FI79970B - FOERFARANDE FOER FRAMSTAELLNING AV KOMPOSITPRODUKTER. - Google Patents

Description

79970

This invention relates to a method of making bonded composite products from a plurality of incompatible materials by extruding a flow of a first plastic through a nozzle to form a profile, forming an overlapping so that it surrounds the protrusions and penetrates the cavities and curing the coating material. Composite products can be wires, pipes, plates or tapes.

The variety of properties that can be achieved with different types of plastics logically leads to attempts to make parts in which two or more different properties are combined using laminates or composite layers. Thus, it has long been known that it would be desirable to be able to make a tube in which the lightness, good strength and rigidity of a glass fiber reinforced thermosetting resin are combined with the flexibility and chemical and wear resistant properties of a thermoplastic such as polyethylene.

Because the former is not very resistant to chemicals, especially under stressful and abrasive conditions, and the latter is not very rigid, especially in extreme heat, polyethylene-lined fiberglass-reinforced thermosetting plastic is an example of a product that would offer an interesting combination of properties.

However, attempts to produce such a product have largely failed. First, it has been found that polar resins such as polyester, which is commonly used in glass fiber reinforced plastics, do not readily bind to non-polar thermoplastics such as polyolefins. Therefore, for example, a polyethylene lined 79970 2 "fiberglass" tube has been found difficult to implement because the liner may collapse and detach due to thermal expansion or under vacuum conditions, forming a harmful blockage in the tube or causing the liner to crack or break. Depending on the use, other undesirable situations may also arise when the liner and outer shell are not sufficiently bonded. For example, one layer may terminate longer or shorter at the ends of the tube due to expansion or elongation than the other, making it difficult to form proper joints.

Some attempts have been made to improve engagement by machining or hitting a groove pattern on the surface to which the adjacent plastic penetrates. But even this technique does not provide sufficient bonding without a hollow or undercut form, which is difficult to achieve in automated processes commonly used in the manufacture of plastic bodies, which are thus suitable for extrusion processes.

Some chemical bonding can be accomplished by special techniques such as open flame or corona discharge treatment. However, these bonding techniques are difficult, unreliable (especially when the surface is smooth) and tend to lose their effect over time, making the product unreliable and insecure as it ages.

British Patent Publication 1,229,938 discloses a method according to the preamble. In it, irregular protrusions and cavities formed on the surface of the profile are provided by heating at least the surface of the profile into a plastic space after which a fine material such as powdered or fibrous thermoplastic material or molten particulate metal, e.g. zinc, is blown into said plasticized surface. This method can, of course, somewhat improve the coating

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I attach to the surface of the profile, but at the same time the work steps in the manufacturing process increase and the manufacturing costs increase.

It is an object of the present invention to overcome the above-mentioned difficulties and disadvantages and to provide a method for manufacturing bonded composite products in an efficient and cost-effective manner by extrusion.

It is a further object of the present invention to provide a method by which two incompatible plastic layers can be formed into composite pipes having a degree of mechanical bonding that makes them safe, reliable and structurally sound.

These objects and other advantages are achieved by a method of making composite products from a plurality of incompatible materials, by which is meant those which have a very low affinity to bind to each other or which do so reluctantly. The method is characterized in that a rough irregular surface is formed by coextruding a second stream, into the first stream, into a profile surface layer of molten plastic through a nozzle mixed with a foreign substance capable of breaking the homogeneous structure of the plastic, and allowing the resulting surface layer to break out of the nozzle. due to shear stresses due to friction against the nozzle surface.

In one embodiment of the invention, a gas-forming substance is used in the second flow, whereby due to the high temperature and the pressure drop in the nozzle opening, the expansion of the gas-forming substance is caused so that the voids are broken.

In its further development, the invention can be carried out by cooling the nozzle area close to the outer opening so that the nozzle 4 79970 is colder than the melt flow, thus causing a certain friction and shear stress in the second plastic flow. Due to the foreign matter disrupting the homogeneous structure of the plastic flow, this flow tends to tear and break, thus forming a rough surface. Thus, it can be seen that the foreign substance need not be a gas-forming substance, but can be any substance that causes weakness in the structure of the plastic so that it breaks.

It can also be modified by incorporating such a foreign substance into the second layer that has an affinity for the second plastic, and because it remains implanted in the second layer, it provides some adhesion to the second plastic coating.

The first stream may be extruded in a profile shape such as a cylindrical tube or may form flat sheets or long narrow strips which may be helically wound to form the inner layer of the composite tube.

This technique can be used to form composite products from a wide variety of incompatible materials. For example, non-polar polyolefins which are difficult to bind to other products and which can be formed on a rough surface according to the process of this invention include common plastics such as polyethylene and polypropylene.

Examples of another material that may be desired to be combined with the former, but which is often incompatible with it, include concrete, polar thermosetting resins such as polyester, and insulators such as cellular polyurethane, polyvinyl chloride, phenol, and cellular polystyrene.

The invention can be better understood from the accompanying description of an embodiment directed to the manufacture of a cylindrical composite tube, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of an extrusion head that can be used in a method of making composite pipes;

Figure 2 is a partial sectional view of the plastic profile as it exits the nozzle end of Figure 1;

Figure 3 schematically shows a later step in the method of forming a composite pipe using the profile shown in Figure 2;

Figure 4 shows a partial sectional view of a composite pipe formed by the method and apparatus shown in Figures 1, 2 and 3;

Figure 5 is a perspective view showing the structure of such a composite pipe; and

Figure 6 shows another method in which the present invention is used to form composite pipes by threading.

The extrusion head shown in Figure 1 is of the type typically used in conjunction with an extruder designed to feed hot molten plastic to the die. The nozzle body 2 of Figure 1 has an inlet 4 from the extruder and connects to the main passage 6. The nozzle shown uses perforated rings 8 and 28 to further mix and homogenize the material flowing therethrough, and the main channel 6 narrows into a narrower nozzle section 10 which is also cylindrical of uniform cross-section.

While the nozzle channel 12 is, in the case of a conventional cylindrical tube, distributed over its entire circumference, the channels 6 6 79970 may be one or two or three or four or more arranged in the same radial spacing around the axis.

The nozzle shown is provided with a second channel 14 leading through a horizontal channel 16 to a perforated ring 18 and a shrink portion 20 and finally to a feed opening 22 immediately adjacent the outer periphery of the outlet of the main channel 10 upstream of the outer periphery of the nozzle channel 12.

The nozzle shown is also provided with a third channel 24 leading to the outlet opening 26 immediately before the inner circumference of the nozzle channel 12. However, in the preferred embodiment described herein, this third channel is closed and not used.

In use, molten plastic such as polyethylene is fed from the extruder cylinder to the nozzle head inlet 4 where the perforated plate 28 provides flow distribution to multiple channels for further mixing and homogenization, then passes through the second channel perforated ring 8 into the main channel 6 and finally , from which it exits at the outlet 30, as in this example as a continuous or endless circle or tube.

As is well known to those skilled in the art, this type of extrudate is typically then passed through a calibrator and cooling bath to maintain the correct dimensions and shape of the extrudate while allowing the plastic to cool and cure to a point where it is rigid enough to remain in shape. Therefore, cooling and calibration are not shown here.

In the embodiment described herein, a second flow of molten plastic (ideally from a second extruder) that also

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7,79970 is polyethylene, but contains on the order of 0.5-3 or 4% of a gas-forming substance mixed therewith, is passed through channels 14 and 16 and from the homogenization grate 18 to an outlet 22 where it becomes coextruded as an outer layer into the main stream flowing from channel 10.

It should be noted that due to the viscosity of the plastic, its friction against the walls of the nozzle channels and the constrictions therein, considerable pressure is required to provide flow to the outlet 30. Depending on the viscosity of the polyethylene, this pressure may be as high as about 200-400 kg / cm 2 at the nozzle it drops as it travels along the channel 12 to a point just before the outlet 30, where it suddenly drops to about zero. Temperatures through the nozzle from 4 to 30 are typically in the range of 210 to 230 ° C.

Such high temperatures would otherwise cause the gas-forming material to evaporate and expand, but the high pressures in the nozzle prevent it from doing so. However, when the extruded material reaches the outlet or nozzle orifice 30, the pressure is suddenly released and the trapped gas-forming material in the outer layer coming from the channels 14, 16 and 20 evaporates and expands under high temperature and the resulting suddenly released pressure to form a large number of small broken bubbles on the entire outer surface.

While the gas generating agent creates voids in the outer layer, some of which burst or rupture open, the friction of the wall of the channel 12 against the surface of the outer layer creates shear stresses in the polyethylene, which also causes the voids to rupture.

It has been found that this occurs especially when the walls of the duct 12 are cooled to a temperature below the norm- β 79970 painfully prevailing (i.e. below the melt flow temperature). The resulting shear stresses cause the rupture of empty spaces and the rupture of the bridges between the empty spaces. The result is a pattern of irregular protrusions and cavities on the surface with a large number of undercut profiles due to the back-bounce or "bounce" reaction of the plastic in its elastic state.

Thus, unlike the typically flat surface of an extruded plastic profile, a tube made in this manner has an extremely rough surface with thousands of very small protrusions and recesses, some of which are inverted or retracted in shape, as shown at 40 in Figure 2.

Since the two flows are the same (or at least compatible) substance, a substantial or even complete fusion of the two layers takes place, whereby the thickness of the pipe wall 32 will be substantially homogeneous and structurally uniform.

We have surprisingly found that such a rough surface provides an ideal means for mechanically bonding materials to the outer surface of the tube 32 that would otherwise be difficult or impossible to chemically bond, such as polar thermosetting resins, e.g., epoxy or polyester of the type used in glass fiber reinforced plastic.

Figure 3 shows schematically how a tube such as that shown in Figure 1 can be converted to a composite tube by first applying a layer of thermosetting resin and then a fiber bond or a second layer 50 (using techniques well known in tube technology) which may be formed of glass fiber impregnated with thermosetting epoxy or polyester resins.

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Alternatively, the mixture of thermosetting resin and glass fibers can be "drawn" onto the inner tube 32 in a known manner, passing the inner tube through a drawing press and applying an outer resin layer thereto, and curing. Other techniques can also be used, such as spraying a mixture of resin and fiberglass onto the outer surface while moving the tube forward.

Whatever coating technique is used, the result is a composite pipe comprising an inner layer of polyolefin (here polyethylene) which is well known for its chemical and abrasion resistance and is capable of protecting a glass fiber reinforced polyester layer. On the other hand, a fiberglass-reinforced polyester layer is a lightweight way to provide substantial ring strength, impact resistance, stiffness, and strength that could not be obtained with more flexible and flexible polyethylene.

In addition, using the technique described herein, the two layers, which would normally be difficult to bond together, are nevertheless firmly mechanically bonded together due to the rough irregular surface of the inner tube 32. The irregular protrusions protruding from the inner tube sink into the resin of the outer layer 50 and a portion of the polyester resin penetrates the folded or retracted cavities of the inner tube, as can be seen from the representation in Figure 4.

Figure 5 shows a tube structure in which a rough-surfaced polyester-lined tube 32 is coated on the outside with a plurality of layers of fiberglass-reinforced polyester, such as 50.

Although a composite pipe having a rough outer surface coated with a second layer has been described above, the nozzle shown in Figure 1 could be used to form a rough rafter on the inner surface 34 of the pipe by passing a gaseous polyethylene stream from channel 24 to outlet 26 by a method similar to that described above.

Such a structure could be used, for example, to attach the inner tube to the inside of the polyethylene sheath when the ring space is to be filled with insulating foam.

Experiments with the prior art have resulted in examples of typical manufacturing conditions, these results are shown in Table I.

For example, in Example 1, HD polyethylene having a melt flow index (MFI) of 0.5 (measured at 190 ° C / 5 kg) and a density of 0.95 and a melting temperature of 220 ° C was used as an inner layer to make a pipe with an inner diameter of 130 mm and a wall thickness of 4 .5 mm. For a coextruded outer layer of HD polyethylene with a melt flow index of 0.8 (190 ° C / 2.16 kg) and a density of 0.95 with 0.8% azodicarbonamide gas-forming agent and a melting point of 225 ° C , a textured surface about 0.5 mm thick was obtained, with an average peak height of 1.7 mm.

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Although the previous preferred embodiment deals with the use of a gas-forming agent in a coextruded second layer forming an outer layer for a polyethylene inner liner, it is possible to achieve substantially the same effect when using another foreign substance (meaning this substance not homogeneous with plastic flow) such as fine particles, water particles. (although some also consider water as a gas-forming agent) and other types of fillers or fibers that disrupt the homogeneous structure of the flow and give it poorer flow properties so that as the plastic flows through the nozzle, the outer layer ruptures and breaks into a rough irregular surface due to shear stresses. In this respect, fillers with low affinity for non-polar polyolefin resins act in much the same way as gas bubbles when the molten polymer exits the nozzle orifice, and also create voids on the surface of the outer layer.

In a further development form, particles of polar polymers such as PVC can be used because they have a good chemical affinity for thermosetting resins and thus form regions on this outer layer that can bind the outer layer (in this case the polyester layer).

Although the preferred embodiment illustrates a tube made by extruding a polyethylene cylinder to form an inner liner which is then coated on the outside with glass fiber reinforced polyester by injection, compression molding, or helical twisting, it is also possible to make a flat tube similar to that shown in Figure 6. and a narrow strip 60 helically wound around the cylinder 62 to form a cylindrical tube length 64. This technique is particularly useful

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13 79970 when it is desired to produce a large-diameter pipe, the walls of which, however, are relatively thin, a structure which, without support, would tend to collapse.

If the strip 60 is extruded according to the method described above using a frangible outer layer, the outer layer of the tube 64 obtains a similar rough structure which can then be coated with a stiffer material such as fiberglass reinforced polyester described at 66 and 69. Additional layers are shown at 68 and 69.

Although the preferred embodiment describes a method of coating a polyethylene liner with another plastic such as polyester, it may be necessary to use other materials that would normally poorly bond to a uniform polyethylene liner, e.g., concrete or clay. Thus, although a preferred embodiment has been described for bonding incompatible plastics (which herein refers to poor affinity or reluctance to bond), this method of forming a rough surface may benefit from other similar uses in forming composite bodies that do not need to have cylinder profiles such as tubular profiles.

With the procedures described above, it is possible to produce a plastic profile with a rough surface by relatively fast, automatic and inexpensive extrusion, and by combining this rough surface with a second plastic layer in the uncured state, it is possible to provide a composite pipe or other body combining two different types of plastic. Difficulties in bonding two incompatible plastics are avoided and a safe, reliable and durable product is obtained.

79970 14

Of course, it will be appreciated that the process and product obtained therefrom may be modified and varied without departing from the inventive idea set forth herein.

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Claims (5)

A method of making composite composite products from a plurality of incompatible materials by extracting a flow of first plastic through a nozzle (2) to form a profile (32), forming irregular protrusions and a pattern of cavity (40) on the surface of the profile (32), adding a profile-compatible material flowing coating (50) on a rough surface so that it surrounds the protrusions and penetrates the cavities (40) and curing the coating material (50), characterized in that the rough irregular surface is formed by coextruding the second stream into the first stream, melting the profile (32) (2) through which a foreign substance capable of breaking the homogeneous structure of the plastic is mixed with the second flow, and by allowing the surface layer thus formed to break as it exits the nozzle, under reduced pressure and frictional forces against the nozzle surface; the impact of the changes. A method according to claim 1, characterized in that the foreign substance belongs to the group comprising a gas-forming substance and a particulate filler, wherein the particulate filler belongs to the group comprising a powdered mineral and a powdered PVC. A method according to claim 1, characterized in that the rupture of the surface layer is achieved by a combination of a high temperature causing the expansion of the gas-forming substance, a sudden decrease in the high extrusion pressure at the nozzle orifice and shear stresses caused by cooling the nozzle. 16 79970 A method according to claim 1, characterized in that the surface layer of the plastic profile (32) is a non-polar thermoplastic polyolefin and the second material is a polar thermosetting resin. Method according to claim 1, characterized in that the profile (32) is a cylindrical polyethylene tube and the coating (50) is a helically twisted glass fiber-reinforced polyester (52).