DE2142855C3 - Process for the production of molded articles from plastic - Google Patents

Description

The invention relates to a method for producing molded bodies made of plastic, which have a good foamed core or a well foamed layer and a non-foamed or only slightly foamed surface exhibit.

Moldings made of plastics with a foam structure have recently been widely used as building materials, used as packaging material and for other purposes because these plastics Not only are they light and have a low cost price, but also because they are excellent have heat-insulating properties and also have a strong shock-absorbing and sound-absorbing effect.

Moldings made of such plastics, however, have the disadvantages of a lower mechanical Resistance to non-foamed plastic moldings. To overcome this disadvantage and thereby to expand the area of application of molded articles made of foamed plastics, one has already tried several times, the mechanical properties of such moldings made of foamed plastics to increase. This is achieved, for example, by having the foamed moldings with a thick and solid surface layer, which not only improves mechanical strength is, but such composite moldings also retain all those favorable properties, which foam moldings have. U.S. Patent 3,455,483 and Japanese published patent application 46-10316 is the production of such composite moldings made of foamed plastics with one or more surface layers. This well-known The method of operation consists in first placing a non-foamed one on the inner wall of a molding tool The surface layer is produced and only then is filled with a foamable plastic, whereupon the Mold is heated for the purpose of carrying out the foaming process. Although on this Wise molded bodies made of foam with a separate surface layer are what it is the disadvantage that the mold in two process stages with the plastic material in question must charge and that the mold must be heated twice, whereby increase manufacturing costs significantly. In addition, it is difficult in this way of working, an intimate and complete bonding between the non-foamed surface layer and the foamed one Manufacture inner layer.

US Pat. No. 3052927 also discloses a one-step process for the production of composite moldings known from foam plastics with special surface layers. This is a uses rotating mold that is rotated at such a speed as centrifugal forces appear. Polyurethane, for example, is used as a foamable material. With this one In the process, the foam formation begins at those points on the mold that are affected by the axis of rotation are further away. Therefore, the density in the obtained molding differs stepwise depending on the direction in the molded body. This mode of operation has the disadvantage that the required for the generation of the high rotational speed, expensive devices are required, and moreover is the Visco-elasticity of the plastics used at the time of foaming is very high, especially when a foamable thermoplastic resin is used.

5 »According to another known way of working, which is described in U.S. Patent 3,542,912 is processed in the mold, a molding compound, which is made of polymers with low and with a high melting point. When the mold rotates, the polymers form with low Melting point the outer layer, while those with high melting point polymers the inner or form core layer. This working method is accordingly based on the use of such polymeric substances

ho restricts which in themselves are not compatible with one another are, and there is also the disadvantage that the outer layer of the molded body is made of the polymer with a low melting point and therefore not sufficiently heat resistant.

μ After an older, but not pre-published Proposal according to DE-PS 2061112 to produce molded articles from thermoplastic Plastic covered by a layer of foam

structure have a non-foamed layer, propellant-containing and blowing agent-free, thermoplastic Resin particles of different heat capacities are used.

The present invention is therefore based on the problem of solving the problems mentioned known method to eliminate and a method for the production of molded articles Plastic available in one process stage too set, in which plastic particles of different particle sizes are used, the shaped Objects have a foam structure on the inside and a surface that is evenly thick and solid Have layer, which the latter is not or only slightly foamed and works well with the inner, foamed Core is connected.

The present invention relates to a method for producing molded articles made of plastic, the one over a core or a layer with a foam structure a non-foamed or only slightly foamed layer have, in which thermoplastic plastic particles of different sizes, of which at least the larger particles contain a propellant and are preferably in the form of granules and the smaller plastic particles are preferably present as a powder, are introduced into a mold which The mold is heated and the mixed particles are agitated in the mold until the particles melt in the heat and the propellant decomposes. This method is now characterized in that the plastic particles contain a crosslinking agent with a significantly larger particle size.

In the method according to the invention, the tool should rotate at such a speed be that practically no centrifugal forces are generated.

In the method according to the invention, the plastic adheres in powder form, i.e. with a small particle size, first on the inner wall of the mold and thereby forms the surface layer, and the plastic with the larger particle size, i.e. in the form of granules, adheres to the surface layer thus formed. Since a relatively large amount of propellant is expediently beforehand is incorporated into the plastic in granulate form, this foams to such an extent that the mold is completely filled. In this way, a molded body is obtained which has a thick and solid surface layer and a well-foamed core, as shown in FIG. 4 and 5 can be seen.

It is important in the context of the invention that at least two plastics are different Particle size are present in the molding composition. To clearly mark this difference, see below generally of plastic in powder form for the smaller particle size component and of Plastic in granulate form for the component with a larger particle size, which is also the propellant contains, spoken. However, this does not mean that with regard to the shape of the \ ui, totof particles any Difference needs to exist. Rather, these details only relate to the relative size difference the plastic particles.

The shape of the individual plastic particles is not important. It can be in any case be powder particles, granules, pellets, cubic or spherical particles. Important is just the size difference. The size of the plastic particles should generally be around differ by a factor of three and preferably by a factor of ten, these sizes being different in the case of spherical shapes, refer to the diameter.

In the method according to the invention, due to the difference in size of the plastic, in Powder form and the plastic in granulate form and

ίο also due to the different speed, with which the plastic particles move in the rotating mold, very easily one Surface layer and a separate, well-foamed inner or core layer. Since this The separation process takes place while the plastics are melting, the melt viscosity is the one used Plastic components without influence.

In addition, it is possible with the method according to the invention to apply additional layers only for the surface layer Use additives, for example fire retardants, antioxidants, UV rays absorbing agents, antistatic agents and reinforcing agents in powder or fiber form. on in this way there is a considerable cost saving in relation to what is usually very expensive Additives.

For example, it is possible to use lightweight but very strong machine supports and other shaped bodies manufacture, which has a surface layer made of, for example, polyethylene or high-density polypropylene, made of ABS resins (acrylonitrile-butadiene-styrene copolymers), from polyamides or from polycarbonates, and with an inner core made of crosslinkable polyethylene with good foam properties.

However, even larger amounts of other, finely divided substances can also be added to the molding compounds used are, for example, hollow glass beads or other lightweight materials, whereby molded bodies are obtained which contain glass spheres or corresponding lightweight materials in the foamed core layer and also have the desired hard surface layer. Such moldings show a excellent heat resistance and are therefore very suitable as thermal insulation material.

It is also possible to incorporate plastic waste into the inner core layer, whereby one the plastic waste is appropriately shredded to a size that is about the same as the foamable plastic granulate corresponds.

It is also possible to produce moldings which have three or more different layers have, and for example from a well foamed inner core, a non-foamed one Layer and a lightly foamed layer exist. For this purpose, a molding compound is used Contains soft plastic particles of three different dimensions. This molding compound consists for example from a very finely powdered synthetic

bo fabric, which is only slightly foamable, consists of a granular, easily foamable plastic and from a coarse powder of a plastic, the particle size of which lies between that of the fine plastic powder and the plastic granulate. By

_b 5 suitable selection of such a plastic in coarse powder form can also produce an extremely strong bond between the surface layer and the inner core layer.

Any thermoplastic material that is suitable as a plastic component in powder form is is networkable. Mixtures of these types of plastic can of course also be used. The above-mentioned crosslinkable plastic can be polymers containing crosslinking agents have been added, for example organic peroxides or acting as crosslinking agents Azides. In addition, thermoplastics can also be used, which previously through the addition of chemical compounds or through appropriate radiation measures up to have been crosslinked to such an extent that the flowability is not impaired thereby will.

It is essential that those present in the molding compound Plastics of small particle size are comminuted in relation to the granular ones Plastics that they melt easily and during the rotational movement of the mold rather get to the inner wall of the same than the granular plastic. However, care must be taken be that the particle size of the powdery plastic is not chosen too small, because Otherwise these fine particles can coagulate during the rotary movement of the mold, whereby their mobility within the mold is reduced. This then becomes the required Separation process between the powdery and granular plastic particles disturbed and it is difficult to produce surface layers of uniform thickness.

The size of the particles of the powdery plastic component must therefore be taken into consideration the type of plastics concerned, the size and shape of the mold and the particle size of the granular plastic can be selected. In general, the particles are said to be powdery Plastic should be smaller than a ten-mesh screen and preferably should the particle size must be smaller than that of a thirty-mesh screen. It is also useful when the particles of the powdery plastic soften more quickly and easily than those of the granular plastic, as in this way the adhesion to the inner wall of the mold is facilitated.

Since, however, according to the teaching of the invention, there are always two plastic types η with different particle sizes are used in the molding compound, it is not absolutely necessary as a powdered plastic component select a type that softens more easily than the granular plastic. For example, a polypropylene with a powdery plastic can be used with good results Melting point of 160 ° C and use a high-density polyethylene as the granular plastic. So that the powdery plastic has good mobility and fits well within the mold dispersed, plastic powders are preferably used which are caused by sedimentation obtained from a solvent. These powders are opposed to those made by mechanical Crushing obtained plastic powders is preferred. A well-balanced range of motion and to ensure easy melting within the mold, it is in some cases expedient to use two different types of powder, for example mixtures of a powder with Particles corresponding to a two hundred mesh sieve and a powder with particles corresponding to a thirty to fifty-mesh screen. According to another embodiment of the invention This method can also improve the mobility within the molding tool be that one additional powdery, non-organic fillers or metal powder with good thermal conductivity and higher density than the plastic powder. These powders of such Substances can simply be mixed in mechanically using a suitable mixing device. Powders of calcium carbonate, magnesium sulfate, zinc white, for example, are suitable for this purpose. Clay, talc or aluminum.

Since, according to the method according to the invention, above all molded bodies with a very solid surface layer Are to be manufactured, are set as plastic in powder form mainly hard Polymers used such as polypropylene, high density polyethylene, polyamides, ABS resins, hard adjusted polyvinyl chloride resin and / or polycarbonate. Moldings produced according to the invention, the surface layer of which is made of a polyvinyl chloride resin, has flame-retardant properties and are therefore particularly suitable as building material and for transport devices. To the To further promote fire retardant properties, a relatively large proportion can be in the surface layer of a non-organic material in powder or fiber form. Because the surface layers the moldings produced according to the invention have the highest possible mechanical strength should have, they are foamed only very weakly, and even if a strong foam formation takes place, this is directed so that the foam cells maintain a spherical shape. If such moldings to be used for transport devices, however, it is often desirable that they be softer Have surface, and in this case the powdered plastic can have a larger proportion of propellants are added so that polyhedral cells are formed in the surface layer. For Such applications are preferably a crosslinkable plastic as a powder component used, the crosslinking agent or blowing agent expediently by means of a roller or an extruder incorporated into the plastic and then this mixture into a fine Crushed powder. If you have a crosslinkable thermoplastic as a powdery plastic component Plastic uses, the shock absorption of the molded body is improved and the

The amount of material flowing out of the mold is reduced. If a molding tool is used whose inner surface has a pattern can also be applied to the surface of the -Form body achieve very nice patterns. the

The thickness of the surface layer in the moldings according to the invention is approximately 0.5 to 15 mm, with Thicknesses of 2 to 7 mm are preferred.

The granular plastic component present in the molding compositions used can be a

be any thermoplastic polymer that has sufficient flowability when the blowing agent decomposes or evaporates. In addition, mixtures of such plastics and natural

chemical or synthetic rubber can be used. In any case, however, it is within the scope of the invention Process important that the granular plastic has a larger particle size than the powdered plastic and that it also has more than 5 parts by weight of a propellant, based on 100 parts by weight of the plastic, and that it also contains a crosslinking agent. In general, the particle size should correspond to a ten-mesh sieve or a coarser sieve, preferably a five-mesh sieve or an even coarser sieve. With a view to a good separation of the granules from the powder particles during the turning process of the molding tool should the Granules are preferably spherical or similar in shape, but small cubes can also be used or use small parallelepipedes that are rectangular. In addition, each is for the granules any shape can be used, such as can be obtained by a simple mechanical crushing or pulverizing of Plastics is obtained. The ratio of powder to granular material can be chosen arbitrarily, but the weight ratio of powder to granular is Plastic generally in the range of 2: 8 to 9: 1.

The moldings produced according to the invention should have a well foamed core, and therefore crosslinkable plastics are used. If the molding compound consists of a non-crosslinkable If there is plastic powder and a crosslinkable plastic granulate, the powdery material melts when the molding tool is heated and forms the outer layer, and at the same time there is a crosslinking and foaming of the networkable; granular plastic instead, creating the foam cells become extremely stable and the gas generated by the propellant escape only with difficulty can. In this way, a sufficient internal pressure is set within the mold and thereby molded articles with good appearance and high dimensional stability are produced and have excellent mechanical strength. In addition, the surface layers are these moldings are very uniform in terms of their thickness and are good with the core layer connected inside.

It has already been pointed out above that the molding compositions processed according to the invention also hollow glass spheres, light-weight aggregates, wood chips or non-foamable plastic may contain, whereby moldings of a modified type can be produced. In particular, can the molded bodies in this way a high heat resistance, a high mechanical strength or the property of buoyancy can be conferred. Plastic waste in particular usually contains wood chips, metal chips, sand or others Fillers, and it is an advantage of the method according to the invention that such plastic waste is obtained can build into the inner core layer of the molded body and thus make it very desirable and advantageous Can confer properties. These further additives should have a particle size of this kind have that this is between the size of the plastic in powder form and between that of the plastic is in granulate form. If you have a mold with one of at least three various plastic components existing molding compound charged and then in the above-described This way, the molding compound foams while rotating the mold, "o is obtained Moldings, which consist of three different layers, with the core being very strongly foamed, this is followed by a non-foamed layer and finally a lightly foamed surface layer follows. Such moldings have a high mechanical strength and despite their light weight a high shock absorption, so that they are particularly suitable as lining material for the interior of automobiles suitable. By suitable selection of the type of plastic with the mean particle size can the adhesion between the inner foamed layer and the surface layer can also be improved, since the type of plastic used for the outer layer is generally not particularly well tolerated of the type used for the foamed core layer.

The blowing agent used in the molding compositions has a value above the softening point of the plastics Decomposition temperature, both organic and inorganic Propellant can act.

A volatile propellant is also used for some applications. The powdery one Propellant added to plastic is usually mixed in by means of a mixing device.

In contrast, the blowing agent is generally applied to the granular plastic by means of a rolling mill or incorporated into an extruder.

Due to the use of a crosslinking agent, the crosslinking process should increase the flowability take place before foaming, and therefore, the decomposition temperature of the blowing agent is usually higher than the decomposition temperature of the crosslinking agent.

The moldings produced according to the invention generally have surface layers which are expanded one to three times in volume, while the inner or core layer is around expanded five to thirty times its volume. The entire shaped body has an increase in volume by about two to ten times.

Shapes that can be closed are usually used as molding tools, but not necessarily must be airtight. However, in order to produce moldings with a good-looking surface, while but the density of the molding itself is low, the internal pressure in the mold must during of the foaming process should be as high as possible. It can be a mold made of a conventional cast metal can be used, but shapes from bent steel plates or by welding can also be used use generated shapes. As the surface of the molded body through the heat transfer is generated from the outside of the mold through heat conduction into the inside of the mold, the plastic in powder form also melts first. If so, a surface layer that is as uniform as possible is to be produced, the molding tool must also be heated uniformly. In some cases However, it is desirable that certain parts of the molded body have a particularly high strength and that these should therefore have a particular thickness of the surface layer. Those parts of the molding tool, which the relevant points

9 10

of the molded body, therefore, steam also prevents the plastic or metal with particularly good thermal conductivity from decomposing the material of the molding tool. To the manufactured, or the shape is particularly thin at this point, separation of the powdery plastic from the ders. It is also possible to provide the inner wall of the plastic granulate within the molding tool with unevenness, so that it is necessary to increase the temperature of the powdery plastic itself at this point of the molding tool without, however, accumulating len. In addition, you can use metal meshes, the molding compound is heated significantly. In this way, or wooden slats on the inner wall of the molding tool, it is ensured that the total is first attached in order to achieve the mechanical strength of the powdered plastic on the inside wall of the surface of the molding at these points. This also makes it possible to increase the height and, at the same time, the formation of a thicker surface layer, which is very rapid heating of the molding tool. Since the expedient. If the molding compound according to the invention is used in the process according to the invention to produce tubular moldings before foaming within the molding tool, and the molding tool has to be moved in the usual way, a proportion of 10 volume tool should be about 10 by means of hot air When heated, a thick layer forms on the surface of the tube as a percentage of the inner cavity of the mold, * not being filled with the molding compound. If on the other hand it is difficult to make a well foamed core layer against the remaining void space in the mold more than inside the pipe. Around this 50 percent and the molding tool can only be encountered in order to avoid difficulties, for example if its axis is rotated, then it is difficult to attach the tool to the central part of the molding piece at both ends of the mold auszubil- a good surface layer, whereby it is then possible to the inner pipe part. of the mold a larger amount of hot air It is to be supplied in the method according to the invention. On the other hand, it is possible to ensure that the molding tool is rotated particularly thinly during the heating cut of the molding tool only rotates at such a speed or that it is a particularly good heat conductor that no centrifugal forces develop, since material such as aluminum, to use. The molding otherwise the separation between the plastic in powder mold is usually heated to temperatures of deform and the plastic in granulate form is not 160 to 400 ° C and the heating time is complete. The appropriate speed of rotation is generally 15 to 120 minutes. However, the fiction depends on the type, the particle size and the moldings are generally rapidly cooled to the specific gravity of both the powdery and for this purpose the molding and the granular plastic and stuffing are usually immersed in a water tank afterwards of the absolute size of the Mold or sprayed with a coolant. Since the from. Preferably, however, the rotation structure of the foamed plastic or the speed is chosen such that the fastest plastic in the surface layer becomes very finely crystalline with cooling due to rapidly rotating parts of the mold and also the speed of at most 15 m / minute and Escape of the lower gas produced during the foaming process, preferably from 5 m / minute to 0.1 m / min, can be prevented, let the minute move. This rotary movement can only take place around an axis in this way, molded bodies of high strength, but in some cases it can be produced. A further advantage consists in the fact that the parts are expedient to enable a rotary movement in order to achieve mechanical strength of the several axes of the molding tool produced according to the invention as a result of the solid and relatively thick moldings. Such a multi-axis rotary movement ken surface layer is sufficiently large, while you can namely achieve that the plastic 45 of the compression resistance inside the mold is distributed evenly on the inner surface of the body due to the non-foamed core layer rela-molding tool, so that one also particularly tiv is small. If such a lower compression gets uniform surface layers. If frame stability is not desired, molded articles of the method according to the invention can be used, but with cavities, incisions or notches, it is not absolutely necessary to select a rotational movement for the movement of the mold of any shape, for example, edge or rectangular tool Shape. In the case of the one according to the invention, instead of or together with the method, a vibration is then also formed on this rotational movement, cavities or incisions a mechanically fixed surface layer by means of such a vibrating movement and a thick surface layer. You can also separate the plastic powder inside the mold from 55 in the cavities or incisions thus obtained in the plastic granulate. If you introduce the stiff material, for example a shaping tool, only such a vibratory movement of clay blocks or pieces of wood. As a further exposure to reinforcement, molded bodies are obtained which on the one hand materials that can be built into the non-foamed or only side a well-foamed layer and on the other weakly foamed surface layer a non-foamed layer at all, are suitable metal plates , Profiles from ways. Such molded bodies are suitable, for example, steel, pipes, wire, metal gauze, wooden slats and the like as back supports for seating in Liches. In this way, the mechanical Fe-transport or traffic facilities. Strength of the moldings improve quite significantly. The molding tool is usually heated. It has already been pointed out above, by means of hot air or steam. In _b 5 that another way to Verbesserang the application of steam, it is possible that temperature mechanical strength consists of the shaped bodies according to the invention hergetur relatively low and the heating time is set short to shark therein, the molding composition th. Thus, steam is preferred. A heating with also granules of a non-foamable or

add only a little foamable plastic. If you do this, it remains as reinforcement serving plastic in the foamed core layer and connects at the same time with the solid Surface layer which covers the entire surface of the molding. That way will accordingly, the mechanical strength is significantly improved. In some embodiments, Even this reinforcing plastic cannot be separated from the foamable before it is mixed with the molding compound Plastic material are connected. For example, you can make two plates or foils from the relevant Connect plastics together and then crush this laminate into a powder and incorporate this powder into the molding compound. According to another embodiment, you can foamable plastic, which is used in granulate form in the molding compound, also initially to one Extrude a thin rod, which is then covered with a non-foamable layer of the reinforcing plastic is covered. This composite rod is then divided into small granules and incorporated into the molding compound.

As can be seen from the above, the moldings which can be produced according to the invention have a very low weight, but still show excellent mechanical properties. You can can therefore also be used for the production of moldings with large dimensions, for example as machine documents. The moldings which can be produced according to the invention are therefore of great importance for many industrial purposes.

The examples illustrate the invention.

example 1

Loo weight of low density polyethylene, 10 Part by weight of azodicarbonamide and 0.8 part by weight of dicumyl peroxide are added to a rolling mill a uniform mass and then kneaded into cubic pellets with an edge length of about

Deformed by 3 mm. 18 g of these pellets are mixed with 72 g of a powdery high density polyethylene (Particle size corresponding to a 100 to 200 mesh sieve) and 0.7 g of azodicarbonamide in one Mixer well mixed and then you put this molding compound in a steel mold of the size 220mm X 50mm x 25mm. The filled steel mold is then made while moving it at a speed rotated by 4 revolutions per minute, heated and heated by hot air for 45 minutes on a Maintained temperature of 300 ° C. The molded body produced in this way has an only slightly foamed solid Surface with a uniform thickness of about

4 mm and a well foamed core part. The molded article shows excellent compression strength and flexural strength.

Example 2

The plastics described in Example 1 are used in granulate and powder form as well the same steel shape. The weight ratio of powdered to granular plastic is However, changed and in this way moldings can be produced, the volume of which by the Foaming is increased by about three times, at the same time the thickness of the surface layer can be varied. The moldings produced in this way also have good flexural elasticity.

Table 1 below shows the thickness of the surface layer and the values for the flexural elasticity of the moldings produced in this way. From the numerical values it can be seen that the flexural elasticity is so is larger, the larger the thickness of the surface layer, and it follows that the adhesion or bonding is extremely strong between the surface layer and the foamed core.

Thickness of the waiter Table I. 10 surface layer mm Flexural elasticity is 0.5 1.0 kg / cm ² 1.5 1100 2.0 1630 2.5
20th 240Ö 3260 4130

Example 3

100 parts by weight of medium density polyethylene, 10 parts by weight of azodicarbonamide and 0.3 Parts by weight of dicumyl peroxide are kneaded into a uniform mass on a roller mill and from this mass one then forms cubic pellets with an edge length of about 5 mm (component A). In addition, 100 parts by weight of a commercially available epoxy resin, 29 parts by weight of dipropylene glycol, 44 parts by weight of pyromellitic anhydride are mixed and 20 parts by weight of a polyethylene glycol having a molecular weight of about 3,000 for three hours at a temperature of 60 ° C.

The resulting plastic product is cooled and turned into a powder with a particle size processed according to a 100-mesh sieve or smaller (component B).

25 g of component A and 75 g of component B are poured into a mold with the dimensions Filled in 220 mm X 50 mm X 25 mm, then heated and foamed for 60 minutes, using hot air heated to 320 ° C and at the same time the mold at a speed of 20 revolutions per minute is rotated. This gives a shaped body with an approximately 3 mm thick surface layer, which is quite uniform, this layer having a higher mechanical strength and a better flexural strength has as a corresponding molded body made of foam plastic, which only consists of the thermoplastic Made of plastic. The moldings also show a sufficient temperature at 100.degree Resistance to deformation under load.

Example 4

Pellets with a diameter of about 3 mm made of low density polyethylene, which also contain a Contain crosslinking agents and a blowing agent, as well as a powder of high density polyethylene (Melt Index 5) with a particle size smaller than 100 mesh and one for three hours Asbestos dried at 4GO ° C (Canadian grade 7M) are mixed together in the proportions given in table Π. These Molding compound is then molded into a shape which is a right-angled parallelepiped with the following dimensions represents: height 25 mm, width 50 mm, length 215 mm, filled in and this form is 30 minutes

heated for a long time by means of hot air to 290 ° C, while they are heated at a speed of 5 revolutions rotates per minute. The mold is then cooled with water and thus foamed is obtained Shaped bodies, the volume of which has increased by a factor of about 3 as a result of the foaming process and which have a surface layer of uniform thickness. In the core layer the increase in volume by foaming was about 11 times and a large amount of that added Asbestos particles are in the surface layer with a thickness of about 2 mm, which are not is foamed. The properties of these moldings are shown in Table Π below. Table Π

Polyethylene Poly asbestos 7.4 Bend low density ethylene 14.7 elasti (Networking higher city * medium and Schäu density containing mer) granules powder G G G kg / cm ² number 1 18.4 66.2 3100 No. 2 18.4 58.9 4000

* Measured with three-point support with a span of 200 mm.

Comparative experiment

A molding compound is produced according to the composition given above, however, the pellets made of low density polyethylene by a corresponding polyethylene in powder form replaced with the powder particles passing through a 100 mesh screen. From this A molding compound is produced in the manner described above, but which has a has a completely uniform structure. The properties of these moldings are shown in the table below ΠΙ reproduced.

Table III

Polyethylene Poly asbestos 7.4 Bend low density ethylene 14.7 elasti (Networking higher city * medium and Schäu density containing mer) powder powder G G G kg / cm ² ' number 1 18.4 66.2 1100 No. 2. 18.4 58.9 1200

* Measured with three-point support with a span of 200 mm.

A comparison of the numerical values in Tables Π and ΠΙ shows that the manufactured according to the invention Moldings have a much better flexural elasticity.

This is likely also due to the fact that the asbestos used as reinforcement material is mainly accumulates in the surface layer.

EXAMPLE 5 The foamable pellets from Example 1 are used to produce sheets 2 mm thick by means of an extruder. A 1 mm thick plate made of high-density polyethylene is then heated and laminated to the first-mentioned 2 mm thick plate. This composite material is then crushed into cube-shaped pellets with an edge length of about 3 mm. If these pellets are processed together with the plastic powder described in Example 1 under the conditions specified there, moldings with very high compression strength are obtained, since a kind of framework made of the non-foamable high-density polyethylene has formed inside the foamed core.

Example 6

To the molding composition described in Example 1, 20 g of granules made from a copolymer of ethylene and vinyl acetate with an edge length of about 1 mm are added. This molding compound is then processed under the conditions of Example 1 to give shaped bodies. This gives a molded article consisting of three layers, one layer consisting of polyethylene, the other layer consisting of the ethylene-vinyl acetate copolymer and the third layer consisting of crosslinked polyethylene.

Example 7

100 parts by weight of an ethylene-vinyl acetate mixed polymer, 5 parts by weight of azodicarbonamide and 1.2 parts by weight of dicumyl peroxide are processed into a uniform mass on a roller mill and then a powder with a particle size smaller than a 50-mesh sieve is made from this mass. 100 g of this powder are mixed with 100 g of the plastic pellets described in Example 1 and this molding compound is poured into a mold made of steel plates with dimensions of 100 mm X 300 mm X 50 mm, the inner surface of the mold being uneven or recessed having. The filled mold is heated for 30 minutes by means of steam at a pressure of 12 kg / cm ² while rotating. In this way, molded bodies are obtained whose volume has increased by about seven times as a result of the foaming process and which have unevenness or notches on the surface which correspond to the pattern on the inner surface of the mold. As a result, the moldings have a

great frictional resistance.

Example 8

To the molding composition of Example 1 are each 5 g of hard-adjusted polyvinyl chloride, and polystyrene

Polyamide added in the form of pellets with an edge length of about 3 mm. Then the molding compound processed further under the conditions specified in Example 1. This gives moldings with a smooth surface layer, the inner

foamed core part that contains hard-adjusted polyvinyl chloride, polystyrene and polyamide.

Example 9

A molding compound of the composition given below is in a mold for production

of machine pads for 70 minutes by means of hot air heated to 350 ° C, with the mold mil: a speed of 0.5 revolutions per

Minute rotates. After completion of the foaming process, the mold is quickly cooled by hosing it down with water and in this way a machine pad with a density of 0.3 g / cm ³ and the one shown in FIG. 1 reproduced appearance produced:

Composition of the molding compound:

High density polyethylene

(Melt index: 2.100 to 200 meshes) 15.3 kg of low density polyethylene

(Melt index: 1.30 to 50 mesh) 4.0 kg

Azodicarbonamide 0.2 kg

Foamable pellets

(Diameter 6 mm, length 6 mm) 2.1 kg

Composition of the foamable pellets: high density polyethylene 50 parts by weight

Low density polyethylene 50 parts by weight azodicarbonamide 10 parts by weight

Dicumy peroxide 0.8 part by weight

This machine base has a mechanically strong surface layer and shows a deflection measured in accordance with JIS-Z-0602, as shown in curve A in FIG. These measured values confirm the high mechanical strength wedge. In addition, the machine pad passed the drop test and exhibited compressive strength in accordance with the provisions of JIS-Z-0602 (Japanese Industrial Standard).

Comparative experiment

If you produce a molding compound of the material composition given above, but from the powdery high-density polyethylene, the powdery low-density polyethylene and the azodicarbonamide first using an extruder pellets of dimensions 6 mm X 6 mm and these with the foamable pellets of the same dimensions to one Combining molding compound and processing this molding compound in the same way, machine bases are obtained whose surface layer is not sufficiently developed, as is evident from the lower strength (compare FIG. 2, curve B).

Example 10

Reinforcing inserts made of steel plates with the design shown in Fig. 3 are on both Inserted ends of a molding tool for producing a machine base according to FIG. 1, and the molding is then produced under the conditions given in Example 9. The reinforcement insert made of steel is inserted into the mold in such a way that the ends are about 3 mm from removed from the surface layer of the machine base are. The greater part of the reinforcement system is therefore located within the surface layer. In this machine base, therefore, the part in which the gripper of a forklift truck engages is significantly reinforced by the metal insert and this machine base therefore shows a good one Shock resistance and a very low deflection (compare Fig. 2 curve C).

Example 11

100 parts by weight of polypropylene with a melt index of 1.3, 5 parts by weight of azodicarbonamide, 5 parts by weight of polybutadiene and 5 parts by weight of 1,10-decane-bis-sulfonazide [N ₃ SO ₂ (CH ₂ ) J ₀ SC) ₂ N ₃ ] are on a Rolling mill processed into a uniform mass, and this is then crushed into pellets with an edge length of 3 mm. 90 g of a molding compound which contains 30 percent by weight of these pellets and 70 percent by weight of a polypropylene powder containing only a small amount of propellant are poured into a mold made of steel plates which has the dimensions 22 cm x 5 cm x 2.5 cm. The filled mold is heated to 300 ° C. for 45 minutes with hot air and rotated at a speed of 1u revolutions per minute. In this way, molded bodies are obtained with a mechanically strong surface layer of uniform thickness of about 2 mm, which also have a high overall mechanical strength (see FIG. 4).

Example 12

A molding compound made of 72 g of powdered polyvinyl chloride with a particle size corresponding to one 100-mesh sieve and smaller, 1 g of azodicarbonamide and 8 g of the crosslinkable described in Example 9 and foamable pellets are filled in an aluminum mold which has an internal volume of 240 ml. The mixture is heated by means of steam at 10 kg / cm for 15 minutes and the Rotate the mold at a speed of 8 revolutions per minute. Then you cool the

jo form by means of water and thereby obtains a shaped body with an even surface layer made of polyvinyl chloride (see Fig. 5). This surface layer has flame retardant properties and also the bond is in the molding between the polyvinyl chloride and the crosslinked one Polyethylene pretty good.

If you in the molding composition given above, the 72 g of powdered polyvinyl chloride through a mixture of 52 g polyvinyl chloride powder and

AO 20 g of granular ethylene-vinyl acetate mixed polymer (particle size with an edge length of about 1 mm) replaced, the result is a molding in which the ethylene-vinyl acetate mixed polymer is embedded in the center of the polyvinyl chloride layer, and in this case the bond is between the inner foamed polyethylene layer and the surface layer made of polyvinyl chloride are very good.

Example 13

2 kg of the crosslinkable plastic pellets described in Example 9 are mixed with 18 kg of powdered ABS plastic (particle size smaller than 100 mesh sieve) mixed and poured into a steel mold, which is designed in such a way that molded bodies with notches of the one shown in FIG. 6 can be obtained Kind can produce. This shape has the dimensions 1000mm X 1000mm X 150mm and lasts 60 minutes heated to 330 ° C for a long time, being heated at a speed of one revolution per minute can rotate. The mold is then cooled down quickly. This shaped body shows a uniform surface layer made of ABS plastic, and it also exhibits excellent properties with respect to the flexural elasticity. In addition, the surface has

b-, chenschicht also at the points of the notches and therefore are used when testing the deflection and compressive strength also measured very good results.

130 216/49

17th
Example 14

50 parts by weight of high pressure polyethylene, 50 parts by weight of medium pressure polyethylene, 1 part by weight Dicumyl peroxide and 5 parts by weight of azodicarbonamide are made uniform on a roller mill Mass processed and then cut into granules with an edge length of about 5 mm.

A molding compound made of 40 g of a powdery medium-pressure polyethylene and ^A Q g of the plastic granules described above

are filled into a mold with the dimensions 200 mm X 50 mm X 25 mm. The filled mold is heated to 250 ° C. for 60 minutes in a thermostat equipped with a shaking device which vibrates with a stroke length of 50 mm in the horizontal direction at a speed of 60 strokes per minute. The molded body produced in this way has a density of 0.35 g / cm ³ and consists of a well-foamed layer and

ίο a rigid, mechanical, solid plastic layer, these two layers are bonded together with good adhesion.

For this purpose 4 sheets of drawings

Claims (5)

21 4 ^ 855 claims: 1. A method for the production of molded articles made of plastic, which over a core or a Layer with foam structure have a non-foamed or only slightly foamed layer, in which thermoplastic plastic particles of various sizes, of which at least the larger ones Particles contain a propellant and are preferably in the form of granules and the smaller plastic particles, preferably in the form of a powder, are introduced into a mold, the mold is heated and the mixed particles are agitated in the mold until the particles are in melt in the heat and the dripping agent decomposes, characterized in that the , Plastic particles with a significantly larger particle size contain a crosslinking agent. 2. The method according to claim 1, characterized in that the plastic particles with significantly smaller dimensions contain a crosslinking agent. 3. The method according to claim 1 and 2, characterized in that the plastic particles with a significantly larger particle size at least by a factor of 3 and preferably by a factor 10 differ from the plastic particles with significantly smaller dimensions, each related to the diameter of a spherical shape. 4. The method according to claim 1 to 3, characterized in that a plastic particle mixture with reinforcing agents, fillers or other additives in powder or fiber form is used. 5. The method according to claim 4, characterized in that a plastic particle mixture is used with plastic waste with a particle size between that the particles with a significantly larger particle size and the particles with a significantly smaller one Particle size is.