Loose leaf binder
BACKGROUND OF THE INVENTION 
     This invention relates to a post binder of the type used for catalogs and reference works and the like in which a relatively thick stack of replaceable leaves is held by a post mechanism having a plurality of straight posts extending through the stack. There is a basic need for a binder of this type which will close to a condition in which it is little thicker than the thickness of the stack of leaves and will open to a condition in which the leaves are loose and separated from each other so as to lie open for convenient examination. 
     There are available on the market a number of extensible-post binders in which the backbone of the cover structure consists of two or more sliding parts which can be pushed to a collapsed condition when closed and pulled to an expanded position when opened. These require a relatively complex structure, are not held collapsed when closed, and in general are awkward and unattractive. See, for example, U.S. Pat. No. 2,784,719 issued Mar. 12, 1957 to C. J. Panfil. Other extensible-post binders on the market rely primarily on the post structure to support the covers and either have no backbone between the covers or have merely flexible facing between the covers which flexes to allow the post structure to be manually expanded and collapsed. See, for example, U.S. Pat. No. 2,253,039 issued Aug. 19, 1941 to G. Lewis. 
     The present invention provides an improved binder in which the post mechanism is automatically expanded as the binder is opened and automatically collapsed as the binder is closed. The binder is especially adapted to be made with a one-piece cover structure formed of stiff plastic sheet material, and which when closed has an especially neat and attractive appearance with no exposed rivets or the like. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, the binder consists of a cover structure, two post-mounting units, and a post mechanism having a plurality of extensible posts. The cover structure is preferably made from a single sheet of stiff plastic sheet stock in which hinges are formed between the backbone and the covers by heat-scoring or the like so that the covers swing on definite hinge lines at the edges of the backbone, and the backbone is of stiff material and of fixed width. Each cover carries a post-mounting unit fixed to its inner face adjacent its hinged edge. Each such unit is formed from an elongated piece of stiff plastic material having a central flexible web portion between two edge strips. One strip, referred to as a base strip, is fixed to the inner face of the cover adjacent its hinged edge, as by ultrasonic welding. The other strip, referred to as a post-mounting strip, is fixed to the mounting bar of an extensible post mechanism. The web portion of each post-mounting unit is made flexible as by heat-scoring or the like on at least two spaced flex lines about which the edge strips may swing relative to each other and which permit a certain degree of offset and other limited movement between the two edge strips. The web portion of the post-mounting unit is desirably also cut away over portions of its length, to leave a plurality of spaced web straps extending between the edge portions. Such straps together have greater flexiblity than the hinges between the covers and the backbone of the binder, to facilitate the operation of the binder and insure that the covers will swing about the hinges of the backbone. 
     The post mechanism may be of a conventional type which has a plurality of extensible posts extending between and perpendicular to elongated flat mounting bars at their ends. The two bars are fixed to the post-supporting strips of the post-mounting units on the two covers, with at least one releasable to permit the usual disassembly of the post mechanism of insertion and removal of leaves in the binder. The arrangement is such that the covers have a closed position in which they are in face-to-face and generally parallel relation, with the post-supporting strips lying substantially flat against their inner faces. The posts are then in shortened state and extend generally perpendicular between the covers. As the covers are swung outward from this closed position about their hinges at the edges of the backbone, they move toward an open position in which they lie substantially coplanar with the backbone. Such movement of the covers carries with them the base strips of the post-mounting units, while the posts, being rigid and perpendicular to their mounting bars and the post-supporting strips, hold such strips in substantially parallel relation, and this causes the webs of the post-mounting strips to be flexed as the covers swing. The covers and the base strips are thus caused to swing angularly both about the cover hinges and with respect to the post-supporting strips, and the latter strips are carried in parallel relation outward to a position of greater spacing than when the covers are closed. This automatically extends and lengthens the posts so that the leaves mounted in the binder may spread and lie well open in the binder for ready examination. 
     The one-piece cover and backbone structure of the binder is desirably made of a stiff plastic sheet of thermoplastic polymer, such as any of a number of polyolefin polymers available on the market. The preferred material is a mixture of polyethylene and polypropylene polymers available on the market under the trademark &#34;Polyallomer&#34;, from Eastman Chemical Products, Inc., Rochester, N.Y. A second preferred material is a medium density polyethylene polymer, which may be formed from a mixture of high density and low density polyethylene stock. Polypropylene and other polyolefin polymers may also be used. The material used is desirably thermoplastic and is adapted to be heat-scored to form integral hinges of good flexibility and long life, and is weldable as by ultrasonic welding. The post-mounting units are desirably formed of the same or similar plastic material but may be of thinner gauge than the cover stock. By way of example, the cover stock may range in thickness from 0.075 inch to 0.125 inch depending on the thickness of the binder, and the post-mounting strips may be 0.075 inch thick. The use of plastic post-mounting units welded ultrasonically to the covers provides an especially effective mounting for the post mechanism, provides automatic expansion as the binder is opened, and gives a binder of attractive appearance which does not require the presence of exposed rivets or other mechanical fasteners. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate the invention, and show the best mode presently contemplated of carrying out the invention. In such drawings: 
     FIG. 1 is an isometric view of a binder embodying the invention, shown in open position; 
     FIG. 2 is a fragmental sectional view taken on the line 2--2 of FIG. 3, showing the operation of the releasable latch of the post mechanism; 
     FIG. 3 is a transverse sectional view of the binder of FIG. 1, with the parts shown in binder-closed position; and 
     FIG. 4 is a sectional view analogous to FIG. 3, showing the binder in open position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The binder shown in the drawings comprises a front cover 10, a rear cover 12, and a backbone 14 to which the covers are hinged at their inner edges for movement between a closed position in which the covers are in face-to-face and generally parallel relation, and an open position in which the covers are substantially coplanar with the backbone 14. Preferably, the covers and backbone are formed from a one-piece sheet of stiff plastic material, by heat-scoring the material on spaced parallel lines to form hinges 16 and 18 between the inner edges of the covers and the backbone 14. For a thick binder such as a 4-inch binder the cover stock may be 0.125 inch thick and for a thinner binder such as a 11/2 to 2-inch binder the cover stock may be 0.075 inch thick. 
     Post-mounting units 20 and 22 are fixed to the inner faces of the covers 10 and 12, adjacent and parallel to the inner hinged edges of those covers. Each post-mounting unit is in the form of an elongated piece of stiff plastic material, of say 0.075 inch thickness, formed to provide an inner base strip 24 along one edge and a post-mounting strip 26 along the opposite edge, with the two strips joined by an intermediate web portion 28. The web portion is heat-scored along two parallel spaced lines to form a pair of spaced hinge lines 30 and 32 at the inner edges of the two strips 24 and 26. Also, the web is desirably cut away over spaced portions 34 to leave the web as a series of spaced flexible straps 36 extending between the two strips 24 and 26. Such straps together are desirably more flexible than the cover hinges. The post-mounting units 20 and 24 are attached to the inner faces of the two covers, by fixing the base strips 24 to such covers along their inner edges adjacent but outward from the hinges 18. Desirably, the base strips are attached to the covers by ultrasonic welding, as at a series of spaced points 38 along the length of the strip 24. 
     The post mechanism is of a conventional type and comprises three extensible posts 40 each having a bar section 41 telescopically received in a tubular section 42. One end of each post is fixed to an elongated flat post bar 44 and stands perpendicular to the plane of that bar. The bar 44 is fixed against the outer face of the post-mounting strip 26 of the post-mounting unit 22 shown at the right side of the backbone 14, and the posts pass through suitable openings in that strip 26. The bar 44 is conveniently fixed to the strip 26 by rivets 46. 
     The opposite end of each extensible post 40 is fixed to a movable post bar 48 which carries a slidable latch bar 50. As shown in FIG. 2, the latch bar 50 is secured to the post bar 48 by a pair of rivets 52 which pass through elongated slots 54 in the latch bar so that the latch bar is slidable lengthwise of the post bar 48. In latched position, the latch bar 50 lies against the front face of the post-mounting strip 26 of the post-mounting unit 20 and is engaged with a pair of studs 56 projecting through the strip 26 from a keeper bar 58 mounted against its back face and secured thereto by rivets (not shown). For engagement over each stud 56, the post bar 46 is formed with a downward-open notch 60 and the latch bar 50 is formed with an L-shaped notch 62 which lies behind the head of the stud 56 when the latch bar 50 is in latching position, as shown in full lines in FIGS. 1 and 2. The latch bar is released from the stud 56 when it is moved lengthwise to bring the vertical leg of the L-shaped notch 62 into alignment with the notch 60. For actuating the latch bar 50, it has an inturned finger or handle 51 at its left end. In FIG. 2, such handle is shown in latched position in full lines, and in released position in dotted lines. 
     In operation, the binder has a closed position as shown in FIG. 3, in which the front and back covers 10 and 12 stand in face-to-face and generally parallel relation with each other and in which the post-supporting strips, with the bars 44 and 58 on their outer faces, lie substantially flat against the inner faces of such covers, held in spaced parallel position by the interconnecting action of the extensible post 40. Because of the presence of the bars 44 and 58, the strips 26 are not coplanar with the base strips 24, but are offset inward therefrom, which offsetting is permitted by the two spaced hinge lines 30 and 32. In the binder-closed position, the posts 40 are in shortened state, with their bar elements 41 telescoped into the tubular elements 42. The binder is adapted to contain a full stack of loose leaves 62 which substantially fills the closed binder so that the covers lie flat against the stack and the overall thickness of the binder is very little greater than the thickness of the stack. When the covers are swung outward from their closed position in FIG. 3 to their open position shown in FIG. 4, they move to a substantially coplanar relationship with the backbone 14. As they swing outward and downward, they carry with them the base strips 24 of the post-mounting units so that those base strips move angularly from a parallel relation to a substantially coplanar relation. The post-supporting strips 26 of the post-mounting units, however, are held parallel by the extensible posts and the plates fixed to the post ends and to the strips. Accordingly, as the base strips 24 swing angularly outward, they rotate through 90° with respect to the parallel post-supporting strips, and this flexes the web straps 36. As shown in FIG. 4, the web flexing is distributed between the two spaced hinge lines 30 and 32. The binder-opening movement carries the post-supporting strips 26 bodily outward and downward from their closed position shown in FIG. 3, and extends the posts 40. The extension may be of the order of 60% or more of the length of the collapsed posts. Such extension loosens the stack of loose leaves and allows them to fall open in a loose and conveniently readable arrangement, as generally indicated in FIG. 4. 
     When the binder is in open position as shown in FIG. 4, the post-supporting strips 26 are flexibly and somewhat resiliently supported by the flexible straps 36 which are flexible about both of the two hinge lines of the hinges 30 and 32. This gives the post-supporting strips 26 some freedom of bodily movement vertically and horizontally, and facilitates the use and operation of the binder. Desirably, the strips 36 and their hinges 30 and 32 are more flexible than the hinges 18 between the covers and the backbone, which facilitates the operation and insures that when the covers are moved between open and closed positions they swing accurately about the hinge lines of the hinges 18. 
     When it is desired to remove and replace one or more leaves in the binder, the latch bar 50 is moved lengthwise to bring the side openings of its notches 62 into alignment with the notches 60, which allows the latch bar 50 and post bar 48 to be released from the studs 56. The stack of leaves is then laid over against the back cover 12 and the upper halves of the extensible posts 40 are removed, and this frees the stack of leaves for removal and replacement in whole or in part.