Foam material

Details Foam material Foam material

1999-03-15

2001-07-10

Nutter, Nathan M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S146000, C521S081000, C521S139000, C428S365000, C428S071000, C428S314800

Reexamination Certificate

active

06258868

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
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-A1 40 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, nitrogenes, combinations thereof etc. Before, is has also been known to produce foams using chemical blowing agents together with nucleating agents, see for example EP-A3-055 437.
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 polyolefinic 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 multi-layer foam consisting of different plastic materials, may create also problems.
SUMMARY OF THE INVENTION
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 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, nitrogen 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 ammoniumhydrocarbonate 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 it 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 copolymer and one homogeneously 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 multi-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 preferred to add the mentioned thermoplastic elastomeric blend composition in such an amount, that in case of a shrinkable polystyrene based foam a possibility 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 threshold-amount, leads to a foam having advantages in terms of separability. This especially for PET-applications. It is possible to separate 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 separation 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 0.8 g/cm
3
. It is preferred to have an amount of such nucleating agent of from about 1 g to 50 g/per kg foam. It is preferred that the foam has a density of 0.06 to 0.75 g/cm
3
.
Especially, for a polystyrene-based foam to be used for the production of printable labels, it is preferred to produce the foam with a thickness of below 0.2 mm. It is possible to produce the foam with a thickness of 0.06-0.195 mm. In case, the foam shall be used to make trays or cups, thicknesses such as 0.4 and 0.5 mm are preferred.
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 WO95/33006. This application is incorporated herein 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 preferred, 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.


REFERENCES:
patent: 5340844 (1994-08-01), Welsh et al.
patent: 5342560 (1994-08-01), Sturm et al.
patent: 5939464 (1999-08-01), Wang
patent: 4011003 (1991-10-01), None
patent: 3055437 (1982-07-01), None
patent: 9533006 (1995-12-01), None

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