Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Reexamination Certificate
2002-10-31
2004-09-28
Teskin, Fred (Department: 1713)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
C264S296000, C264S300000, C264S301000, C525S194000, C525S206000, C525S209000, C525S212000, C525S221000, C525S479000, C525S536000, C525S539000, C525S934000
Reexamination Certificate
active
06797222
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for powder slush molding a thermoplastic composition which exhibits excellent low temperature properties coupled with heat and scuff resistance and is useful for auto and boat interior applications.
2. Background of the Invention
As generally known, slush-molding technology is broadly used for the manufacture films or sheets of material such as imitation leathers for the upholstery of cars, boats, and other car and boat interior applications, and in particular for the covering of dashboards and door panels. Said technology allows for obtaining even highly three-dimensional imitation leathers easily and with low costs; moreover, slush molding gives the molded sheet a leather design of excellent quality, and also allows carrying 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 H., 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 International Conference on PVC 1990 April 24th-26th 1990, Brighton U. K. pp. 31/131/14.
The following patents also contain descriptions related to slush molding: U.S. Pat. No. 2,736,925; U.S. Pat. No. 3,039,146, EP-A-0 339 222, EP-A-0 476 742 and WO 0207946.
Slush molding technology is based on a method that typically includes 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 micrometers;
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.
Polyvinyl Chloride (PVC) has a solid place for use as a sheet material in automotive interior applications but is under attack due to the fact that it contains halogens and plasticizers. One of the applications of PVC in auto interiors is as slush molded material for door panels and dashboards. For the slush molding process, powders arm used. The plasticizers contained in these formulations facilitate the flow and the fusing of the powder in the slush molding process where the powder is brought in contact with a hot mold from where it has to be released thereafter. The presence of a high amount of plasticizers has however the negative effect of exaggerated fogging of the interior surfaces of windows, particularly the front window, during hot summer days. This effect as well as the high chlorine content of PVC has triggered the search for polymeric plasticizers or highly temperature stable plasticizers as described in U.S. Pat. No. 5,036,124, and the search for halogen-free slush molding systems. The most frequently used halogen-free systems are systems based on TPU (Thermoplastic Polyurethane). However, due to their high cost, they are not an economical solution for the majority of cars. Alternatives have been promoted based on elastomer powders or polypropylene (PP). U.S. Pat. No 5,308,699 claims a slush moldable Ethylene Propylene (EP) rubber with a cross-linked EP phase, U.S. Pat. No. 5,744,086 claims a PP based system. The drawback of these systems is the insufficient chemical resistance of these systems against chemical agents such as fluids which eventually require a costly surface protection, such as a lacquer on top of the slush molded sheet.
WO 0207946 addresses problems presented in typical slush-molding art by combining a slush-molding method with cross-linking. The process is characterized in that, before or after the stripping-off stage (stage h, noted above), the semi-finished product as a film is cross-linked by means of radiation in order to obtain a covering leather.
The present invention provides a method of slush molding that combines slush molding and in-situ cross linking without the use of radiation and overcomes the drawbacks of the prior art. The drawbacks are overcome by providing, as the powder dosed to the mold in a slush molding process, a composition comprising a powder comprising polar and thus solvent (fuel) resistant polymers which crosslinks in situ without radiation during the slush molding process.
SUMMARY OF THE INVENTION
The present invention provides a slush molding process during which the slush moldable polyolefin composition of this invention crosslinks in-situ during the slush molding process to provide a slush-molded composition that has superior chemical and temperature resistance.
The slush-molded composition is useful in automotive and non-automotive applications including essentially all applications where flexible vinyl sheet or articles molded therefrom have been or can be used.
The process of the present invention is a slush-molding process characterized by employing, as the powder to be slush molded, the composition of the present invention made under conditions of time and temperature to ensure the composition does not significantly react/crosslink prematurely, preferably 60-150° C., more preferably 90-120° C. The powder, preferably with sufficient promoter and more preferably further with sufficient release agents, is dosed into a hot mold held at a sufficiently high temperature for a sufficient time to cause cross-linking, preferably between 180-270° C., more preferably between 200-250° C. The powder melts, levels out, and cross-links in-situ to form a homogeneous skin, which can be removed from the mold following a heating cycle of about 2-6 min and cooling.
The composition of the present invention comprises
(a) 5-95% by weight of a copolymer comprising at least 50% by weight of ethylene, 1-35% by weight of an (acid containing) unsaturated carboxylic acid, and 0-49% by weight of a moiety selected from at least one of alkyl acrylate, alkyl methacrylate, vinyl ether, alkylene, carbon monoxide and sulphur dioxide, and further wherein the acid groups are optionally partially neutralized with metal ions; and
(b) 95-5% by weight of a copolymer comprising at least 50% by weight of ethylene, 0.5-25% by weight of at least one reactive moiety selected from the group consisting of
(i) an unsaturated epoxide of 4-11 carbon atoms,
(ii) an unsaturated isocyanate of 2-11 carbon atoms,
(iii) an alkoxy or alkyl silane wherein the alkyl group is from 1-12 carbon atoms,
(iv) an alkyl halide, and
(v) oxazoline, and
0-49% by weight of a moiety selected from at least one of an alkyl acrylate, alkyl methacrylate, vinylether, alkylene, carbon monoxide and sulphur dioxide, where the alkyl and ether groups are of 1-12 carbon atoms; and preferably
(c) sufficient amount of cross-linking promoter such as tertiary amines or alkyl halides; and more preferably, in addition to the promoter,
(d) a sufficient amount of at least one release agent to reduce adhesion to metal molds.
The compositions may further comprise any additive which could be useful to enhance or modify properties, such as fillers, ultraviolet light (UV) or thermal stabilizers, anti-oxidants, free-radical scavengers, leveling agents, anti-popping agents, and pigments.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention is a slush-molding process having steps of d
Hausmann Karlheinz
Kodokian George K.
Prejean George W.
E. I. du Pont de Nemours and Company
Teskin Fred
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