Patent Publication Number: US-2005123708-A1

Title: [easily tearable film and method for preparing the same]

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the priority benefit of Taiwan application serial no. 92134288, filed Dec. 5, 2003.  
     BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The present invention relates to an easily tearable film and a method for preparing the same. More particularly, the present invention relates to an easily tearable film made from a unidirectionally tearable film, such as, a uniaxially oriented film, and a method for preparing the same. The easily tearable film can be easily torn in a direction different from the tearing direction of the unidirectionally tearable film.  
      2. Description of the Related Art  
      A unidirectionally tearable film is a film having a single tearing direction, which features that the force needed to tear the film in the tearing direction is much smaller than the force needed to tear the film in any other direction. Such a unidirectionally tearable film is applicable to various industries, and can be used as, for example, a packing material of electronic products or foods, or stationery supplies.  
      However, since a unidirectionally tearable film has only one tearing direction, its application is limited. For example, a unidirectionally tearable film can be used to prepare a “Post-it” product, which has an advantage that a piece of any required size can be easily torn off from it. Nevertheless, since the unidirectionally tearable film has only one tearing direction, the dimensional variation is restricted to only one direction. Therefore, the use of such a Post-it product is not so flexible.  
     SUMMARY OF INVENTION  
      In view of the foregoing, this invention provides an easily tearable film that can be easily torn in a direction different from the tearing direction of the unidirectionally tearable film, so as to promote applications of unidirectionally tearable films in various industries.  
      This invention also provides a method for preparing an easily tearable film that can be easily torn in more than one directions.  
      The easily tearable film of this invention includes a unidirectionally tearable film with multiple cutting lines thereon. The unidirectionally tearable film has a tearing direction. Each cutting line has a first end point and a second end point, and has a joining point with an imaginary straight line parallel to the tearing direction that passes the first end point of the next cutting line.  
      The above unidirectionally tearable film can be a uniaxially oriented film, a synthetic paper sheet or a plant fiber film.  
      According to a preferred embodiment of this invention, each cutting line on the easily tearable film can be a straight line or a curved line, while several cutting lines can be arranged along a straight line, a curved line or other type of specially designed line that will result in a desired edge shape directly after the film is torn apart along the cutting lines. In addition, the distance between two adjacent cutting lines and the shape of each cutting line both can be uniform or variable.  
      In the method of preparing an easily tearable film of this invention, a unidirectionally tearable film having a tearing direction is provided. Multiple cutting lines are then formed on the unidirectionally tearable film. Each cutting line has a first end point and a second end point, and has a joining point with an imaginary straight line parallel to the tearing direction that passes the first end point of the next cutting line.  
      According to a preferred embodiment of this invention, the cutting lines can be formed on the unidirectionally tearable film with a rolling method, a pressing method, an etching method, a water knife, an air knife, scissors, dispenser or laser.  
      Since the cutting lines are formed on the easily tearable film with the aforementioned arrangement, the easily tearable film of this invention can be easily torn in a direction different from the tearing direction of the unidirectionally tearable film. Therefore, the unidirectionally tearable film that was originally tearable in only one direction can be used more flexibly to meet various requirements.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.  
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
       FIG. 1  schematically illustrates a top view of an easily tearable film according to a preferred embodiment of this invention.  
       FIG. 2  schematically illustrates a top view of an easily tearable film according to another preferred embodiment of this invention.  
       FIG. 3  schematically illustrates a top view of an easily tearable film according to yet another preferred embodiment of this invention, wherein the arrangement of the cutting lines is changed.  
       FIG. 4  schematically illustrates a top view of an easily tearable film according to still another preferred embodiment of this invention, wherein the shape of each cutting line is changed.  
       FIG. 5  shows a flow chart of preparing an easily tearable film according to a preferred embodiment of this invention.  
    
    
     DETAILED DESCRIPTION  
       FIG. 1  schematically illustrates a top view of an easily tearable film according to a preferred embodiment of this invention. The easily tearable film  100  is constituted of a unidirectionally tearable film  104  with multiple cutting lines  102  formed thereon, wherein the unidirectionally tearable film  104  is, for example, a uniaxially oriented film. Each cutting line  102  has a first end point  101   a  and a second end point  101   b , and the first/second end point  101   a/b  is adjacent to the second/first end point  101   b/a  of a neighboring cutting line  102 . The unidirectionally tearable film  104  has a tearing direction  106 , and the force needed to tear the film  104  in the tearing direction  106  is much smaller than the force needed to tear the film  104  in any other direction.  
      On the easily tearable film  100 , each cutting line  102  has a joining point with an imaginary straight line  108  parallel to the tearing direction  106  that passes the first end point  101   a  of the next cutting line  102 . In this embodiment, the joining point is exactly the second end point  101   b  of the cutting line  102 . Therefore, when the easily tearable film  100  is being torn in a direction different from the tearing direction  106 , the unidirectionally tearable film  104  is split from the second end point  101   b  of a cutting line  102  to the first end point  101   a  of the next cutting line  102  along the corresponding straight line  108 . By repeating the splitting process between two cutting lines  102 , it is easily to tear the unidirectionally tearable film  104  in a direction different from the tearing direction  106 .  
      The material of the unidirectionally tearable film  104  may be a uniaxially oriented polymer, and the polymer is selected from the group consisting of nylon, polyvinyl alcohol (PVA), polyester, polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polystyrene (PS), polysulfone, polyimide (PI) and polyvinyl chloride (PVC).  
      The unidirectionally tearable film  104  may also be made from synthetic paper, which is selected from the group consisting of PP synthetic paper, polyester synthetic paper and PE synthetic paper.  
      In addition, the unidirectionally tearable film  104  may be a plant fiber film.  
      Moreover, the easily tearable film  100  may further include an adhesive layer (not shown) on the surface of the unidirectionally tearable film  104 , so that the easily tearable film  100  can stick to an object after it is torn. The adhesive layer can be a solvent sensitive adhesive layer, a pressure sensitive adhesive layer or a heat sensitive adhesive layer. It is also feasible to print various patterns on the easily tearable film  100 , so that the easily tearable film  100  can be used as a material for advertisement purpose, a personal token or a personalized product. Moreover, the unidirectionally tearable film  104  may be a uniaxially oriented film having a thickness smaller than or equal to 0.25 mm, or a uniaxially oriented sheet that has a thickness exceeding 0.25 mm.  
      In another embodiment, the joining point of a cutting line with an imaginary straight line parallel to the tearing direction that passes the first end point of the next cutting line is not the second end point of the cutting line. Referring to  FIG. 2 , the easily tearable film  200  is constituted of a unidirectionally tearable film  104  and has a tearing direction  106  as above, while the imaginary straight lines  108  parallel to the tearing direction  106  are also shown. However, the joining point of a cutting line  202  with an imaginary straight line  108  parallel to the tearing direction  106  that passes the first end point  201   a  of the next cutting line  102  is not the second end point  201   b  of the cutting line  202 . Accordingly, when the easily tearable film  200  is being torn in a direction different from the tearing direction  106 , the unidirectionally tearable film  104  is split from the second end point  201   b  of a cutting line  202  to the next cutting line  202  along a straight line  208 , which does not pass the first end point  201   a  of the next cutting line  202 .  
      Moreover, there can be some alternatives in the arrangement of the cutting lines on the easily tearable film of this invention. Referring to  FIG. 3 , the easily tearable film  300  is constituted of a unidirectionally tearable film  104  and has a tearing direction  106  as above, while the imaginary straight lines  108  parallel to the tearing direction  106  are also shown. However, the cutting lines  302  are arranged along a curved line (in the region  310 ) or a zigzag line (in the region  312 ), rather than a straight line as shown in  FIG. 1 . Except the above examples, the cutting lines can also be arranged along other specially designed line that will result in a required edge shape directly after the film is torn apart.  
      Furthermore, the shape of the cutting lines on the easily tearable film of this invention can also be changed. Referring to  FIG. 4 , the easily tearable film  400  is constituted of a unidirectionally tearable film  104  and has a tearing direction  106  as above, while the imaginary straight lines  108  parallel to the tearing direction  106  are also shown. However, the cutting lines  402   a  and  402   b  are curved lines, rather than straight lines ( 102 ) as shown in  FIG. 1 . Moreover, the shape of each cutting line on the same easily tearable film  400  can be uniform or variable as required.  
      On the other hand, a flow chart of preparing an easily tearable film according to this invention is shown in  FIG. 5 . In step  500 , a unidirectionally tearable film having a tearing direction is provided, wherein the examples of the material of the unidirectionally tearable film are described above. The step  500  may be followed by other steps, such as a step of forming an adhesive layer on the surface of the unidirectionally tearable film. When an adhesive layer is formed on the easily tearable film, it can stick to an object after being torn apart.  
      In the subsequent step  510 , multiple cutting lines are formed on the unidirectionally tearable film. Each cutting line has a first end point and a second end point, and has a joining point with an imaginary straight line parallel to the tearing direction that passes the first end point of the next cutting line. The joining point can be the second end point of the cutting line ( FIG. 1 ), or a point between the first end point and the second end point ( FIG. 2 ). The cutting lines can be formed on the unidirectionally tearable film with a rolling method, a pressing method, an etching method, a water knife, an air knife, scissors, dispenser or laser.  
      As mentioned above, since the cutting lines having the aforementioned arrangement are formed on the easily tearable film, the film can be easily torn in a direction different from the tearing direction of the unidirectionally tearable film. Therefore, the unidirectionally tearable film that was originally tearable in only one direction can be used more flexibly to meet various requirements.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.