DE1778947A1 - Flexible foam sheets and blocks made from olefin polymers - Google Patents

Description

Badische Anilin- & Soda-Fabrik AG 1778947

Our reference: O.Z. 25 644 Dd / Km Ludwigshafen am Rhein, June 21, 1968

Flexible foam sheets and blocks made from olefin polymers

The invention relates to a method for producing flexible Plates and blocks of greater thickness by gluing together several relatively thin sheets or sheets of foamed Olefin polymers.

Flexible sheets made from foamed olefin polymers are known; they are used e.g. for packaging, upholstery and insulation purposes. So far, such records have only been made up to a maximum thickness of 5 cm. However, there is a need for plates or blocks of greater thickness, e.g. Insulation of freezer containers that require an insulation thickness of 20 to 30 cm.

It is known from French patent specification 1 522 651 that such webs or plates can be produced by sintering foam-like particles of crystalline olefin polymers containing crosslinked portions (gel portions). The approximately spherical particles, which usually have a diameter of 3 to 20 cm, are poured into a closed mold, heated above the softening point, for example with hot air, and then by 40 to 60 % of the original

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Bulk volume compressed and thereby welded together .

Since the particles made of foamed polyolefins are very flexible, one can, for example, if the embankment is too high of 10 cm, do not produce foam blocks with a uniform structure and density. The foam particles become excessively compressed in the outer zones that are first exposed to the pressure, before the pressure is increased in the interior of the embankment to such an extent that the particles weld together to form void-free foams. So it is during the pressing inevitably leads to compaction in the outer zones in the Can be determined in comparison to the inside. This is disadvantageous in practice, since non-homogeneous foams are also not uniform Possess properties. For example, plates with uneven thermal conductivity when used in refrigeration technology does not provide adequate insulation. Furthermore, one would have to have a larger density foam block free of voids obtained, apply such a high pressure that the density of the foam would be greatly increased, which the economic Application possibility would diminish.

The task was therefore to find a method according to which one can produce relatively thick foam sheets and blocks with a uniform Can produce structure and uniform properties.

It has been found that flexible foam panels and - Can produce blocks more than 2 cm thick through

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Bonding of foam sheets or panels with a thickness of more than 1 cm, which have been produced by welding foam particles from olefin polymers with a gel content of 5 to 80 percent by weight, if the surface of the panels to be bonded is spaced apart by at least 0.5 mm Heated for 2 seconds to 5 minutes to a temperature of at least 5 ° C above the lower softening limit of the polyolefin used, compresses the plate on the hot surfaces for more than a tenth of a second by at least 1 % of its volume and then releases the pressure again.

According to the invention, a product is then obtained which, in addition to a uniform structure and a uniform volume weight, also nor a very low thermal conductivity and a low water vapor permeability while maintaining flexibility.

Compared to the usual closed-cell foams, e.g. based on polystyrene, the water vapor permeability is many times lower. This can help you when laying the foam sheets as insulating material in many cases dispense with the otherwise necessary vapor barrier, because the foam itself represents a vapor barrier.

For the purposes of the invention, olefin polymers are to be understood as meaning crystalline olefin polymers whose X-ray crystallinity at 25 ° C. is above 25 % . Homopolymers of ethylene, propylene and are suitable for the process

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Butene or copolymers of these monomers; Particularly suitable are polyethylene, especially high pressure (LD) polyethylene and copolymers of ethylene with ethylenically unsaturated monomers, e.g. with butyl esters of acrylic or methacrylic acid.

Foam-like olefin polymers with predominantly closed-cell Structures are produced according to the usual methods, e.g. by placing a volatile blowing agent on the extruder agent incorporated and relaxed after leaving the extruder or by adding blowing agents, which then decompose to gaseous products when heated.

For the process according to the invention, foam-like particles are used, the density of which is preferably between 20 and 50 g / l and whose diameter is between 3 and 30 cm. You fall in the above-described foaming process either directly in this size or by crushing the during the foaming process produced moldings.

The foam-like particles should contain crosslinked components, that is, some of the molecules should be in crosslinked form. Such particles are particularly suitable for the method from olefin polymers, which have a gel content of 5 to 80 percent by weight, preferably contain from 20 to 70 percent by weight gel fractions. Under gel fraction is the weight fraction of the To understand polymers that are insoluble in solvents at temperatures above the crystallinity melting point. In the case of olefin polymers, for example, the gel content is through

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Determined η 10O ⁰ C 1 filtration and drying of the insoluble fractions.

The particles are heated in toluene to temperatures of 100 ^° C. and

The foam-like particles containing crosslinked components can be used obtained by various methods. Among these, a mode of operation in which the foam-shaped closed-cell particles are treated with high-energy rays. For example, X-rays or electron beams can be used let act on the particles. One way of producing the particles that is particularly suitable is to use the small-sized ones Treated olefin polymers with electron beams, the dose of which is between 5 and 60 Mrad.

But it is also possible to crosslink foam-like particles with To use proportions that are obtained by reacting with compounds that decompose into radicals.

Sometimes it is advisable to add peroxides to such mixtures, which cause further crosslinking of the molecules of the olefin polymers. The comminution products of moldings, for example, are suitable from olefin polymers obtained by foaming using azodiisobutyronitrile.

The particles of the foamed olefin polymers can also Polymers and other components, such as flame retardants, dyes, fillers, lubricants or other polymers, e.g. polyisobutylene, contain. Sometimes it is advantageous to mix the foam-like particles with coarse-grained or aqueous filling or reinforcing

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processing materials. Wood fibers, for example, come as such porous other materials or fibers made of thermoplastic plastics in question. Coarse-meshed fabrics or grids, e.g. made of thermoplastics, can also be used as reinforcement inserts work into the moldings.

The welding of the particles to sheets or webs is done according to the usual method described in French patent 1 522 651 by heating in closed molds with hot air, infrared rays or hot liquids and then compressing by 5 to 60 % of the original bulk volume.

The gluing of the relatively thin foam sheets and panels according to the invention can be carried out in various ways: For example, it is possible to heat the surface of the inside of the panels with a stream of hot air between two panels placed at a short distance from one another and then press them together. The heated inner surfaces can also be slightly inclined to one another during heating, for example in a wedge shape, so that the heating is started at the point of the smallest distance and, with increasing compression, the weld is extended over the entire surface of the plates.

The method can also be set up in such a way that rolling foam webs are continuously guided at short distances from one another , the heating being provided in the middle between the two webs.

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In all variations, however, it is essential that the distance between the panels or tracks is at least 0.5 mm when heated, otherwise the panels can stick together in an irregular manner even before they are pressed together. _{You can also stretch an approximately 100 /} u thin film made of the same polyolefin as the foam between the panels or webs to be bonded. It melts when it is subsequently heated and enables better bonding.

The heating itself is usually done with a stream of hot air carried out; but it can also be achieved by short-term irradiation with infrared heating or by leading the surface to be heated past a heated wedge-shaped metal plate will.

The temperature during heating can briefly up to 60 C above the softening point of the polyolefin used. The softening points for polyolefins are determined using the penetrometer melting point method (DIN 53 445) measured. Usually no Specify a defined softening point, but only specify a softening range, e.g. for high pressure (LD) polyethylene at 105 to 115 ° C and for polypropylene at 157 to 163 ° C.

The temperature that is used during bonding should be at least 5 ^° C. above the lower limit of the softening range (“lower softening limit”), otherwise the polyolefin no longer melts sufficiently and the bonding becomes incomplete.

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In the case of foam sheets with a lower gel content, e.g. those from copolymers of ethylene with vinyl esters or Esters of unsaturated carboxylic acids or are made from polybutene, it is advisable to avoid excessive heating, otherwise the foam will shrink during heating.

The duration of the heating depends on the difference between the temperature used and the softening temperature of the Plastic. If there is a large difference, you should only warm up briefly, if there is a small difference, longer. You have to use the foam sheets However, hold or plates at the bonding temperature for at least 2 seconds, otherwise the plastic will not be sufficiently Dimensions melted and not enough after the subsequent pressing sticks. However, you should not heat for longer than 5 minutes, otherwise the foam particles will deform can. It is essential that the heating is continued until the surface has softened sufficiently is.

One can find the optimal heating temperature and time in a simple Way to determine by experiments, assuming that the foam sheets or sheets to about a depth of 0.2 to 2 mm should soften so that the panels or sheets stick together sufficiently.

When the time necessary for sufficient heating has passed, the plates or webs are pressed together. The bigger

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the pressing pressure, the shorter the pressing time can be. In order to ensure a sufficiently strong bond, however, it must be pressed for at least a tenth of a second. The pressing pressure must not be so strong that the foam is irreversibly deformed: it should, however, be at least so strong that a volume contraction of the plate by at least 1 % occurs during pressing. This causes the plates to come into contact with one another on the heated surface and stick together. By gluing, the panels or sheets are inseparably connected to one another. When trying to separate them again, the foam webs tear within the individual particles.

After the end of the gluing process, the pressure is released again; the plates then stretch almost on top of it again previous volume. A small volume contraction caused by the welding of the foam particles on the heated surface is retained.

The parts given in the example are parts by weight, those mentioned Percentages by weight.

example

Two foam sheets 40 mm thick, which consist of foam-like, crosslinked particles containing particles from a crystalline polyethylene produced by the high pressure process with a melt index of 1.5 and a softening range from 105 to HO ⁰ C are presented. The particles were in front of the

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Production of the foam sheets subjected to radiation of 15 Mrad in an electron accelerator. After this treatment, the gel fraction of the particles was 45 %.> The particles are inseparably welded to one another in the foam sheets. The two plates are brought closer to one another at one end to within 1 mm. Is now on the inside of the plates, starting blown at the end side with 1 mm spacing, an air stream of 16O ⁰ C against the surfaces. After a heating time of 5 seconds, the two plates are pressed against one another on this face and at the same time the hot air flow is moved in the direction of the face with the greater distance. As the distance progresses from the end face, which has already been pressed together, the two plates are simultaneously pressed together by 30 % in an even sequence, namely by pressing between rotating rollers. The heating and pressing is continued uniformly until the entire surface is heated and, after pressing, is welded.

The result is a flexible foam sheet with a thickness of 78.5 mm, which is very suitable for the thermal insulation of containers. As they are flexible, the plates can be placed against the container wall and fixed on the outside with a bandage.

The plate has a uniform density of 28 g / l, a thermal conductivity of 0.033 Kcal / m.hour. ⁰ C at O ⁰ C and a water vapor diffusion resistance factor of 950.

In a similar way, the production of several thin plates

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or webs can be set up so that foam sheets are larger Thicknesses, which are made up of 2 to 6 individual strips, arise.

For comparison, a plate of the same thickness of 78.5 mm was produced under the same conditions under which the individual panels had been produced (according to the method described in French patent specification 1 522 651). This is not completely free of voids; it has a density of 25 g / l on the inside of the plate and 65 g / l on the edge; the thermal conductivity fluctuates between 0.033 and O _s O38 Kcal / m * hour · ⁰ C at O ⁰ C; the water vapor diffusion resistance factor is less than 300.

Such a plate is not suitable as a thermal insulation material.

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Claims (1)

- 12 - O.Z. 25th Patent right Process for the production of flexible foam sheets and blocks with a thickness of more than 2 cm by gluing together foam sheets or sheets with a thickness of more than 1 cm, which have been produced by welding foam particles from olefin polymers with a gel content of 5 to 80 percent by weight, characterized in that the surface of the plates to be bonded is heated at a distance of at least 0.5 mm from one another for 2 seconds to 5 minutes to a temperature of at least 5 ° C. above the lower softening limit of the polyolefin used, the plates "an" .Hot surfaces together for more than a tenth of a second by at least 1 % of their volume and then releases the pressure again. Badische Anilin- & Soda-Pabrik AG «Tue 10Si * 32 / U22 BATH ORIGINAL