1. Field of the Invention
This invention relates to fluid containers which exhibit increased resistance to premature burst caused by mechanical shock. In particular, this invention relates to containers for holding fluid photographic processing materials for in-camera developing. These containers comprise a polymeric sealing composition along certain of their marginal areas. This invention also relates to photographic film units having improved fluid containers.
2. Description of the Prior Art
Polymers useful in a sealing composition for forming preferentially bursting seals in containers for photographic materials are known. Such a sealing composition is generally located along a marginal area of a container which is intended to burst and release a fluid, such as a photographic processing fluid, when pressure is applied to the container in a camera. The sealing composition is generally coated over an inner layer of the container which is resistant to chemical action by the contained fluid. In the case of photographic processing fluids, the inner layer of the container is resistant to alkaline conditions.
Many burst sealing compositions known in the art are mixtures of polymers. However, such mixtures typically form heterogeneous layers when coated. The resulting seals from such heterogeneous layers exhibit low adhesive strength over a wide range of sealing temperatures and are susceptible to fluid leakage. As a result, the seals tend to burst prematurely when subjected to mechanical shock from fabrication, shipping, handling and the like.
Some polymers have been used alone as sealing compositions. U.S. Pat. No. 4,054,233 issued Oct. 18, 1977 to Cawley discloses crosslinkable homopolymers which act as adhesives when crosslinked. Copolymers of 2-acetoacetoxyethyl methacrylate and 2-norbornylmethyl methacrylate are disclosed in U.S. Pat. No. 4,054,232 issued Oct. 18, 1977 to Cawley. The polymers disclosed in this patent also act as adhesives only when crosslinked. However, these crosslinkable materials tend to crosslink prematurely and are considerably more costly than noncrosslinkable adhesives. Non-crosslinkable sealing compositions are disclosed in Research Disclosure, Vol. 127, November, 1974, publication 12713, published by Industrial Opportunities, Ltd., Homewell, Havant Hampshire P09 1EF, United Kingdom. Among these sealing compositions is poly(2-norbornylmethyl methacrylate). A method of making this polymer and related copolymers and their use in non-photographic products are disclosed in U.S. Pat. No. 3,243,416 issued Mar. 29, 1966 to Caldwell et al.
Unfortunately, fluid containers sealed with poly(2-norbornylmethyl methacrylate) sometimes rupture when subjected to mechanical shock during fabrication, handling and shipping. The tendency to rupture appears to increase with age, that is, after storage for some time. Further, poly(2-norbornylmethyl methacrylate) lacks desired burst sealing strength over a wide range of sealing temperatures.
Hence, it is desirable to have a fluid container which is resistant to bursting or failure when subjected to mechanical shock. It is also desirable to have sealing compositions for these containers which exhibit desired burst sealing strength over a wide sealing temperature range, such as 125.degree. to 250.degree. C. It is also desirable for such compositions to retain this strength over a long period of time. Furthermore, these compositions should be non-crosslinkable so as to avoid the problems of premature crosslinking and higher production costs.