NO750885L - - Google Patents

Description

"Procedure for the production of accusative substances from polystyrene polymers"

Dosme invented a new method for the production of foaming substances by using powder-shaped particles of code polymers of styrene under pressure and forging.

The process for extracting mold logs with a cellular structure, which has particularly gained acceptance in industry, involves propellant-containing atyron poiyroer £$5rot pre-oppakummss<p>g the thus obtained particles after a short storage time are heated in a mold, so that they foam up further and enter the mold body, including the interior of the mold used. According to this procedure

sr dot mislig froEistille formiememer mad complicated design,

such disoe, for example, anvondon pom©mballasjoinnlegø.

According to Austrian patent no. 249 9855, a method is known for the production of precursors from particles of foamed otyron polymers, where completely foamed particles are heated to the softening temperature of the otyron polymer and then sintered under the influence of pressure.

According to disoe methods, an okumctoffer rasd space weights from 10 to approx. 100 g/l» The foam fabrics have an extensive 'use as icole-ringsicatcriale©Iler as shock-absorbing material in ©mbalaging., A disadvantage is these, formlegoi<y>.ers. great sensitivity to organic solvents. For example, when wetting with softening agents, as these are used in paint, varnish, glue, etc., collapse of the oak structure can occur. For adhesives and adhesives, dot must therefore be used in conjunction with such non-toxic substances or special types that contain harmful © looningoraidler.

The invention aims at providing foams by synthesizing foamed particles of thermoplastic polymers under pressure and shaping, which foams do not exhibit the aforementioned disadvantages.

According to the invention, this problem is solved by using propellant-foamed particles of podo<p>ol<y>mers of styrene, possibly styrene and other monomers, on olefin polymers in the production of foam molded bodies of thermoplastic polymers.

It is an advantage that by sintering particles of graft polymers of styrene on olefin polymers according to the invention for molded bodies which in their design correspond to the inner cavity of the mold used. It is thus possible to obtain shaped bodies with a relatively complicated design and cell-like foam structure by a technically simple working method.

In the present context, graft polymers are understood to mean graft polymers of styrene on olefin polymers, as these are obtained by polymerization of styrene in the presence of olefin polymers. the styrene content of the graft polymers is advantageously between 10 and 95% by weight, preferably between 30 and 90% by weight. In the production of the graft polymers, in addition to styrene, monomers copolymerizable with styrene can also be used in such quantities that the proportion of styrene, calculated on the monomers, amounts to at least 50% by weight. As such copolymerization components can be used, for example: cc-methylstyrene, core halogenated styrenes, acrylonitrile, esters of acrylic acid or methacrylic acid and alcohols with 1-8 carbon atoms, vinylcarbazole or also small amounts of compounds containing two pblymerizable double bonds, such as butadiene, divlnylberizen or butanediol diacrylate.

The graft polymerization is carried out in a manner known per se.

Thus, for example, a granule of olefin polymers can be melted together with styrene and polymerization initiator in the mixing chamber of an extruder at a higher temperature while excluding air. In this way, the styrene is grafted onto the olefin polymer.

Suitable olefin polymers are in particular polymers of ethylene, propylene or butene-1. Among these, ethylene homo- and copolymers are preferred. Thus, for example, ethylene homopolymers produced by high-pressure or low-pressure polymerization with a density between 0.85 and 0.965 g/cm can be used. Suitable ethylene copolymers contain as comonomers either other olefins or, for example, vinyl esters of cytes with 2-4 carbon atoms, such as vinyl acetate, vinyl propionate or acrylic and methacrylic acid esters© of alcohols with 1-10 carbon atoms. carbon monoxide, styrene, vinyl chloride, sulfur dioxide, fumaric and maleic acid esters can also be used, mixtures of the olefin polymers can also be used, for example mixtures of high-pressure or low-pressure polyethylene and ethylene copolymers, such as copolymers of ethylene and vinyl acetate.

The comonomer content in the ethylene copolymer is preferably between 1 and 49% by weight, especially between 3 and 35% by weight. The copolymer's melting index can vary within wide limits and is particularly 0.1-1000 g/10 min (190°c/2.16 kg).

The procedure can be carried out according to different working methods. A method that has proven particularly beneficial involves foaming propellant-containing particles of graft polymers and sintering the foam-shaped particles under pressure. Particles with a transverse dimension between 0.1 and 5 mm, preferably between 0.5 and 2.5 mm, are used. As a propellant, the particles suitably contain low-molecular organic substances with a boiling point between -50 and 100°C. Preferably, under normal conditions, gaseous or liquid, aliphatic or cycloaliphatic hydrocarbons are used, such as propane, butane, pentane, hexane or cyclohexane, isobutane, isopentane or isohexane. Also suitable are halogenated hydrocarbons, such as methyl chloride, methylene chloride, ethyl chloride, dichlorodifluoromethane, trifluorochloromethane. Furthermore, ethers, such as dimethyl or diethyl ether, or ketones, such as acetone, can be used. These propellants can be used alone or in mixtures. They are present in the finely divided graft polymers in amounts between 2 and 15% by weight, preferably between 5 and 10% by weight. It can also be advantageous to incorporate into the propellant-containing graft polymers alcohols in amounts of 1-10% by weight, for example ethanol, in addition to the propellants.

The propellant-containing particles of the graft polymers can be produced by various methods, which in and of themselves do not belong to the invention. Thus, for example, the finely divided pdde polymers can be brought into contact with the propellants; this can happen at normal temperature under normal pressure or at overpressure. The propellants cause the polymers to swell and distribute themselves homogeneously in the particles. To achieve an even distribution of the propellants in the particles, a residence time in the propellant-containing atmosphere of 0.5 to approx. 50 hours, preferably 1-30 hours. The particles can also be produced by graft polymerization of styrene in the presence of the aevole fine polymers and propellants in aqueous suspension.

The graft polymers can be processed in a mixture with other substances.

Thus, the graft polymers can contain fire retardants, dyes, fillers, lubricants or also other polymeric materials, for example rubber-like substances, such as polyisobutylene. Sometimes it is advantageous that coarse or fiber-like fillers or reinforcements are added to the polymers. You can also incorporate coarse-meshed fabric or braid-like materials made of thermoplastic polymers as reinforcing inserts in the foam materials.

The foamed particles must be sintered under pressure and shaped. For this purpose, closed molds are used of such a nature that air and other gaseous or liquid components can escape from the mold during the heating of the particles under pressure, without the foamy graft polymers escaping. It is appropriate to use molds whose walls are perforated, or molds where the walls have built-in nozzles with small openings through which a heated forge in the watch can penetrate into the mold and air can flow out from the mold. For special embodiments of the method, it is necessary to use such molds where at least one wall is movable, so that the contents of the mold can be pressed together during or after heating.

The shaping can also be carried out in continuously working devices, for example those used in the continuous production of shaped bodies from finely divided foamed styrene polymers. Such devices consist, for example, of four conveyor belts which are arranged in such a way that they form one channel; In this channel, the foamy particles are introduced at one end, then further foamed, and the resulting foam string is taken out at the other end of the channel. The conveyor belts can also be arranged so that the particles are pressed together before sintering. Furthermore, the running belts can be plate-shaped divided so that they form a light chain. When producing very wide tracks, it is usually only required to have two parallel conveyor belts, at the end of which fixed or movable walls are arranged, so that the system forms a channel.

The foamy particles must be heated in the mold to temperatures at which they sinter. These temperatures depend on the chemical composition of the polymers and on other material additions. In most cases, this temperature is above the polymer's softening temperature.

According to a particularly advantageous working method, the particles are first pre-foamed outside the mold, that is to say they are heated to foaming, during which sintering is avoided. This can happen, for example, by heating with hot air or steam in containers, where the particles are moved mechanically, for example with the help of a stirrer. After storage for some time, the formed cells are filled as the air diffuses in, so that the particles expand further upon renewed heating. One can now place such "pre-foamed" particles in a mold or heat them again, so that they expand and sinter under the pressure of the air or other gaseous constituents enclosed in the cells.

However, it is also possible to repeat the pre-foaming several times, so that particles with a particularly low specific weight are obtained. In this case, it is appropriate to heat the particles in the mold and sinter it while applying external pressure. This can - as described above - happen by moving one of the walls in the mold or a piston towards the inside of the mold. The particles are advantageously compressed to a volume corresponding to 0.95-0.5 times the volume before compression.

The heating of the particles of the graft polymers or the foamed graft polymers before sintering in the mold can be carried out using different heating media. Thus, for example, it is possible to introduce hot gases, water vapor or liquids into the mold. It is particularly advantageous to blow water vapor into the moulds, the inner cavity of which is filled with foamy particles, so that the particles expand further and sinter. The heating of the particles in the mold can also take place by heating the walls of the mold, it is also possible to introduce particles that have been heated to temperatures above the sintering temperature outside the mold, and sinter the particles quickly in the mold under pressure, which is exerted on a mold wall from the outside.

Compared to foams of styrene, homo- and copolymers, the foams obtained according to the invention show better mechanical properties, in particular better elasticity, less brittleness at low temperatures and insensitivity to solvents, such as toluene and acetic acid ester.

The parts given in the examples are parts by weight, and the percentages are on a weight basis.

Example 1

100 parts of a styrene graft polymer, which was prepared by graft polymerization of styrene with dibenzoyl peroxide on high pressure polyethylene with a density of 0.918 g/cm and a melt index of 4 g/10 min. (190°c/2.16 kg), and which has a styrene content of 50% by weight, becomes in the form of a fine. granules with a particle diameter of 1 mm and a particle length of 1-1.5 mm mixed with 2 parts panthan and 5 parts raethylchlordld for 15 minutes in a mixer that can be closed gas-tight. The mixture is then allowed to stand for 24 hours in the mixer. You get a separable granule that contains the propellant mixture completely in homogeneous distribution"

The propellant-containing granules are treated with water vapor for 10 seconds and at an initial pressure of 1.5 ato in a pre-foaming apparatus of the type used for pre-foaming styrene polymers. The particles rise up and have a room weight of approx. 46 g/l.

After an intermediate storage of 12 hours, the particles are placed in a mold of the kind used for foaming pre-foamed styrene polymers. This mold is filled with the pre-foamed particles of the graft polymers and closed. Steam is then supplied under a pressure of 1.5 ato to the forman until there is no longer condensation from the outlet valve, after which the valve is closed. The molded body that is obtained, and which is formed by welding the pre-foamed particles, can, after a cooling time of approx. 10 minutes are removed from the mold. You get a foam material with a density of 45 g/l, a compressive strength of 4.5 kp/cm<2> and an impact strength of 0.9 cm kg/cm 2 (according to DIN 53 452$).

Example 2

100 parts of an ethylene-vinyl acetate copolymer with a vinyl acetate content of 12% by weight and a density of 0.935 and a sms1te index of 4 g/10 min. (190°C/2.16 kg) is grafted with 186 parts of styrene using 1.2 parts of dibenzoyl peroxide as initiator. A graft polymer with 65% by weight of styrene is obtained. The polymer is granulated to a particle diameter of 1-1.5 mm. These particles are treated - as described in example 1 - with a mixture of 3 parts pentane and 6 parts methyl formate, whereby an expandable granule is obtained which contains the propellants in an even distribution.

The particles are then pre-foamed using steam

of 1.5 ato, whereby pre-foamed particles with a density of 30 g/l are obtained. After a storage time of 8 hours, the particles are sintered in a mold into a foam material. The heating is carried out using steam

of 1.5 ato. After a cooling time of 60 minutes, a foam is obtained which has a density of 30 g/l and a compressive strength according to DIN 53 421

at 10% compression of 1.6 kg/cm. The foam material is resistant to toluene and acetic acid ester, i.e. it does not collapse.

Example 3

100 parts of a stycBn graft polymer prepared by graft polymerization of styrene and a mixture of 60 parts of a high-pressure polyethylene with a density of 0.918 g/cm<3> and a melt index of

2 g/10 min. (190°c/2.16 kg) and 10 parts polypropylene with a density of 0.89 g/cm<3> and a melt index of 6 g/10 min. (230°C/5 kg) with 30 parts styrene, is placed as in example 1 with a particle diameter of 1-1.5 mm in a gas-tight mixer together with 8 parts isopentane. The propellant-containing granules can be foamed with flowing steam for 4 minutes, whereby particles with a liter weight of 21 g are obtained. After intermediate storage for 24 hours, the pre-foamed particles can be foamed into a molded body in a mold with a steam pressure of 0.4 ato during of one minute. The foam body has a density of 22 g/l and a compressive strength of 2.3 kp/cm. It can be glued with adhesives containing toluene and ethyl acetate.

Example 4

According to a working method as described in principle in example 1, expandable particles are produced from the graft polymers indicated in the table under A-F, which particles are pre-foamed and used for the production of foams.

The sensitivity to toluene was investigated by placing a test body (5x5x5 cm) of the foam material in toluene. After 2 hours the shape was unchanged. Admittedly, the foam absorbs solvent, but after drying it is unchanged. Such results are indicated by a +. A sample of pure styrofoam is completely dissolved after a few minutes.

Claims (11)

1. Process for the production of foams by sintering foam with particles of thermoplastic polymers under pressure and shaping, characterized by using propellant-foamed particles of graft polymers of styrene or styrene and other monomers on olefin polymers. 2. Method according to claim 1, characterized in that the olefin polymers consist of polyethylenes which have a density between 0.850 and 0.965 g/cm 3 , and that the podonomer is styrene. 3. Method according to ksav 1, characterized in that the olefin polymers consist of polyethylenes having a density between 0.850 and 0.965 g/cm 2 , and that a mixture of styrene and α-methylstyrene is used as the submonomers. 4. Process according to claim 1, characterized in that the olefin polymers consist of polyethylenes which have a density between 0.850 and 0.965 g/cm 2 , and that a mixture of styrene and acrylonitrile is used as the submonomers. 5. Method according to claim 1, characterized in that the olefin polymers consist of ethylene vinyl acetate copolymers and that the podonomer is styrene. 6. Method according to claim 1, characterized in that the olefin polymers consist of a mixture of polyethylene and polypropylene and that the podonomer is styrene. 7. Method according to claims 1-6, characterized in that the graft polymers of styrene, optionally of styrene and other monomers, on the olefin polymers are produced by graft polymerization in the presence of an organic peroxide. 8. Method according to claim 1, characterized in that low molecular weight organic substances with a boiling point between -50 and 100°C are used as propellants. 9. Method according to claims 1, 2 and 7, characterized in that a mixture of pentane and methyl chloride is used as propellant. 10. Method according to claims 1, 5 and 7, characterized in that a mixture of pentane and methyl formate is used as propellant. 11. Method according to claims 1, 6 and 7, characterized in that isopentane is used as propellant.