JP2000500083A - Improved performance of vibration welded thermoplastic joints - Google Patents

Abstract

  (57) [Summary] The present invention provides an improved method of vibration welding thermoplastic joints. Such welding involves vibrating two fiber reinforced thermoplastic parts under pressure along their common interface to generate frictional heat, melting their surfaces and fusing them together. Done. Fibers from at least one surface penetrate into both the weld and the other surface. As a result, the welded fiber reinforced thermoplastic surface has a higher tensile strength than previously achievable. Vibration welding of a reinforced thermoplastic surface according to the present invention achieves a maximum tensile strength of about 120% of the weld formed by the unreinforced surface of the corresponding thermoplastic material.

Description

DETAILED DESCRIPTION OF THE INVENTION Correlation of Vibration Welded Thermoplastic Joints with Improved Performance Related Applications This application is hereby incorporated by reference into US patent application Ser. No. 60 / 006,334. BACKGROUND OF THE INVENTION The present invention relates to vibration welding, and more particularly, to vibration welding of thermoplastic joints. In recent years, there has been an increasing demand for the use of thermoplastics instead of metal parts of automobiles, such as air guidance systems. It is estimated that 21.4 million air intake manifold members will be manufactured using welding technology by 2010. The present invention relates to an improved method for vibration welding thermoplastic joints and to a vibration welded article produced by the method. Vibration welding of thermoplastics such as nylon 6 and nylon 66 is well known in the art. V. K. Stokes, "Vibration Welding of Thermoplastics, Part I: Phenomenology of the Welding Process", Polymer Engineering and Science, 28, 718 (1988); K. Stokes, "Vibration Welding of Thermoplastics, Part II: Analysis of the Welding Process", Polymer Engineering and Science, 28, 728 (1988); K. Stokes, "Vibration Welding of Thermoplastics, Part III: Strength of Polycarbonate Butt Welds", Polymer Engineering and Science, 28, 989 (1988); K. Stokes, “Vibration Welding of Thermoplastics, Part IV: Strengths of Poly (Butylene Terephthalate), Polyetherimide, and Modified Polyphenylene Oxide Butt Welds”, Polymer Engineering and Science, 28, 998 (1988) and C.I. B. See Bucknall et al., "Hot Plate Welding of Plastics: Factors Affecting Weld Strength", Polymer Engineering and Science, 20, 432 (1980). Vibration welding can be performed by vibrating the two parts under pressure along their common interface to generate frictional heat, thereby fusing their surfaces and fusing them together. Vibration welding is a fast and inexpensive method for joining irregularly shaped parts of various sizes. Heretofore, vibration welding has been used for low load applications. In automotive underfloor applications such as air intake manifolds, air filter housings, and resonators, the use of more engineering plastics may be desirable to achieve weight and cost savings. However, achieving sufficient weld strength for such use has not heretofore been possible. Since welding results are extremely sensitive to parameters of uniformity, those slight variations can result in significant changes in welding quality. Vibratory welding parameters such as pressure, frequency, amplitude, vibration (welding) time, dwell time and weld thickness all affect the tensile strength of the weld. It is an object of the present invention to provide a method of vibration welding a fiber reinforced thermoplastic surface to provide a weld having greater tensile strength than previously achievable. U.S. Pat. No. 4,844,320 teaches that welding strength is not affected by welding amplitude or welding time above a certain level. In conventional vibration welding, the weld is formed with a vibration amplitude between 0.03 and 0.70 inches. In contrast, the inventors have found that welding amplitude and welding time are exceptionally important criteria for increasing weld strength. The vibration welding of the present invention uses a vibration amplitude of at least about 0.075 inches. It has been found that conventional vibration welding of reinforced thermoplastic surfaces only achieves a maximum tensile strength of about 80% of the weld formed by the unreinforced surface of the corresponding thermoplastic material. For glass fiber reinforced thermoplastics, changes in the orientation of the glass fibers in the weld joint contribute to this low tensile strength. According to the present invention, vibration welding of reinforced thermoplastic surfaces achieves a maximum tensile strength of about 120% of the weld formed by the unreinforced surface of the corresponding thermoplastic material. This is because fibers from at least one surface penetrate into both the weld and the other surface. This provides surprisingly extra tensile strength to the weld. DESCRIPTION OF THE INVENTION The present invention is a method of joining a first surface containing a first fiber reinforced thermoplastic composition to a second surface containing a second thermoplastic composition, wherein the first and second surfaces are joined together. And vibration welding the contacted first and second surfaces under conditions sufficient to form a weld between the first and second surfaces. A weld comprises a blend of the first and second thermoplastic compositions and provides a method wherein fibers from the first surface have penetrated both the weld and the second surface. The present invention also provides a first surface comprising a fiber reinforced first thermoplastic composition; a second surface in contact with the first surface comprising a second thermoplastic composition; A vibration welded article comprising a weld between the first and second surfaces comprising a blend of a second thermoplastic composition, wherein fibers from the first surface comprise the weld and the second surface. Also provide items that have invaded both. Methods of vibration welding and apparatus for performing vibration welding are well known in the art, as exemplified by US Pat. No. 4,844,320, which is incorporated herein by reference. There are four stages in vibration welding of thermoplastics. Interfacial heating by friction; unsteady melting and lateral flow of material; establishment of a melting zone at steady state conditions; and unsteady flow and solidification of material in the welding zone when vibration stops. is there. Welding is a standard vibration welding apparatus, but can be performed with a vibration welding apparatus modified to achieve the parameter conditions required for the present invention. Important parameters include pressure, amplitude, frequency, welding cycle time, and dwell time. Vibration welding equipment is commercially available, such as the Mini-Vibration Welder and 90 Series Vibration Welder Model VW / 6 from Branson Ultrasonics Corporation of Danbury, Connecticut, USA. However, these rated amplitude ranges are 0.040-0.070 inches at 240 Hz output frequency and must be adjusted. Vibration welding can be performed by bringing the first thermoplastic surface and the second thermoplastic surface into contact with each other under pressure. At least one, and preferably both, thermoplastic surfaces are fiber reinforced. The surfaces to be welded are brought into contact with each other and the interface between the surfaces is maintained at a predetermined pressure, for example by placing them on a platform under pressure applied by a pneumatic or hydraulic cylinder. A linear reciprocating motion is then applied to one surface to cause frictional scrubbing, generating heat, melting those surfaces, and blending the thermoplastic material from the first and second surfaces. Prior to welding, the fibers in the fiber reinforced thermoplastic material are substantially unoriented. In prior art vibration welding methods, the contacting surfaces are melted and blended to form a weld, but the fibers within the weld are only oriented in the plane of the weld. In contrast, when performing vibration welding in accordance with the present invention, the surface or fibers reinforcing the surface are pressed into the opposite contact surface. This achieves the previously unattainable welding strength when the weld is cooled. According to the invention, the two thermoplastic surfaces that can be welded are composed of any compatible thermoplastic polymer material. Suitable thermoplastic polymers include, but are not limited to, polyamides, polyesters, polycarbonates, polysulfones, polyimides, polyurethanes, polyethers, vinyl polymers, and mixtures thereof. Polyamides such as Nylon 6 and Nylon 66, for example, AlleidSignal Inc. of Morristown, NJ, USA. Polyesters such as phthalate are most preferred. Dissimilar thermoplastic surface materials can also be used as long as they are compatible with each other. At least one, and preferably both, thermoplastic surfaces are fiber reinforced. Suitable reinforcing fibers include materials that do not soften, i.e., lose their rigidity, at temperatures typically used for injection molding, such as temperatures up to about 400 <0> C, but without excluding others. Absent. Preferably, the fiber reinforcement comprises materials such as glass fibers, carbon fibers, silicon fibers, metal fibers, inorganic fibers, polymer fibers and mixtures thereof. Glass fiber reinforcement is most preferred. In a preferred embodiment, the fibers are rigid and have a diameter of about 8 to about 12 micrometers, preferably about 9 to about 11 micrometers, and most preferably about 10 micrometers. Preferred fiber lengths are from about 120 to about 300 micrometers, more preferably from about 130 to about 250 micrometers, and most preferably from about 140 to about 200 micrometers. In a preferred embodiment, the fibers comprise about 6 to about 40% by weight of the thermoplastic composition, more preferably about 13 to about 25% by weight of the thermoplastic composition. The linear peak-to-peak travel or distance of rubbing one surface against the other is the vibration amplitude. In a preferred embodiment, the vibration amplitude is at least about 0.075 inches. More preferably, the vibration amplitude is from about 0.075 to about 0.15 inches, and most preferably, from about 0.075 to about 0.090 inches. The aforementioned vibration amplitude is at an apparent output vibration frequency of 240 Hz. At other vibration frequencies, the amplitude will vary. For example, at an apparent output vibration frequency of 120 Hz, a preferred vibration amplitude is at least about 0.09 inches, more preferably about 0.13 to about 0.16 inches, and most preferably about 0.135 to about 0.145 inches. Would be a range. Vibration amplitudes for other frequencies can be easily determined by those skilled in the art. In a preferred embodiment, the contact surfaces are maintained under a pressure of about 0.6 to about 1.5 MPa relative to their normal during vibration welding. More preferably, the pressure is from about 0.6 to about 1.2 MPa, and most preferably, from about 0.7 to about 0.8 MPa. Vibration or rubbing time preferably ranges from about 2 to about 7 seconds, more preferably from about 4 to about 6 seconds. The dwell time or cooling time, at which the pressure is maintained after stopping the vibration, preferably ranges from about 2 to about 8 seconds, more preferably from about 4 to about 5 seconds. The weld thickness preferably ranges from about 160 to about 400 micrometers, more preferably from about 200 to about 350 micrometers, and most preferably from about 250 to about 330 micrometers. When vibration welding is performed under the conditions described above, some of the fibers from the reinforced surface enter the weld and the opposite surface. When both surfaces include reinforced thermoplastic, any of the fibers from each surface will penetrate the weld and the opposite surface. In a preferred embodiment, the estimated percentage (by tensile strength) of fibers penetrating from one or both reinforcing surfaces into the opposite surface is from about 2 to about 8%, preferably from about 4 to about 8%, more preferably Ranges from about 5 to about 8%. As a result of the vibration welding method of the present invention, the weld of one reinforced thermoplastic surface to the other thermoplastic surface is higher than the weld formed by the unreinforced surface of the corresponding thermoplastic material. Achieve maximum tensile strength. The tensile strength of the vibration weld on the reinforced thermoplastic surface ranges from at least about 85%, preferably from about 85 to about 120%, of the weld formed by the unreinforced surface of the corresponding thermoplastic material. Without being bound by a particular theory, it is inferred that the vibration welding parameters of the present invention allow for fiber penetration from one reinforcing surface to the other. For example, the application of pressure and the vibration time and vibration amplitude must help to push the fibers from one molten surface into the other. Too low a weld thickness or too high a fiber loading will prevent the fibers from traversing into the opposite surface, as there will be insufficient space for fiber rotation. The following non-limiting examples illustrate the invention. It will be understood that variations in the proportions of the components of the photosensitive coating composition and variations in the components themselves will be apparent to those skilled in the art and are within the scope of the present invention. Example 1 AlleidSignal Inc., Morristown, NJ, USA. Available from Injection molded into 3 "x 4" x 1/4 "and 3" x 4 "x 1/8" blocks containing 0-50% by weight of glass fiber reinforcement. The same blocks are vibration welded together with a Mini-Vibration Welder from Branson Ultrasonics Corporation or 2400 Series Welder using the following parameters: maximum clamp load: 4.5 kN; vibration amplitude: 0.762 to 2.76. 28 mm (0.030 "to 0.090"); welding time: 4 to 8 seconds; apparent welding frequency: 240 Hz. The welding parameters, ie pressure (load), amplitude and time were varied to optimize the tensile strength of these welded joints. Only samples that achieved a tensile strength higher than the tensile strength of the basic unfilled material were selected and the morphology of the weld zone was studied. Details of the zone interface and fiber orientation were included in this analysis. The morphology of the sample was examined using an optical microscope, and at the same time the fiber length was quantified using image analysis. Analysis of glass fiber filling in welding zone %. However, as the joint is formed, the actual fiber loading in the weld zone can vary if either the fiber or the nylon matrix is preferably extruded from the weld zone. To ensure that the fiber loading in the excess flow zone at the weld is different from the material body, the weight percent of fiber is taken by taking the weight difference between the excess before and after the matrix is pyrolyzed. Measurement Table 1 summarizes the results. These results show that the fiber loading of the various nylon 6 materials tested is about 0.5-1% by weight lower than the composition body. Measured from HS nylon 66 samples. The results are shown in Table 2 and indicate that the fiber loading of nylon 66 in the weld zone burrs is about 0.5% by weight lower than the composition body. These fluctuations in fiber content are rather small and are close to measurement errors in fiber content. Analysis of glass fiber length in welding zone In order to confirm whether or not the fiber was broken excessively in the welding zone, the fiber length was analyzed. The fiber length of fibers from burrs (recovered from pyrolysis ash) was measured by optical microscopy and image analysis. Glass fiber samples were withdrawn from the ash and spread on glass slides with 2,2,2-trifluoroethanol (TFE) solvent. Ten optical micrographs were taken of each sample, and a total of 1000 to 2000 fibers were counted and measured by an image analyzer. Table 3 summarizes the results. This analysis shows that the average fiber length for all samples is in the range of 120-180 micrometers. This is comparable to the average fiber length of the sample measured from the original molded tensile specimen away from the area of the weld zone. Furthermore, examination of the weld zone failure surface by scanning the electron microscope indicated that there was no excessive fiber destruction in the weld zone. Analysis of glass fiber orientation distribution in welding zone The fiber orientation distribution (FOD) of glass fiber (GF) in the welding zone was examined by an optical microscope and a scanning electron microscope. For each sample, both cross-sections in the plane and in the thickness direction were prepared and metallographically polished into samples for optical microscopy studies. Optical micrographs at relatively low magnification (25x and 50x) show the overall FOD around the weld zone as well as the fiber orientation in the weld zone. Optical micrographs are taken from polished sections of nylon 6 samples with 6 wt% GF, 14 wt% GF, 25 wt% GF, 33 wt% GF and 50 wt% GF, respectively. Micrographs show both fiber orientation near the weld zone and fiber orientation away from the weld zone. Further, the apparent thickness of the weld zone can be measured directly from the FOD change with the location shown in the micrograph. It is noted that for samples with 14 and 25 wt% GF, there is clear evidence of several fibers oriented in the tensile direction perpendicular to the weld plane. It was noted that the effect of strengthening at optimized welding conditions appeared to be independent of the glass fiber orientation in the forming plaque selected for welding. Tensile Strength of the Welded Joint For each vibration welding condition (ie, set pressure, amplitude and welding time), 10 specimens were tested under the standard ASTM D638M-93 tensile test procedure for plastics. Table 4 summarizes the results for the welded joint tensile strength at the optimized welding parameters. Inspect the effect of glass fiber loading on tensile strength. These results show that all welded joint samples have higher tensile strength than that of unreinforced nylon 6. For reinforced nylon 6 material, the maximum tensile strength is 93.1 MPa. This occurs around the 14-25 wt% glass fiber loading. By comparison with unreinforced materials having a tensile strength of 79.3 MPa, this maximum weld strength found with these reinforced grades corresponds to a 17% increase in weld joint tensile strength. The tensile strength of welded nylon 6 material appears to be slightly higher (about 4%) than that of welded nylon 66 under the same welding and strengthening conditions. These data also show that the glass fiber / nylon 66 composition at the interface is similar to that of the composite body. Several factors may be responsible for the high weld strength of glass-filled nylon 6 observed under optimal welding conditions. For nylon 6, selecting some compositions and welding parameters, it appears that a certain percentage of the glass fibers traverse the weld plane at the interface. The width of this welding zone of about 200-300 micrometers is comparable to the average length of the fibers. This allows the fibers to move in a direction other than the primary resin flow direction during welding, i.e., the fibers are restricted to move along the flow direction, as in a narrow weld zone. It is not. The thickness of the weld zone as observed from the micrograph can be plotted as a function of fiber loading. It is noted that the weld zone thickness passes through a maximum at a fiber loading of 14% by weight. This maximum occurs at the same position as the maximum in the tensile strength curve (14% to 25% by weight of glass fiber (GF)). This further suggests that the thickness of the weld zone has a positive effect on the tensile strength of the weld joint. By preparing a weld specimen with an orientation different from the predominant fiber orientation, the welding performance as a function of the glass fiber orientation distribution in the GF nylon 6 plaque could be examined. The results of this data suggest that at the weld interface, the fiber orientation achieved in the region of the weld zone is independent of the predominant orientation of the glass fibers in the nylon 6 body adjacent the weld. This data for linear vibration welded polyimide butt joints shows an increase in tensile strength of up to 35% compared to published data in the prior art.

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated countries EP (AT, BE, CH, DE, DK, ES, FI, FR, GB, GR, IE, IT, L U, MC, NL, PT, SE), CN, JP, KR (72) Inventor Rui, Shi-Ching             United States New Jersey 07060,             Watching, Tuttle Road 91 (72) Inventor Smith, Gregory Earl             United States of America New Jersey 07960             −5145, Morristown, Skyline             Drive 60

Claims (1)

[Claims]   1. A first surface comprising a fiber reinforced first thermoplastic composition is applied to a second thermoplastic Bonding to a second surface containing a conductive plastic composition, wherein the first and second surfaces are bonded together. 2 surfaces are contacted, and the contacted first and second surfaces are referred to as the first and second tables. A method comprising vibration welding under conditions sufficient to form a weld between the surfaces. Wherein the weld comprises a blend of the first and second thermoplastic compositions; And a method wherein fibers from the first surface penetrate both the weld and the second surface .   2. Each of the first and second thermoplastic compositions is a polyamide, a polyether. Steal, polycarbonate, polysulfone, polyimide, polyurethane, polyether Thermoplastics selected from the group consisting of polyesters, vinyl polymers, and mixtures thereof. The method of claim 1, comprising a conductive plastic polymer.   3. The fiber is made of glass, carbon, silicon, metal, mineral, polymer, or a mixture thereof. The method of claim 1, comprising a material selected from the group consisting of compounds.   4. The fibers have a weight of about 6%, based on the weight of the reinforced first thermoplastic composition. The first thermoplastic composition is present in the first thermoplastic composition in an amount of from about 40% by weight. The method of claim 1.   5. The fibers may have a weight of about, based on the weight of each thermoplastic composition, A reinforced first thermoplastic composition and a reinforced second thermoplastic in an amount of 6 to about 40% by weight; The method of claim 1, wherein the method is present in both of the plastic compositions.   6. A first surface comprising a fiber reinforced first thermoplastic composition, and a second thermoplastic A second surface in contact with the first surface, comprising a conductive plastic composition; And a blend between the first and second surfaces comprising a blend of a second thermoplastic composition. A vibration welded article including a contact portion, wherein fibers from the first surface are An article penetrating both of the second surfaces.   7. A second thermoplastic composition is fiber reinforced, and a second surface 20. The article of claim 18, wherein the fibers from are penetrating both the weld and the first surface.   8. Each of the first and second thermoplastic compositions is a polyamide, a polyether. Steal, polycarbonate, polysulfone, polyimide, polyurethane, polyether Thermoplastics selected from the group consisting of polyesters, vinyl polymers, and mixtures thereof. 19. The article of claim 18, comprising a conductive plastic polymer.   9. The fiber is made of glass, carbon, silicon, metal, mineral, polymer, or a mixture thereof. 19. The article of claim 18, comprising a material selected from the group consisting of a compound.