Pressure Sensitive Adhesive Tape

1. Field of the Invention

The present invention relates to a pressure sensitive adhesive tape or sheet and more specifically, to a pressure sensitive adhesive tape or sheet containing a plurality of artificial filament yarns buried in the tape and arranged in parallel to the longitudinal direction of the tape and, having a high tensile strength in the longitudinal direction of the tape.

2. Description of the Prior Art

Conventional strong pressure sensitive tapes with buried-in artificial filament yarns are known, for example, in accordance with the description in the Japanese official bulletin "Published unexamined patent application, Showa 29-2989." This adhesive tape is produced by providing, in advance, an adhesive single-coated tape which has the pressure sensitive adhesive layer on one side of the supporting sheet consisting of resin, paper, etc. A plurality of glass filament yarn fibers are disposed on the adhesive layer parallel to the longitudinal direction of said sheet, with another adhesive layer being applied thereto. In this structure, said filament yarns are thoroughly buried in said pressure sensitive adhesive layer, but they have no contact with the supporting sheet. Such an adhesive tape has the defects that lifting or puckering occurs when unwinding the rolled adhesive tape because the filament yarns are buried in the adhesive layer provided on the supporting sheet and thus, when the rolled adhesive tape is peeled at the end, only the supporting sheet peels off. In addition, the tape itself has the defect that, depending on the types of the applied adhesives, it is liable to age and change its properties in the course of time and, as a result, the filament yarns arranged in parallel along the longitudinal direction of the tape, at the point of manufacture, tend to snake while they are stored on the shelf, and thus the commercial value of the tape is extraordinarily lowered. Accordingly the conventional adhesive tape has serious defects in its manufacturing processes and also in its structure.

Accordingly an object of the present invention is to provide a pressure sensitive adhesive tape, in which filament yarns are arranged in parallel to the longitudinal direction on the supporting sheet, which eliminates lifting and puckering when the rolled tape is unwound and avoids peeling-off of only the supporting sheet at the end of the tape.

Another object of the present invention is to provide a pressure sensitive adhesive tape in which filament yarns arranged in parallel to the longitudinal direction of the supporting sheet at the point of manufacture cause no snaking due to aging and changing its properties in the course of time while it is being stored on shelf.

A further object of the present invention is to provide a pressure sensitive adhesive tape which can be produced by a simple manufacturing process.

The pressure sensitive adhesive tape of the present invention consists of a supporting sheet made of a thermoplastic resin, a plurality of artificial filament yarns buried in one side of said sheet and in parallel to the longitudinal direction of the sheet to the extent that at least half of the sections of the filament yarns are embedded in and adhere to one side of the supporting sheet and an adhesive layer being aplied to the side of the supporting sheet containing the artificial filament yarns.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is an enlarged sectional view taken across the width of the adhesive tape of the present invention;

FIG. 2 is an enlarged sectional view taken across the width of conventional adhesive tapes of the same type; and

FIG. 3 describes the manufacturing process of one embodiment of the adhesive tape according to the present invention.

According to the present invention a molten thermoplastic resin sheet was applied to one side of a plurality of artificial filament yarns arranged in parallel to the longitudinal direction of the sheet until at least half of the cross-section of said filament yarns is buried in said resin sheet. Thereafter, an adhesive layer is applied to the other side of said filament yarns. By such a procedure, the manufacturing process can be simplified and no lifting, puckering, peeling-off or snaking takes place since the plurality of filament yarns are not completely buried in the adhesive layer.

According to the above-mentioned concept, many experiments were carried out. For example, molten polyethylene-vinyl acetate copolymers mixed with wax were coated as a sheet on one side of a plurality of filament yarns arranged in parallel to the longitudinal direction of the resin sheet by using an ordinary roll coater method. Alternatively, a plurality of filament yarns arranged in parallel to the longitudinal direction of the resin sheet to be produced were placed into a gap between a cooling roll and a pressure roll of an ordinary polyethylene laminator and the molten resin sheet was supplied continuously into said gap while said laminator was in operation and a thermoplastic resin sheet, in which one-half of the cross-section of said filament yarns were buried, was provided. Thereafter, an adhesive layer was applied to the filament containing side of said thermoplastic resinous sheet and thus, the pressure sensitive adhesive tape of the present invention was obtained.

It has been confirmed from the results of the tests of these tapes that no lifting or puckering of the resin sheet takes place when unwinding the rolled tape, and no peeling-off of only the resin sheet was seen. Also no snaking of the filament yarns were observed over a long period of time, because at least a part of the filament yarns were buried in the resin sheet and thus strongly adhered to the resin sheet. On the basis of the above-described experiments, the present invention has been completed.

The adhesive tape of the present invention will be described in comparison with the conventional tapes by referring to the drawings as follows:

FIG. 1 and FIG. 2 are enlarged sectional views taken across the width of the tape of the present invention and the conventional tape, respectively.

In the tape of the present invention shown in FIG. 1, elements 1a are glass filament yarns, element 2a is a polyethylene resin sheet and element 3a is a known adhesive layer. As shown in the figure, it is required that at least one-half of the filament yarns sections 1a are buried in the resin sheet 2a.

In the conventional tape showing in FIG. 2, elements 1b are glass filament yarns, element 2b is supporting sheet made of paper or resin, and 3b is a known adhesive layer. As shown in the figure, filament yarns 1b are completely buried only in the adhesive layer 3b. As mentioned above, at least half of the sections of the filament yarns of the tape of the present invention are embedded in the resin sheet, whereas, on the contrary, the entire filament yarns of the conventional tape are embedded in or surrounded by the adhesive layer. Accordingly, in the tape of the present invention, the filament yarns are not isolated from the supporting resin sheet, but are embedded in both the sheet and the adhesive. In these respects, these two tapes are thoroughly different from each other in their structure and, as a result, different effects are obtained therefrom.

In the above description of the FIG. 1, polyethylene is adopted as the material for the resin sheet, but it is readily apparent that other thermoplastic resins, such as polyvinylchloride, ethylene-vinylacetate copolymer, polypropylene, styrene resin, etc. can also be used. As filament yarns, artificial filament yarns, for example, inorganic filament yarns of glass or metal, regenerated filament yarns of rayon or bemberg and synthetic filament yarns of polyesters and polyamides, etc. can be used.

Filament yarn mentioned in the present invention include monofilament yarns, multifilament yarn twisted together with monofilaments and plied yarns twisted together with multifilament yarns.

It is required that the filament yarn should have higher melting points than the resin materials used for the sheet and that they should adhere to said resins mechanically and/or chemically. Therefore, an appropriate combination of yarns and resins should be chosen, and, in some cases, surface treatment should be done on the filament yarns to improve its adhesive strength. In addition, to obtain perfect adhesion between filament yarns and the resin sheet, at least half of the section of the filament yarns should be buried in the resin sheet.

One embodiment of the present invention will be described according to the manufacturing process as follows:

In this embodiment, the adhesive tape is produced with the use of a known polyethylene laminator. Referring to FIG. 3, elements 4 and 5 are a cooling roll and a rubber coated pressure roll, respectively of the polyethylene laminator and are arranged with a predetermined gap 6. Element 7 represents a predetermined number of filament yarns positioned in parallel with a predetermined spacing in the longitudinal direction, and being conveyed on the pressure roll 5 from the right, to the gap 6 between the two rolls, and passing under the cooling roll 4 and pulled out from the bottom to the left. Element 8 is a T die arranged above the gap 6 between the rolls 4 and 5, reference numeral 9 is the molten polyethylene resin sheet pushed out from the T die 8, and element 10 is the polyethylene resin sheet in which the filament yarns to make the basic material for the tape of the present invention are buried. Glass filament yarns used in the embodiment are ECG 75-1/0 1Z (tex according to JIS R 3413: 67.5, thickness: 0.16 mm, minimum tensile strength 30 g/tex) produced by Fuji Fiber Glass Co. Ltd. in Japan. After arranging these filament yarns in parallel in 1000 mm widths at the rate of 36 yarns in a 25 mm width in the gap 6 between the cooling roll 4 and pressure roll 5, the two rolls 4 and 5 are put into operation and, at the same time, polyethylene resin molten at 300.degree. C. is made to continually flow down from T die 8 as a resin sheet 9 and the filament yarn 7 are coated by the resin in the gap 6 in such a way that about one-half of the sections of the filaments are enveloped in the molten resin. The molten resin in which the filament yarns 7 are buried is cooled by the cooling roll 4, to become a polyethylene resin sheet 10 containing buried filament yarns to make the basic material of the adhesive tape which is wound at the end. Subsequently, a known adhesive, e.g., a rubber-base adhesive is applied by a known method to that side of the resin sheet 10 containing the filament yarns and thus the tape of the invention can be easily obtained.

The properties of the tape obtained were tested in accordance with paragraph 8 (adhesive strength) paragraph 9 (low speed unwinding force), paragraph 10 (high speed unwinding force) and paragraph 15 (shelf life) of JIS Z 0237 "Testing method of pressure sensitive adhesive tapes and sheets" and the results thereof are shown in comparison with the identical test results of the conventional tapes:

According to the above table it is clear that, when compared with a conventional tape which has filament yarns thoroughly buried in the adhesive layer and isolated from the supporting sheet, the tape of the present invention has superior properties such that there is no lifting, puckering nor peeling off of the resin sheet in unwinding the tape and the filament yarns do not become disarranged while the tape is on the shelf because at least a part of the filament yarns are buried directly in the thermoplastic resin supporting sheet and thus firmly adhere to one another.

Though it is not mentioned in the above embodiment, the adhesive tape with the identical properties is also obtainable by coating molten resin, which is a mixture of ethylene-vinyl acetate copolymer and wax on one side of the filament yarns arranged in parallel by an ordinary roll coater method without using a laminator, and then coating a known adhesive layer on the other side of the filament yarns to make an adhesive tape. It is, however, possible to more efficiently produce the tape of the present invention with the use of the laminator.

In addition, an adhesive tape with filament yarns thoroughly buried in the resin sheet is obtainable by applying a molten resin on both sides of a plurality of filament yarns arranged parallel in the longitudinal direction. In this case, the process is somewhat complicated.