Plastic and nonmetallic article shaping or treating: processes – Recycling of reclaimed or purified process material – Of process trim or excess blanked material
Reexamination Certificate
1997-11-14
2001-04-24
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Recycling of reclaimed or purified process material
Of process trim or excess blanked material
C264S173140, C264S177200, C264S920000
Reexamination Certificate
active
06221288
ABSTRACT:
European patent application No. 94500081.8 (published after the priority data of the present application) concerns a procedure for manufacturing laminated thermoformable panels for use as vehicle doors, trays or packaging containers by simultaneous extrusion of (I) a matrix (also termed central layer) made of what is termed a homogenized and gelled pre-mix of organic fibers plus a polyolefin formed in a counter-rotating double-screw extrusion press, and (II) two external layers made of polyolefin and a mineral filler formed by means of a co-rotating double-screw extrusion press.
Such double-screw or “twin screw” extruders of both the counter-rotating as well as the co-rotating type are known in the art and European patent 0 426 619 illustrates a particular preferred extruder of the latter type.
According to the European application EP94500081.8 mentioned above, organic fibers are used as filler for the central layer, apparently intended to serve as a carrier or bulk layer for the laminate; a 50/50 mixture of an olefin with organic fibers is mentioned in the example of EP94500081.8 for the central matrix layer while a 60/40 mixture of an olefine and a mineral filler is used to extrude the external layers which are said to provide a better finish of panels made of these materials if compared with prior art panel materials. Further, it is alleged in EP94500081.8 that the panel structures described therein have a different structure and are made of components that provide for better quality and characteristics than prior art panels.
The present invention, according to a first aspect thereof, aims at a method of producing a composite stratiform material by co-extrusion of at least three layers, each comprising polypropylene and at least one filler, said co-extrusion being effected by means of at least two, and preferably three, extruders each having a pair of co-rotating screws, characterized by co-extrusion of: (I) a carrier layer formed of a mixture containing polypropylene and a particulate organic filler; (II) a first outer layer consisting essentially of a mixture containing polypropylene and an inorganic filler; and (III) a second outer layer consisting essentially of a mixture containing polypropylene and an inorganic filler; said co-extrusion being carried out in a manner to ensure an integral structure, i.e. provides for interfusion of the carrier layer with each of the first and second outer layers at mutually opposite interfaces between the carrier layer and the outer layers.
It is believed to be essential for a preferred embodiment of the present invention in view of abrasion resistance that at least one and preferably both outer layers essentially consist of, rather than contain, polypropylene and in inorganic filler which, in turn, is particulate and generally not fibrous. Preferably, average particle sizes of the inorganic filler are in the range of from about 1 to about 500 &mgr;m, preferably in the range of from about 5 to about 100 &mgr;m, and specific examples will be given below.
If the outer layers contain other components, e.g. stabilizers, dyes or pigment, such other components should, in general, not exceed an amount of 10%, by weight, based upon the weight of the composition forming the outer layers. Inorganic pigment is, of course, regarded as “mineral filler”. It is to be noted that maximum abrasion resistance is of essence for that outer layer which will be exposed to maximum abrasion. Now, in the preferred use of the stratiform material according to the invention, i.e. for manufacture of fruit or vegetable containers in the form of crates or boxes, such containers generally will have an “outer” and an “inner” surface, each of which is exposed to different types of wear. Typically, in the case of fruit or vegetable boxes, the abrasion wear of the “outer” surface (i.e. the one frequently exposed to contact with the ground or other external bodies) will be substantially greater than that of the “inner” surface, i.e. the one in contact with the content of the containers, viz. vegetables or fruits.
When considering the general performance and use-properties of crates or boxes for packaging of fruits or vegetables and similar goods, two criteria—in addition to the costs of materials and manufacturing methods—are of primary importance, namely minimum weight and maximum stability, the latter notably including abrasion wear resistance.
Now, while mineral fillers increase abrasion wear resistance of a polypropylene composition containing them, such fillers will also tend to increase the specific weight of the composition containing them. Contrariwise, organic fillers will decrease the specific weight of a polypropylene composition containing them but impart less abrasion resistance, if any, to such a composition.
Hence, another preferred composite material according to the invention, as well as a container made of such material, will have a first outer layer consisting essentially of polypropylene and particulate mineral filler finely dispersed therein for maximum abrasion wear resistance, a central layer containing polypropylene and a major amount, at least, of an organic particulate filler for minimum specific weight, and a second outer layer with a balance of sufficient high wear resistance and sufficiently low specific weight. Such second outer layer will be used at the inner surface of the container made of such an “asymmetric” composite material. “Asymmetric” structure in this context is intended to refer to a composite material according to the invention where one of the outer layers contains a higher proportion of mineral filler than the other.
Generally, the term “particulate” is used herein in the sense of a material consisting of essentially compact particle shapes that show no clear preference for a specific, i.e. longitudinal, dimension. With reference to the organic filler used for the central layer to minimize the specific weight thereof, particulate wood in the form of wood flour, saw-dust and the like conventional forms of particulate wood with a typical average particle size in the range of from about 0.01-5 mm is preferred but other forms of particulate organic and preferably vegetabilic nature can be used depending upon availability, price and other ecological, commercial, and technological considerations.
If the polymer/filler material used for production of the central layer, and/or—optionally—for one of the outer layers of an asymmetric composite, is derived from recycled material, e.g. obtained from production scrap or by comminuting articles made of the inventive stratiform material by thermoforming or the like shaping or molding methods, such central layer will contain some mineral filler in addition to the particulate organic filler while one outer layer of an asymmetric composite will contain some organic filler.
The amount of mineral filler present in the central layer should, of course, be kept at a sufficiently low level to insure a sufficiently low specific weight of the composition of the central layer while the amount of organic filler in one outer layer of an asymmetric composite according to the invention should be sufficiently low to insure sufficient abrasion resistance.
The term “polypropylene” as used herein refers to all forms of polymerized propylene including it's various tacticities, e.g. isotactic, syntactic as well as syn-isotactic forms, and encompassing homopolymers as well as thermoplastic copolymers, graft-copolymers etc. that typically have a softening temperature of at least about 150° C. Polypropylene materials of various commercial provenience and having such molecular weights, melt viscosities and other processing parameters as are known to be suitable for extrusion purposes can be used in the present invention.
According to a general preferred embodiment, the present invention provides for a composite stratiform material having at least three interfused layers each containing polypropylene and at least one filler, characterized in that said material comprises: (I) a carrier layer formed of a mixture co
Blank Rome Comisky & McCauley LLP
Eashoo Mark
ICMA San Giorgio S.p.A.
Silbaugh Jan H.
LandOfFree
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