Abstract:
A moisture proof container includes a container body having a flange portion for cooperatively receiving a closure member, the closure member includes a top portion joining an inner sealing surface and an outer surface both defining a channel, the channel being configured to engageably receive the flange portion, and wherein the outer surface includes spaced-apart retention members in the channel that provides a means for venting air pressure from within the container to outside the container.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a moisture proof container for a photographic film cartridge. More particularly, the invention concerns a combination of a plurality of protuberances and a plurality of retention members positioned in a channel of the container cover providing a vent duct to release deleterious gas pressure incurred during high-altitude shipping.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is common to use a two-piece plastic container to provide product integrity (prevention of deleterious moisture and dirt) for photographic film cartridges. There exists two basic types of containers in the marketplace as described in U.S. Pat. No. 4,639,386. One type has a closure with a retention feature cooperating with a groove or grasping ring on the inner diameter near the open end of the body part. The second type has a closure with a retention feature cooperating with a bead protrusion or flange on the exterior of the open end of the outer diameter of the body part. There is a great deal of art concerned with product integrity (closure and body fitness) with the first type. Examples of this prior art are: U.S. Pat. Nos. 4,844,961 and 4,960,626. However the second type typically exhibits inconsistent closure retention force and Moisture Vapor Transmission Rate. It is therefore the object of the present invention to provide a container for photographic film with a low and consistent Moisture Vapor Transmission Rate (MVTR) while providing a suitable and consistent retention force (or fitting strength as disclosed in U.S. Pat. No. 4,639,386) for a container with a flange on the exterior of the body part. A suitable closure retention or separation force is within a force range that is a) acceptable to consumers to be easily removed and b) resists the rigors of manufacturing; supply chain; distribution and retail environment to provide product integrity until it reaches the consumer. In the case of a container for consumer 35 mm photographic film, this acceptable force range is typically 9 to 22 Newtons.  
         [0003]     A common means for providing mold release and desired Moisture Vapor Transmission Rate performance for containers and in particular those for photographic film is to use lubricant or slip additives such as fatty acid amides or esters. Fatty acid amide slip additives however can be detrimental to closure retention force when the amount approaches a level suitable for maintaining a low Moisture Vapor Transmission Rate. The present invention overcomes this stated mutually exclusive condition of achieving the desired Moisture Vapor Transmission Rate performance while at the same time achieving a suitable and consistent closure retention force.  
         [0004]     The present invention provides a container that meets the above objectives. The closure for the container of the present invention is composed of a blend of various density polyethylenes resins along with suitable amounts of additives for improvements such as color, opacity, appearance, lubricity, Moisture Vapor Transmission Rate (MVTR), moldability and coloration during processing. The container body for the container of the present invention is composed wholly of high-density polyethylene (HDPE) along with suitable amounts of additives for improvements such as color, opacity, appearance, lubricity, Moisture Vapor Transmission Rate (MVTR), moldability and coloration during processing.  
         [0005]     It is common for containers for photographic film to have a closure comprised wholly of a singular polyethylene resin with a specific density range plus small amounts (less than 5% by weight each) of additives for improvements such as color, opacity, appearance, lubricity, Moisture Vapor Transmission Rate (MVTR), moldability and coloration during processing. These resins are commonly identified as low-density polyethylene (LDPE) with density ranging from 0.910-0.925 g/cm 3 , medium-density (MDPE) from 0.926-0.940 g/cm 3 , and high-density polyethylene (HDPE) with density ranging from 0.941-0.965 g/cm 3 . Molding grades of these resins commonly have Melt Flow Rate (MFR) ranging from 5 to 50 g/10 min.. It is known that as the density of polyethylene increases so does the flexural modulus or bending stiffness. Likewise it is known that as MFR increases the stiffness of the bending stiffness decreases. However the interaction of stiffness to MFR is much less than the interaction of stiffness to density. The density of polyethylene is to a large part determined by the extent of branching of the polyethylene molecule, which determines the extent of crystallinity whereas the MFR is to a large part determined by the length of the polyethylene chain.  
         [0006]     The flexural modulus for LDPE ranges from about 700 to about 2100 Kg/cm 2 , for MDPE from about 2500 to 4500 Kg/cm 2  and for HDPE from about 6300 to 10500 Kg/cm 2 .  
         [0007]     A common type of container for photographic film (as described in U.S. Pat. No. 4,639,386) has a closure with a sealing channel forming a sealing surface that interfaces with the inside of the body part and a skirt circumscribing the outside of the body part with a continuous retention bead that overlaps a bead or flange around the outside top of the body. The retention force of the closure is a function of the stiffness of the closure, lubricity of the body and/or closure material and the cooperating geometry of the cover retention bead and the body part flange.  
         [0008]     It is also common in molding of closures for photographic film containers to use lubricants such as fatty acid amide as a mold release agent to decrease molding cycle time.  
         [0009]     In the present invention, one way of compensating for the loss in cover retention or separation force due to the lubricant is to increase the stiffness of the material by using blends of various density polyethylene materials. It is noted that a closure comprised wholly of low-density (LDPE) or high-density polyethylene (HDPE) is too flexible or too stiff and the closure retention or separation force is highly variable. It is also noted that the cost of medium-density polyethylene ( MDPE) material is considerably higher than a blend of LDPE and HDPE.  
       SUMMARY OF THE INVENTION  
       [0010]     It is, therefore, an object of this invention to provide a container for photographic film with a closure of suitable and consistent retention force.  
         [0011]     Another object of this invention is to provide a container for photographic film with a low and consistent Moisture Vapor Transmission Rate (MVTR).  
         [0012]     Another object of this invention is to provide a container for photographic film and low material cost.  
         [0013]     Accordingly, in one aspect of the invention, a moisture proof container includes a container body having a flange portion for cooperatively receiving a closure member. The closure member has a top portion joining an inner sealing surface and an outer surface defining a channel. The channel is configured to engageably receive the flange portion. The outer surface comprises a plurality of spaced inward facing retention members arranged in the channel.  
         [0014]     The invention provides a container that meets the above objects. The closure for this container is composed of a blend of LDPE and HDPE resins along with suitable amounts additives for improvements such as color, opacity, appearance, lubricity, Moisture Vapor Transmission Rate (MVTR), moldability and coloration during processing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a depiction of the prior art for photographic film containers as disclosed by Akao et al. (U.S. Pat. No. 4,630,386).  
         [0016]      FIG. 2  is a depiction of the prior art for the fitting structure for a photographic film container to Type 2 as disclosed by Akao et al. (U.S. Pat. No. 4,960,626).  
         [0017]      FIG. 3   a  is a an enlarged cross sectional view of the fitting structure between removable closure member in the body of the container.  
         [0018]      FIG. 3   b  is an isometric partially removed section exposing the inner structure on the removable closure member.  
         [0019]      FIG. 3   c  is a cross section of the assembled container.  
         [0020]      FIG. 4   a  is an enlarged cross section view of the fitment structure cut through the retention member of the removable closure.  
         [0021]      FIG. 4   b  is a partial section view of the fitment structure showing vent ducts within the fitment structure.  
         [0022]      FIG. 4   c  is an isometric partially removed section exposing the inner structure on the removable closure member.  
         [0023]      FIG. 4   d  is a cross section of the  FIG. 4  of the assembled container. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Referring to  FIG. 1 : Two types of moisture proof containers such as those used for photographic film are depicted as previously disclosed in U.S. Pat. No. 4,630,386 (Akao). Type 1 (plug style) is composed of a removable closure member  1 ′ and a body portion  2 ′. Referring to Type 2 (snap-over style). The moisture proof container is composed of a removable closure member  1  and body member  2 . The closure member  1  further comprises a receiving channel  3  for cooperatively receiving a flange portion  4  of body member  2  providing protection from the ingress of moisture and resistance from inadvertent separation yet allowing easy opening by the customer for access to the product contained therein. Moisture ingress is typically measured as an average weight gain per unit time.  
         [0025]     Referring again to  FIG. 1 , in the case of photographic film it is preferable to have a maximum allowed moisture ingress of about 12 mg/wk. The preferred separating force range is from a minimum of about 9 newtons to prevent inadvertent separation to a user-friendly maximum of about 22 newtons.  
         [0026]     Referring to  FIG. 2 , this figure from U.S. Pat. No. 4,960,626 (Akao et al) depicts an enlargement of the prior art for the fitting structure of the cover member  1  to the body member  2 . The receiving channel  3  of the cover member  1  is composed of: a top portion  8  joining a cover member inner sealing surface  6  cooperating with a body member inner sealing surface  5 ; and a receiving channel outer surface  9  and a continuous circumferential retention member  7  protruding axially to cooperate with the continuous circumferential flange member  4  of the container body member  2 .  
         [0027]     Referring to  FIGS. 3   a ,  3   b  and  3   c , these figures again depict the prior art for moisture proof containers of the snap-over style used for protecting photographic film. The cutaway view ( FIG. 3   b ) of the removable closure member  1  clearly shows the continuous circumferential nature of the receiving channel  3 , the top portion  8 , the closure member inner sealing surface  6  and the retention member  7 . Of particular note in  FIG. 3   a  is the primary seal  11 , secondary seal  12  and the tertiary seal  13  between the closure member  1  and the container. The use of multiple seals to improve the fitment or moisture proofness of the closure member  1  to the body member  2  is taught in U.S. Pat. No. 4,844,961.  
         [0028]     Referring again to  FIGS. 3   a ,  3   b  and  3   c , a common problem with moisture proof containers of the snap-over type is that the closure member  1  has a nigh rate of blowing off when subjected to a drop of environmental pressure such as that associated with air shipping at high altitudes. The redundant seals while being beneficial to preventing moisture ingress prevent the venting of higher pressure inside the container than that of a low-pressure environment. A high-pressure differential induces removal forces on inside of closure member  1  to lift axially from body member  2 . However the tertiary seal  13  formed by the continuous circumferential retention member  7  and flange portion  4  of body member  2  prevents venting of the higher-pressure gas inside the container. The forces induced on the inside of the closure member  1  from the higher differential pressure is often higher than the maximum user friendly removal force of about 22 newtons for which the structure of the container was designed.  
         [0029]     Referring to  FIGS. 4   a ,  4   b ,  4   c  and  4   d , these figures depict the present invention and the preferred embodiment. The present invention has a cover member  1  with a receiving channel  3  composed of: a top portion  8  joining a closure member sealing surface  6  and a receiving channel outer surface  9 . A plurality of spaced retention members  7  are directed radially from the outer surface  9 , and a plurality of spaced protuberances  10  are positioned on the top portion  8 .  
         [0030]     Referring again to  FIG. 4   b , the protuberances  10  and retention members  7  are spaced in a manner forming at least one vent duct  14  from the primary seal  11  to the exterior of the container. The vent duct  14  allows venting of higher-pressure gas, such as those incurred in lower pressure environments encountered in high altitude shipping, from inside of the container  15  (see  FIG. 4   d ). This equilibration of pressure prevents the pressure-induced forces on the inside of the closure member  1  from exceeding the maximum user-friendly removal force of about 22 newtons for which the structure of the container closure member  1  and body member  2  were designed.  
         [0031]     Referring again to  FIGS. 4   a  and  4   d , the container closure member  1  and body member  2  are commonly composed of olefin based resins such as polyethylene or polypropylene selected for their inherent resistance to moisture transmission. A lubricant such as fatty acid amide is commonly used as an additive to the materials composing the closure member  1  and/or the body member  2  to improve fitment for moisture proofing, affect the cover member  1  removal force, and affect extraction during forming by means of injection molding, thermoforming or compression forming. The preferred additive are selected from a group of naturally occurring fatty acid amide slip agents represented at a rate from about 1500 parts per million (0.15 weight percent) to about 4000 parts per million (0.40 weight percent). A representation rate lower than about 1500 parts per million resulted in deformation of the retention members  4 . A representation rate higher than about 4000 parts per million resulted in a deleterious residue on the product contained inside. Further. it is noted that moisture proofing (i.e, MVTR) is acceptable with only the primary seal  11  required thru the slip agent additive range of about 1500 to 4000 parts per million.  
         [0032]     Referring again to  FIGS. 4   a ,  4   b ,  4   c  and  4   d , these figures depict the preferred embodiment relative to the material composition of the present invention. The closure member  1  is composed of a blend of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) resins (with a Young&#39;s Modulus of about 2140 Kg/cm 2 ) along with suitable amounts of color and slip agent additives. The HDPE resin is represented at a rate of about 15 to 20 weight percent. The LDPE resin is represented at a rate of about 75 to 80 weight percent. The fatty acid amide slip agent is represented at a nominal rate of about 0.2 weight percent. The remainder is composed of coloring and opacifying agents (if required) such as titanium dioxide (TiO2) and carbon black. The blend representation of HDPE and LDPE provides the specific stiffness needed for the structure of the closure member  1  to satisfy the maximum user-friendly opening force requirement of about 22 Newtons. The required specific stiffness could also be obtained by blending amounts of linear low-density polyethylene (LLDPE), polypropylene or other suitable low moisture transmission thermoplastic resins.  
         [0033]     The invention has been described in detail with particular reference to certain preferred embodiments thereof. It will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
       Parts List  
       [0000]    
       
           1  Closure member with receiving channel  
           1 ′ Closure member  
           2  Container body having flange portion  
           2 ′ Container body with plug receiver  
           3  Receiving channel  
           4  Flange member  
           5  Body member inner sealing surface  
           6  Closure member inner sealing surface  
           7  Retention member  
           8  Top portion  
           9  Receiving channel outer surface  
           10  Protuberances  
           11  Primary Seal  
           12  Secondary Seal  
           13  Tertiary Seal  
           14  Vent duct  
           15  Container