Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Forming articles by uniting randomly associated particles
Reexamination Certificate
2003-01-21
2004-08-17
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Forming articles by uniting randomly associated particles
C264S494000, C264S496000, C264S302000, C264S306000, C264S308000, C264S310000
Reexamination Certificate
active
06776950
ABSTRACT:
The present invention relates to a slush-molding method for the manufacture of imitation leathers, in particular for the upholstery of cars.
As generally known, the slush-molding technology is broadly used for the manufacture of imitation leathers for the upholstery of cars, and in particular for the covering of dashboards and door panels. Said technology allows to obtain even highly three-dimensional imitation leathers easily and with low costs; moreover, slush molding gives the leather a leather design of excellent quality, and also allows to carry out even two-color leathers.
The slush-molding method is well known and reported in scientific literature, for instance in the following recent articles:
Pabst H. G., Shaper S., Schmidt R., Terveen A. (AUDI—VW Group)—VDI Conference—Mannheim 1988—“Development and large-scale use of dashboards produced by Slush Molding PVC”
Khue N. N., Kunper-Martz M., Dankmeier O., (EVC Group)—“Development of optimum powder blend for slush molding”—4
th
International Conference on PVC 1990—Apr. 24
th
-26
th
1990, Brighton U.K. pp. 31/1-31/14.
The following patents also contain descriptions related to slush molding:
FR-A- 916.055, FR-A 1.131.153, FR-A 1.381.850, FR-A 1.560.675, U.S. Pat. No. B2,736,925, U.S. Pat. No. B3,039,146, GB-A-865.608, GB-A-1.025.493, GB-A-1.056.109, GB-A-1.337.962, DE-A-1.554.967, DE-A-3.417.727, IT-A-22197 A/80, EP-A-0 339 222, EP-A-0 476 742, and so on.
The aforesaid molding technology is based on a method including the following stages:
a) an open-air tank is first filled with a suitable polymer powder in a sufficient quantity and with grain sizes typically below 500 &mgr;m;
b) a mold, usually electroplated with nickel, is then heated to a given temperature;
c) the tank and the mold are then coupled in a closed system with suitable coupling means;
d) the system is moved so that the tank transfers the powder onto the mold, thus obtaining a uniform layer of partially or completely melted powder which adheres to said mold;
e) the closed system is then opened after being brought to the initial conditions again; at this stage the possible excess polymer powder deposits again into the tank and can thus be regenerated;
f) the mold can now be heated in order to complete the melting;
g) the mold is then cooled with suitable cooling means;
h) the formed leather is stripped off as a semi-finished product which can then be assembled with a support in order to obtain the finished product in the form of dashboard, door panels, and so on, for the upholstery of cars.
The greatest success recently obtained with imitation leathers for car dashboards has been reached by slush molding of PVC powders, with operations allowing to obtain even one- or multicolored leathers.
A problem which is still to be solved is how to obtain leathers by means of slush molding of materials other than PVC (polyvinyl chloride) with low costs, so as to avoid all the environmental and recycling problem arising from the use of a halogenated plastic material such as PVC.
PVC resins, suitably plasticized and having originally a sufficiently high molecular weight, when worked, gel and reach a minimum viscosity value allowing it to spread onto the mold without any shear efforts (typically desirable characteristic if the slush-molding technique is used), whereas the other plastic materials cannot combine a high molecular weight with such a low melt viscosity to give rise to the same phenomenon. As a matter of fact, high molecular weights, which would allow to obtain good performances as far as mechanical qualities and heat resistance are concerned, are also characterized by a very high melt viscosity, thus preventing the distribution and the spreading onto a mold without any shear effort.
On the other hand, the absence of shear efforts prevents the leather obtained by slush molding from having unwanted frozen inner stresses. Obviously, the possible presence of inner stresses would first reduce the resistance and non-deformability according to temperature. Moreover, leather in such conditions would show an increase of shrinkage in those critical situations of ageing which are required by car makers.
The use of techniques other than slush molding for the manufacture of leather result in the abovementioned disadvantages.
In particular, the kind of “hand” which can be obtained with the aforesaid slush-molding technique cannot be easily imitated with other techniques, such as plate thermoforming. Moreover, the kind of leather design, which is perfectly reproduced with slush molding and is not deformed as in thermoforming, cannot practically be obtained with other techniques. Within the same slush-molding technology various attempts have also been made to replace PVC with other materials.
For instance, thermosetting liquid polyurethanes are now sprayed onto a metal mold. Said materials are first particularly expensive with respect to PVC and THEREFORE make the process more expensive than the use of PVC. In addition, the products obtained by means of said materials have shown several faults, such as the presence of inhomogeneous leather shims and the imperfect compacting of leather resulting in a decrement of the mechanical performances of the product.
Moreover, the corner portions and the possible undercuts on the leather forming mold are typically concerned, during the deposit of liquid polyurethane, by areas with an excess filling of material, which causes further imperfections on the product and scraps.
Powdered thermoplastic polyurethanes (TPU) have also been used, but their cost is again very high and they are not well accepted since their recycling is difficult and they cause toxic decomposition products.
On the basis of the existing art, briefly described above, and of the disadvantages resulting from it,the preferable kinds of products in case PVC should be replaced, both for environmental and for economical reasons, are those made of polyolefins, which have long been focused on by technicians.
The problems arising from the use of polyolefin materials are different because of several reasons.
First of all, polyolefins show a low melting point (only homopolymer polypropylene, or polypropylene copolymerized with low amounts of comonomers, would be suitable, but it is often stiff and does not show a good resistance to ageing, to solvents, to abrasion and to scratching); their molecular weights are low because of that, and therefore, the materials offer a lower resistance to ageing.
Copolymerization further lowers their melting point, thus limiting the resistance to high temperatures which is required in specifications.
In case of thermoforming from calendered or extruded plates, the aforesaid disadvantages can be partially overcome, since the initial molecular weights are high, with all the advantages resulting from that as far as mechanical resistance, resistance to ageing and heat resistance, etc., are concerned.
To overcome the above problems are already know polyolefins cross-linking methods giving to the obtained semi-finished product a higher heat resistance. For instance, the Japanese published patent No. JP 01275640 describes a copolymer of alpha-olefin with butene-1 and other comonomers with the addition of peroxides, in order to obtain an expanded product which is resistant to high temperatures. This patent briefly mentions the possibility to obtain cross-linking with radiations.
Another Japanese published patent, No. JP 63069837, pursues the same aim as the previous one with an expansible composition containing organic peroxides, said composition being extruded without expansion and expanded after cross-linking, obtained with &bgr;-radiations (1 to 30 Mrad) with a cross-linking degree from 30 to 65% (gel fraction).
The Japanese patent JP 57197161 describes a laminated film of polyolefins or any kind of copolymers thereof (with vinyl acetate, octene, butene, etc.), said film having a high mechanical resistance, a high resistance to heat and a good weldability, cross-linked with doses from 1 to 10 Mrad (1 Mrad=10 kGy=10
4
J/kg) of X-rays, &bgr;
Cittadini Paolo
Ignatov Vladimir
Barnes & Thornburg
Conte James B.
Industrie Ilpea S.p.A.
Ortiz Angela
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