after pipe forming, so when used as water pipes, they are undesirable from the viewpoints of contaminating tap water and low resistance to chlorine water.

The blending amount of this metal soap is 0 relative to the ethylene polymer.
．． 01-1% by weight. Preferably 0°02-0.5
2% by weight, particularly preferably in the range from 0.03 to 0.3% by weight. If the amount is less than this amount, the effect of preventing wrinkles will be small, but if it is more than this amount, the effect will reach saturation and the cost of the product will increase.Also, when used as a water pipe, tap water may bleed due to bleed. This is undesirable because it tends to cause problems such as outflow of water and chlorine water resistance.

(2) Preparation of composition Methods for producing a composition by blending the above components include melt-kneading with a kneader such as a direct roll, Banbury, or kneader extruder; A method in which the mixture is mixed in advance with ethylene polymer powder using a Henschel type mixer, etc., and then melt-kneaded in the mixer described above, or a method in which a highly concentrated masterbatch is first made and then diluted with unblended ethylene polymer. Various known methods such as can be applied.

In addition, if necessary, other miscible resins such as polypropylene, branched polyethylene (high-pressure radical polymerization polyethylene), ethylene/vinyl acetate copolymer, or other oxidation inhibitors may be used within a range that does not significantly impair the effects of the present invention. agent,
Additives such as neutralizing agents, lubricants, anti-blocking agents, antistatic agents, ultraviolet absorbers, light stabilizers, fluorescent whitening agents, or colorants and fillers such as organic pigments and inorganic pigments. It can also be added directly or in the form of a masterbatch such as a resin. However, the addition of these substances may reduce the wrinkle prevention effect, so care must be taken when selecting the types and amounts added.

(0) Pipe Forming The pipe forming method of the present invention is versatile, and there are no particular restrictions on the size or structure of the forming apparatus, as long as it is an outer diameter sizing forming method that is characterized by outer diameter size control.

However, the purpose of the present invention is to not impair the smoothness of the inner surface of the pipe even if the wall thickness is large, and in order to use a resin composition that has been improved to achieve this, the pipe wall thickness is preferably 3 mm or more. 41 or more, particularly preferably 6 mm or more, produces a great effect.

Further, this pipe does not necessarily have to be circular, and includes, for example, a pipe classified as a rectangular extrusion molding. Note that the wall thickness in this case means the minimum wall thickness point. Furthermore, it is also possible to form a multilayer pipe as long as the effects of the present invention are achieved.

[Experiment example]

Examples 1 to 3 and Comparative Example 1.2 (a) Preparation of resin composition A so-called Phillips type ionic polymerization catalyst in which chromium oxide and titanium oxide were supported on silicon dioxide in the presence of a trace amount of oxygen by a gas phase process. MFRo, 5 g/10 min, density 0.922 g.
A linear ethylene/butene-1 copolymer of /7 was obtained. Commercially available reagents such as zinc stearate, calcium stearate, and a phosphorus stabilizer were added to the copolymer in the amounts shown in Table 1, mixed in a Henschel type mixer, and elution-kneaded in a single-screw extruder with a screw diameter of 40 mta. A pellet of the resin composition was obtained.

(b) Pipe molding The resin composition obtained in (a) above, with an outer diameter of 30 cm,
Screw diameter 4 with straight die of inner diameter 20
At a resin temperature of 190°C in a 0nos single screw extruder,
Extrusion molding was carried out to have an outer diameter of 27 mm, an inner diameter of 15 mm, and a wall thickness of 6 mm, and the outer surface of the pipe was cooled in a water tank while controlling the outer diameter with a vacuum sizing device to obtain a single-layer pipe.

The degree of wrinkling on the inner surface of the pipe obtained by such a molding method was visually observed and determined.

These results are shown in Table 1.

Comparative example 3.4 Comparative example 2 except that the inner diameter of the pipe was changed and the wall thickness was changed.
I did the same thing. The results obtained are shown in Table 2.

Comparative Example 5.6 The same procedure as Comparative Example 2 was carried out except that the ethylene polymer was changed. The results obtained are shown in Table 2.

Claims (1)

[Claims] 1. The resin is subjected to an outer diameter sizing molding method so that the wall thickness is 3 mm.
In the method for molding the above pipe, MF is used as the resin.
A composition in which 0.01 to 1% by weight of a metal soap with a melting point of 100 to 130°C is blended with a linear ethylene polymer having an R of 0.05 to 2 g/10 min and a melt tension of 3 g or more at 190°C. A resin pipe molding method characterized by the use of 2. The method for molding a resin pipe according to claim 1, wherein the ethylene polymer is a linear ethylene homopolymer or a linear ethylene/α-olefin copolymer obtained using a chromium oxide-based Phillips type catalyst. 3. Ethylene polymer has a density of 0.915 to 0.930 g/
cm^3 ethylene/α-olefin copolymer,
A method for molding a resin pipe according to claim 1 or 2. 4. Claims 1 to 4, wherein the metal soap is zinc stearate.
3. The method for molding a resin pipe according to any one of 3.