JPS586736B2 - Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing crosslinked moldings from crosslinkable polymeric materials, such as thermoplastic polymers, copolymers, elastomers, and mixtures thereof.

In this specification, the term "molded article" should be interpreted in its broadest sense.

The invention is therefore not limited to moldings obtained, for example, by injection molding, compression molding or transfer molding, but also applies to all other methods applied to the processing of polymeric materials, such as extrusion, rolling, lamination, It also includes those molded by methods such as pouring and blowing.

It is not necessary that these molded articles consist only of polymeric materials.

It may contain commonly used fillers and other additives,
Furthermore, they may also contain reinforcing materials and, in special cases, may be cables with a metal core coated with an insulating and/or semiconducting layer of polymeric material.

Millions of tons of synthetic polymeric materials are used for various purposes each year, and there appears to be little need to improve the properties of these materials.

However, due to certain limitations in the physical properties of the material,
These materials cannot be utilized for many purposes for which they are otherwise ideally suited.

For example, polyethylene (PE) will require improvement in the following points.

(1) Creep resistance (plastic flow) at room temperature and elevated temperatures (2) Solvent resistance at elevated temperatures (3) Environmental stress cracking resistance (4) Brittle fracture resistance: Brittle fracture lasts for a long time After the pressure test of
This can occur in non-crosslinked PE tubes, especially after testing at elevated temperatures.

The advent of high-density polyethylene (HDPE) was an important advance on the way to solving these problems, but crosslinking, a process similar to rubber vulcanization, provided further improvements in the properties described above. It was done.

In the crosslinking of crosslinkable polymeric materials, chemical crosslinks are produced by heat treatment and/or with the aid of promoters, activators and/or auxiliaries using free radical generators, usually consisting of organic peroxides. This is a well-known technique.

In the best known methods of producing crosslinked moldings from crosslinkable polymeric materials, free radical generators must be added or incorporated into the polymer prior to molding.

Such incorporation of free radical generators is generally carried out in conventional mixing equipment.

If the material is, for example, low density polyethylene (LDPE), a two roll mill or a Banbury mixer can be used.

The mixer is heated to about 110° C. and the polyethylene is added and processed for a suitable period of time until a homogeneous melt is obtained.

Polyethylene may contain fillers, antioxidants, and auxiliaries.

The free radical generator is then added followed by an additional 2 to 5 minutes.
Mixing for a minute will usually be sufficient.

After adding the free radical generator, the temperature should generally be maintained below 120°C.

Once the mixing process is complete, the material is granulated by known methods and ready to be fed to an extruder or plastic molding machine.

In these molders, the particles are finally molded at such low temperatures that premature crosslinking or scorching does not occur.

The heat treatment necessary to create crosslinks within the molded article can be accomplished in a variety of ways.

In the case of extrudates, heat is generally supplied continuously from steam (in continuous vulcanization or catenary vulcanization equipment), salt baths, and fluidized beds, or in the form of infrared light or microwave energy. can do.

The first four heat sources listed above must support the moldings to be crosslinked in some way, or else the non-crosslinked materials will melt at the high temperatures required for crosslinking. The disadvantage is that deformation at high temperatures, which would otherwise occur, must be avoided.

Therefore, these methods cannot be applied, for example, to the production of φ shapes or tubes made of crosslinked polymeric materials, but only to the production of cables.

In the case of cable manufacturing, the conductor can support the polymeric material in place during the crosslinking operation.

A fifth method of supplying the necessary heat to the molded article, namely by microwave energy, involves the use of polymeric materials that themselves have a dielectric loss tangent (tgδ) or are filled to provide a high dielectric loss. It is limited to polymeric materials containing additives such as carbon black.

Instead of the highly complex heat transfer methods described above, direct methods have been proposed.

In this method, particles containing a free radical generator are extruded through an extrusion head or through a special mold while providing sufficient heat to create crosslinks within the material.

However, this method tends to cause the crosslinked material to clog the extruder, the extrudate is prone to warping and cracking, and a smooth surface may not be obtained.

The above-mentioned method of crosslinking crosslinkable polymeric materials, i.e. adding a free radical generator before molding, can be used, for example, if the material is H
It cannot be used in the case of DPE.

In the case of HDPE, relatively high operating temperatures are required both during addition of the free radical generator and during shaping, so that premature crosslinking or scorching necessarily occurs.

Another known method that can be applied to the production of crosslinked extrudates of HDPE is generally to mix powdered HDPE and peroxide in a screw mixer that feeds a heated mold in the shape of the final product under high hydraulic pressure. , and an auxiliary agent.

This method has two essential drawbacks:

(1) This processing operation can only be performed using a special machine.

(2) This processing operation is not suitable for producing crosslinked moldings of HDPE containing fillers.

When molding articles of crosslinkable polymeric material by known methods such as compression, transfer or injection molding, it is necessary to incorporate a free radical generator before feeding the material into the molding machine.

This results in unfavorable molding conditions.

This is because premature crosslinking or scorching can only be avoided by lowering the operating temperature;
Also, the crosslinking process must occur in the mold in which the article is molded.

Therefore, the material is not endowed with optimal properties and the time required to hold the article in the mold becomes a limiting factor in manufacturing, which makes the processing operation uneconomical for many products. .

In order to eliminate these drawbacks, articles have been manufactured from polymeric materials without added crosslinking agents and then crosslinked using ionizing radiation.

However, this processing operation is limited to articles with specific cross-sections.

Moreover, this processing operation requires complex and expensive equipment and high power consumption.

DE 2214628 describes a method for producing foamed crosslinked polymer moldings from LDPE, which involves suspending polymer particles (granules) in an aqueous emulsion containing a crosslinking agent. It consists of heating until it becomes cloudy and crosslinking takes place.

After that, only the foaming and molding steps need to be performed. The foaming agent can be added to the particles at the same time as crosslinking or after crosslinking.

This method of crosslinking particles before shaping is associated with various drawbacks.

Highly crosslinked particulate polymeric materials cannot be molded by conventional molding methods such as extrusion or injection molding.

This is because highly cross-linked particles do not melt or form a continuous shape like the original particles under such molding conditions, but retain the geometrical shape they had at the time of cross-linking. This is because, in addition, the adhesion between particles will be reduced.

Particulate polymeric materials that are moderately crosslinked cannot be molded by conventional molding methods because they require extremely high pressures during processing.

Considering the subsequent shaping of the material, the generally preferred degree of crosslinking is so low that for many purposes such a process would be completely unsuitable.

The object of the invention is to provide a method for producing crosslinked products from crosslinkable polymeric materials that have all the known favorable properties without the technical disadvantages and drawbacks mentioned above.

According to the invention, in the presence of a liquid medium containing one or more peroxides, such as emulsions, suspensions, solutions, these peroxides penetrate into the molded article. By heating the molding under conditions and continuing said heating with increasing temperature until the desired uniform degree of crosslinking is obtained, it is further substantially stable within the initially applied temperature range. By using a peroxide which decomposes to a substantial extent to free radicals within the temperature range applied in the final heating step, the cross-linking reaction can be further carried out with the density of the polymeric material being approximately the same. The above-mentioned object is achieved by encapsulating the molded article in a liquid of high density.

In the process according to the invention, the moldings to be treated are manufactured in a conventional manner from customary starting materials to which no crosslinking agents, such as free radical formers, have been added; and/or may contain an antioxidant and/or a crosslinking aid.

The selection of starting materials is limited only by two factors:

In other words, the properties required in the final product and the properties required in the machine used.

For example, if the processing operation does not produce a stress-free molding without internal stresses (this is due to the extruder or other processing machinery used), it may be preferable to introduce an intermediate stress relief step. .

As the stress relief step, for example, there is a method of heating the molded article before introducing the molded article into a medium containing a crosslinking agent.

When moldings are to be manufactured from HDPE, it is natural to select a type of HDPE that provides optimal operating conditions so that the manufacturing process is smooth and complete and the moldings are endowed with optimal properties. Probably.

Furthermore, the method according to the invention is not limited to molded articles produced by extrusion molding and injection molding;
It can be applied in connection with any method by which moldings of polymeric materials can be produced.

Once the moldings have been shaped by known methods, one or more customary crosslinkers or free radical formers are introduced.

These include, for example, organic peroxides such as di-t-butyl peroxide and dicumyl peroxide, or t-
There are organic hydroperoxides such as butyl hydroperoxide.

A particularly preferred peroxide is 1,1-bis-(1-butylperoxy)-3,3,5-trimethylcyclohexane, which forms crosslinks already at very low temperatures (approximately 100°C) and therefore During the crosslinking period, only a particularly small degree of deformation takes place.

The selection of the crosslinker or crosslinkers in a given system depends in particular on the polymeric material to be crosslinked; if the crosslinker or crosslinkers are dissolved in the polymeric material,
The inventive method can in principle be applied to all crosslinkable polymeric materials.

Ultimately, the method of this invention will make it possible to satisfy the following conditions singly or in combination.

These conditions are particularly important for producing moldings for special purposes.

(1) This processing operation can be adjusted to produce the desired degree of crosslinking.

Thus, for example, the crosslinking of HDPE can be adjusted to a sufficiently high degree, but not so high that the density of the material is reduced such that it is no longer HDPE.

(2) This processing operation can be adjusted so that dimensional changes in the molded product are acceptably small. The amount of peroxide can be avoided.

The crosslinking agent can be introduced, for example, by immersing the molded article in an emulsion-like aqueous dispersion of one or more crosslinking agents.

This milk suspension-like dispersion is prepared by mechanical processing such as a high-pressure homogenizer, or by an emulsifier, a protective colloid, or the like.

It has surprisingly been found that, by appropriate heat treatment, the crosslinking agent can be distributed relatively uniformly in the molding, so that the crosslinking bonds can penetrate to a very good depth after the crosslinking process has ended. It was done.

The crosslinking itself can be achieved by appropriate treatments associated with the molding step and/or the step of introducing a crosslinking agent or a combination of crosslinking agents;
Alternatively, it may be carried out in a separate step by appropriate treatment, for example heat treatment.

In the former case, the heat required for the molding process can be used in whole or in part in the subsequent crosslinking process.

A particularly preferred variant of the inventive process is one in which the introduction of the crosslinking agent or crosslinking agents and the crosslinking are carried out in one and the same liquid medium in a closed pressure-tight system.

It is desirable that the liquid medium has approximately the same density as the molding so that the molding does not deform during heat treatment.

Therefore, the media density may be modified by adding one or more salts if necessary.

In order to control the degree of crosslinking particularly reliably, the peroxide-containing medium is replaced by a peroxide-free medium after heating, during which the crosslinking agent penetrates into the molding, thereby It is also desirable to prevent further peroxide from penetrating during the subsequent heating period.

Particularly in cable manufacturing, it is important to prevent sticking of coiled crosslinked products, and with this invention it would be possible to braid the cable after penetration of the crosslinking agent but before the end of the crosslinking process.

As mentioned above, it has been found that the method of the invention provides crosslinking with very good penetration depth and uniformity without deforming the molded article.

A standard test for the degree of crosslinking consists of determining the insoluble portion of the crosslinked polymeric material by extraction in a boiling stabilizing solvent.

For HDPE, it was found that 80-100% of the material was insoluble after crosslinking with the method of this invention by extraction in boiling stabilized decalin.

The treatment time, both for the introduction of one or more crosslinking agents and for the crosslinking itself, is influenced inter alia by the course of the treatment temperature, the
Depending on the species or polymeric materials, the wall thickness, the nature of the crosslinker or crosslinkers, and the desired degree of cross-straightening, it typically varies from a few hours to 24 hours.

Similar considerations apply to the process pressure, and the process of the invention can be carried out at atmospheric pressure or at higher or lower positive pressures.

In general, parameters such as temperature, treatment time and pressure can be varied within very wide limits.

The desired properties of the final product, such as degree of crosslinking, dimensional stability, permissible residual peroxide content, etc., are determined in this connection.

These properties are determined by the peroxide selected as well as by the course of the process.

The nature of this peroxide dictates the temperature, time, and pressure ranges.

In particular, by volatile components resulting from e.g. fillers,
Alternatively, the blistering caused by the decay products caused by the crosslinking agent and known in the above-mentioned continuous vulcanization (bl)
ister) can be prevented in the method of this invention.

This is achieved by appropriate selection of the parameters mentioned above.

For example, by treatment for a sufficiently long time the decay products can be dispersed, while the formation of the aforementioned blisters can be suppressed in whole or in part, for example by increasing the applied pressure.

In the method of this invention, as mentioned above, auxiliary agents can also be used.

They can be introduced during the molding process or mixed into the peroxide-containing liquid medium used.

Auxiliaries that can be used consist of polyunsaturated organic compounds such as triallyl cyanurate, sorbic acid, ethylene glycol dimethacrylate.

The crosslinking of the moldings after the introduction of one or more crosslinking agents can also be carried out, instead of by heat treatment, by treating the moldings at low temperatures with activators or accelerators of the crosslinking agents.

The method of the present invention will be explained below with reference to Examples. Example 1 Two tubes having an outer diameter of 17.0 mm and a wall thickness of 3.0 mm.
and 600x65xll. 515 g of polyethylene (trade name: 1 Hostale Tower (H
GM5010", melt index MFI 0.39/10min, density 0.955g/cc
, containing 2.5-3.0% carbon black) was placed in a cylindrical autoclave with a diameter of 80 mm and a length of 680 mm.

An emulsion was prepared from the following ingredients: An autoclave was filled with the above emulsion and distilled water, and the liquid was circulated through the autoclave by a piston pump which simultaneously acted as a homogenizer.

The liquid temperature was increased to 120° C. over 2.5 hours and maintained at this temperature for 4 hours.

The temperature was then raised to 133°C and maintained at this temperature for 14 hours.

After creating the crosslinks in this manner, the outer diameter of the tube increased from 17.0 mm to 17.2 mm, while the density decreased from 0.955 to 0.925 g/cc.

According to decalin extraction, this tube showed 97% gel content.

The tube showed no stickiness after being removed from the autoclave.

The 11.3 mm thick slab showed a gel content of 92% at a depth of 1 mm from the surface.

At a depth of 3-4 mm from the surface, the gel content was 80%.

Example 2 Length 60-65cm, outer diameter 17.0mm, wall thickness 2.8m
495 g of polyethylene (trade name 1 Hostalen GM5010'') consisting of 7 polyethylene tubes of m was placed in the same cylindrical autoclave as used in Example 1.

An emulsion of the same composition as used in Example 1 was prepared.

An autoclave was filled with this emulsion and distilled water, and the liquid was circulated through the autoclave at a rate of 6 l/mit by means of a gear pump.

The liquid temperature was increased to 115° C. over 2 hours and maintained at this temperature for 3 hours.

The temperature was then increased to 158° C. over 5 hours and maintained at this temperature for a further 7 hours.

After creating crosslinks in this manner, the outer diameter of the tube increased from 17.0 to 17.2 mm, while the density decreased from 0.955 to 0.918 g/cc.

According to decalin extraction, this tube is 99-100%
showed a gel content of

The tube showed no stickiness after being removed from the autoclave.

Example 3 One pressurized polyethylene slab of 100X70X12.5 mm (polyethylene without filler trade name 1 Hostalene GM6050", MFIO.3 g/1omir
, density 0.946g/cc), and 600x60xl
475 g of polyethylene, consisting of a 1.3 mm single extruded polyethylene slab (polyethylene, trade name "Hostaren GM5010"), was placed in the same cylindrical autoclave as used in Example 1.

An emulsion of the same composition as used in Example 1 was prepared.

After filling an autoclave with this emulsion and distilled water,
Polyethylene was crosslinked under the same conditions as in Example 2.

After crosslinking in this way, 'GM605
0" polyethylene slab, approximately 6" from the surface.
A gel content of 77.4% was observed at a depth of mm.

In the polyethylene slab of 'GM5010',
A gel content of 99.7% was observed at a maximum depth of 2.5 mm from the surface.

At a depth of 5-6 mm from the surface, the gel content was 86.2%.

Example 4 An unplasticized polyvinyl chloride profile with a wall thickness of approximately 1.5 mm was crosslinked.

An emulsion having the same composition as that used in Example 1 was prepared and applied to the emulsion in an amount equivalent to 10% by weight of peroxide based on the weight of the polyvinyl chloride molded article.

This emulsion was filled into a 2 l stainless steel autoclave with polyvinyl chloride moldings.

Gradually raise the temperature inside the autoclave to 125℃ (approximately 2
(for 48 hours) and maintained at that temperature for 48 hours.

After this treatment, the following changes were observed in the polyvinyl chloride molded product.

(a) Soxhlet extraction with tetrahydrofuran showed 25% insoluble residue (0% for untreated sample).

(b) According to the thermal deformation test (EMKO (10) 5 102/71Sec, 15a), when maintained at 95°C for 1 hour, a dent of 2.25 mm was observed (
4.0 mm for untreated samples).

(c) Mechanical measurements on an Instron tensile tester showed a Young's modulus of 70 bar/% (140 bar/% for the untreated sample).

Example 5 569 g of polyethylene consisting of 7 polyethylene tubes with a diameter of 17 mm and a wall thickness of 2.5 mm was prepared in Example 1.
placed in the same cylindrical autoclave used in .

These chews are Hostalen GM5010" or "Lupolen 5261z" (trade name, density 0.950, melt index (DIN 53)
735) 1.7 to 2.3 (at a load of 21.6 kg)).

For some of these tubes, use the following auxiliary agents, 2
The main tube was subjected to stress relief.

An emulsion was prepared from the following composition: After filling the emulsion into an autoclave and circulating it with a centrifugal pump at 82°C for 7 hours, the emulsion was mixed with Na2S03.
It was replaced with defoamed water containing 50g.

The temperature was increased to 1 at a rate of 3-5°C/hour for 12 hours.
The temperature was raised from 05°C to 150°C.

This temperature increase was lowest at relatively low temperatures.

After crosslinking, the density, gel %, and shrinkage along the length of each tube were measured and the results are shown in the table below.

Example 6 A 420v polyethylene tube consisting of eight polyethylene tubes with a diameter of 17 mm and a wall thickness of 2.5 mm was prepared in Example 1.
placed in the same cylindrical autoclave used in .

These tunes are one-tone mRepolen 5261Z", some are Rigidex H02054P" (
Product name, density 0.954, melt index (DIN
53735) 2.0 (at 21.6 kg load)).

The same emulsion used in Example 5 was prepared, but with 1.1-
Bis(t-butylperoxy)-3,3,5-trimethylcyclohexane 20I was the only peroxide component.

This emulsion was filled into an autoclave and circulated using a centrifugal pump.

The temperature was maintained at 94°C for 6.5 hours and then raised to 150°C over 9 hours, and the temperature increase was limited to 2-4°C/hour up to 110°C.

The temperature was maintained at 150°C for 2 hours.

After crosslinking, the following values were shown:

Claims (1)

[Claims] 1. Thermoforming a crosslinkable olefin or vinyl chloride polymeric material to form a molded article such as a tube, cable, slab, or profile having dimensions significantly longer in at least one direction than in the other; In the method for producing a crosslinked molded article, which comprises treating under heat with an organic peroxide, the heat treatment may involve the presence of an aqueous medium containing one or more peroxides and no swelling agent. a first heating step of heating the molded article under conditions in which the peroxide is immersed in the molded article but no substantial crosslinking occurs; and a peroxide in the same aqueous medium as the first heating step; The temperature is raised to such a temperature that the peroxide decomposes into substantial free radicals in a separate aqueous medium containing no chlorine, and the desired uniform degree of crosslinking of the polymeric material is obtained, and heating is continued. A method for producing a crosslinked molded article comprising two heating steps, wherein at least the second heating step is carried out by encapsulating the molded article in an aqueous medium preferably having approximately the same density as the density of the polymer material. .