This invention relates generally to a light-impervious laminate material, and a method of manufacturing it.
Flexible light-impervious sheets are quickly used in window shades, in curtains, for photographic endeavors, and in many other applications. These flexible sheets must be low in cost, yet the light-impervious nature of the sheet must be perfect, or nearly so. In modern practice, these light-impervious sheets are laminates; that is, they comprise a number of relatively thin polyvinyl chloride plies or sheets which are bonded together. A striped laminate, which is not necessarily light-impervious, is described and claimed in U.S. Pat. No. 4,110,497.
Most if not all currently offered light-impervious sheets include five layers in the laminate. At the top is a white sheet of some 2 mils thickness. Below this white sheet is a 2 mil thick black sheet, and below the black sheet is a fibrous scrim sheet. Since the fibers overlay one another to at least some extent, this scrim sheet is about 10 mils thick. Below the scrim sheet is a second 2 mil thick black sheet. Below the bottom black layer is another white sheet of about 2 mils thickness. A common adhesive, which is white or light-colored, permeates the scrim and bonds the two black sheets to the opposite scrim sides. The outer light-colored sheets are bonded to the inner, dark sheets by heat and pressure.
Attempts have been made to construct light-impervious vinyl laminates of only four layers by eliminating one of the two interior or black sheets. These attempts have not always been entirely successful, however; in both the four-sheet and the five-sheet laminates, flaws can and do appear.
More specifically, close inspection of the finished product sometimes reveals "pinholes". These "pinholes" are small areas of imperfection in the manufactured product which permit light to pass through the sheet. Sometimes "slits"--generally elongated imperfections permitting light passage--can appear. "Thins" can also appear: these are spots where one or more laminate plies are of insufficient thickness, and an extended area of low light imperviousness results. Small air bubbles or other flaws can occur during the manufacturing process.
In the four-sheet laminate, two plies are bonded to one side of the scrim sheet and only one thin ply is bonded to the opposite side of the scrim sheet, and an "unbalanced" construction is thus provided. This "unbalanced" construction can mean that the finished product is susceptible to curling, and to separation and tearing at the black sheet, or occasionally at the other sheets.
The five-layer laminate is relatively expensive to manufacture. Aligning all five sheets of the finished product can be difficult and requires continuous close quality control efforts by production personnel. If a white sheet is thin or imperfectly made, the underlying dark sheet can show through, giving an unpleasant or impermissible "smudged" look to the finished product.
It is accordingly an object of the present invention to provide light-impervious flexible sheeting of high quality yet low cost.
More specifically, it is an object to provide a light-impervious flexible sheet product without air bubbles, "pinholes", "slits", "thins" or "smudges". A related object is to provide a method of manufacturing which minimizes or eliminates these imperfections in the end product.
Another object is to provide an end product sheet and a method of manufacturing this material which permits the manufacture of the desired end product at low cost.
Other objects and advantages of the invention will become apparent upon reading the following detailed description, and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.