Patent Publication Number: US-2020298455-A1

Title: Method for producing a roof element of a motor vehicle and roof element having a moulded section

Description:
The invention relates to a process for the production of a roof element of a motor vehicle, and to a roof element with the features of the preamble of claim 6. 
     Roof elements of motor vehicles are in many cases composed of a glass panel, and form a cover element of a roof-opening system to which, for coupling to the vehicle structure, a peripheral foam edging has been provided, which is composed of a polyurethane material and into which fixing brackes can be embedded. The peripheral foam edging is produced in a foaming mold which has a cavity into which the polyurethane material is introduced for the formation of the foam edging. The polyurethane material consists of a polymer mixture, in particular a polyol mixture, and an isocyanate compound. During the molding process or foaming process, the polymer mixture and the isocyanate compound are passed into a mixing head, where they are mixed, and are then introduced into the cavity for completion of the reaction. After reaction of the polyurethane material has been completed and said material has hardened, the finished workpiece, i.e. the glass panel with the foam edging, can be demolded from the foaming mold. 
     In order that no damage occurs to the workpiece during demolding from the foaming mold, it has hitherto been necessary to provide a release agent to the mold cavity of the foaming mold, or to the mold wall delimiting the mold cavity. This is achieved manually by means of a release agent applicator which has to be kept available by the foaming mold for this specific purpose, and which generally comprises what is known as a release agent gun, and incurs high cost. The release agent forms, on the molded section shaped in the mold cavity, a release film that prevents adhesion of the molded section on the foaming mold. Because the release agent is applied manually, the thickness of the release film can vary greatly. There are therefore likewise large differences in any possible residues on the molded section manufactured in the foaming mold. The release agent residues can have a considerable effect on the adhesive-bonding capability of the molded section. 
     During the course of a production shift, i.e. during the manufacture of a large number of mold sections in the relevant mold, the release agent moreover forms a release film with increasing thickness. This release film has to be removed at the end of the relevant production shift, i.e. the mold has to be cleaned to remove the release agent. 
     The application procedure moreover leads to formation of a release agent mist, to which the respective operator is exposed, and which can be hazardous to health. 
     The invention is based on the object of providing a process which can produce a roof element of a motor vehicle and in which the abovementioned problems resulting from the release agent are eliminated. 
     According to the invention, said object is achieved by the process with the features of claim 1. 
     The invention therefore proposes a process for the production of a roof element of a motor vehicle, with the following steps:
         Provision of a polymer mixture;   Admixture of an organosiloxane compound with the polymer mixture;   Mixing of the polymer mixture, with the organosiloxane compound admixed, with an isocyanate compound to give a polyurethane material and introduction of the polyurethane material into a mold cavity of a foaming mold in a manner such that the polyurethane material reacts to completion and a molded section of the roof element is shaped in the mold cavity wherein the organosiloxane compound is accumulated at the surface of the molded section; and   Demolding of the roof element from the foaming mold.       

     The process of the invention therefore uses a polyurethane material which comprises, in the form of a high-molecular-weight, long-chain organosiloxane compound, an internal release agent, the concentration of which at the surface of the molded section formed in the mold cavity of the foaming mold becomes relatively high during the foam process, thus ensuring demolding of the roof element comprising the molded section from the foaming mold. It is therefore possible to omit use of an external release agent, with which the foaming mold has hitherto been sprayed in the region of the mold cavity. 
     There is therefore no requirement for a complicated release agent applicator associated with the foaming mold. With no use of an external release agent, it is also possible to operate the foaming mold with shorter cycle times, because the release agent cycle for the application of the external release agent is omitted. It is moreover possible to ensure that the organosiloxane compound providing an internal release agent forms a substantially constant release agent layer at the surface of the molded section, because said agent is present with uniform distribution in the relevant surface-structure matrix of the polyurethane material. The physical properties of the molded section are not adversely affected by the organosiloxane compound in comparison with those of a molded section without organosiloxane compound as internal release agent. Instead, the molded section has an unchanged polymer matrix, which is a decisive factor for physical properties such as hardness, tensile strength and elongation at break. There is moreover no need for any further reactivity-balancing additives, because the organosiloxane compound does not change the chemistry of the molded section in its central regions. Specifically, during the reaction of the polymer mixture with the isocyanate compound, the organosiloxane compound is displaced outward in the direction of the mold wall. This takes place because of the heat produced during the reaction, leading to phase separation. The temperatures of rising during the reaction of the polymer mixture with the isocyanate compound can be above 100° C. The organosiloxane compound has no effect on the reactivity of the polyurethane system formed from the polymer mixture and from the isocyanate compound for conduct of an RIM (Reaction Injection Molding) process. 
     During the reaction, therefore, the long-chain molecules of the organosiloxane compound are displaced to the surface of the polyurethane material via migration, convection and exothermic energy, and specifically within the first milliseconds of the reaction. Because the organosiloxane compound has a long-chain structure, it remains, in the manner of a surfboard, at the surface, i.e. in the region of the interface with the mold wall in the region of the mold cavity of the foaming mold. Toward the end of the reaction, the organosiloxane compound is to some extent incorporated by bonding into the polyurethane matrix. A uniform, fine dispersion of the organosiloxane compound is achieved here at the surface of the molded section. This behavior of the organosiloxane compound was demonstrated by means of gas chromatography and mass spectrometer studies. The organosiloxane compound thus forms, between the fully reacted polyurethane material and the mold wall, a release film which prevents adhesion of the polyurethane on the mold wall. The organosiloxane compound specifically permits cohesive fracture between the foaming mold and the molded section, thus providing deformability. 
     An organosiloxane has the following general structural formula: 
     
       
         
         
             
             
         
       
     
     where n is an integer and R 1 , R 2 , R 3  and R 4  are organic groups. 
     When the intention is to arrange, within the polyurethane material, inserts made of a coated metal, in particular cathodically electrocoated metal, these bond successfully to the molded section, despite the organosiloxane compound, because the cathodic electrocoating material itself comprises binders, pigment paste and water-miscible organic solvents. The substantial constituents of the binder and of the pigment paste are frequently epoxy-resin-amine adducts and blocked isocyanates. The binders and the pigment paste form the major portion of the solids present in the solution for production of the cathodic electrocoating material. The binder of the cathodic electrocoating material, especially the isocyanate, ensures production of a sufficient number of linkage points between the cathodic electrocoating material and the molded section of the polyurethane material. 
     In a specific embodiment of the process of the invention, which ensures good deformability of the roof element from the foaming mold, with no impairment of the physical properties of the molded section, a quantity of from 0.5% by weight to 8% by weight of the organosiloxane compound is admixed with the polymer mixture. 
     The molar mass of the organosiloxane compound used can be from 15 000 g/l to 50 000 g/l. 
     The organosiloxane compound used therefore comprises long-chain organosiloxanes, and is an internal release agent, and specifically is unlike short-chain siloxanes, which can be cell stabilizers and do not serve as release agents. 
     The polymer mixture provided during the process of the invention is preferably a polyol composition. Firstly, the organosiloxane compound is added thereto. Secondly, the isocyanate compound is admixed with the polyol composition in a mixing and metering head, and the mixture is then introduced into the mold cavity. 
     In a preferred embodiment of the process of the invention, the molded section is shaped onto a panel consisting of glass or of a plastics material. The molded section then in particular forms a peripheral foam edging of the panel. When the roof element is a cover element of a roof-opening system, the peripheral foam edging is used to receive inserts, by way of which the panel can be covered to a kinematic system of the roof-opening system. The peripheral foam edging can moreover be used to receive a seal, or else can be used as sealing equipment intended, in a closed position of the cover element, to permit adequately leakproof closure of an appropriate roof opening of the relevant motor vehicle. 
     The organosiloxane compound which has relatively high concentration at the surface of the molded section also has no adverse effect on the coupling of the molded section to the glass panel, because a primer has been provided to the latter. The primer comprises binding elements that have affinity for isocyanate. At the surface having a relatively high concentration of the organosiloxane compound, despite the presence of the organosiloxane compound, there is still a sufficient quantity of free isocyanates present from the isocyanate compound of the polyurethane material, and these can link to the binding elements of the primer. 
     The process of the invention is used by way of example in high-pressure foaming processes which are known as RIM (Reaction Injection Molding) processes, or in low-pressure foaming processes in which the polyurethane material is introduced at ambient pressure into a mold and appropriate low-pressure metering equipment is used to introduce the material to the mold cavity. In the latter case, particular mention may be made of what are known as WST (Window Spray Technology) processes. 
     The invention also provides a roof element of a motor vehicle, comprising a molded section which has been manufactured from a material comprising polyurethane by a foaming process and which comprises an organosiloxane compound accumulated at its surface. 
     The organosiloxane compound is an integrated constituent of the molded section, and has been absorbed by the structure of the polyurethane material in fully reacted form thereof, where the organosiloxane compound consisting of high-molecular-weight, long-chain molecules forms, in the manufacturing mold for the molded section, a release film which permits demolding of the roof element without using of an external release agent. 
     In particular, the organosiloxane compound forms a surface layer of the molded section, the thickness of said layer being from 0.5 μm to 20 μm. The molar mass of the organosiloxane compound is preferably from 15 000 g/l to 50 000 g/l. 
     As already explained above in conjunction with the process of the invention, the roof element can be a cover element of a roof-opening system. The molded section then forms by way of example a peripheral foam edging of a panel which has been manufactured from glass or from a plastics material. 
     Further advantages and advantageous embodiments of the subject matter of the invention can be found in the description, the drawing and the claims. 
    
    
     
       An embodiment of a roof element of the invention and of a process for the production of the roof element are depicted in simplified diagrammatic form in the drawing, and are explained in more detail in the description below. 
         FIG. 1  is a plan view of a cover element of a roof-opening system of a motor vehicle; 
         FIG. 2  is a section through the cover element of  FIG. 1  along the line II-II in  FIG. 1 ; 
         FIG. 3  shows a device for the preparation of a liquid polyol composition; 
         FIG. 4  is a detail of a sectional view of a mold for the production of a mold section of the cover element of  FIG. 1 , in closed position; and 
         FIG. 5  is a depiction of the foaming mold corresponding to  FIG. 4 , but in open position. 
     
    
    
       FIGS. 1 and 2  show a cover element  1  of a roof-opening system, in other respects not depicted in any greater detail, of a vehicle roof. By means of the cover element  1  it is possible, as desired, to close, or at least to some extent open, a roof opening of the vehicle roof. 
     The cover element  1  comprises a glass panel  2  that is in essence rectangular, to which a glass frit and a primer have been provided. 
     To permit coupling of the cover element  1  to a kinematic system for roof opening there is, provided to the glass panel  2  along its periphery, a foam edging  3  into which, at each of the edges that are lateral in relation to a vertical plane running centrally along the length of the roof, there are three retaining brackets  4  embedded as inserts. The retaining brackets  4  have each been manufactured from a cathodically electrocoated metal sheet. 
     The foam edging  3  consists of a polyurethane material with which an organosiloxane compound has been admixed. The organosiloxane compound is concentrated/accumulated within a surface layer  5  of the foam edging  3 . The surface layer  5  has a thickness of some micrometers. 
       FIGS. 3 to 5  depict diagrammatically the production of the foam edging  3  of the cover element  1 . The production process uses a foaming mold  6 , depicted in  FIGS. 4 and 5 , in which there is a mold cavity  7  which corresponds to the shape of the foam edging  3  and which is delimited by an upper mold section  8  and a lower mold section  9  of the foaming mold  6 . 
     During the production of the foam edging  3 , the glass panel  2 , to which the glass primer and the glass frit have been provided, is placed onto the lower mold section  9  while the foaming mold  6  is in the open position depicted in  FIG. 5 , where the upper mold section  8  and the lower mold section  9  have been moved apart. The retaining brackets  4  are moreover fixed in a manner not depicted. The upper mold section  8  is then moved toward the lower mold section  9  to form the mold cavity  7 . The polyurethane material can then be introduced into the mold cavity  7  of the closed foaming mold  6  and reacted to completion there. The retaining brackets  4  also become embedded into the polyurethane material here. 
     An organosiloxane compound with molar mass from 15 000 g/l to 50 000 g/l has been admixed with the polyurethane material used. During the reaction of the polyurethane material to completion, the heat produced in the reaction causes a phase separation which forces the organosiloxane compound toward the cavity-delimiting surfaces formed by the upper mold section  8 , the lower mold section  9  and the glass panel  2 , thus forming the surface layer  5  with relatively high concentration of the organosiloxane compound on the foam edging  3 . The finished cover element  1  can then be demolded. As can be seen from  FIG. 3 , the polyurethane material is passed from a metering and mixing head  100  into the foaming mold  6  and, respectively, the mold cavity  7 . 
     In the mixing head  100 , a polyol composition with which the organosiloxane compound has been admixed, and which has been prepared in a device  10 , and an isocyanate compound available from a container  60  are mixed with one another and then metered into the mold cavity  7 . 
     The device  10  for the preparation of the polyol composition, which is a reactive polymer for the polyurethane system, can be seen in  FIG. 3 . 
     The device  10  comprises a feed container  12  in which the polyol composition can be stored and to which a stirrer  14  has been provided in order to eliminate any possible layering of the polyol composition as a result of storage. The storage container  12  has connection by way of a line  16 , with a pump  18  arranged therein, to degassing equipment  20 , which is composed of a vacuum deaerator. Attached to the vacuum deaerator there is an output line  22 , which has another pump  24  and a mass flow meter  26  arranged therein and which leads to homogenizing equipment  28 , composed of a toothed colloid mill. Upstream of the homogenizing equipment  28  there is arranged, on the line  22 , a metering valve  52  which is a constituent of gasification equipment and by way of which an additive gas can be added to the polyol composition. 
     Downstream of the metering valve  52  and upstream of the homogenizing equipment, an input line  54 , which has been connected to a feed container  56  for the organosiloxane compound and to which there is also a valve  58  provided, enters the line  16 . 
     The homogenizing equipment  28  has an output line  30  which leads into a container  32  in which the prepared polymer mixture can be placed for intermediate storage, and provided to which there is a stirrer unit  34 . A gauge pressure of from 1 to 6 bar prevails in the container  32 . The output line  30  leads into the container  32  in a manner such that the prepared polymer mixture is introduced below the existing upper surface of the polymer mixture already present in the container  32 . The upper surface, or fill level, of the polymer mixture in the container  32  is always maintained between two marks; there is a first sensor  36  provided to the lower mark and a second sensor  38  provided to the upper mark. The sensor  36  allocated to the lower mark indicates when the level falls below the specified fill level in the container  32  and further liquid polymer mixture has to be prepared. The second sensor  38  allocated to the upper mark indicates when the level rises above the specified fill level, and the preparation of the liquid polymer mixture by means of the device  10  has to be stopped. 
     The container  32  has connection by way of an onrunning line  40  to the metering and mixing head  100  which is allocated to the foaming mold  6  for the production of the foam edging  3  of the cover element  1  and in which the isocyanate compound is added to the polyol composition to form the polyurethane system. A return line  42  moreover leads into the container  32  and, with the ongoing line  40 , forms a circuit for the supply of a plurality of processing units. 
     For the control of the preparation of the polyol composition, the device  10  has control equipment  44  which has connection by way of a line  46  to the mass flow meter  26  and by way of a line  48  to a gas mass flow meter  50  likewise allocated to the gasification equipment, and to the metering valve  52 , by means of which an additive gas, for example carbon dioxide or an inert gas, can be introduced into the liquid polyol composition, and specifically upstream of the homogenization equipment  28  and downstream of the mass flow meter  26 . The control equipment moreover has connection to the valve  58  for the metered addition of the organosiloxane compound from the feed container  56  by way of the line  54 . 
     The polyol composition can be prepared by means of the device  10  in the manner described below. 
     The polyol composition, which is stirred in the storage container  12 , is conveyed by means of the pump  18  into the degassing equipment  20 , where it is freed from undefined gases. The degassed polymer mixture consisting of the polyol composition is then conveyed through the output line  22  by means of the pump  24 . The quantity of the polyol composition is first determined here by means of the mass flow meter  26 , and then, as required by said measurement, by means of the control equipment  44 , additive gas is added by way of the gas mass flow meter  50  of the metering valve  52  and the organosiloxane compound is added by way of the valve  58 . Downstream of the valve  58 , the polyol composition, now with additive gas and with the organosiloxane compound, is passed through the homogenizing equipment  28  in order to achieve fine dispersion, in the polyol composition, of small gas bubbles composed of the additive gas. The polyol composition thus prepared is then passed into the container  32  by way of the discharge line  30  so that it can be further processed, in particular via addition of an isocyanate to give a polyurethane system that can be used for the production of the rigid-foam edging of the cover element  1  or the like. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Cover element 
           2  Glass panel 
           3  Foam edging 
           4  Retaining brackets 
           5  Surface layer 
           6  Foaming mold 
           7  Mold cavity 
           8  Upper mold section 
           9  Lower mold section 
           10  Device 
           12  Storage container 
           14  Stirrer 
           16  Line 
           18  Pump 
           20  Degassing equipment 
           22  Output line 
           24  Pump 
           26  Mass flow meter 
           28  Homogenizing equipment 
           30  Discharge line 
           32  Container 
           34  Stirrer unit 
           36  Sensor 
           38  Sensor 
           40  Ongoing line 
           42  Return line 
           44  Control equipment 
           46  Line 
           48  Line 
           50  Gas mass flow meter 
           52  Metering valve 
           54  Supply line 
           56  Storage container 
           58  Valve 
           100  Metering and mixing head