LEVER TYPE EASY PULL CROWN CAP

Information

  • Patent Application
  • 20100096355
  • Publication Number
    20100096355
  • Date Filed
    August 31, 2009
    14 years ago
  • Date Published
    April 22, 2010
    14 years ago
Abstract
A lever type easy pull crown cap. The lever type easy pull crown cap has a body with a boss extending from a central portion that transitions into a rim with an edge. A pull-ring is fastened to the crown body without piercing the body. An inner surface of the body includes a score line extending from the edge along the rim and across the central portion towards the boss and returns outward across the central portion after travelling around the boss to terminate in a tail segment. The tail segment extends along a portion of the rim without reaching the edge. Pulling upward on the pull-ring fractures the body along the score line and separates a tear strip portion from the body, breaking the seal between the lever type easy pull crown cap and the bottle.
Description
CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. 119(a) to Chinese patent application no. 200820175601.6, which was filed Oct. 21, 2008 with the State Intellectual Property Office of the People's Republic of China.


BACKGROUND OF THE TECHNOLOGY

Bottle caps are used to seal the opening of a bottle. A bottle cap is typically a small, circular piece of material, and is designed to be pressed over and around the opening of a bottle to grab a chrysanthemum edge on the bottleneck. FIG. 1 illustrates a lever-type bottle cap 10 that includes a crown body 11, pull tab ring 12, pull tab 13 and lever 15. The pull tab 13 is fastened directly to the crown body 11 by a rivet 14 that pierces the crown body 11. Riveting the pull tab 13 to the crown 11 may negatively affect the ability of the cap 10 to properly form a seal with the bottle. Any loosening or movement of the rivet 14 with respect to the pull-ring 12 and the crown body 11 may break the seal and lead to contamination of the liquid within the bottle, potentially causing a heath risk.


The pull tab ring 12 is seated on the top surface 19 of the crown body 11, which is often a flat surface. Because the pull tab ring 12 is not positioned or held in place on the top surface 19 in any manner, the pull tab ring 12 may rotate and become damaged. The pull tab ring 12 is usually embossed on the top surface 19 of the crown body 11, increasing the overall height of a bottle cap and often preventing the cap 10 shown in FIG. 1 from being used in a conventional bottling process.


The inner surface of the cap body 11 (not shown) includes two score or cutting lines 16a and 16b (shown as hidden lines in FIG. 1), and typically form an angle θ of approximately 20-70 degrees between the lines. The relatively large angle θ makes it difficult to open the bottle (a pulling force of about 8 kg is necessary), and tends to cause a jet burst of the pressurized liquid inside the bottle upon opening the cap 10 (if the liquid is carbonated).


The cutting lines 16a and 16b do not extend all the way to the rim 17 of crown body 11, but instead terminate at or near the pull tab ring 12. The cutting lines 16a and 16b also maintain substantially the same depth profile into the inner surface of the crown body 11 along the length of the cut line 16a and 16b.


After a bottle is filled with a liquid, the bottle cap 10 is crimped around a circular bottle opening (not shown) to maintain a pressure within the bottle and prevent the liquid from leaking out of the bottle. The bottle cap 10 shown in FIG. 1 is removed from a bottle by pulling up on the pull tab ring 12, which causes the lever 15 to remove a portion of the crown body 11 along the cut lines 16a and 16b. By doing so, the seal between the crown body 11 and the bottle opening is broken and the cap 10 may be removed from the bottle opening.





BRIEF DESCRIPTION OF THE DRAWINGS


FIG. 1 depicts a plan view of a lever-type bottle cap, according to the prior art.



FIG. 2 depicts a plan view of an embodiment of a lever type easy pull crown cap.



FIG. 2A depicts a magnified view of section 2A shown in FIG. 2.



FIG. 3 depicts a plan view of the lever type easy pull crown cap body shown in FIG. 2 with the pull-ring removed.



FIG. 4A depicts a plan view of the pull-ring assembly shown in FIG. 2.



FIG. 4B depicts an isometric view of the pull-ring assembly shown in FIG. 4A.



FIG. 4C depicts a side cross-sectional view of the pull-ring shown in FIG. 4A.



FIG. 5 depicts a side cross-sectional view of the lever type easy pull crown cap shown in FIG. 2.



FIG. 6 depicts the side cross-sectional view of the lever type easy pull crown cap shown in FIG. 5 secured to a bottle opening.



FIG. 7 depicts an isometric view of the lever type easy pull crown cap shown in FIG. 2 with a tear strip portion partially separated from the crown cap body.





DETAILED DESCRIPTION

The technology disclosed herein pertains to a lever type easy pull crown cap that may be secured to a bottle opening to prevent a liquid (or any other material) within the bottle from leaking out of the bottle, perishing, or losing carbonation (if the liquid is carbonated). The lever type easy pull crown cap includes a pull-ring that, when pulled upwards and away from the top surface of the crown cap body, fractures the crown cap body along a score line. A tear strip portion of the lever type easy pull crown cap is separated from the body, which breaks the seal formed between the lever type easy pull cap crown body and the bottle opening.



FIG. 2 illustrates a lever type easy pull crown cap assembly 100 (also referred to herein as a “bottle cap”) that includes crown body 102 and pull-ring 104. Crown body 102 includes central portion 106 (also referred to as the “top surface”) that transitions outward into rim 108 with outer edge 110. Central portion 106 of crown body 102 forms boss 112 that extends upward from cap body 102. FIG. 2 illustrates that boss 112 is located substantially in the center of crown body 102 (from the plan view shown in FIG. 2) and has a diameter d1. By way of example only, diameter d1 of boss 112 is between 2-5 mm. It is within the scope of the technology described herein for diameter d1 of boss 112 to vary. Rim 108 is configured to crimp over the edge of a bottle opening (not shown) and form a seal between the inner surface of crown body 102 and the chrysanthemum edge on the bottleneck.



FIG. 2 illustrates that an inner surface 105 of crown body 102 and rim 108 are scored with a score line 114 (shown in hidden lines). For the sole purpose of describing score line 114 herein, score line 114 will be described in reference to four sections 114a-114d. A first section 114a of score line 114 extends from edge 110 of cap body 102, upward towards central portion 106 along rim 108, and along central portion 106 of crown body 102 towards boss 112. The second section 114b of score line 114 wraps around boss 112 (from the plan view perspective shown in FIG. 2) in a semi-circular path. The third section 114c returns back along central portion 106 of crown body 102 towards rim 108. The tail section of score line 114, section 114d, continues to travel downward along rim 108 in a semi-circular fashion. In one embodiment, tail section 114d of score line 114 does not extend to edge 110. Instead, tail section 114d remains a distance D1 from edge 110 at its closest point to edge 110. The distance D1 may vary. In some embodiments, the range of distance D1 is 2-3 mm. In one embodiment, the distance D1 is 2.3 mm. It is within the scope of the technology described herein to allow a portion of tail section 114d of score line 114 to extend completely to edge 110 of crown body 102. Score line 114 may have any depth in inner surface 105 of crown body 102, and is not required to have a uniform depth for each of sections 114a-114d described above.


Section 114a of score line 114, at edge 110 of cap body 102, forms two arcs 114e and 114f (best shown in FIG. 2A), each having a radius R0. By way of example only, radius R0 ranges between 0.5 mm to 3.0 mm. As will be described in more detail later, pulling up on pull-ring 104 fractures crown body 102 along score line 114 and creates a tear strip portion 121 that completely separates from crown body 102 along sections 114a-114c of score line 114 yet has a segment 125 that remains connected to crown body 102. Arcs 114e and 114f extend to edge 110 to prevent creating a sharp edge upon separating tear strip portion 121 from cap body 102 along section 114a of score line 114, which improves the safety features of the cap 100. The range of radius R0 is exemplary, and is not intended to limit the scope of the technology described herein. Tail section 114d of score line 114 has a radius R1, which by way of example only, ranges between 1 mm-5 mm. In some embodiments, radius R1 is 3 mm. The range of radius R1 is exemplary, and is not intended to limit the scope of the technology described herein.



FIG. 2 illustrates that first and third sections 114a, 114c of score line 114 forms an angle Φ between them. By way of example only, angle Φ is preferably between 1-20 degrees. The range of angle Φ is exemplary only, and is not intended to limit the scope of the technology described herein. An angle Φ greater than 20 degrees likely requires a larger force to open crown body 102 along score line 114. In addition, a larger angle Φ may result in a jet burst of the pressurized content (such as beer, gas-contained beverage, etc.) contained within the bottle when opening crown cap 100, possibly creating a dangerous situation for a user opening crown cap 100. An angle Φ between 1-20 degrees results in a required pulling force of approximately 2 kg, and allows tear strip section 121 to smoothly separate from the crown body 102 along score line 114. In some embodiments, angle Φ is 9 degrees. A relatively small pull force such as this is preferred so that most individuals will have sufficient strength to open a bottle using the crown cap 100 described herein. Crown body 102 may be manufactured from any number of materials. In some embodiments, crown body 102 is a softer tinplate material that requires less force to open and tear while still providing sufficient sealing of the contents within the bottle.


In some embodiments, tail section 114d may extend to edge 110 of the rim 108. In this case, score line 114 forms a complete opening arc extending from edge to edge or cap 100. Pulling pull-ring 104 will fracture crown body 102 along score line 114 and completely separate tear strip portion 121 from crown body 102. An individual opening the bottle will have two separate pieces to dispose of: tear strip portion 121 and the crown body 102 remaining on the bottle opening.



FIG. 3 illustrates crown body 102 without pull-ring 104 secured to it, which allows two protrusions 150 to be visible. Protrusions 150 may be spaced apart by any distance less than the width W of lever tab 118, and are not limited to the exact location shown in FIGS. 2-3. The bottom surface of lever tab 118 rests on protrusions 150 when pull-ring 104 is keyed to boss 112. Protrusions 150 may contact bottom surface 119 of lever tab 118 more towards distal end 122 of lever tab 118 or closer towards grasping portion 116 of pull-ring 104. It is also within the scope of the technology described herein for the crown body 102 to only have a single protrusion 150. When the pull-ring 104 is secured to the crown body 102 and the lever tab 118 is resting on protrusions 150 so that pull-ring 104 is stabilized with respect to the crown body 102. In particular, the protrusions 150 prevent the pull-ring 104 from rotating in relation to central portion 106 of crown body 102.



FIGS. 4A-4C illustrate additional detail of pull-ring 104. FIG. 4A illustrates that pull-ring 104, which includes a grasping portion 116 and a lever tab 118, is formed from a single piece of material. Pull-ring 104 may be manufactured by any manufacturing technique know in the art such as, but not limited to, stamping. Other methods of manufacture are within the scope of the technology described herein.


Pull-ring 104 includes grasping portion 116 integrally formed with lever tab 118. Lever tab 118 extends from grasping portion 116 to a distal end 122. The distal end 122 of lever tab 118 includes a fastening hole 120. Distal end 122 of lever tab 118 is nested on, or keyed to, boss 112 when pull-ring 104 is fastened to crown body 102.


Grasping portion 116 is circular in shape to conform to the shape of central portion 106 of crown body 102. Grasping portion 116 of pull-ring 104 is formed by furling two sections 160, 162 of the material underneath, creating a bottom surface of grasping portion 116 consisting of sections 160, 162. FIGS. 4A-4C illustrate that sections 160, 162 abut against each other and form a substantially smooth outer edge 164 and inner edge 166. As will be discussed in more detail later, an individual opens crown cap 100 by initially grasping outer edge 164 or inner edge 166 of pull-ring 104 with their fingers and pulls upward away from crown body 102 (see, for example, FIG. 7).


The smooth edges 164, 166 of grasping portion 116 helps to minimize possible injury to the individual pulling on pull-ring 104 by ensuring that edges 164, 166 of grasping portion 116 do not contain any sharp edges or burs. By having sections 160, 162 abut against each other, liquid is prevented (or minimized) from entering into cavity 170 of grasping portion 116 of pull-ring 104 (e.g., when the bottle stores a liquid), which prevents or minimizes grasping portion 116 of pull-ring 104 from rusting.



FIG. 4B illustrates that lever tab 118 is also formed by furling sections 168 underneath against bottom surface 119 of lever tab 118. Furling sections 168 underneath increase the stiffness of lever tab 118 without having to increase the thickness of lever tab 118. This reduces the total amount of material required to form lever tab 118. Minimizing the thickness of lever tab 118 also reduces the pulling force required by an individual to successfully pull grasping portion 116 of pull-ring 104 upward to begin the process of separating tear strip portion 121 from crown body 102 along score line 114.



FIG. 4B also illustrates that the portion of lever tab 118 that transitions to grasping portion 116 includes a pair of notches 124. The two concave arc-shaped notches 124 are formed on both edges of lever tab 118 at the transition point to grasping portion 116 of pull-ring 104. Notches 124 effectively narrow the width W of lever tab 118 at the point of transition to grasping portion 116. The narrow section of lever tab 118 creates the weakest folding point of lever tab 118 and encourages lever tab 118 to fold along folding line 172 when grasping portion 116 of pull-ring 104 is lifted upwards. Folding line 172 creates a lever fulcrum during opening of crown cap 100 such that lever tab 118 can efficiently act to reduce the pulling force required to fracture crown body 102 along score line 114.



FIG. 4C is a cross-section of pull-ring 104 shown in FIG. 4B along line 4C, and illustrates that distal end 122 of lever tab 118 has a bowl-like shape with a sloped wall 176. Bottom surface 178 of distal end 122 has opening 120 therein. As will be described in more detail below, diameter d2 of opening 120 is substantially similar to diameter d3 of the portion of boss 112 lever tab 118 is keyed to. Bottom surface 178 of distal end 122 of lever tab 118 extends below the surfaces of sections 160, 162 (from the FIG. 4C perspective).



FIG. 5 is a cross-section of crown cap 100 shown in FIG. 2 along line 5, and illustrates that score line 114 (shown in bold) is along inner surface 105 of crown body 102. Again, section 114a extends to edge 110 of crown body 102 and section 114d does not. In some embodiments, score line 114 is covered by a Polyvinyl chloride (PVC) or Polyethylene (PE) lining to prevent score line 114 from being exposed to the atmosphere or the liquid, food, product, etc. stored inside of the bottle. Other materials may be used to cover score line 114, as long as the material complies with requirements set forth by the Food and Drug Administration. By scoring only inner surface 105 of crown body 102, the exterior or visible surface of crown body 102 (when cap 100 is secured to a bottle opening) is not compromised by any scoring (e.g., any design on the exterior surface of crown body 102 is not disturbed).



FIG. 5 illustrates that central portion 106 of crown body 102 includes a first recessed surface 140 and a second recessed surface 142. Surfaces 160, 162 of grasping portion 116 of pull-ring 104 are seated on first recessed surface 140 when pull-ring 104 is keyed to boss 112. Bottom surface 178 of distal end 122 is seated on second recessed surface 152 when pull-ring 104 is keyed to boss 112. Grasping portion 116 of pull-ring 104 protrudes slightly above top surface 106 of cap body 102 by a height H2. Height H2 may vary. In one embodiment, height H2 is 0.2 mm. First recessed surface 140 ensures that pull-ring 104 is slightly recessed into crown body 102, and hence allows crown cap 100 to pass through a conventional bottling device without any modification to the bottling device. First recessed surface 140 also minimizes height H1 of cap 100 and allows crown cap 100 to conform to existing height dimensions required by conventional bottling lines. Height H1 may vary between 6.6 mm-6.9 mm.


Second recessed surface 142 provides several features of cap body 102. The lower height of second recessed surface 142 (from the FIG. 5 perspective) provides room for lever tab 118 to key to shaft 180 of boss 112. In some embodiments, the height difference between second recessed surface 142 and first recessed surface 140 is slightly greater than the height difference between bottom surface 178 of lever tab 118 and surfaces 160, 162 of grasping portion 116. This way grasping portion 116 of pull-ring 114 is in tension on crown body 102 while pull-ring 114 is keyed to boss 112. Second recessed surface 142 also minimizes the overall height of the cap 100 and allows the cap 100 to pass through an existing bottling line. Second recessed surface 142 also increases the strength of cap body 102 to ensure that it meets conventional pressure-resistant requirements.



FIG. 5 also illustrates that boss 112 is formed from the same piece of material as crown body 102. Pull-ring 104 is fastened to crown body 102 by keying distal end 122 of lever tab 118 onto boss 112. No separate rivet is required to fasten pull-ring 104 to crown body 102. Pull-ring 104 is fastened to body 102 without piercing body 102, which better ensures that the content within the bottle is safe and hygienic (e.g., eliminates a possible leak).


Boss 112 includes a shaft 180 with a larger diameter cap 182, forming lip 184. As described above, opening 120 in distal end 122 of lever tab 118 has a diameter substantially the same as the diameter of shaft 180 of boss 112. By way of example only, lever tab 118 is secured in place on boss 112 by press fitting opening 120 over boss 112. The larger diameter of cap 182 prevents pull-ring 104 from sliding off boss 112 due the lip 184.



FIG. 6 is the cross-section of crown cap 100 shown in FIG. 5 secured to a bottle opening 2. When crown cap 100 is secured to bottle opening 2, the pressurized air within the bottle (assuming that the liquid in the bottle is carbonated) attempts to escape out of the bottle and presses against central portion 106 of crown body 102. The pressurized air causes first and second recessed surfaces 140, 142 to “pop-up” until first recessed surface 140 becomes substantially flush with the top surface of crown body 102 such that the top surface of crown body 102 appears to have a single recessed surface 142. Raising first recessed surface 140 effectively pushes pull-ring 104 upward (from the perspective of FIG. 6) such that grasping portion 116 of pull-ring 104 is no longer partially below the top surface of pull-ring 104 and is easier to grasp.


Raising first recessed surface 140 when the crown cap 100 is crimped on the bottle opening 2 substantially eliminates lip 190. Grasping portion 116 of pull-ring 104 is no longer recessed beneath the top surface of crown body 102. Grasping portion 116 of pull-ring 104 is seated on the top surface of crown body 102, which enables an individual to grasp and pull up on grasping portion 116 of pull-ring 104 and open crown cap 100. For example, suppose an individual pulls up on grasping portion 116 of pull-ring 104 by placing their fingers under outer edge 164 of grasping portion 116. Raising first recessed surface 140 to the position shown in FIG. 6 makes it easier to access outer edge 164 get fingers underneath.



FIG. 7 illustrates that, when it is desired to open a bottle sealed by crown cap 100, an individual may insert a finger (or fingers) or fingernail beneath grasping portion 116 of pull-ring 104 and lift grasping portion 116 upward. An upward pull on grasping portion 116, generally away from crown body 102, will result in upward movement of pull-ring 104 and cause lever tab 118 to fold along fold line 172. Further pulling upward on pull-ring 104 will cause lever tab 118 to pull boss 112 upward, causing crown body 102 to initially fracture along section 114b of score line 114. Continued pulling upward of pull-ring 104 towards edge 110 of rim 108 results in the tearing of crown body 102 along sections 114a and 114c of score line 114, creating tear strip portion 121. Tear strip portion 121 is generally defined as the section of crown body 102 located within score line 114 that separates from body 102. When tear strip portion 121 reaches score lines 114e and 114f, tear strip portion 121 completely separates from crown body 102 and breaks open cap 100. When tear strip portion 121 reaches tail segment 114d, further pulling on pull-ring 104 will follow along curved tail segment 114d of score line 114. This segment 125 of tear strip portion 121 does not completely separate from crown body 102 as section 114d of score line 114 does not extend to edge 110. Continued pulling of pull-ring 104 will remove cap 100 from the bottle opening.



FIG. 7 illustrates that segment 125 of tear strip portion 121 remains an integrated piece of crown body 102 after crown cap 100 has been opened. This is because tail section 114d of score line 114 does not extend to edge 110 of rim 108. Keeping tear strip portion 121 together with cap body 102 upon opening crown cap 100 makes it easier for an individual to dispose of crown cap 100 because crown cap 100 is removed form the bottle opening as a single piece. Keeping pull-ring 104 together with cap body 102 upon opening crown cap 100 is also more convenient for recycling of cap assembly 100. As described above, in some embodiments, tail section 114d of score line 114 may extend to edge 110. In this case, tear strip portion 121 completely separates from crown body 102 upon opening crown cap 100. By continuing to pull pull-ring 104 as shown in FIG. 7, crown cap 100 is eventually lifted off the bottle opening.


The crown cap described herein is not limited to use with a bottle. The crown cap 100 described herein may also seal other types of containers such as, but not limited to, food containers, consumer packaging, and the like. The crown cap 100 is also not limited for use with a bottle, container, etc. manufactured from any specific material. The crown cap 100 may be used to secure bottles, containers, etc. that are manufactured from a number of materials such as, but not limited to, metal, plastic, glass, and the like.


The foregoing detailed description of the technology has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the technology to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the technology and its practical application to thereby enable others skilled in the art to best utilize the technology in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the technology be defined by the claims appended hereto.

Claims
  • 1. A crown cap, comprising: a body having a central portion with a boss extending therewith that transitions into a rim with an edge, the body having an inner surface;a pull-ring having a grasping portion and a lever tab, the lever tab is fastened to the boss, the inner surface of the body includes a score line extending from the edge along the rim and across the central portion towards the boss and returning outward across the central portion after travelling around the boss to terminate in a tail segment that extends along a portion of the rim, whereby pulling the pull-ring upward fractures the body along the score line.
  • 2. The crown cap as recited in claim 1, wherein the central portion further includes a first protrusion and a second protrusion proximate to the boss, and the lever tab of the pull-ring is seated on the first and second protrusions.
  • 3. The crown cap as recited in claim 1, wherein the lever tab is fastened to the boss without piercing the body.
  • 4. The crown cap as recited in claim 1, wherein the section of the score line travelling across the central portion of the body from the edge towards the boss forms an angle ranging between 1-20 degrees with the section of the score line travelling across the central portion back towards the rim after the score line has traveled around the boss.
  • 5. The crown cap as recited in claim 1, wherein the tail segment of the score line has a radius ranging between 1-5 mm.
  • 6. The crown cap as recited in claim 1, wherein the grasping portion of the pull-ring has furled edges.
  • 7. The crown cap as recited in claim 1, wherein the score line is covered by one of the following materials: Polyvinyl chloride or Polyethylene.
  • 8. The crown cap as recited in claim 1, wherein the tail segment does not extend to the edge.
  • 9. A crown cap, comprising: a body having a central portion with a boss that transitions into a rim with an edge, the body having an inner surface with a score line; anda pull-ring having a grasping portion and a lever tab extending from the grasping portion to a distal end that is keyed to the boss, the body fractures along the score line and partially separates a tear strip portion from the body when the pull-ring is pulled upward, the tear strip portion includes the boss.
  • 10. The crown cap as recited in claim 9, wherein the score line extends from the edge of the rim, along the rim, and across the central portion towards the boss and returns outward across the central portion back towards the rim after travelling around the boss, and terminates in a tail segment that extends along a portion of the rim.
  • 11. The crown cap as recited in claim 10, wherein the lever tab includes a first edge and a second edge, the first and second edges having a notch formed therein at the location where the lever tab extends from the grasping portion of the pull-ring.
  • 12. The crown cap as recited in claim 11, wherein the boss is integrally formed with the central portion of the body.
  • 13. The crown cap as recited in claim 12, wherein the lever tab is keyed to the boss without piercing the boss or the body.
  • 14. The crown cap as recited in claim 11, wherein the central portion of the body includes a pair of protrusions and the lever tab is seated on the pair of protrusions.
  • 15. The crown cap as recited in claim 10, wherein the section of the score line that extends from the rim across the central portion towards the boss forms an angle with the section of the score line returning outward across the central portion back towards the rim after travelling around the boss, the angle having a range between 1-20 degrees.
  • 16. A crown cap, comprising: a body having a central portion with a boss that transitions into a rim with an edge, the body having an inner surface with a score line;at least one protrusion extending from the central portion of the body and proximate to the boss; anda pull-ring having a grasping portion and a lever tab, the lever tab is fastened to the boss without piercing the body and is seated on the at least one protrusion.
  • 17. The crown cap as recited in claim 16, wherein the lever tab is keyed to the boss.
  • 18. The crown cap as recited in claim 16, wherein the score line includes a tail section that terminates along the rim without reaching the edge.
  • 19. The crown cap as recited in claim 18, wherein the tail section of the score line is a non-linear line and has a radius between 1 mm-5 mm.
  • 20. The crown cap as recited in claim 19, wherein the score line travels from a point along the edge of the body to the tail section after traveling around the boss.
Priority Claims (1)
Number Date Country Kind
200820175601.6 Oct 2008 CN national