NO750830L - - Google Patents

Description

The present method relates to a method

for expanding (driving, esing) thermoplastic poly-

more and a composition for use as a propellant.

The applicants have found that zinc carbonates and certain

andré carbonates can be used as propellants for the expansion of thermoplastic high-temperature polymers.

Accordingly, the present invention provides a method for expanding a thermoplastic polymer,

which consists in heating a composition containing the polymer and a -temperature-decomposable propellant so that the propellant decomposes, and is characterized by using zinc and/or cadmium carbonate as the primary propellant.

The term "primary propellant" is used in this connection to indicate that the propellant makes up at least 50 percent by volume of the gas that is developed when the composition is heated. The primary propellant preferably makes up at least 70%, and preferably at least 90% or more, by weight of the total propellant. It is further preferred that the composition to be expanded is essentially free of strong acids (e.g. contains less than 5%, preferably less than 2%, on a weight basis, acid) and that the propellant is essentially free of ammonia-evolving organic propellant (i.e. .contains less than about 10%).

Accordingly, the invention provides a method for expanding a thermoplastic polymer which consists in heating to a temperature below the polymer's degradation temperature, but higher than the thermoplastic polymer's softening point and than the in situ decomposition temperature of the propellant, and preferably above 220°C, of a composition which preferably contains less than 5% added strong acids and less than 10% ammonia-evolving organic propellants, which composition contains a thermoplastic polymer and as propellant a compound selected from particulate zinc carbonate, lead carbonate, cadmium carbonate and/or lithium carbonate.

According to the invention, a storage-stable, expandable thermoplastic polymer composition is also provided consisting of a thermoplastic polymer, especially one that has a working temperature above 200°C, and as primary propellant a compound selected from zinc carbonate and/or cadmium carbonate. Preferably, the propellant in the composition contains less than approx. 20% other propellants, especially ammonia-evolving organic propellants. Instead of or in addition to zinc and cadmium carbonates, lead and/or lithium carbonates can be used.

The term "strong acid" in the present context denotes an acid which has a pK 2 value of less than 3 for any neutralization point. The decomposition temperature for the carbonate propellant is the temperature at which a gas phase develops, i.e. water vapor and/or carbon dioxide, and is not limited to the temperature at which the CO 2 anion in the carbonate decomposes.

The available carbonate propellants are often commercially available in the form of so-called basic carbonates and for the sake of simplicity the term carbonate is used in the present description and associated claims and shall include where it makes sense both the carbonate and the basic carbonate. The actual carbonates can be used in the form of their hydrate, 3ZnC0.2Zn0.3H20, although in connection with certain polymers (particularly polycarbonates) it may be necessary to use essentially anhydrous propellants. If desired, mixtures of carbonates can be used, although it is preferred to use one carbonate (especially zinc carbonate). It is also preferred that the carbonate constitutes at least 90% (preferably 100%) by weight of the primary propellant in a polymer composition, although the carbonates can be used together with other propellants that are not ammonia-based, e.g. with carbonates such as potassium carbonate which have a lower decomposition temperature.

The propellant for use in the present context is particulate and preferably has a particle size of less than 100 nyu, preferably less than 30 nyu. Ideally, the particles should have a size range from 0.1 to 20 nyu. These size ranges are easily measured with aiming methods.

The carbonate propellants for the present use decompose and give off carbon dioxide when heated. They do not form ammonia, as many commercially available propellants do, nor do they give rise to strong acidic or basic residues in the expanded thermoplastic polymer. The present carbonate propellants can thus be advantageously used for the propulsion of polymer compositions containing ingredients adversely affected by ammonia. These components can be the thermoplastic polymer itself, e.g. a polycarbonate, polyphenylene sulphide, a polysulfone, polyamide, polyester or styrene homopolymer or copolymer, mixture or "alloy", if all said polymers have physical properties adversely affected by ammonia and to a lesser extent by water. Optionally, the vulnerable component may be a fiber reinforcement in the composition, particularly one that is coated with an ammonia-vulnerable coating (e.g. polysiloxane coating) to improve adhesion between the fiber and the thermoplastic polymer, or may be a filler such as asbestos that does not tolerate ammonia well . Carbonates for the present use also have value in that they do not form gases or residues that appreciably attack the equipment or the stop molds in which the polymer compositions are expanded. The carbonate propellants thus also find use for the expansion of many different high-temperature polymer mixtures which are not damaged of ammonia.

Thermoplastic polymers that can be used in connection with the present invention are those that require processing at temperatures above 200°C and include e.g. polycarbonates, polysulfones, polyesters (for example polyterephthalates), polyamides (for example polyadipamides such as nylon), polyacetals, polyphenylene oxides and -sulfides, polystyrenes,<1>poly(acrylonitrile/butadiene/styrene), poly(styrene/acrylonitrile), polyolefins ( eg HD polyethylene or polypropylene) and

fluorinated or chlorinated ethylene polymers (for example PTFE

and chlorinated ethylene). The polymers can be fibre-reinforced, e.g. with glass, asbestos, carbon or boron fibres. If desired, blends, alloys or copolymers of thermoplastic polymers may be used.

The polymer composition will typically contain between 0.05 and 5%, preferably 0.2 to 3%>, by weight, of dry carbonate propellant, based on the weight of thermoplastic polymer. When a polymer premix is prepared as described later, this can contain from 10 - 50%, e.g. 20 - 30% carbonate propellant based on the weight of the polymeric .

The polymer composition may contain ingredients other than polymer and propellant, e.g. other carbonate propellants, dyes, pigments, other polymers, fillers, anti-oxidizing agents, de-icing agents or fire retardants. In order to improve the cell structure in the expanded polymer, it is preferred that a nucleating agent is present during the decomposition of the propellant. The term nucleating is used in this connection for a compound which helps to form gas bubbles in the plastic polymer composition during expansion of the mass. Suitable nucleators are particulate solids, in particular solids with an average particle size below 100 m^u and liquids which are immiscible in the liquid phase of the plastic or molten polymer system. The nucleating agent may be a separate ingredient that is added to the polymer composition with or after the propellant. Optionally, the core former may consist of one or more of the substances already present in the polymer composition to which the propellant is added. Thus, suitable core formers can be pigments and/or fillers in the polymer composition and/or a liquid component such as a wetting agent or a metal soap present in the polymer composition as a lubricant.

However, it will most often be beneficial to add a solid nucleating agent in mixture with the propellant. Suitable fasting. ' nucleators include magnesium and aluminum silicates (e.g. talc or mica), clays, e.g. attapulgite clay, porcelain clay or "ball clay"), oxides (e.g. fumed silica), or magnesium oxides. Preferably, the solid core former has an average particle size of less than 100 nyu, typically less than 20 nyu and preferably less than 1 nyu. It is also within the scope of the invention to use a core former which is solid when mixed with the propellant, but which melts immediately during expansion of the polymer composition. Such substances are waxes and/or organic acids. Use

of organic acids is preferred since these often help to regulate the decomposition of the propellant and in some cases act as core formers. Acids for this purpose are characterized by being weak organic carboxylic acids, i.e. all neutralization points have a pK^ above 5, typically 5-7. Suitable acids include C10_2Q fatty acids such as palmitic acid, oleic acid, lauric acid, stearic acid and myristic acid and aromatic acids.

The nucleating agent is added or is preferably present in amounts of from 0 - 50%, preferably of from 5 - 30%, based on the weight of the carbonate propellant. When the propellant is not an acid, it is advantageous to add up to 50%, and preferably 3-30 percent by weight (based on the carbonate propellant) of a weak acid as mentioned above to the composition to be expanded.

Mixtures of solid particulate carbonate propellant and core formers are new and thus, according to the invention, a particulate composition is also provided which comprises zinc carbonate, lead carbonate, cadmium carbonate and/or lithium carbonate in a mixture with a solid core former, in particular rock oxides, silicates or clays (e.g. .eg magnesium oxide, fumed silicon oxide and/or talc). The particle composition contains from 5-50 parts of core formers per 100 parts by weight of carbonate. It is also preferred that the particulate composition contains from 5-50 parts of weak acid as described above per 100 parts by weight of carbonate. If desired, this particulate composition can also contain solid diluents (e.g. other iæball carbonates), liquid diluents (e.g. paraffins), lubricants (e.g. metal stearate such as magnesium stearate), antioxidants and the like. Since carbonate propellants for the present use do not require the addition of strong acid during the expansion of the polymer, the propellants can be formulated as storage-stable mixtures for direct addition to the polymer as a single component for use.

The polymer composition containing the thermoplastic polymer, carbonate propellant and the other components (when such exist) can be mixed according to known methods, for example into preparations in granule form, powder form, emulsion or liquid. Thus, the compositions can be made by dry mixing the components or preferably by mixing the carbonate in a liquid carrier medium and mixing the dispersion in the polymer. If desired, a solid diluent or carrier may be mixed with the carbonate propellant to help distribute the latter evenly throughout the polymer. However, a preferred method is to mix the carbonate propellant, optionally together with other ingredients (especially solid core former) with only a part of the thermoplastic polymer or another polymer that can be combined with it, to a concentrated premix which is then mixed with more polymer for use.

The polymer compositions containing the carbonate propellant are expanded and stopped or shaped in the usual way. Thus, the mixture can be formed into sheets or webs by extrusion, filling, calendering or spreading as a powder mixture. If desired, the layer can be formed on a substrate such as resin, impregnated felt, coated paper etc. The layer can optionally be coated with a protective plastic layer. Alternatively, the composition can be stuffed by ordinary spray molding, blow molding or other molding techniques into a hollow or solid object.

The composition is heated in one of the usual ways, e.g. in hot air ovens or by infrarbdt heating,<1>preferably to at least 220°C, for decomposition of the propellant and expansion of the composition. The optimum decomposition temperature for the propellant will vary with the carbonate used and other components in the composition. For zinc carbonate, decomposition temperatures of 220 - 300°C are generally usable. The heating time will naturally depend on the temperature and the desired degree of decomposition.

The procedure will now be illustrated with the help of the following examples where all quantities and percentages are on a weight basis if nothing else is stated:

Example 1

(a) Granular polycarbonate resin with an intrinsic viscosity equal to 0.495 (marketed as "Lexan 900") was tumble mixed with 0.4% propellant consisting of a mixture of 85% basic zinc carbonate (average particle size 15 nyu) of general formula ZnCO^.2ZnO»3H20 and 15% talc. The mixture was fed into a sprby stop machine equipped with a fixed steel mold. The cylinder temperature was 280° (funnel)/280°/285°C (nozzle). The total switching period (switching on and off) was 70 seconds. The stock had a density of 0.85 g/cm 2 , an intrinsic viscosity of 0.450 and a uniform fine cell structure with a smooth surface. The block had an impact strength of 4.835 kg/m measured on a 6.3 cm disc cut from the block and measured by the drop weight method with a ball with a diameter of 2.5 cm. The surface was free of miss-staining, which indicates minimal degradation of the polymer. (b) For comparison, the example was repeated with azodicarbonamide (an ammonia-evolving propellant) instead of zinc carbonate. The cell structure of the product was good, but the intrinsic viscosity was approx. 0.2 (indicating severe degradation) . The physical properties of the foam were unsatisfactory, the polymer was strongly discolored, which means the claim that the polymer was strongly degraded.

Example 2

Granular poly(acrylonitrile/butadiene/styrene) supplied

of Sterling Molding Materials, Grade B 300, specific gravity 1.16 g/cm^ was tumble mixed with 0.8% propellant composition described under Example 1(a). The mixture was stbpt as in Example Xa) with cylinder temperatures of 225<0>/260°/260<o>/26©° and a stbpe cycle of 70 seconds. The stbpe piece had a tightness on it

0.75 g/cm^, a uniform fine cell structure and stain-free surface. Example 5 (a) Example 2 was repeated with a 1.1% propellant composition as under example 1(a). The bulk article had a density of 0.69 g/cm 2 , a fine cell structure and a surface without discoloration. (b) For comparison, the example was repeated with azodicarbonamide instead of zinc carbonate. The stop objects had a fine cell structure, but suffered from dark brown discoloration.

Example 4

Example 2 was repeated with 0.(% zinc carbonate as propellant. The block had a specific gravity of 0.82 g/cm^,

good surface and cell structure, but the cell structure was poorer than obtained in examples 2 and 3(a).

Example 5

(a) Example 2 was repeated with granular 45% asbestos fiber reinforced polypropylene, cylinder temperatures 200°/ 235°/235°/235° and stuffing cycle of 66 seconds. The product had a specific weight reduction of 30%, a smooth, fine cell structure and a smooth, stain-free surface. (b) For comparison, the example was repeated with azodicarbonamide instead of zinc carbonate. The stop objects had a fine cell structure, but were black-stained.

Example 6

Example 2 was repeated with polypropylene reinforced with 20% glass fibre, cylinder temperatures 200<o>/235°/235<O>/235°C and stopping period equal to 66 seconds. The product had a specific weight reduction of 30%, an even, fine cell structure and a smooth, stain-free surface.

Example 7

Example 4 was repeated with polypropylene reinforced with granular 20% asbestos fiber, cylinder temperatures 200°/235°/235°/235°C and a stuffing cycle of 66 seconds. The product had a specific weight reduction of approx. 30%, good cell structure and the surface was without discoloration.

Example 8

Granular nylon 6 (marketed as "Akrulon", Grade

2 SpeciaL), specific gravity 1.2 g/cm , was tumble mixed with 1% propellant composition as described in example 1(a). The mixture was stopped as in example 1 with cylinder temperatures 275°/270°/270<0>/270<0>C and stop cycle equal to 65 seconds. The base piece had a specific gravity equal to 0.75 g/cm 2 , a uniform, fine cell structure and a smooth surface without discoloration.

Example 9

Polystyrene ("Shell S173") was tumble mixed with 0.8% propellant composition according to example 1(a). The mixture was stopped as in example 1(a) with cylinder temperatures of 190°/220°/220°/220°C and stop cycle of 70 seconds. The stopeggen stand had a specific weight reduction of 23% and a uniform, very fine cell structure.

Example 10

Granular polycarbonate resin ("MaKrolon 3200") with intrinsic viscosity equal to 0.531 was tumble mixed with 0.3% propellant as shown in the table and spray stopped at cylinder temperatures of 280°/280<o>/285<O>/285°C. The propellant composition and impact strength as well as the intrinsic viscosity are shown in the table below. The stoppers were 16 cm square plates 1 cm thick. The impact strengths were measured on 6.3 cm disks cut out of the stop pieces, according to the drop weight method with a ball with a diameter of 2.5 cm.

Example 11

A polymer premix suitable for use as a propellant together with polymer according to Example 2 was prepared by dry mixing low melting point polyethylene powder ($0 parts) and 30 parts of a mixture of zinc carbonate (75%), tracum (15%) and lauric acid ( 10%). The mixture was extruded at 110°C and the extrudate chopped up into pellets. The procedure from example 2 was repeated using these pellets as propellant.

Example 12

A thermoplastic composition was produced by tumbling polystyrene granules with high impact resistance ("Shell S173 styrene") with a weight percent propellant composition containing a mixture of basic zinc carbonate (75%), talc (15%) and lauric acid (10%). The mixture was spray tested with a temperature profile of 180<0>/220°/230°/230<0>C, an injection time of 1 second and a mold cooling time of 60 seconds. Stop pieces with a uniform cell structure and a good surface were obtained.

Example 13

A thermoplastic composition was prepared with polypropylene ("Carlona K571") as in Example 12, and was spray tested with a temperature profile of 220°/240<0>/240<0>/240°C, with a 1 minute cycle.

Example 14

A thermoplastic composition was made with HD polyethylene ("Rigidex 50") as in example 12, and this was spray tested at a temperature profile of 220<o>/235°/235<O>/235°C, in a 1 minute stop cycle.

Example 15

A thermoplastic composition was made by tumbling "Noryl FN215" granules (modified PPO) with 1% by weight propellant consisting of basic zinc carbonate (85%) and talc (15%). The mixture was spray tested with a temperature profile of 260°/275<O>/275<O>/275°C in a 1 minute stop cycle. Example 16 (a) A thermoplastic composition was made by tumble mixing reinforced polycarbonate ("Makrolon 3000" and "Lexan FL900") with 0.3% by weight propellant as in example 15, and sprbytestbte with temperature profile 285°/295<0>/295° /295<0>C. A 2% drop in intrinsic viscosity was obtained. (b) Under the same conditions, azodicarbonamide gave a 50% drop

in the intrinsic viscosity.

Example 17

A flame retardant grade of polypropylene was tumble mixed with 0.8% by weight propellant according to Example 15 and spray tested with a temperature profile of 210°/2g5°/235°/235°C and a 1 minute spray testbpt cycle.

Example 18

A thermoplastic composition was made by tumbling polyethersulfone ("200P" from ICI) with 0.7% by weight propellant, according to Example 15, and spray-testing the mixture with a temperature profile of 330<o>/330°/330<o>/350°C and a stop cycle of 50 seconds.

Trihydrazinotriazine, a propellant that decomposes and releases nitrogen and ammonia, produced cracked objects.

Example 19

Example 1 was repeated with 0.5% of a mixture of basic cadmium carbonate (Cd C0^.2Cd0.3H20, 85%) and talc (15%).

Example 20

Example 2 was repeated except that the propellant consisted of basic zinc carbonate (85%) and potassium carbonate (15%). In this case, the product had a slightly finer cell structure than in example 2.

Claims (26)

r. Method for expanding thermoplastic polymers, consisting in heating a composition containing the thermoplastic polymer and a propellant so that the propellant decomposes thermally, characterized in that a carbonate in the form of zinc carbonate or cadmium carbonate is used as the primary propellant. 2. Method for expanding thermoplastics polymers, characterized by heating a composition containing a thermoplastic polymer and a propellant selected from zinc carbonate, lead carbonate, cadmium carbonate and/or lithium carbonate to a temperature of between 200°C and the polymer's decomposition temperature, which temperature is higher than the propellant's decomposition temperature in situ and higher than the thermoplastic polymer's softening point, and where the composition contains less than 5%, preferably less than 2% added strong acid and preferably less than 30% of the active propellant is an ammonia-evolving organic propellant. 3. Method as stated in claim 1 or 2, characterized in that the carbonate forms at least 90% of the active propellant in the composition. 4.. Method as stated in claim 1 or 2, characterized in that the composition contains an ingredient that is adversely affected by ammonia, e.g. a thermoplastic polymer selected from polycarbonate, polyamide, polyester, polyphenylene sulfide, polysulfone or styrene homopolymer, copolymer, alloy or blend. 5. Method as specified in one or more of the above claims, characterized in that a core former which preferably has an average particle size of less than 100 nyu is also present in the mixture. 6. Method as stated in claim 6, characterized in that the core former consists of a pigment, a filler, magnesium silicate, aluminum silicate, a clay, rbkt oxide, silicon oxide or magnesium oxide. 7. Method as specified in one or more of the above claims, characterized in that there is an added organic carboxylic acid with a pK^ for all neutralization points greater than 5, e.g. a fatty acid C] _q_20 <*> 8. Process as stated in one or more of the above claims, characterized in that the mixture contains a solid, particulate nucleating agent and/or an added acid whose neutralization points all have a pK^ value greater than 5, in an amount of up to 50 weight percent of the carbonate. 9. Procedure as indicated in an elike several of them the above requirements, characterized by the carbonate being mixed with a solid, particulate nucleation- agent and/or an organic carboxylic acid whose neutralization points all have a pK^ value greater than 5, and that the mixture is then mixed with a thermoplastic polymer. 10. Method as stated in one or more of the above claims, characterized in that the carbonate is used in the form of a premix with the same thermoplastic polymer or another compatible polymer. 11. Process for expanding ammonia-vulnerable thermoplastic polymers, characterized in that zinc carbonate is added to the mixture as primary propellant in an amount of from 0.05 to 5 percent by weight, which thermoplastic polymer has a processing temperature of at least 200°C, the composition preferably contains less than 2% added strong acid and is substantially free of ammonia-evolving organic propellants, and heats the composition to at least 200°C so that the primary propellant decomposes, preferably during extrusion or stopping of the composition. 12. Expanded thermoplastic polymers produced according to a method as stated in one or more of claims 1-11. 13. Expanded thermoplastic polymers containing thermal decomposition products of a carbonate selected from zinc carbonate, lead carbonate, cadmium carbonate and/or lithium carbonate and substantially free of strong acid or its zinc, lead, cadmium or lithium salt and free of thermal decomposition products of ammonia- developing organic propellants. 14. Storage-stable, expandable, thermoplastic polymer compositions, characterized in that they contain a thermoplastic polymer and as propellant zinc carbonate, lead carbonate, cadmium carbonate and/or lithium carbonate. 15. Composition as stated in claim 14, characterized in that it contains less than 20% other propellants. 16. - Composition as specified in claim 14, characterized in that it is substantially free of ammonia-evolving organic propellants. 17. Composition as stated in one or more of claims 14-16, characterized in that the thermoplastic polymer has a forming temperature of at least 200°C. 18. Storage-stable compositions suitable for use in expanding thermoplastic polymers with forming temperatures above approx. 200°C, containing a solid, particulate mixture of a compound selected from among zinc carbonate, lead carbonate, cadmium carbonate and/or lithium carbonate together with a solid, particulate nucleator, which nucleator is preferably selected from oxides, silicates and clays. 19. Composition as stated in claim 18, characterized in that the core former constitutes from 5 to 50 parts per weight part core former per 100 parts carbonate. 20. Composition suitable as a primary propellant for thermoplastic polymers with a forming temperature of at least 200°C, characterized in that it consists of a particulate mixture of zinc carbonate and one or more of the compounds magnesium oxide, silicon oxide and/or talc. 21. Composition as stated in claim 18, characterized in that the carbonate is zinc carbonate and the core former is magnesium oxide, fumed silicon oxide and/or talc. 22. Composition as stated in one or more of claims 18-21, characterized in that it also comprises an organic carboxylic acid whose neutralization points all have a pK^ value of over 5. 23. Composition as specified in one or more of claims 18-22, characterized in that it is essentially free of ammonia-evolving organic propellants and strong acids. 24. Composition as stated in one or more of claims 18 - 23, characterized in that it contains a polymer and the carbonate makes up from 10 - 50 percent by weight of the polymer. 25. Method for expanding thermoplastic polymers, characterized in that a composition according to one or more of claims 18 - 24 is used as propellant so that from 0.05 to 5 percent by weight carbonate is provided. 26. Expandable, thermoplastic polymer composition, characterized in that it contains zinc carbonate and/or cadmium carbonate as primary propellant.