Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Reexamination Certificate
2000-08-10
2002-11-05
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
C264S280000
Reexamination Certificate
active
06475420
ABSTRACT:
FIELD OF THE INVENTION
To decorate injection-molded shaped parts with printed polymethyl methacrylate films (PMMA) there are used PMMA films with thicknesses in the range between 80 and 300 &mgr;m for the purpose of achieving a certain “depth effect” of the printing. For decoration, either printed PMMA films colaminated with thermoplastic laminate substrates are preformed and stamped to the desired geometry then placed in the injection-molding die and back-molded, or printed PMMA film in the form of rolled stock is guided into an injection-molding die and back-molded.
Back-molding takes place on the printed side, so that the printing is protected by the PMMA film, which contains UV absorbers. Examples of materials for use in back-molding include the following thermoplastics and polymer blends: ABS, PC/ABS blends, PVC, PC, PC/ASA blends, PP, PP blends.
For decoration, either printed film-type formed parts (optionally preformed) are placed in the injection-molding die and back-molded, or printed PMMA film in the form of rolled stock is introduced into the injection-molding die and back-molded, or PMMA film is laminated onto a thermoplastic laminate substrate and (optionally preformed) placed in the injection-molding die and back-molded. As laminate substrates which can be laminated with the inventive and printed film, there can be used, for example, the following thermoplastics: ABS, polycarbonate-ABS blends, ASA (copolymers of acrylic ester, styrene and acrylonitrile), polycarbonate-ASA blends, polyolefins such as polyethylene and polypropylene, PVC and polyphenylene-containing blends. All thermoplastic materials can be reinforced by glass fibers or inorganic fillers.
The PMMA film assumes the function of a protective lacquer. In contrast to injection-molded parts which are protected with protective lacquer or which are directly printed or printed by transfer methods (thermal transfer, water-based transfer), surface decoration with printed PMMA films offers the following advantages:
clear cost reduction (surface finish and decoration are achieved in one process step)
solvent-free process
no expensive capital spending and environmental directives
simple change of the printed design
greater design freedom
The decoration of thermoplastic shaped parts with printed films concurrently with the injection-molding process is generally known as “in-mold film decoration”. The best known form of this method is called “insert molding”. For this purpose the decoratively printed PMMA film is stiffened by colamination with a thermoplastic laminate substrate. For this purpose there are preferably used ABS, ASA, PC, PVC, PP, PPE and blends of these materials.
The film laminate is formed and stamped to the desired geometry by means of a thermoforming process. The preforms are then fed to the back-molding process for actual manufacture of the shaped parts. For this purpose the preforms are placed in the injection-molding die, for the most part automatically, and back-molded with thermoplastic plastics. For back-molding there are preferably used ABS, ASA, PC, PVC, PP, PPE and blends of these materials. If the laminate substrate is used in sufficient thickness, there is no need for back-molding and the unformed, stamped or cut laminate can be used directly as the shaped part.
By virtue of the extremely streamlined process control and the possibility of rapid design change, “in-mold film decoration” offers the processers or manufacturers of shaped parts substitute options for more traditional, more complex methods.
For example, PMMA film printed with transparent elastic lacquers then back-molded with transparent thermoplastics can be used in extremely rational manner for the manufacture of automobile tail-light lenses. As the transparent thermoplastics there are preferably used PMMA molding compounds, SAN, polystyrene molding compounds, polycarbonate and PMMA/SAN blends.
This method offers the possibility of rapid design change without having to build new, costly multicomponent injection-molding dies. Moreover, the complex step of coloration of the PMMA molding compounds which are complex for multicomponent injection molding is obviated.
In this type of application, “in-mold film decoration” permits the manufacture of complete external parts for automobile bodies, which parts can optionally contain the tail-light lens as a functional surface.
In this application the PMMA film printed with transparent elastic lacquers can optionally be back-molded, prior to the process of manufacture of the shaped part, together with transparent, thermoplastic laminate substrates in order to increase stiffness for protection of the lacquer from the hot, pressurized, molten thermoplastic material used for back-molding.
A special embodiment of “in-mold film decoration” which operates very economically uses combined mechanical forming and back-molding dies, with which both mechanical forming of the films and back-molding take place in one process on the basis of printed films in the form of rolled stock. This method is generally known as “film-insert molding”.
In the use of PMMA films for decoration of injection-molded shaped parts by means of “in-mold film decoration”, exacting requirements are imposed on the PMMA film material:
good ease of manipulation in the printing process, or in other words adequate extensibility
high surface hardness (at least pencil hardness HB), to prevent scratching of the shaped part decorated with PMMA film
high surface gloss of ≧120 (measuring technique per DIN 67530)
low haze development to less than 2% haze, corresponding to the method described on page 17
low surface haze of <1.5%
extremely low gel-body count of at most 1 gel body per 200 cm
2
high weathering resistance; comparable with that of standard PMMA
adequate absorption of UV light; UV absorption in the region between 290 and 370 nm <1%.
PRIOR ART
German Patent DE 3842796 (Röhm GmbH) describes PMMA films based on PMMA molding compounds with small-sized elastomer particles and high elastomer content. As regards the “surface hardness” parameter, the inventive films cannot be manufactured with these molding compounds.
International Patent WO 96/30435 and European Patent 763560 (Mitsubishi Rayon) describe the manufacture of PMMA films with thickness up to 0.3 mm on the basis of a specified PMMA composition: an impact-strength modifier based on polybutyl acrylate with specified particle diameter as well as PMMA matrix polymer III and the (optional) addition of a melt-strength modifier (polymer I).
The film is manufactured by means of a single-roll process (otherwise known as the chill-roll melt-casting process), in which the thermoplastic melt is brought into contact with a single metal roll and cooled during the cooling and solidification process. It is expressly pointed out that the thermoplastic melt for manufacture of films of the claimed thickness range cannot be formed between two metal rolls.
Compared with the two-roll process this method suffers from significant disadvantages, which have a decisive influence on film quality. In forming on the single chill roll, in contrast to the two-roll (smoothing) process, gel bodies, which in principle tend to be formed by impact-strength-modified PMMA molding compounds, are not forced underneath the film surface and thus remain visible as optical defects. This is particularly detrimental as regards the subsequent printing process for the manufacture of decorated films, in which clearly visible flaws are apparent in the region of the gel bodies. Furthermore, the film surface opposite the chill roll and cooling naturally in the air exhibits pronounced surface haze, which results from the differences between volume contraction of the elastomer particles and the PMMA matrix. Hereby there is produced a pronounced “peak-and-valley” surface structure, which scatters light and thus causes a detrimental haze effect.
German Patent DE 19544563 (Röhm GmbH) describes the impact-resistant PMMA molding compounds used to manufacture the inventive films.
German Patent DE 4018530 (Röhm GmbH) des
Hofmann Klaus
Kaube Peter
Numrich Uwe
Schmidt Horst
Vetter Heinz
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Roehm GmbH
Tentoni Leo B.
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