1. Field of the Invention
The pressure sensitive adhesively backed disposable measuring tape and a method of manufacture.
2. Description of the Prior Art
Since the advent of standardized lengths, measuring tapes have found a myriad of uses. Flexibility of the measuring instrument permits portability of a device that can measure large lengths.
Applying a coating of a pressure sensitive adhesive to the back of the measuring tape permits many new uses. The use of a conventional measuring tape to measure much more than five feet requires two individuals, one at each end, to hold the tape straight and taut. Inaccuracies are introduced, for example, when measuring in a horizontal direction on a vertical surface such as a wall, because of the inevitable sag in the center of the suspended tape. With an adhesively backed tape one fastens the tape to the object being measured as he moves along its surface. The second reson is not required since the tape is attached to the surface being measured. There is no sagging due to weight because the tape is supported by its attachment to the surface along its length.
In many of the uses for which a ruler or yardstick is inappropriate, a longer, adhesively backed tape is the answer. One illustrative example which will be discussed in length is the use of an adhesively backed measuring tape as a stud finder. In the construction of buildings, walls are generally composed of either gypsum board or wet plaster fastened to vertical 2.times.4 studs. These studs are spaced sixteen inches apart, center to center. One wishing to attach a structure such as shelves or a cabinet to the wall must fasten the structure to the studs to gain secure support. Once one of the studs in the wall is found it is a simple matter to measure in multiples of sixteen inches from that stud to find all of the other studs in the wall.
The properties of adhesively backed measuring tapes can be described using a number of technical terms and criteria. Available adhesively backed measuring tapes exhibit both desirable and undesirable characteristics under these criteria.
Accuracy: One currently available adhesive backed measuring tape achieves accuracy by use of a high modulus plastic tape, i.e. tape of such character that it does not stretch under the forces normally applied during application. For example, in the stud finding problem, one may wish to measure a distance of more than eight feet. If there is a one percent error in the accuracy of the measuring device at least some of the fasteners driven into the wall might miss the studs even though the original stud had been accurately located.
Tensile strength: for ease of use, an adhesively backed measuring tape should be tearable by a user of ordinary strength who is holding one side of the tape with a single finger against the surface to which it adheres and has the roll tape in his other hand. The use of the tool such as a sharp knife or scissors to cut the tape is inconvenient because the tool must be carried on the person in order to be within reach and it must be handled with one hand while the other hand holds the tape roll.
The plastic tape mentioned above achieves dimensional stability by the use of a high modulus plastic base. A concurrent property with the high modulus is a high tensile strength. The plastic tape sacrifices ease of tearing to gain higher accuracy. As a result the tape is difficult to tear and many users must use a tool of some sort in order to cut the pieces.
Adhesion strength: A desirable adhesively backed measuring tape must adhere to the surface to which it is applied so that as parts of it are lifted in order to obtain a true straight line, the whole tape will not peel from the surface. However, there must not be so tight a bond that it is difficult to remove the tape after use or that it requires too much stress to remove the tape from the roll.
Markability: The surface of an adhesively backed measuring tape from which one reads the indicia should be readily markable. This greatly facilitates its use, for example, as a stud finder, where it is not already marked in graduations of sixteen inches. Because people do not always nave the perfect marking tool on their persons, the tape should be able to accept a wide variety of writing media such as pencils, crayons and porous tipped marking pens. The plastic tape mentioned above scores poorly in this regard. Almost anything written on its surface smudges easily, assuming one can make a mark at all.
Elasticity: An adhesively backed measuring tape should adhere to a slightly irregular surface without losing its capability to lay in a straight line. The tape cannot be accurate if it cannot be laid in a straight line. The problem occurs when the unevenness lies in a direction transverse to the one being measured. As the tape is twisted in the transverse direction, there is a tendency for the tape to gradually change direction as it is laid. This occurs because as one presses the tape against the wall, one edge of the tape must travel further than the other. The tape turns in the direction of the edge which deviates farthest from the flat plane of the wall. The high modulus plastic tape suffers severely from this tendency. The high modulus is the opposite to elasticity. As a result when the plastic tape encounters an irregularity it deviates from a straight line as laid or if forced into a straight line, will form a wrinkle.
Cost: In order to enjoy widest use, an adhesively backed measuring tape must be inexpensive. Consumers are unwilling to pay a high cost for a product which is used once and thrown away. Re-use of such a product is undesirable since foreign material is picked up on the adhesive surface and the tackiness of the tape is lost after only a few uses. Also, generally when one cuts the tape to a certain size only by chance will he have a second use for that particular length of tape.
An inexpensive and practical way to print measuring tapes is on a drum printer. The tape is passed between two rolls. The side on which the printing is to appear contacts a drum with a printing matte around its periphery. The matte used is typically composed of rubber. As the rubber matte is placed on the drum, the back side contacts the drum surface and to some extent is compressed. The front side (facing away from the drum) is to some extent stretched. The reason for this is because of the slightly different diameters of the internal surface and the external surface of the matte as it is mounted on the drum. The circumferences of the internal and external surfaces are different. In the flattened configuration they would be the same. If the true measurements are embossed on the rubber matte when flat, this leads to an error of almost one-eighth inch per foot if one uses a matte which is one-sixteenth inch thick and a true twelve inches in length when flat.
In order to prevent stretching or creep of the matte on the drum as the tape is being printed, the matte is mounted on an adhesive surface of the drum. That way each individual portion of the printing surface of the matte is fixedly attached to the periphery of the drum. The adhesive surface is generally provided by a double-sided adhesive tape mounted on the drum.
However, as the matte is mounted, the first portion is generally mounted on the drum with simple pressure and no stretching. As the matte is laid around the circumference of the drum, its external surface exhibits a gap at the juncture of the two-ends of the matte. In order to remedy this the operator will peel off the second half to two-thirds of the matte, stretch it and reapply it. This causes an inconsistency in the size of the subindicia within the extent of the surface of the matte. That is, for example, in dealing with a matte of twelve inches in length, the first four inches applied to the surface of the drum will have the same length as they would have on the matte at rest. However, the last six to inches, because of the stretching phenomenon in the mounting procedure, will have a slightly longer length than they would have on the matte at rest.