Various types of envelopes, mailers, and paper assemblies typically include an opening or “window” through which information and data are displayed. The methods of constructing a “window” in an envelope or mailer, for instance, are well known in the art and include die-cutting a portion of a paper substrate to form a hole or “window.” The die-cut window may remain uncovered or, alternatively, may be covered with a patch of a translucent or transparent material that has sufficient clarity to allow information and data to be displayed through the window when the paper substrate is assembled into an envelope, mailer or other paper assembly. The translucent or transparent material typically used to construct the patch is a durable material, such as glassine. Glassine patches are disposed over a back surface of a die-cut window and adhered to an inner surface of a envelope, mailer or paper assembly. Glassine and other types of patches used to form prior art windows, however, produce finished pieces that do not exhibit good lay flat characteristics, since such patches are not integral and contiguous with the paper substrate with which such pieces are constructed. In effect, prior art window patches do not allow envelopes, mailers or other paper assemblies to lay flat or stack evenly once assembled. Uneven stacks often cause feeding difficulties as a single envelope, mailer or paper assembly is fed from an uneven stack into printing and other processing equipment. Uneven stacks reduce the number of finished pieces that can be contained by trays feeding processing equipment. In addition, processing equipment often becomes jammed due to feeding from uneven stacks, thereby increasing downtime and reducing production throughput.
Prior art chemical processes of producing a translucent or transparent window in a paper substrate provide an alternative to open or patched windows and typically include application of a transparentizing material to a paper substrate. Such a prior art method of transparentizing is disclosed in U.S. Pat. No. 5,418,205, which provides a method of transparentizing whereby an area of a paper substrate is prepared or processed prior to application of a transparentizing material. According to this method, the area of the paper substrate is made thinner than the remainder of the paper substrate in order to enhance penetration of the transparentizing material into the paper substrate once applied. The area can be made thinner by a variety of well-known means, including mechanical grinding and compressing or crushing the area to a desired thickness. However, such preparatory steps constitute additional time in the transparentizing process, as well as additional processing in the overall production of envelopes, mailers and other paper assemblies.
Therefore, it is desirable to provide a method of transparentizing that eliminates or at least substantially reduces the number of preparatory or other process steps required, while producing a translucent area or “window” with sufficient clarity and reflectance to display information and data. In addition, it is also desirable to provide a paper substrate or assembly with a translucent area or “window” that allows finished pieces to exhibit good lay flat characteristics.