FOAM MATERIAL

Abstract: Polystyrene-based foam material for the production of for example label material, wherein the foaming has been made with a blowing agent is for example a decomposable blowing agent (chemical blowing agent) or consists of for example carbon dioxide, nitrogene gas or even water, and with a thermoplastic elastomeric blend composition consisting at least of one styrenic block copolymer and one homogeneously branched ethylene-interpolymer.

Description: Foam material The invention is concerned with a polystyrene-based foam and a method to produce such foam for the production f.e. of label material. Such foams are known in various embodiments. Reference is made for example to DE-A140 11 003. This state of the art refers to a foam, which has recently been developed in order to avoid CFCs by using blowing agents in form of hydrocarbons, carbondioxides, nitro- genes, combinations thereof etc. Before, is has also been known to produce foams using chemical blowing agents together with nucleating agents, see for example EP-A3-055437. A technical problem with such polystyrene-based foams is especially their brittleness, resulting in easy tearing and inferior elasticity. In order to improve these properties, it has already been proposed to put the polystyrene-based foam as one layer in a multi-layer foam, with one of the layers being a polyo- lefinic layer. However, this is affected with comparatively high production costs and extrusion problems. As it is often desired, for recycling purposes, to have only one kind of material, such raulti-layer foam consisting of different plastic materials, may create also problems. An object of the present invention is to propose a polystyrene-based foam, which has improved properties in view of the brittleness without a reduction in the properties being relevant for making them usable for especially label material. This problem has been solved with a foam as described in claim 1 of the present application. Such foams are produced with a blowing agent and preferably also a nucleating agent, whereby the blowing agent can be one of the blowing agents known in the state of the art. These are for example chemical or decomposable blowing agents, carbondioxide, nitrogene gas or even water. As nucleating agents, the common nucleating agents can be used. These are f.e. talc and/or sodium hydrogene carbonate and/or ammoniuinhydrocarbonate and/or calcium carbonate and/or clay and/or citric acid etc. The nucleating agents can be used in amounts of about 0,05 to about 5% per weight of the foam, preferably in a range from about 0,3 to about 2,0% by weight. The amount can be even as low as 0,01%. Further is of importance, that the foaming will be made, with a polystyrene material combined with a thermoplastic elastomeric blend composition, consisting at least of one styrenic block copolymere and one homogeniously branched ethylene interpolymer. Surprisingly, it has been found, that such a foam has a remarkably reduced brittleness and improved elasticity but is nevertheless producable with the common production methods such as by extrusion, for example in flat-die extrusion, annular die extrusion, horizontal blown film extruders or the like. No multi-layer foam with an polyolefinic layer is necessary to meet high requirements . However, it is possible to make in a per se known manner a coextrusion of a non-foamed layer with a foamed layer, both layers based on polystyrene. Nevertheless, it is also possible, according to the invention, to make ulti-layer-foam as in the state of the art, but with remarkably thinner polystyrene based layers. Accordingly, there can be also layers of different raw material. Individual layers can be foamed or non-foamed. It is especially prefered to add the mentioned thermoplastic elastomeric blend composition in such an amount, that in case of a shrinkable polystyrene based foam a possiblity to shrink into recesses, such as to follow concave structures, is reached. It has further been found, that the amount of the mentioned thermoplastic elastomeric blend composition, starting from a certain treshold-amount, leads to a foam having advantages in terms of seperability. This especially for PET-applications. It is possible to seperate such foam from PET for example by water. The foam does swim on top, whereas the PET sinks to the bottom. It is believed, that this is due to a high amount of closed cells in the polystyrene foam, whereas the cells in the foam of the state of the art are ruptured in a high amount. Therefore, the foam of the state of the art will get filled with water and such foam also goes to the bottom in case of the mentioned seperation procedure. In a further development of such foam, an important feature is to add such an amount of nucleating agent, that the foam has a density of lower than 0, 8g/cm 3 . It is prefered to have an amount of such nucleating agent of from about lg to 50g per kg foam. It is prefered that the foam has a density of 0,06 to 0, 75g/cm 3 . Especially, for a polystyrene-based foam to be used for the production of printable labels, it is prefered to produce the foam with a thickness of below 0,2mm. It is possible to produce the foam with a thickness of 0,06-0, 195mm. In case, the foam shall be used to make trays or cups, thicknesses such as 0,4 and 0,5mm are prefered. Such foam does also have a very good printability, due to a high surface quality. Surprisingly, also the gloss is remarkably improved. The foam described here has a gloss which is superior to the gloss of all polystyrene-foams foamed according to any known method in the state of the art. The mentioned elastomeric blend compositions are especially such compositions as are disclosed in the PCT-application O95/33006. This application is included here by reference, especially in order to include one of the features mentioned in that reference into a claim of the present application. The mentioned elastomeric blend compositions do to a certain extend replace the polystyrene resin used to produce the polystyrene-based foam. Such replacement can be in an amount of 1-60%. It is prefered, to replace the polystyrene resin in an amount of 15-40%, even more preferably in an amount of 15-30%. The elastomeric blend composition is mixed with the remaining amount of polystyrene resin and thereafter the resin is used in the production as a usual polystyrene resin. The following examples may further illustrate the invention: 1. It has been produced a polystyrene based foam using a usual amount of nucleating agent as mentioned, but with 5% by weight of the mentioned thermoplastic elastomeric blend composition (TEBC) . The resulting foam showed an Elmendorf Tear in cross direction higher than in the state of the art foam. Further, such foam showed a gloss value (according to the 20° Gloss test) about 15% higher compared to a usual value. The 2% Secant Modulus in machine direction, measured in MPa, was compared to a usual value of about 850 remarkably reduced for about 15%. The 2% Secant Modulus in cross direction, measured again in Mpa, was compared to a usual value of 270 reduced for about 20%. The Tensile Yield in machine direction, measured again in MPa, was compared to usual value of 22,5 reduced for about 13%. The Ultimate Tensile value in machine direction, measured in MPa, was, con-pared to a usual value of about 21 reduced for about 15%. The Tensile Yield in cross direction, measured in Mpa was, compared to 6 with a usual foam for about 10% reduced. The Ultimate Tensile in cross direction, measured in Mpa, was, compared to a value for a normal foam of 6,1 reduced for about 12%. The Ultimate Elongation in cross direction, expressed in %, was similarly low as for normal foam, but nevertheless significantly lower. 2. It has been made a foam according to example 1, however, with an amount of 10% "TEBC" . The charac- teristic values were copmpared to the values of state of the art polystyrene foam as follows: Elmendorf Tear CD, g + 70% 20° Gloss + 35% 2% Secant Modulus MD, MPa - 20% 2% Secant Modulus CD, Mpa - 30% Tensile Yield MD, Mpa - 15% Ultimate Tensile MD, Mpa - 15% Tensile Yield CD, Mpa - 15% Ultimate Tensile CD, Mpa - 15% Ultimate Elongation CD, % same 3. A polystyrene based foam has been made as before, however, with an amount of 20% of "TEBC" . The following values were obtained: Elmendorf Tear CD, g + 60% 20° Gloss + 90% 2% Secant Modulus MD, Mpa - 22% 2% Secant Modulus CD, Mpa - 40% Tensile Yield MD, MPa - 5% Ultimate Tensile MD, Mpa same Tensile Yield CD, Mpa - 12% Ultimate Tensile CD, Mpa - 12% Ultimate Elongation CD, % - 30% 4. A polystyrene based foam has been produced according to the examples mentioned before, however, with an amount of "TEBC" of 30%. The following values were obtained: Elmendorf Tear CD, g + 125% 20° Gloss + 130% 2% Secant Modulus MD, MPa - 22% 2% Secant Modulus CD, MPa - 22% Tensile Yield MD, MPa - 10% Ultimate Tensile MD, MPa - 5% Tensile Yield CD, MPa + 15% Ultimate Tensile CD, MPa + 15% Ultimate Elongation CD, % - 30% Remarkable is, that the 2% Secant Modulus in cross direction, significant for the brittleness, goes through a minimum, at foams having around 20% of the mentioned thermoplastic elastomeric blend composition, and is then rising again for higher amount of TEBC.

Claims: C L A I M S 1. Polystyrene-based foam material for the production of f.e. label material, whereby the foaming has been made with a blowing agent and preferably a nucleating agent, whereby the blowing agent is f.e. a decomposable blowing agents (chemical blowing agent) or does consist of f .e. carbondioxide, nitrogene gas or even water, and with a thermoplastic elastomeric blend composition consisting at least of one styrenic block copolymer and one hαmogeniσusly branched ethylen-interpolymer. 2. Foam according to claim 1, characterized by a density of lower than 0, 8g/cm 3 . 3. Foam according to claim 2, characterized by a density of 0,06-0,75g/cm 3 . 4. Foam according to one of the claims 1-3, characterized by a thickness of lower than 0,7mm, especially 0,5 or 0,4mm. 5. Foam according to one of the claims 1-4, characterized by a thickness of lower than 0,2mm. 6. Foam according to claim 5, characterized by a thickness of 0,06-0, 195mm.

Inventors: HEYMANN PETER, HEYMANN, PETER
Applicants: GERRO PLAST GMBH, HEYMANN PETER, HEYMANN, PETER
Application year: 2000
Main classification: C08J9
IPC codes: C08J9, C08L23, C08L25, C08L51, C08L53