德玛格工艺注塑指导 Word 文档.doc

In-Mold Decoration In-mold Textile Lamination - Machine Technology and Process Control H a n d o u t - I n - m o l d T e x t i l e L a m i n a t i o n In-mold Textile Lamination - Machine Technology and Process Control Historical development 2 2 The structure of in-mold textile laminated components 3 Special machine equipment for in-mold textile lamination 10 Mold technology for in-mold textile lamination 11 Automation equipment for in-mold textile lamination processes 12 Page 1 of 16 2004-03-25 Handout - In-mold Textile Lamination In-mold Textile Lamination - Machine Technology and Process Control Todays processors can choose from of a variety of surface finishing techniques designed to en- hance the optical and tactile characteristics of an injection molded product. In addition to the classic methods such as metallization, galvanizing or decorative coating of injection molded components, the market also offers injection molding alternatives which integrate decoration into the injection molding process such as in-mold-decoration (IMD) or in-mold-labelling (IML). One such technique, called in-mold textile lamination, involves injection onto the back of materials such as grained film, textile material or velours. This paper deals with the in-mold lamination of smooth, cut-to-size material blanks with textile prop- erties of a multi-layered design which are suitable for forming. Thermoformed film, which is handled by grippers and directly inserted into the mold, will not be discussed in this paper. Historical development In-mold textile lamination started out under the name low pressure processing, first introduced at K86 by US exhibitors. It took five years for European manufacturers of injection molding machines to adopt this technique and develop it into a process-safe technology. This technology spread and became quickly established in the market, particularly in the European automotive industry. The evolution of this technique was driven by a combination of increasingly exacting consumer require- ments with respect to the optical and tactile properties of components as well as their perceived quality, the constant demand for innovation in automotive engineering and a heightened trend to- wards more rationalization in all areas of production technology. In most cases, in-mold textile lamination is applied in substitution for laminating techniques (bond- ing) used for decorating the surface of injection molded components. Contemporary in-mold textile lamination is a proven process which has become well established as a special injection molding technique, as is evident in the high number of mass-produced automotive components. Typical in- mold textile laminated applications are components such as A, B or C column cladding, storage tray covers, interior flooring, map pockets, interior door cladding and many more (Fig. 1). Fig.1: Typical applications for in- mold textile lamination in automo- tive engineering Page 2 of 16 2004-03-25 Handout - In-mold Textile Lamination The structure of in-mold textile laminated components In-mold textile lamination as a processing method is by no means exclusive to automotive applica- tions. Rather, the acquired knowledge about problems and their solution provides sufficient potential for introducing in-mold textile lamination to other industrial segments such as in the production of furniture (particularly for seat covers or back rests), domestic goods or leisure articles (e.g. suit- cases, spectacle cases etc.). There are still many opportunities for new applications in automotive engineering or in the interior decoration of airplanes and trains. In-mold lamination of textile fabrics has several advantages. The process dispenses with the need for solvents, which are emitted during the lamination bonding pro- cess, and does not require any logistic effort, a drawback of other multi-stage processes, while the reduced floor space requirements of the line as well as lower storage and delivery offer extensive financial benefits. Compliance with the prescribed property profiles and quality requirements necessitated an im- provement of the decorative materials as well as the development of a special processing technique which involved a number of modifications to the conventional injection molding variables. The deco- rated surface of in-mold textile laminated components is visible. Therefore, its quality can be used as a marker for the most important process requirements. Figure 2 shows the typical structure of in- mold laminated decorative materials. Fig. 2: The structure of in-mold textile laminated components In principle, care must be taken that the existing surface structure (e.g. leather grain) or the textile fibre structure not be damaged or adversely affected in its optical appearance even near the gate. During processes which involve the use of film, the heat introduced by the melt must be carried off to prevent a potential recovery of the surface structure after calendering Processes involving textile fibres require special attention to the re-orientation of the fibres after in-mold lamination. Moreover, color changes which may occur as a result of thermal damage or due to the translucence of the decorative surface must be prevented. Special care must be taken to avoid detriment to the decorative surface due to the permeation of melt through the material itself or emergence of melt Page 3 of 16 2004-03-25 Handout - In-mold Textile Lamination from the edges of the material blank. The adhesion between the carrier and decorative material is also of major importance. Damage to the component by excessive heat and/or pressure aside, the product may also be im- paired by the occurrence of visible sink marks on ribbed structures, a frequent occurrence where thin fabrics or film is being processed. Thin materials are also prone to defects caused by its accu- mulation at the joints or wrinkling. Particular quality criteria must be met when combining special decorative and carrier materials or in-mold textile lamination of unusual component geometries (Fig. 3). Fig.3: Causes for the occurrence of quality deficiencies/defects during in-mold textile lamination 1. Process control requirements Achieving a high-quality bond between the decorative material and the carrier involves compliance with the well-known process control requirements of conventional injection molding as well as a host of additional demands. The most crucial parameters affecting the results of in-mold textile lamination listed below are the subject of the following paragraph: Melt temperature profile inside the mold cavity Cavity pressure profile Wall shear stress The heat introduced by the melt and the pressure on the decorative structure can irreparably dam- age the three-dimensional structure of the textured fibre or the surface structure of the film. Moreo- ver, excessive wall shear stress can result in unwelcome displacement of the decorative material. Local emergence of the melt onto the decorative surface is one possible consequence. Damage to the quality of the decorative material can be prevented by fine-tuning the crucial machine parame- ters to ensure optimum process control. The melt temperature inside the mold can be adjusted for during the entire the injection phase by changing the preset barrel temperature and adapting the temperature for both mold halves. In most cases, the insulating properties of the decorative material suggests the selection of a lower tem- Page 4 of 16 2004-03-25 Handout - In-mold Textile Lamination perature for the mold half containing the decoration material and a correspondingly higher tem- perature on the fixed mold half. Experience has shown that the selection of a low melt temperature inside the mold is a high priority. In addition to these parameters, which have a direct effect on the melt temperature inside the mold, the injection speed is also of high importance. A low injection speed is desirable for the creation of a sufficiently low mold cavity pressure and wall shear stress. The mold cavity pressure can be minimized further by continuing the process without holding pres- sure and ensuring a well-timed switch over to the hold phase. Filling the cavity however, requires a minimum of compression. Remedies such as an effective arrangement of the feed points and the introduction of cascade injection molding or compression-injection molding provide a safe solution to most potential problems with in-mold textile lamination. 2. Requirements of the decorative material Experienced users, e.g. car manufacturers, select the decorative material they require in advance. Inexperienced suppliers are recommended to consult injection molding machine manufacturers, mold makers or manufacturers of decorative textile fabrics in order to optimally adapt the selected materials, mold technology and process control to the requirement profile of the finished compo- nent. As mentioned earlier, it is of utmost importance to find a perfect balance between the proper- ties of the decorative material such as elasticity or resilience, the requirements of the component and the characteristics of the selected carrier material. An application-oriented analysis of the deco- rative material focuses mainly on its thermal sensitivity, the elasticity of the structure and its poten- tial adhesion to the carrier material. Thermal sensitivity Standard decorative material made from polyester is usually suitable for temperatures of about 266F (130C) at a pressure which typically occurs during this processing method. PVC film will have a similar melt temperature while ABS film can withstand higher processing temperatures. Standard injection molding however, involves significantly higher melt temperatures. Therefore, in- mold textile lamination frequently requires the use of an insulating polyester backing mat which also serves as a stabiliser preventing the permeation of melt or the creation of wrinkles. Intermediate layers made from polyurethane or polyamide are possible, but they are often too expensive. It is important to ensure that the mat backing of the decorative material is completely saturated by the polymer melt to ensure reliable adhesion to the carrier material. Failure to meet this requirement may result in relative movements between the mat and the top material with the consequence of an irregular surface structure. Elasticity The elasticity of decorative material is an important criterion for its potential area of application. While a lack of elasticity leads to tearing of the material, excessive elasticity can cause local over- stretching with the result of lightness variations in the decorative material. Moreover, the wall shear stress which occurs during the injection phase may cause very elastic fabric to pile up at the flow front with the result of flow lines or wrinkle formation. While the majority of films or carpets are rela- tively easy to process, very thin fabrics, the standard material for column cladding, can cause par- ticular problems. Carrier materials Mass-produced components are mostly made from carrier materials such as talcum-reinforced polypropylene grades (PP), ABS or PC/ABS blends. Today, PP is the general favorite, since it is relatively inexpensive and available with special properties. PP is preferred over ABS and particu- larly over PC/ABS because of its lower flow resistance and the resulting, lower pressure build-up. Page 5 of 16 2004-03-25 Handout - In-mold Textile Lamination PC/ABS blends are useful for applications which require materials with a high low-temperature im- pact resistance. However, PC/ABS blends are best combined with resistant decorative materials. 3. Machine technology for optimum process control Today, the mass-production of in-mold textile laminated components is a standard procedure, once important criteria such as an efficient mold design, adherence to the process parameters discussed above, a finely-tuned machine operation as well as the selection of suitable carrier and decoration materials are observed. Current developments in the machine manufacturing segment have the objective of delivering technology-related solutions for in-mold textile lamination which allow a cost- efficient production of repeatable, high-quality products. To this end, they employ special techniques alone or in combination and promote the integration of ancillary equipment. The following section introduces some corresponding technical solutions. Compression control The flow length/wall thickness ratio of conventional injection molding processes creates mold cavity pressure conditions which are often far higher than the decorative material can withstand. Com- pression control was developed to reduce the mold cavity pressure occurring during injection mold- ing processes. This mechanism extends the opening of the mold during the injection phase. The mold cavity pressure is dependent on the mold opening and the resulting flow resistance (Fig. 4). Fig. 4: Injection-compression molding During injection-compression molding, the mold is not fully closed prior to the injection phase, which results in a wider flow gap in the mold. At the end of the filling phase, the cavity has been filled only partially. The subsequent compression process, i.e. the slow closing movement of both mold halves, leads to a complete filling of the cavity and can even compensate for a potential lack of holding pressure. Page 6 of 16 2004-03-25 Handout - In-mold Textile Lamination Injection-compression molding however, does not only reduce the flow resistance. A widening of the flow gap also slows down the flow front velocity. The result is a lower shear rate and a reduced wall shear stress. The mold cavity pressure during the filling phase may be up to 90% lower. The mold cavity pressure profile shows a decompression at the end of the injection phase followed by a pressure increase during mold closure. Decompression can be avoided by starting the com- pression stroke as early as the mold filling phase, i.e. simultaneous movements of the fixed mold half and the moving mold half. Independent of the injection speed, the starting point of the simulta- neous compression movement correlates with a predefined mold filling stage, since the starting point of simultaneous compression is dependent on the position of the screw. Similar to the screw forward movement during injection molding, the mold movement during injec- tion-compression molding affects the flow front velocity, i.e. the pressure build-up and the quality of the component. For this reason, the mold movement speed can be adjusted along a three-stage speed profile. All processing parameters for the compression control are entered into the operator panel on the machine side. All programs can be activated or deactivated by means of a program switch. The required travelling speed of all movements and the position of start can be selected. The compres- sion gap can be set up to a width of 1.18 in (30 mm) with a precision of 0.004 in (0.1 mm). The ac- tual positions of both the mold and the screw are measured by ultrasonic stroke transducers with an accuracy of 0.004 in (0.1 mm) and are shown as actual values. Highly sensitive decorative materials require careful positioning onto the mold contour to prevent tearing or overstretching of the structure during mold close or injection. Sensitive TPO films must be heated prior to processing - particularly where major forming processes or molds with deep cores are concerned. The recommended procedure involves heating the material in the space directly above the mold. After insertion, the heated film can be preformed by one stroke of the mold. This involves machine closure to a minimum compression gap and subsequent opening to the width of the filling gap. A preforming program can be useful to execute preforming tasks independently of the parameters of injection-compression molding. It allows the adjustment of the mold closing speed to exclusively suit the quality of the decorative material. After the decorative material has been placed onto the mold contour, the mold is opened as far as the compression gap and the filling process can begin (Fig. 5). Page 7 of 16 2004-03-25 Handout - In-mold Textile Lamination Fig. 5: View of the operators side during the compression phase of the in-mold textile lamination process Since the movement of the platen on toggle clamp units requires very long crosshead travel even for the smallest compression strokes, the platen movement can be adjusted and controlled easily and with high precision. The selection of a sufficiently wide compression gap is dependent on the required mold cavity pres- sure and the required heat transfer from the melt. If the compression gap is too wide, the melt will accumulate around the small circular space surrounding the gate, where it cannot transfer enough heat to the cavity wall with the result of local overheating of the decorative material. The compres- sion speed must be selected to achieve only a minimum rise in pressure when the cavity is filled by the compression stroke, while maintaining a sufficiently low viscosity of the melt to ensure complete filling of the cavity. Compression molding requires the installation of vertical flash faces which prevent an uncontrolled emergence of the melt during the injection into the opened m