Patent Publication Number: US-2011052864-A1

Title: Thermal adhesive tape and manufacturing method of the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a thermal adhesive tape and a manufacturing method of the same, and more particularly, to a thermal adhesive tape that is melted between objects to be adhered, when heat is applied, thereby adhering the objects to each other, and a manufacturing method of the same. 
     2. Description of Related Art 
       FIG. 1A  is a structural diagram of a conventional thermal adhesive tape. 
     As shown in  FIG. 1A , the conventional thermal adhesive tape is provided with a non-woven fabric  10  in the middle thereof and a first adhesive sheet  20  and a second adhesive sheet  30  on both sides of the non-woven fabric  10 . 
     Adhesion of two adherends with each other using the conventional thermal adhesive tape is carried out in such a manner that the thermal adhesive tape is first disposed between the adherends and heat is directly applied to the adherends by a thermocompressing apparatus to be then transferred to the first melting sheet  20  and the second melting sheet  30  through the adherends, and thereby the first melting sheet  20  and the second melting sheet  30  are melted and adhered to the adherends. 
     Therefore, to adhere the conventional thermal adhesive tape to the adherends, at least one of the two adherends should be a heat-transferable material (for example, SUS, metal, etc.). 
     That is, since the heat should be transferred to the thermal adhesive tape placed between the adherends, at least one of the adherends should have a high thermal conductivity. 
     In the case of adhering two adherends, both having low thermal conductivity, e.g. synthetic resins, another adhering method is used since the conventional thermal adhesive tape as described above has a problem that the adherends are deformed by the heat before the first melting sheet  10  or the second melting sheet  20  is melted. 
     For example, a conventional technique for adhering a case and a LCD cover of a portable terminal will be described. 
       FIG. 1B  is a sectional view showing that a case and a LCD cover of a portable terminal are adhered. 
     In general, a case  41  and a LCD cover  42  of a portable terminal and a small electronic appliance are adhered with a double sided tape  43  as shown in  FIG. 1B . 
     In recent, with miniaturization of a portable terminal and enlargement in a size of a LCD, an area of the double sided tape  43  that comes into contact with the LCD cover  42  and the case  41  has been reduced. 
     However, the reduction in the adhesion area of the double sided tape  43  results in an insufficiency in adhesive strength for coupling the LCD cover  42  and the case and resultant easy separation of the LCD cover  42  from the case  41 . 
     Also, it may be possible to carry out the adhesion using a silicon bond instead of the double sided tape  43 , but there is a problem that productivity is significantly dropped since a compression and dry process in a jig for 10 hours or more is required after the bonding process. 
     Further, the silicon bond has a problem that its impact resistance becomes worse with time to thereby cause trouble. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to a thermal adhesive tape, in which a conductor that generates heat by a high frequency wave is disposed in the middle of the thermal adhesive tape to thereby improve productivity and give strong adhesive strength while thermally adhering materials having a low thermal conductivity with each other. 
     In one embodiment, a thermal adhesive tape for a portable terminal, which couples a case and a LCD cover of the portable terminal with each other, includes a heated sheet made of a conductor; a first melting sheet adhered to one face of the heated sheet; and a second melting sheet adhered to the other face of the heated sheet, wherein the first and second melting sheets are made of a polyester composition, the heated sheet is made of aluminum or copper, and the first and second melting sheets are melted upon heating of the heated sheet by a high frequency induction to adhere the case and the LCD cover with each other. 
     Preferably, the second melting sheet is provided with a removable transparent base film on a side thereof opposite to the heated sheet. 
     Preferably, the heated sheet is formed with a through hole that penetrates therethrough in a direction from the first melting sheet to the second melting sheet and vice versa. 
     Preferably, the heated sheet has a thickness thinner than those of the first and second melting sheets. 
     In another embodiment, a method of manufacturing a thermal adhesive tape, which includes a heated sheet made of a conductor; a first melting sheet adhered to one face of the heated sheet; and a second melting sheet adhered to the other face of the heated sheet, and couples a case and a LCD cover of a portable terminal with each other, wherein the first and second melting sheets are compressed and heated by a heating roller toward the heated sheet on opposite sides of the heated sheet, respectively, to thereby be adhered to the heated sheet. 
     Preferably, the heated sheet is formed with a through hole that penetrates therethrough in a direction from the first melting sheet to the second melting sheet and vice versa, and the first and second melting sheets are adhered with each other through the through hole when the first and second melting sheets are compressed and heated toward the heated sheet. 
     The thermal adhesive tape for a portable terminal has advantages as follows. 
     It is possible to adhere adherends made of synthetic resin having a low thermal conductivity such as polycarbonate, acryl and ABS as the heated sheet, which is heated by a high frequency induction, is disposed between the first melting sheet and the second melting sheet, give an adhesive strength stronger than a general bonds as the adhesion is carried out by heat, and improve productivity as the adhesion is carried out in a short time. 
     As the base film made of a transparent material is attached on the second melting sheet, the location is easily seen when the thermal adhesive tape is mounted on the case and this facilitates assembly. 
     As the base film is removably attached on the second melting sheet, the base film can be easily removed upon the assembly and this improves the productivity. 
     As the through hole is formed in the heated sheet, the first melting sheet and the second melting sheet are coupled directly to each other and this improves the adhesive strength between the adherends coupled by the first melting sheet and the second melting sheet. 
     As the heated sheet has a thickness thinner than those of the first and second melting sheets, it is possible to reduce the heat transferred to the case and the LCD cover when the heated sheet is heated and to thereby prevent the case and the LCD cover from being deformed by the heat. 
     As the first melting sheet and the second melting sheet are disposed between the heating roller and adhered by compression and heating, the work is carried out continuously and speedily to improve the productivity, and the first melting sheet, the heated sheet and the second melting sheet are modularized to facilitate the work upon the adhesion of the case and the LCD cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural diagram of a conventional thermal adhesive tape. 
         FIG. 2  is structural diagram of a thermal adhesive tape in accordance with an embodiment of the present invention. 
         FIG. 3  is a view illustrating a manufacturing process of the thermal adhesive tape for a portable terminal in accordance with an embodiment of the present invention. 
         FIG. 4  is structural diagram of a case module for a portable terminal using the thermal adhesive tape in accordance with an embodiment of the present invention. 
         FIGS. 5 through 8  are views illustrating processes of assembling a case module for a portable terminal the thermal adhesive tape in accordance with an embodiment of the present invention. 
         FIG. 9  is structural diagram of a thermal adhesive tape in accordance with another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to accompanying drawings. 
       FIG. 2A  is a plan view of a thermal adhesive tape in accordance with an embodiment of the present invention,  FIG. 2B  is a sectional view taken along a line A-A of  FIG. 2A ,  FIG. 3  is a view illustrating a manufacturing process of the thermal adhesive tape for a portable terminal in accordance with an embodiment of the present invention,  FIG. 4A  is a plan view of a case module for a portable terminal using the thermal adhesive tape in accordance with an embodiment of the present invention, and  FIG. 4B  is a sectional view taken along a line B-B of  FIG. 4A . 
     As illustrated in  FIGS. 2 and 3 , a thermal adhesive tape in accordance with an embodiment of the present invention includes a heated sheet  200 , a first melting sheet  310 , a second melting sheet  320  and a base film  400 . 
     Also, as illustrated in  FIG. 4 , a case module for a portable terminal using the thermal adhesive tape in accordance with an embodiment of the present invention includes a case  110 , a LCD cover  120 , the heated sheet  200 , the first melting sheet  310 , and the second melting sheet  320 . 
     The case  110  is an element that forms an appearance of a display part of a portable terminal and is disposed on a front face of a LCD module. 
     Also, the case  110  is openly formed of a screen part  111  so that a screen of the LCD module is seen from the outside. 
     The screen part  111  is formed in a rectangular shape through the case in front and rear directions and has a width smaller than a width of the LCD cover  120 , which will be described later. 
     Further, the case  110  is formed of a mounting recess  112  in which the heated sheet  200 , the first melting sheet  310  and the second melting sheet  320  are inserted. 
     The mounting recess  112  has a rectangular shape, is communicated with the screen part  111  and is opened in a direction toward the front, i.e. a direction toward the LCD cover  120 . 
     Also, the mounting recess  112  has a depth greater than sum of the thicknesses of the heated sheet  200 , the first melting sheet  310  and the second melting sheet  320 , which will be described later. 
     The LCD cover  120  is formed in a shape of a thin plate and is made of a transparent material so that the screen of the LCD module mounted in an inside of the portable terminal is seen from the outside. 
     Also, the periphery of the LCD cover  120  has an opaque design of a border shape so that the rest components other than the LCD module are not seed from the outside and tidy appearance can be obtained. 
     Further, LCD cover  120  has a width greater than the width of the screen part  111  and smaller than the width of the mounting recess  112 . 
     This LCD cover  120  is disposed so as to face the case  100  and is inserted in the mounting recess  112  so as to seal the screen part  111 . 
     Meanwhile, the heated sheet  200  is disposed between the case  110  and the LCD cover  120 . 
     The heated sheet  200  is formed in a shape of a hollow rectangular and is made of aluminum or copper through which current flows well. 
     Of course, the heated sheet  200  can be formed of other conductor other than the aluminum or copper, but it is preferred to employ the aluminum or copper which has high thermal conductivity and electric conductivity and is easily worked. 
     Also, the heated sheet  200  has a thickness of about 7 to 14 μm, which is, as will be described later, smaller than the thicknesses of the first melting sheet  310  and the second melting sheet  320 . 
     The heated sheet  200  is adhered with its one face to the first melting sheet  310  and with the other face to the second melting sheet  320 . 
     The first melting sheet  310  and the second melting sheet  320  are formed in a hollow rectangular shape like the heated sheet  200 , and have a thickness of about 70 μm. 
     Also, the first melting sheet is thermally adhered with the case  110  and the second melting sheet  320  is thermally adhered with the LCD cover  120 . 
     As the heated sheet  200  has the thickness thinner than those of the first melting sheet  310  and the second melting sheet  320  as described above, it is possible to reduce the heat transferred to the case  110  and the LCD cover  120  when the heated sheet  200  is heated and to thereby prevent the case  110  and the LCD cover  120  from being deformed by the heat. 
     Also, the first melting sheet  310  and second melting sheet  320  are made of polyester composition. 
     The polyester is a generic term of a polymer compound having an ester group as a linker. 
     Also, all of the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  are formed in the same hollow rectangular shape and have an inner width greater than the width of the screen part  111  and an outer width smaller than the LCD cover  120 . 
     That is, the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  are formed so as to be disposed within a section in which the LCD cover  120  and the case  110  are overlapped with each other. 
     As the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  have the inner width greater than the width of the screen part  111  and the outer width smaller than the LCD cover  120  as described above, the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  are disposed only in the section where the LCD cover  120  and the case  110  are overlapped with each other, thereby capable of reducing waste and decreasing the manufacturing cost. 
     Also, the sum of the first melting sheet  310 , the heated sheet  200 , the second melting sheet  320  and the LCD cover  120  is smaller than the depth of the mounting recess  112 . 
     As the sum of the first melting sheet  310 , the heated sheet  200 , the second melting sheet  320  and the LCD cover  120  is smaller than the depth of the mounting recess  112  as described above, the LCD cover  120  is inserted so as not to projected out of the case  110  and is prevented from being separated from the case  110  by external force. 
     Also, the second melting sheet  320  is provided with the base film  400  on a side thereof opposite to the heated sheet  200 . 
     The base film  400  is formed in a thin rectangular shape and is made of a transparent material. 
     As the base film  400  is made of a transparent material, the location is easily seen when the first melting sheet  310  as described above, the heated sheet  200  and the second melting sheet  320  are mounted on the case and this facilitates assembly. 
     Also, the base film  400  is mounted removably on the second melting sheet  320 . 
     Specifically, the base film  400  is provided with a removable adhesive layer on the face thereof at the side of the second melting sheet  320 . 
     The removable adhesive is suitable to temporarily adhere the base film  400  to the second melting sheet  320  since it has excellent re-adhesive property and re-detachability. 
     As the base film  400  is mounted removably on the second melting sheet  320  as described above, the base film  400  can be easily removed upon the assembly and this improves the productivity. 
     Hereinafter, a process for manufacturing the thermal adhesive tape in accordance with an embodiment of the present invention having the structure as described above will be described. 
     As illustrated in  FIG. 3 , the first melting sheet  310  and the second melting sheet  320  are adhered to the heated sheet  200  by heat. 
     Specifically, the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  are sequentially stacked between two heating rollers  50   a  and  50   b.    
     At this time, the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  are wound on a bobbin in a state of a raw material, respectively. 
     The heating rollers  50   a  and  50   b  having a cylindrical shape are heated to about 100° C. and rotate at a speed of 5 m/min. 
     As these heating rollers  50   a  and  50   b  rotate in opposite directions, the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  are compressed and heated from the upper and lower sides. 
     At this time, the first melting sheet  310  and the second melting sheet  320  are slightly melted by the heat of the heating rollers  50   a  and  50   b  and adhered to the heated sheet  200 . 
     After that, the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  adhered to each other are wound again on another bobbin disposed in the transport direction. 
     As the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  are disposed between the heating rollers  50   a  and  50   b  and adhered to each other by compression and heating as described above, the work is carried out continuously and quickly and this improves the productivity. 
     After that, the base film  400  is stacked on the second melting sheet  320  and adhered to the second melting sheet  320  using a roller. 
     Finally, the first melting sheet  310 , the heated sheet  200  and the second melting sheet  320  except for the base film  400  are cut into a hollow rectangular shape to remove the unnecessary portions therein. 
     Hereinafter, a method of adhering a case and a LCD cover for a portable terminal using the thermal adhesive tape in accordance with an embodiment of the present invention having the structure as described above will be described. 
       FIGS. 5 through 8  are views illustrating processes of assembling a case module for a portable terminal the thermal adhesive tape in accordance with an embodiment of the present invention. 
     As illustrated in  FIG. 5 , the adhering method using the thermal adhesive tape in accordance with an embodiment of the present invention is carried out in a sequence of interim-adhesion step (S 10 ), base film release step (S 20 ) and main-adhesion step (S 30 ). 
       FIG. 6  illustrates the interim-adhesion step (S 10 ),  FIG. 7  illustrates the base film release step (S 20 ) and  FIG. 8  illustrates the main-adhesion step (S 30 ). 
     As illustrated in  FIG. 6 , in the interim-adhesion step (S 10 ), the first melting sheet  310  is adhered to the case  110 . 
     Specifically, the first melting sheet  310  is inserted in the mounting recess  112  together with the heated sheet  200 , the second melting sheet  320  and the base film  400 , and the first melting sheet  310  is disposed to face one face of the case  110 . 
     After that, the base film  400  is compressed and heated toward the case  110  with a heated mold  60 . 
     Of course, a jig or the like is disposed below the case  110  so that the case is not bent. 
     The mold  60  has a rectangular shape, of which width is smaller than or equal to the width of the mounting recess  112  and greater than or equal to the width of the first melting sheet  310 . 
     This mold  60  is heated to about 60° C., which is lower than the melting points of the base film  400 , the first melting sheet  310  and the second melting sheet  320 . 
     Also, the melting point of the base film  400  is higher than those of the first melting sheet  310  and the second melting sheet  320 . 
     That is, the temperature of the mold  60  is lower than the melting points of the base film  400  and the first melting sheet  310 , but is close to the melting point of the first melting sheet  310  rather than the melting point of the base film  400 . 
     Therefore, when compressing and heating the base film  400  with the mold  60 , the base film  400  is not melted but the first melting sheet  310  is slightly melted by the heat of the mold transferred through the base film  400  and coupled with the case  110 . 
     Of course, the adhesive strength of the first melting sheet  310  with the case  110  is not large since it has not been completely melted. 
     As the base film  400  has a melting point higher than the melting point of the first melting sheet  310  and the temperature of the mold  60  is set to be lower than the melting points of the base film  400  and the first melting sheet  310  in the interim-adhesion step (S 10 ) as described above, the temperature of the mold  60  is closer to the melting point of the first melting sheet  310  than to the melting point of the base film  400  to thereby minimize deformation of the base film  400 . 
     In the base film release step (S 20 ) after the interim-adhesion step (S 10 ) is ended, the base film  400  is removed from the second melting sheet  320  as illustrated in  FIG. 7 . 
     The base film  400  is easily detached since it is attached to the melting sheet so as to be detached well from the melting sheet. 
     As the base film  400  is mounted removably on the second melting sheet  320  as described above, the base film  400  can be easily removed upon the assembly and this improves the productivity. 
     After that, in the main-adhesion step (S 30 ) as illustrated in  FIG. 8 , the LCD cover  120  is adhered to one face of the second melting sheet  320  from which the base film  400  is removed. 
     Specifically, the LCD cover  120  is inserted in the mounting recess  112  so that it is in contact with the second melting sheet  320 , and the LCD cover  120  is pushed toward the case  110  by a press. 
     Of course, a jig or the like is disposed below the case  110  so that the case is not bent. 
     Also, the press  90  is not heated unlike the mold  60  but remains at room temperature. 
     Further, a coil  70  through which current flows is disposed outside the heated sheet  200 . 
     The coil  70  has thick diameter and is formed in a rectangular shape around the heated sheet  200 . 
     This coil  70  is connected with a high frequency induction heater  80 , and the high frequency induction heater  80  applies an alternate current in a high frequency range to the coil  70 . 
     An output power of the high frequency induction heater  80  is 10 to 15 kw, and applies current to the coil  70  for 3 to 15 seconds. 
     When an alternate current is applied to the coil  70 , a magnetic field is formed in an internal space surrounded by the coil  70  and current flows through the heated sheet  200  by the principle of electromagnetic induction. 
     That is, alternate magnetic flux is generated while the alternate current flows through the coil  70 , and to thereby make an induced current flowing through the heated sheet  200 . 
     As the induced current flows through the heated sheet  200 , Joule&#39;s heat is generated by an eddy current loss. 
     At this time, the heated sheet  200  is heated to 120 to 150° C. 
     As the coil  70  is disposed outside the heated sheet  200  and a high frequency alternate current is applied to the coil  770  in the main-adhesion step (S 30 ) as described above, current flows in the inside of the heated sheet  200  by the principle of electromagnetic induction and the heated sheet  200  is heated itself without direct power apply thereto. 
     Then, by this heat, the first melting sheet  210  and the second melting sheet  320  are melted, and they are hardened to thereby couple the case  110  and the LCD cover  120  with each other when a predetermined time is elapsed with the LCD cover  120  being pressed on the case  110  after the removal of the coil  70 . 
     That is, the first melting sheet  310  is melted to couple the heated sheet  200  and the case  110 , and the second melting sheet  320  is melted to couple the heated sheet  200  and the LCD cover  120 . 
     At this time, the heated temperature of the heated sheet  200  is lower than the melting points of the case  110  and the LCD cover  120  and higher than the melting points of the first melting sheet  310  and the second melting sheet  320 . 
     As the heated temperature of the heated sheet  200  is lower than the melting points of the case  110  and the LCD cover  120  and higher than the melting points of the first melting sheet  310  and the second melting sheet  320  as described above, it is possible to minimize deformation of the case  110  and the LCD cover  120  upon the heating of the heated sheet  200 . 
     It is possible to adhere adherends made of synthetic resin having a low thermal conductivity such as polycarbonate, acryl and ABS as the heated sheet  200 , which is heated by a high frequency induction, is disposed between the first melting sheet  310  and the second melting sheet  320  to couple the case  100  and the LCD cover  120 , give an adhesive strength stronger than a general bonds as the adhesion is carried out by heat, and improve productivity as the adhesion is carried out in a short time. 
     If necessary, the heated sheet  250  may be formed of a through hole  251  that penetrates therethrough in a direction from the first melting sheet  310  to the second melting sheet  320  and vice versa. 
       FIG. 9  is structural diagram of a thermal adhesive tape in accordance with another embodiment of the present invention. 
     As illustrated in  FIG. 9 , the through hole  251  having a cylindrical shaped is formed in plural in the heated sheet  250 . 
     The through hole  251  makes the first melting sheet  310  and the second melting sheet  320  adhered with each other therethrough upon the manufacture of the thermal adhesive tape or in the main-adhesion step (S 30 ). 
     The first melting sheet  310  and the second melting sheet  320  are made of a polyester composition, and it is possible to show stronger adhesive strength when the first melting sheet  310  and the second melting sheet  320  are adhered with each other rather than when they are adhered to the heated sheet  250  made of aluminum or copper. 
     As the through hole  251  is formed in the heated sheet  250  as described above, the first melting sheet  310  and the second melting sheet  320  are coupled directly to each other and this improves the adhesive strength between the adherends coupled by the first melting sheet  310  and the second melting sheet  320 . 
     While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.