Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1997-06-25
2001-07-10
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S079000, C521S134000
Reexamination Certificate
active
06258862
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions based on polyolefins and on ethylene-vinyl acetate (EVA) copolymer, which are found to be advantageous especially for manufacturing sheets that can be employed in the motor vehicle industry, and in particular foam sheets. It also relates to the articles manufactured from these compositions and to a process for manufacturing them.
TECHNOLOGY REVIEW
For many years the market for the internal trim of motor vehicles has been dominated by the use of PVC sheets, either in combination with ABS for the dashboards, or highly plasticized for the door trims and the manufacture of sun visors.
Although the properties of these materials are advantageous, there are nevertheless some disadvantages in employing PVC in this application. Apart from those related to the use of plasticizers, such as “fogging” (evaporation of volatile constituents, in particular of plasticizers, and their deposition on the windows) or embrittlement with time, PVC is not compatible with the majority of the other polymers employed in the motor vehicle industry, and this requires its separation from the other motor vehicle components before it may be recycled.
There is therefore a requirement in the motor vehicle industry for a new material combining the good intrinsic properties of plasticized PVC (high and low temperature behaviour, thermoformability, high-frequency weldability, flexibility, etc.) with the possibility of being easily recycled, especially by direct thermal recycling or by reemploying it with other polymers employed in motor vehicles.
The proposed compositions ought not only to ensure excellent mechanical and stability properties in the products which result therefrom, but ought also to be high-frequency weldable with a view to being usable in the envisaged application. In addition, it is appropriate that the rheology of these compositions should be such as to permit high quality thermoforming—and in particular graining.
Various compositions based on polyolefins, in particular on a propylene homopolymer or copolymer, on ethylene-vinyl acetate copolymer and optionally on peroxide used as crosslinking agent during the processing, have already been proposed.
Document WO-93/24568 mentions compositions which make it possible to obtain, especially by extrusion, high-frequency weldable products for various applications in the medical field, such as pouches, bags, tubes and closures. The polymer composition used contains at least one ethylene-vinyl acetate copolymer, at least one propylene polymer, approximately 0.01% to 5% by weight of a crosslinking agent and approximately 0.1% to 35% by weight of one or several other polymers.
The sheets initially obtained from these compositions are, however, difficult to thermoform.
SUMMARY OF THE INVENTION
The invention aims to provide high-frequency weldable compositions which can especially advantageously replace PVC in motor vehicle internal trim applications without entailing prohibitive costs.
These compositions must meet the usual criteria in this area of application, especially insofar as grainability, behaviour towards heat and towards UV, mattness and fire resistance are concerned, while being recyclable. In particular, they must be thermoformable and must, for this purpose, exhibit a suitable rheology.
They must additionally be suitable for the manufacture of articles in the form of foams, in particular sheets, and this requires very specific—especially rheological—properties. It has already been proposed to manufacture foams from compositions containing a crosslinking agent. However, in such a case a high degree of crosslinking is generally necessary to obtain satisfactory rheological properties, and this is extremely awkward in view of the recycling: in effect, a high degree of crosslinking results in the formation of gels, and this considerably perturbs the recycling.
In addition, during the manufacture of crosslinked foams, the crosslinking generally takes place after the extrusion, making this manufacture more complicated.
It is furthermore desirable to develop compositions that can be employed in the manufacture of multilayer sheets of the sheet/foam type, such as those commonly employed in motor vehicle internal trim. A common model of such multilayer sheet includes a surface sheet based on thermoplastic polyolefins and a foam based on plasticized PVC; it is clear that the recycling of such sheets presents serious problems and, in the majority of cases, requires complex systems for separating the materials.
DETAILED DESCRIPTION OF THE INVENTION
Consequently, the present invention relates to a composition including, by weight:
from 40 to 80% of at least one uncrosslinked composition (A) including at least one polyolefin (PA);
from 60 to 20% of at least one crosslinked composition (B) including at least one propylene polymer (PB) and at least one ethylene-vinyl acetate (EVA) copolymer.
In particular, good results have been obtained by employing a crosslinked composition (B) including, by weight, at least 10%, preferably at least 20%, of at least one propylene polymer (PB), the quantity of which is not more than 49%, preferably not more than 40%.
Besides propylene, the propylene polymer (PB) may optionally contain one or several other monomers preferably chosen from alpha-olefins; it may equally well be a homopolymer or a random or a block copolymer, a terpolymer and the like. The propylene polymer (PB) advantageously includes at least 50% by weight of propylene. It preferably includes at least 75% by weight of propylene. It is particularly preferably a propylene homopolymer. Its melt index (MFI) (230° C.; 2.16 kg; measured according to ISO standard 1133-1991 version) is advantageously lower than 10 g/10 min and preferably lower than 4 g/10 min. It is furthermore advantageously at least 0.1 g/10 min, preferably at least 0.4 g/10 min.
It is preferred that the crosslinked composition (B) should have been prepared beforehand by processing at least one propylene polymer (PB), at least one EVA copolymer, and from 100 to 1500 ppm by weight of at least one crosslinking agent.
The crosslinked composition (B) advantageously additionally includes, by weight, at least 51%, preferably at least 60%, of at least one ethylene-vinyl acetate (EVA) copolymer in a quantity of not more than 90%, preferably not more than 80%. The weight content of this vinyl acetate copolymer is generally at least 12%, preferably at least 18%, while being not more than 40%, preferably not more than 32%.
It is furthermore advantageous that the total vinyl acetate content of the composition (B) should be at least 12%, preferably at least 15%, and not more than 25%, preferably not more than 22%, relative to the total weight of the propylene polymer (PB) and of the PVA copolymer.
An MFI value (190° C.; 2.16 kg; also measured according to ISO standard 1133) higher than 0.5 g/10 min, and very particularly higher than 1.5 g/10 min, is preferred in the case of the EVA copolymer. This value is advantageously lower than 25 g/10 min, preferably lower than 9 g/10 min.
According to an advantageous alternative form of the invention the melt indices of the propylene polymer (MFI
PB
) and of the EVA copolymer (MFI
EVA
) (measured in the abovementioned respective conditions and expressed in g/10 min) should correspond to the relationship
MFI
PB
·
P
PB
MFI
EVA
·
P
EVA
<
1
,
and
preferably
MFI
PB
·
P
PB
MFI
EVA
·
P
EVA
<
0.7
in which P
PB
and P
EVA
denote the respective weight proportions of these constituents PB and EVA (P
PB
+P
EVA
=1).
To bring about the crosslinking of the composition (B) during its preparation a crosslinking agent is employed, the quantity of which is generally less than 1500 ppm (parts by weight per million), preferably less than 900 ppm, particularly preferably less than 700 ppm. Its quantity is furthermore generally more than 100 ppm, preferably more than 200 ppm. These very small quantities make it possible to produce a limi
Matz Pierre
Mulkens Edmond
Foelak Morton
Schneller Marina V.
Solvay ( Societe Anonyme)
Venable
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