MXPA99005302A - Apparatus for radio-frequency bonding of thermoplastic members - Google Patents

Abstract

A bonding apparatus for bonding a thermoplastic pad (38) having a predetermined peripheral shape to a first surface of a carpet (c) using radio frequency energy includes a die electrode (22) and a backing electrode (14). Both the die electrode and the backing electrode have a peripheral shape that corresponds to the peripheral shape of the pad. In addition, both the die electrode and the backing electrode may have a relief feature (18, 24) thereon that are correspondingly sized and located. Concentrations of electric field intensity in the vicinity of the peripheral edge of the die electrode and along the edges of the relief feature on the die electrode are minimized so that bonding of a pad to a carpet may be effected without thermal runway. The pad is fully bonded to the carpet without the occurrence of localized burning of the carpet pile or perforation of the pad.

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an apparatus for directly attaching thermoplastic elements such as a mat or block or thermoplastic pad to a carpet of hairs when using radiofrequency electromagnetic energy (energy). of RF).

Description of the prior art The presence of wear-resistant mats or blocks or pads in the carpeted floor areas of the interior of a car is familiar to all drivers. In most cases, such mats are made of a thermoplastic sheet material having a predetermined peripheral shape. Typically, the mat is manufactured from a sheet or sheet of vinyl, such as polyvinyl chloride. The thermoplastic mat is glued either by adhesive or directly to the carpet. In the typical glue or adhesive bond, a thermoplastic adhesive is applied between the mat and the carpet and radiofrequency (RF energy) or heat is used to melt the adhesive and make the glue between the mat and the mat.

REF .: 30157 carpet. In a sticking by adhesive situation, overheating or burning is not usually a problem because the melting point of the thermoplastic adhesive is sufficiently lower than that of the carpet or mat hair materials. In the direct bonding, the radiofrequency energy is applied to the mat and to the carpet to effect the glue between them. Direct adhesion using radiofrequency energy is also known as "dielectric adhesive". Such direct glue from the mat to the carpet is preferred since no adhesive is required and since the glue cycle time is reduced. However, as will be explained. fully in the present, in some instances, especially in production environments, the direct glue from a carpet to a carpet is difficult to obtain without overheating or discoloration of the carpet hair. This overheating or discoloration occurs due to the increased field strengths caused by the edge effects associated with the geometry of the electrodes of the gluing apparatus acting on the carpet material having a particular temperature dependence on its susceptibility to the radiofrequency energy. The term "susceptibility" as used herein means the ability of a material to convert electric field strength to heat. An apparatus for direct bonding generally indicated by the reference character 10 used in the prior art for applying radiofrequency energy, to effect a bond between a first thermoplastic element, such as a thermoplastic mat P to a first surface of a second Thermoplastic element, such as a thermoplastic carpet C, is shown in Figures IA and IB. A finished automotive Carpet C having the mat P stuck thereto is shown in Figures 2A and 2B. As suggested in Figure 2A, the mat P has a predetermined peripheral shape depending on the region of the interior of the automobile in which it is arranged. The mat E may also have raised areas R located on it within the periphery. Flat regions F are formed on the mat P along the peripheral edge of the mat and on the mat intermediate to the raised areas R. The gluing apparatus 10 includes a first die electrode 14 and a second electrode 22 of support, backing or reinforcement. The electrodes 14, 22 are arranged in a confronting manner with respect to each other. The matrix electrode 14 includes a generally flat mounting portion 16 to which a shaped matrix or mold element 18 is attached. Both, of the matrix electrode 14 (formed of the mounting portion 16 and the matrix element18) also as the supporting electrode 22 are manufactured from an electrically conductive material, such as metal or a conductive compound. The matrix element 18 has a peripheral shape corresponding to the peripheral shape of the mat P to be joined in the apparatus 10. In addition, the operating surface of the matrix member 18 has one or more relief features 18F, the edges of the which are defined by the depressions 18D. The relief features 18F of the matrix element 18 correspond to the flat regions F on the mat P, while the depressions 18D on the matrix element 18 correspond to the raised areas R on the mat P. The dimensions of the width of the depressions 18D (such as the dimensions 18W1, 18W2) and the depth dimension of the depressions 18D (such as dimension 18E) and thus, the width and height dimensions of the raised areas R are determined in accordance with the design a be imparted to the mat P. Typically, the depth dimension 18E is of the order of several millimeters. In the apparatus 10 of the prior art, the support electrode 22 is generally planar. The electrodes 14, 22 are mounted on a frame or frame 28 of a press 26 (FIG. IA). Although the electrodes are shown arranged horizontally with the matrix electrode 14 which is located on the adhesion electrode 22, it should be understood that throughout this application, any convenient orientation of the electrodes 14, 22 with respect to the frame 28 and each other may be used. The press 26 includes an actuator 30 operable to move the electrodes 14, 22 one relative to the other (as suggested by the directional arrow 34) from an open position (shown in FIG. IA) to a closed position (suggested in FIG. Figure IC). Both electrodes 14, 22 are electrically connected to an appropriate source 36 of high voltage radio frequency energy. Normally, the source 36 emits a radiofrequency signal in the range of about one megahertz (1 MHz) to one hundred megahertz (100 MHz) at a voltage in the range of about three thousand volts (3 KV) to about ten. one thousand volts (10 KV). The typical power levels of the apparatus for radiofrequency bonding are in the range of five ilowatts (5 KW) to one hundred kilowatts (100 KW). In order to glue a mat P to the carpet C, the mat P is placed on the matrix element or shaped mold of the matrix electrode 14, as seen in FIG. The carpet C is then placed with its surface S of hairs in contact with the lower surface of the mat P. The surface of the rear part B of the carpet C is presented towards the support electrode 22. A resilient cushion layer 38, normally made of a material (such as silicone rubber), which has a low susceptibility to radiofrequency energy, is interposed between the surface of the support B of the carpet C and the supporting electrode 22. After the materials have been laminated in its relative positions as described and illustrated in FIG. A, a paste cycle is initiated. The actuator 30 is moved to the backup electrode 22 towards the drive electrode 14 to clamp the laminated materials with a predetermined clamping pressure. The clamping pressure is usually specified in terms of the resultant space (FIG. IC) defined between the raised area 18F of the array electrode 14 and the support electrode 22. In practice, the space is limited by a retainer or physical obstacle in FIG. the press mechanism (not shown). With the materials attached, the source 36 is activated and radiofrequency energy is applied between the electrodes 14, 22 to the layered materials fastened therebetween. The radiofrequency energy is applied at a predetermined voltage (usually of the order of three thousand to ten thousand volts) for a predetermined period of time called the "heating cycle" (usually, of the order of five to twenty seconds), to heat the materials of the mat P and the hair of the carpet C. The source 36 is deactivated and the materials remain clamped for a second predetermined period of time, called the "soak cycle". (normally, also of the order of five to twenty seconds) to allow the materials that were heated to cool and the bond between them to set. In an acceptable glue, the mat material is adhered over the entire interfacial area between the mat P and the carpet C (that is, the mat is "fully adhered") without discoloration or melting of the mat P or discoloration or excessive melting of the mat. carpet hair adjacent to the periphery of the rug. The range of combinations of voltages and times allow to produce a fully adhered mat is called the "window (or space) of operation". It has been found that, especially in a production environment, a conventional glueing apparatus is not suitable for producing a satisfactory bond between a carpet and a carpet when the hair of the carpet is colored nylon by the producer having a resistant material spotted topical No matter what voltage and time parameters are chosen for the operation window, either (1) the P mat is not fully adhered to the C carpet, (2) the discoloration or perforations in the P mat adjacent to the corners occurs. or edges of the raised areas R and / or (3), discoloration or melting of the carpet C adjacent the periphery of the carpet P. It is believed that the inability to obtain a satisfactory bond is due to the combination of: (1 ) localized increases in the electric field strength due to the edge effects resulting from the geometry of the coupled electrodes of the joining apparatus, (2) the temperature-dependent susceptibility to radiofrequency of the carpet material and (3) ) the characteristics of susceptibility to radiofrequency and thermal conductivity of the reinforcement of the carpet. Figure IC illustrates the electric field lines (shown as fine lines) between the matrix electrode and the support electrode in the portion of Figure IA enclosed in the block of broken lines. For clarity of illustration, the materials to be stuck that fall within the space are not shown. Relatively sharp edge characteristics are defined along the periphery of the matrix element 18, also as along the relief features 18F thereof. The peripheral edges and edges of the relief feature, together with the support electrode 22, produce an electrical field configuration in which the field lines tend to converge in the vicinity of the edges. The spacing of the adjacent field lines in Figure IC indicates the intensity of the field. A quantitative plot of the square of the field strength (normalized) that is illustrated graphically in Figure IC is shown in Figure 4 by the broken line indicated by the "Prior Art" reference label. The graph is taken along a reference line 4-4 that falls at a distance equal to ten percent of the width G of the space between the electrodes 18, 22. The abscissa of the graph is the relative lateral position in both that the ordinate of the graph is the square of the field strength (normalized to the field strength between the center region of a relief feature 18F and the support electrode 22). In automotive applications, the surface S of the hair of the carpet C is usually formed of a thermoplastic polymeric material, usually a polyamide such as nylon. The nylon is the proferido due to its characteristics of wear. However, nylon (and especially nylon 6,6) differs from other polymeric materials such as polyester and polypropylene used for carpets, due to the susceptibility of nylon to radio frequency energy that increases with increased temperature. A material that has such susceptibility dependent on the characteristic temperature is subject to a phenomenon known as "thermal leakage". In a situation of thermal leakage, the carpet material melts in such a way that the strands or individual strands lose their definition. Discoloration may also occur. The surface S of carpet hair thus takes on a rough amorphous appearance. The peak or maximum in the field strength associated with a peripheral edge of the array electrode (as indicated in reference character 40 in FIG. 4) and / or the peak or maximum in field strength associated with an edge of the relief characteristic of the matrix electrode (as indicated in reference character 42 in Figure 4), each coupled with the particular temperature dependent nylon susceptibility characteristic used in the carpet, results in localized superheating which causes thermal leakage in localized regions of the carpet hair material in the vicinity of the edges on the matrix element 18. Adjacent to the periphery of the P mat may be discoloration and a rough, amorphous appearance. In the interior regions of the mat P, the thermal leakage of the carpet pile material in combination with the radiofrequency heating of the mat material may cause perforations of the mat, particularly at the edges and especially at the corners of the characteristics of the mat. relief. Depending on the material used, carpet support can also contribute to the problem of global overheating. The presence of additives such as colored pigments and / or materials resistant to topical dyeing further increase the temperature dependence of nylon susceptibility to radiofrequency energy and exacerbate thermal leakage problem. It is believed that the additional increase in temperature dependence is due to the mobility of the ions in the material resistant to topical spotting. In view of the foregoing it is believed that it is advantageous to provide a sticking apparatus which minimizes the problems of localized overheating when a first thermoplastic member is adhered or glued to a second thermoplastic element. More particularly, it is believed to be advantageous to provide a sticking apparatus that minimizes the problem of thermal leakage when sticking a thermoplastic mat to a carpet of nylon hairs.

BRIEF DESCRIPTION OF THE INVENTION The present invention is concerned with a gluing apparatus for gluing a first thermoplastic element, such as a thermoplastic mat having a predetermined peripheral shape to a first surface of a second thermoplastic element, such as a carpet, when using radiofrequency energy. The carpet has a surface of hairs made of a polymeric material susceptible to thermal leakage. The apparatus for gluing includes a first die or mold electrode and a second support electrode. The matrix electrode has a peripheral shape that corresponds to the peripheral shape of the mat. The matrix electrode may also have at least one relief feature thereon. The matrix electrode has peripheral edges on it. The relief features (if provided) also have borders on them. In accordance with the present invention, the support electrode has a junction element having a peripheral shape corresponding to the peripheral shape of the matrix electrode. The support electrode also has relief feature (s) sized and located (s) to correspond to the size and location of the relief feature (s) (if any) on the die electrode. Thus, the concentrations of the electric field strength in the vicinity of the peripheral edges of the matrix electrode (and in the vicinity of the edges of relief feature, if any) are minimized in such a way that the bonding of a mat to A carpet can be made without thermal leaks. The mat is fully adhered to the carpet without the presence of localized overheating of the carpet hairs or perforation of the carpet. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, in which: Figure IA is a cross-sectional side elevational view of an apparatus for gluing the prior art, while figure IB is inclined (in the form of a clam-shell), in perspective view (with the materials to be glued not shown for clarity of illustration) of the apparatus for gluing of figure A and figure IC is a schematic view showing the portion of the apparatus for gluing of Figure IA enclosed by the block of broken lines and illustrating the lines of the electric field between the matrix electrode and the support electrode therein; Figure 2A is a perspective view of a carpet attached to the carpet when using the sticking apparatus of Figures IA and IB and Figures 3A and 3B, while Figure 2B is a sectional view taken along the lines 2B-2B in Figure 2A; Figure 3A is a side elevational view in section of an apparatus for gluing according to the present invention, Figure 3b is an inclined perspective view (in the form of a clam-shell) of the apparatus for gluing of Figure 3A with the electrodes exposed to show the corresponding relief characteristics on the surfaces of the matrix electrode and the joining element and Figure 3C is a schematic view showing the portion of the apparatus for gluing of Figure 3A enclosed by the block of broken lines and that illustrates the electric field lines between the matrix electrode and the conjugate joining element on the support electrode thereon; Figure 4 is a graph showing a comparison of the square of the electric field strengths illustrated graphically in Figure 1C (the prior art) and the square of the electric field strengths illustrated graphically in Figure 3C for the apparatus of the present invention, the graphs are (normalized to the field strength between the central region of a relief feature 18F and the support electrode 22); and Figure 5 is a side elevational view, in section, illustrating further alternative modifications to an apparatus for gluing in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION Throughout the following detailed description, similar reference numerals refer to similar elements in all figures of the drawings. It is to be understood that although the invention is described in terms of sticking a thermoplastic mat to the surface of a carpet of nylon hairs, the invention is generally applicable to gluing a first thermoplastic element to a second thermoplastic element. Figures 3A and 3B illustrate an apparatus for gluing 'in which the thermal leakage is minimized by reducing the localized concentration of the field strength between the coupled electrodes. According to the present invention, a conjugate attachment element 24 is mounted in electrically conductive contact with the support electrode 22. As is the case with the matrix electrode 14 and the support electrode 22, the conjugate element 24 is manufactured of an electrically conductive material such as metal or a conductive compound. The conjugate attachment element 24 has a peripheral shape corresponding to the peripheral shape of the matrix electrode 18. In addition, the conjugate adhesion element 24 also includes a relief feature 24F dimensioned and located to correspond to the size and location of each feature of relief 18F on the matrix electrode 18. Thus, each edge formed on the conjugate adhesion element 24, whether it is a peripheral edge or an edge on a relief feature, corresponds to an edge provided on the matrix electrode 18. The conjugate attachment element 24 is preferably manufactured or assembled in a manner that the amount of time required to assemble the conjugate adhesion element 24 to the support electrode 22 in the press 26 is minimized. Preferably, this is carried out by forming the conjugate binding element 24 as an integral element from a single piece of electrically conductive material. When formed in this manner, the conjugate attachment element 24 includes a base portion 24B of the nominal thickness 24T from which the relief features 24F extend. Alternatively, the conjugate element 24 can also be mounted on a unitary structure from individual modular pieces, which are joined (such as by appropriate fasteners) to a base or directly to the surface of the support electrode 22. If desired, the conjugate attachment element 24 (configured in any way) can be separated from the support electrode 22 by using any convenient form of electrically conducting spacers or insulators (not shown). Either way it is formed, each relief feature 24F is defined on the conjugate joining member 24 by depressions 24D which are located as mirror images of the depressions 18D on the matrix electrode 18. Each depression 24D has a predetermined width dimension according to the width of the corresponding depression 18D on the matrix electrode 18. Preferably, the width dimension of the depressions 24D (and thus the width of the relief feature 24F defined therein) are substantially equal to the width dimension of the corresponding depression 18D (and thus, the width of the relief feature 18F defined therein). Substantially the same means that the widths can vary up to about ten (10) percent. The dimensions of the width of the depression 24D can vary from the width of the conjugate joining element 24. Thus, as seen from Figure 3A, the dimensions of the width 24W1 and 24W2 on the conjugate joining element 24 vary according to the dimensions of width 18W1 and 18W2 on the matrix electrode 18. Each depression 24D has a depth dimension indicated by the reference character 24E. The operative face of each relief feature 24F is thus disposed at least the predetermined distance 24E above the surface of the base portion 24B of the conjugate joining element 24. Due to the 24T thickness dimension of the base 24B, such arrangement places the peripheral edge of the support electrode 22 at a distance 24H (equal to the distance 24E plus the thickness 24T) of the surface of the support electrode 22. It has been found that a distance greater than about two (2) centimeters it is enough for distance 24E. It should be noted that the distance 24E is approximately one order of magnitude greater than the depth dimension 18E of the depressions in the matrix electrode 18. As long as the distance 24E meets the minimum requirement described above, the intensity concentrations of the electric field in the vicinity of the peripheral edges of the matrix electrode 18 and along the edges of the relief features on the matrix electrode 18 are minimized. This is illustrated with reference to Figures 3C and 4. Figure 3C is similar to Figure IC and illustrates the electric field lines (again shown as fine lines) between the matrix electrode and the conjugate joint element 24 on the backup electrode 22 in the portion of figure 3A enclosed by the block of dashed lines. Again, for clarity of illustration, the materials to be joined that fall or lie in space are not shown. The peripheral edges and edges of the relief features of the matrix electrode 18, together with the corresponding edges on the conjugate joint element 24, produce an electrical field configuration in which the field lines tend to converge in the vicinity of the edges to a smaller extent than in the case of Figure IC. A qualitative graph of the electric field strengths illustrated in Figure 3C is indicated in Figure 4 by the solid line called "Conjugate Electrode". The graph is taken along a reference line 4 '-4' which falls at a distance equal to ten percent of the width G of the space between the matrix electrode 18 and the conjugate joining element 24. The peak or maximum in the square of the field strength associated with a peripheral edge of the matrix electrode is indicated with the reference character 40 'in Figure 4, while the peak or maximum in the square of the field strength associated with an edge of the relief characteristic of the matrix electrode is indicated by the reference character 42 '. The peaks or maxima 40 ', 42', are given in the same relative lateral positions as the peaks or maxima 40, 42 respectively. The decrease in the concentration of the field strength resulting from the apparatus of the present invention can be appreciated by comparing the magnitudes of the peaks 40, 40 '(corresponding to a peripheral edge on the matrix electrode) and the magnitudes of the peaks. 42, 42 '(corresponding to an edge of a relief feature on the matrix electrode). It can be easily seen that in each case the concentration of the field strength is reduced in a junction apparatus 10 'having a conjugate attachment element 24 according to the present invention. The concentration of the field strength adjacent to the edges can be further decreased by using the additional modifications described in Figure 5. In an alternative arrangement, a sleeve 52 is a sleeve arranged around the side of a relief feature 24F. The sleeve 52 is formed of a rigid, non-electrically conductive material that has a low susceptibility to radiofrequency energy, such as quartz, glass or a low loss composite. In another alternative arrangement, a crown 54 is disposed on the operating surface of a relief feature 24F. The crown 54 is also formed from a rigid, non-electrically conductive material having a low susceptibility to radiofrequency, such as quartz, glass or a low loss composite. Consistent with the configuration that is imparted to the "mat, a sleeve 56 or a crown 58 can be provided to the relief features 18F on the matrix electrode 18. It should be appreciated from the foregoing that the sticking apparatus of the present invention allows a first thermoplastic element to be fully bonded to a second thermoplastic element without the presence of localized overheating or discoloration. Even if the materials to be joined do not exhibit a susceptibility to radiofrequency depending on the characteristic temperature, the use of an apparatus for gluing according to the invention allows the bonding or bonding to be presented with higher radiofrequency voltages applied and times of shorter bond cycle. Those of ordinary skill in the art in obtaining the benefit of the teachings of the present invention as summarized herein may make numerous modifications thereto. For example, the walls defining the depressions 24D can be inclined or curved in or out of the vertical orientation shown in Figure 3A to define a relief feature that is wider (ie, widened) or narrower (this is, recessed) adjacent to the base portion 24B. These alternatives are indicated generally by the reference characters 56 and 58 in Figure 5. The periphery of the conjugate element can have similar alternative configurations if desired. Consistent with the configuration that is imparted to the mat, similar modifications can be made to the walls defining the depressions 18D on the matrix electrode 18. Such modifications are to be construed as belonging to the present invention, as defined by the appended claims . It is noted that, in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it refers.

Claims (6)

1. Claims Having described the invention as above, the content of the following claims is claimed as property: 1. An apparatus for gluing which serves to glue or join a first thermoplastic element having a predetermined peripheral shape to a first surface of a second element thermoplastic when using radiofrequency energy, the thermoplastic elements are made of materials that absorb radiofrequency energy, the apparatus for gluing includes a first matrix electrode and a second support electrode (reinforcement or backup), the matrix electrode has a peripheral shape corresponding to the peripheral shape of the first thermoplastic element, the matrix electrode has edges on it, the improvement is characterized in that it comprises: the support electrode has a conjugate joining element thereon, the conjugate joining element has a shape peripheral that corresponds to the form to peripheral of the matrix electrode, whereby, the concentration of the electric field in the vicinity of an edge of the matrix electrode is minimized in such a way that a first thermoplastic element is fully bonded to a second thermoplastic element without the presence of overheating and be in one or another element. The gluing apparatus according to claim 1, characterized in that the matrix electrode has at least one relief feature thereon and wherein the conjugate joint element has a relief feature sized and positioned to correspond to the size and location of the relief feature on the matrix electrode, whereby the concentration of the electric field in the vicinity of the confronting edges of the relief feature on the matrix electrode and the relief feature on the conjugate joining element is minimized 3. An improved gluing apparatus for sticking or joining a thermoplastic mat having a predetermined peripheral shape to a first surface of a carpet when using radiofrequency energy, the carpet has a hair surface made of a polymeric material susceptible to thermal leakage , the apparatus for gluing includes a first matrix electrode and a second support electrode, the matrix electrode has a peripheral shape corresponding to the peripheral shape of the mat, the matrix electrode has at least one relief feature on the same, the matrix electrode has peripheral edges and edges of the characteristic of relief on it, the improvement is characterized in that it comprises: the support electrode has a conjugate joining element on it, the conjugate joining element has a peripheral shape which corresponds to the peripheral shape of the matrix electrode and a relief characteristic di mentioned and located to correspond to the size and location of the relief characteristic on the matrix electrode, whereby the concentrations of the electric field in the vicinity of the peripheral edges of the matrix electrode and in the vicinity of the edges of the characteristic of relief on the matrix electrode are minimized in such a way that the union of a carpet to a carpet can be carried out without thermal leaks, in such a way that the union of the carpet to the carpet is fully stuck to the carpet without the presence of overheating of the carpet. the hairs of the carpet. The gluing apparatus according to claim 3, characterized in that each feature of relief on the conjugate joining element has an operative face thereon, the operative face of each relief feature on the conjugate joining element extends through at least about two centimeters above the surface of the support electrode. 5. The gluing apparatus according to claim 3, characterized in that each relief feature on the conjugate adhesion element has an operative face thereon., the apparatus for gluing further comprises a crown disposed on the operative face of at least one relief feature on the conjugate joining element, the crown being formed of a non-conductive material having a low susceptibility to radio frequency. The attachment or adhesion apparatus according to claim 3, characterized in that each feature of relief on the conjugate connecting element has a side thereon, the apparatus for gluing further comprises a sleeve arranged around the side of at least a feature of relief on the conjugate joining element, each shell is formed from a non-conductive material having a low susceptibility to radiofrequency energy.