Cohesive bonding process for forming a laminate of a wear resistant thermoplastic and a weather resistant rubber

Abstract: A polymer laminate produced by crosshead ex­ trusion suitable for wear resistant applications such as a vehicle glass run channel comprises a layer of a weather resistant rubber such as an ethylene-propylene-­ diene (EPDM) rubber and a layer of a wear resistant thermoplastic such as polypropylene. The laminate is passed through an oven at an elevated temperature suffi­ cient to cure the EPDM rubber, for example, at about 375°F, with ambient temperature cooling fluid being blown over the exposed surface of the polypropylene thermoplas­ tic The interior polypropylene surface or interface is heated by the EPDM rubber which is at a high temperature as a result of the heat of extrusion and heat generated by cure thereof. As a result, the polypropylene interior surface or interface melts and causes it to flow and form a mechanical bond with the EPDM rubber while the exposed surface as well as a substantial portion of the polypro­ pylene is kept from melting by the cooling fluid. The EPDM rubber can be extruded in the form of a channel having a longitudinal web 20 which supports and is bonded to the polypropylene wear strip 34 to form a glass run channel 10.

Description: The present invention relates to a process for bonding a wear resistant thermoplastic to a weather resistant rubber to form a laminate, which finds a particular use in the manufacture of glass run channels. It has not been known to produce a glass run strip having a channel shaped gasket of EPDM rubber with a polypropylene wear strip laminated to the base of the channel. In the prior art, US-A-4596734 discloses laminating rubber to metal through an intermediate layer of polyethylene, provided as powder which melts as the rubber cures. GB-A-1434719 discloses adhesive-free bonding of stretched pre-cured rubber layers to thermoplastic form-retaining layers which are then cured to give heat-recoverable articles. GB-A-1141029 (≡ BE-A-675726) and GB-A-1423541 describe bonding rubber to thermoplastics by fusing as the rubber is cured. US-A-3918206 describes a window guide channel strip with a PTFE friction-reducing layer along the channel base. US-A-4538380 describes use of polypropylene to form a low-friction surface in a weatherseal strip. US-A-4104098 describes cooling a hose surface during curing, leaving an uncured surface portion for incorporation of a reinforcing braid. The present invention provides a process for making a laminate of a layer of weather-resistant rubber having a first surface and a layer of wear-resistant thermoplastic having top and bottom surfaces and a melting point not above 177°C (350°F), comprising crosshead extruding the rubber layer and the thermoplastic layer, the crosshead extrusion causing the thermoplastic layer's bottom surface to form an interface with the rubber layer's first surface; bonding the rubber and thermoplastic layers by heating the rubber layer to a temperature above the melting point of the thermoplastic layer and sufficient to cure the rubber layer, and cooling the top surface of the thermoplastic layer so that only a portion of the thermoplastic layer at the interface is melted. The cooling fluid may be air. The process results in an effective adhesive-free mechanical fusion of the thermoplastic and rubber layers. A glass run strip can be produced by this process. The glass run strip includes a rubber housing having an enclosed internal channel and typically a crosshead extruded low friction thermoplastic wear strip bonded to the base of the channel. The combination of the crosshead extruding and the curing processes results in an efficient and effective method of manufacturing a glass run strip. In the drawings, Fig. 1 is a perspective view of a vehicle door containing a glass run strip, and Fig. 2 is a cross-sectional view taken on line 2-2 of Fig. 1 showing a vehicle window engaging the glass run strip. The present invention relates to a polymer laminate and to a process for forming the same comprising a layer of a wear resistant thermoplastic such as polypropylene adhered to a layer of a weather resistant rubber, e.g., ethylene-propylene-diene (EPDM) rubber. The layers are extruded through a crosshead die and the extrudate is passed through an oven at a temperature which is sufficient to cure the rubber layer. Such cure temperature is typically above the melting point of the thermoplastic. A cooling fluid such as an air stream at ambient or low temperature is passed over the exposed surface of the thermoplastic layer so that only a portion thereof is sufficiently heated so that it is melted. The melted thermoplastic is thus fused to the rubber and forms a mechanical bond. Once the rubber has been cured, the laminate is rapidly cooled by blowing an ambient or low temperature water jet or air mist over the exterior base portion of the rubber. It is preferable to utilize a wear resistant rubber which cures rapidly and which has good adhesion to the thermoplastic layer. Such weather resistant rubbers are known to the art and to the literature. Examples of such rubbers include EPDM rubber, styrene-butadiene rubber, polychloroprene rubber, nitrile-polyvinyl chloride rubber blends, and the like. Such weather resistant rubbers are utilized inasmuch as they have good oxidation resistance, good ozone resistance, and generally do not degrade or deteriorate when exposed to the earth's atmosphere. EPDM rubber is preferred. It is to be understood that the various silicone rubbers are not within the scope of the present invention. Considering the preferred EPDM rubber, better adhesion results when the amount of ethylene units therein is from about 45 percent by weight to about 75 percent by weight and desirably from about 50 to about 60 percent by weight based upon the total weight of the ethylene units and the propylene units. The diene is a non-conjugated monomer having from about 5 to about 10 carbon atoms with from 6 to 9 carbon atoms being preferred. Monomers which yield a fast cure are desired. Specific non-conjugated dienes include pentadiene, hexadiene, norbornene, methyl norbornene, ethylidene norbornene, heptadiene, and the like. An example of a particularly well-suited diene is ethylidene norbornene. Inasmuch as it is desirable that the EPDM rubbers have high amounts of unsaturation therein, the amount of the diene monomer repeating unit is generally from about 4 to about 15 percent by weight of the terpolymer system with from about 6 to about 12 percent being desired and from about 8 to about 11 percent being preferred. The thermoplastic compound is generally a polymer which has good wear resistance, a low coefficient of friction, and typically melts at a temperature of 177°C (350°F) or less. Examples of such thermoplastic compounds include polyethylene, polypropylene, and the like with polypropylene being preferred. The thermoplastic generally has a high density, that is, from about .9 to about 1.2 grams/cc, with from about 0.9 to about 1.1 grams/cc being preferred and about 0.95 grams/cc being optimum. The polypropylene utilized in the present invention has a melting point from about 135°C (275°F) to about 177°C (350°F), with from about 149°C (300°F) to about 166°C (330°F) being preferred. Mechanical bonding or fusion of the thermoplastic to the rubber is achieved by melting the thermoplastic interface, for example polypropylene, in contact with the rubber. Generally less than 10 percent of the total amount of the thermoplastic melts. Of course, a larger or smaller amount of the thermoplastic can be melted. The amount of the perimeter of the thermoplastic layer will also vary depending upon the amount thereof in contact with the rubber. In the preferred embodiments set forth hereinbelow, approximately 60 percent of the thermoplastic perimeter melts. The glass run strip of the invention is generally indicated by the numeral 10 in Fig. 2 and includes a resilient gasket 12 and a wear strip 30. The gasket 12 is formed having an interior channel 18 having a bottom web 20 joined on either longitudinal side to a transverse side wall 22. Each side wall 22 has a lip 24 which extends in and down toward the center of the channel 18. The lips 24 form a closure for the channel 18. A thermoplastic wear strip 30 such as polypropylene having a suitable depth or thickness as about 1.9 mm (0.075 inches) has a central portion 32 bounded on each longitudinal side by a shoulder 34. The shoulders 34 abut with recesses 36 formed between the web 20 and the side walls 22 to help hold the wear strip 30 in position within the channel 18. The upper surface of lips 24 can contain flock 38 thereon to provide a seal for the window foot 40. The foot 40 is generally a urethane material. One edge rides in the channel along the wear strip while the other end of the foot 40 provides a seat for the window pane 42. Thus, window foot 40 pries lips 24 apart and resiliently engages the same through flock layer 38. The base of foot 40 contacts the longitudinal polypropylene wear strip 30. Accordingly, as window 42 of a vehicle is rolled up and down, the base portion of window foot 40 engages the thermoplastic wear strip and not the low wear resistant rubber gasket. According to the concepts of the present invention, the thermoplastic layer such as polypropylene and the rubber gasket such as EPDM are extruded in a crosshead die. Any conventional type of extruder known to the art as well as to the literature can generally be utilized. Inasmuch as a thermoplastic material or wear strip is not melted but processed at ambient or a warm temperature, a crosshead die is utilized. That is, the wear strip 30 is extruded through a crosshead die which places it into contact with the heated gasket 12 under a sufficient uniform pressure such that the gasket and wear strip are pushed or forced together. Due to the high temperature of the extruded rubber, as well as the exotherm created by the curing reaction, a narrow strip or interior layer along the bottom of the thermoplastic wear strip which engages or forms interface with the rubber is melted. The extrusion temperature of the rubber is suitably high such that it can be easily worked and extruded. Temperatures of from about 88°C (190°F) to about 104°C (220°F) are often suitable, especially with EPDM rubber. Immediately upon the crosshead extrusion, the glass run strip is fed to an oven at a temperature usually above the melting point of the thermoplastic such that a suitable cure rate of the rubber is obtained. In order to prevent the entire wear strip from melting, a cooling fluid is blown through the channel formed by bottom web 20, side walls 22, and lips 24 which serve to form a complete enclosure. A suitable cooling fluid is ambient temperature air, although other compounds can be utilized. Naturally, the cooling fluid is applied at a rate sufficient to prevent the exposed surface, that is the non-rubber contacting surface of the thermoplastic wear strip from melting. The cooling fluid is supplied to the interior of the channel until the glass run strip is removed from the oven at which time cool or ambient temperature moist air is added to quickly cool the bottom exterior surface, that is the channel portion of the glass run strip. Glass run strips produced in accordance with the present methods may be utilized wherever a rubber type gasket material having good wear resistance is desired. As set forth in Fig. 1, one such use is as a wear channel for a vehicle window.

Claims: A process for making a laminate of a layer of weather-resistant rubber having a first surface and a layer of wear-resistant thermoplastic having top and bottom surfaces and a melting point not above 177°C (350°F), comprising crosshead extruding the rubber layer and the thermoplastic layer, the crosshead extrusion causing the thermoplastic layer's bottom surface to form an interface with the rubber layer's first surface; bonding the rubber and thermoplastic layers by heating the rubber layer to a temperature above the melting point of the thermoplastic layer and sufficient to cure the rubber layer, and cooling the top surface of the thermoplastic layer so that only a portion of the thermoplastic layer at the interface is melted. A process according to claim 1 in which less than 10% of the thermoplastic layer is melted by heat from the rubber layer. A process according to claim 1 or claim 2 in which the cooling of the thermoplastic layer's top surface is by blowing a cooling fluid over it as the rubber layer cures. A process according to claim 3 in which after curing of the rubber the laminate is cooled by blowing a water jet or air mist, cooled or at ambient temperature, over its exterior. A process according to any one of the preceeding claims in which the crosshead extrusion presses the thermoplastic layer against the rubber layer. A process according to any one of the preceding claims in which the rubber layer is of styrene-butadiene rubber, polychloroprene rubber, nitrile-polyvinylchloride rubber blend, EPDM rubber or some combination selected from these. A process according to claim 6 in which the rubber layer is EPDM rubber having from 50 to 60 wt% of ethylene units based on the total of ethylene and propylene units, and non-conjugated diene units which have from 6 to 9 carbon atoms and constitute from 6 to 12 wt% of the rubber. A process according to any one of the preceding claims in which the thermoplastic layer is of polyethylene or polypropylene. A process according to claim 8 in which the thermoplastic layer has a density of from 0.9 to 1.2 g/cm³. A process according to any one of claims 1 to 5 in which the rubber layer is of EPDM rubber having from 45 to 75 wt% ethylene units based on the total weight of ethylene and propylene units therein, and from 4 to 15 wt% non-conjugated diene units having from 5 to 10 carbon atoms, and the thermoplastic layer is of polypropylene having a density of from 0.9 to 1.1 g/cm³ and a melting point of from 149°C to 166°C (300°F to 330°F). A method of making a glass run strip having a low-friction thermoplastic wear strip (30) along the interior of the base (20) of a weather resistant rubber channel (12), comprising bonding the wear strip (30) to the channel base interior by a process according to any one of claims 1 to 10. A method according to claim 11 in which the channel (12) has flexible inward lips (24) extending in from the top of side walls (22) to form an enclosed channel space, the bonding process is according to claim 3 and the cooling fluid is blown along the enclosed channel space.

Inventors: BROOKS MARK L, WILSON KEITH E, BROOKS, MARK L., WILSON, KEITH E.
Applicants: GENCORP INC, GENCORP INC.
Application year: 1988
Main classification: B32B25
IPC codes: B32B7, B32B27, B32B37, B32B25, B60J10