Patent Application
20080050568
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
As used herein, the term “tape” is meant to indicate electrical insulation tape.
As used herein, the term “film” is meant to indicate the matrix for lately coated adhesive;
As used herein, the term “breakdown voltage” is meant to indicate the minimum voltage to break the tape;
As used herein, the term “thickness ratio” is meant to indicate the thickness ratio of different layers in back film;
The second layer of the tape backing film of the invention is a blend of EPDM rubber and PE. Suitable PE includes low density PE (LDPE), high density PE (HDPE), or linear low density PE (LLDPE). The PE may have a molecular weight of about 50,000 g/mol to 300,000 g/mol, or about 100,000 g/mol to 200,000 g/mol, and comprise about 40-60 parts by weight of the mixing layer. The EPDM rubber may include 50-90 parts by weight of ethylene, 5-50 parts by weight of propylene, and 0-3 parts by weight of diene, and about 60-40 parts by weight of the mixing layer.
The first layer of PE may also be low density PE (LDPE), high density PE (HDPE), or linear low density PE (LLDPE). The PE of the first layer also may have a molecular weight of about 50,000 g/mol to 300,000 g/mol, or about 100,000 g/mol to 200,000 g/mol.
The tape backing film of the invention can optionally have added to it about 0.05-20 parts by weight of a flame retardant; about 0.05-15 parts by weight of a colorant or a dye; about 0.05-30 parts by weight of a filler such as SiO2, TiO2, CaCO3, MgCO3, CaSO4, BaSO4, Al2SiO5, or the like; and about 0.05-10 parts by weight of a processing aid such as demolding agent, coupling agent, lubricant, UV stabilizer, plasticizer, germicide, antioxidant, or wax.
As shown in
The tape backing film of the invention has a tensile strength of 1.05 to 2.5 kgf/mm2, an elongation at break of 100% to 800%, a breakdown voltage of 39 to 150 kv/mm, and a recovery from deformation of 10 to 20%, similar to PVC film and EPDM rubber/PE single layer film, with breakdown voltage of the film of the invention exceeding that of the PVC. After heating for extended periods, the small molecules of EPDM rubber do not migrate to the surface of the film, with no corresponding cracking. Analysis of the stress-strain test of the film of the invention shows stretching and contracting similar to a PVC film. The film of the invention, while indiscernible from conventional PVC film in properties such as elasticity, robustness, and shrinkage, is halogen free and easily recovered, and may completely replace the PVC tape and EPDM rubber/PE single layer tape backing film.
In fabrication of the tape backing film according to the invention, the disclosed PE and EPDM rubber are blended with fillers, processing aids, or additives in a mixer or an extruder. Mixing parameters are not limited, although mixing rate is generally higher for better results. The blending ratio of parts by weight for PE/EPDM can be 40/60, 50/50, 60/40, and other suitable ratio.
While the mixture can be directly used to form film, it can also be pelletized before sequential processes for convenience of storage and machine operations. The pellets can be formed by twin screw extrusion at about 100 to 240° C.
The mixture or pellets may be melted at about 220 to 280° C. to form a mixing layer. The mixing layer may be formed by, for example, single screw extrusion molding, twin screw extrusion molding, or calendaring. When using single screw extrusion, the screw has a preferable length to diameter ratio of about 30. A PE layer can be coated on the mixing layer, and then molded at, for example, 170 to 320° C. to form a thick film. The molding method includes multi-layer co-extrusion and single layer extrusion.
Next, the thick film may be drawn to form a thin film with stretch ratio in a longitudinal direction is about 1:1 to 1:10, or 1:1 to 1:5; and stretch ratio in a transverse direction about 1:1 to 1:10, preferably 1:1 to 1:5, respectively. After drawing, the thin film has physical properties similar to PVC backing film.
The thin film may be optionally subjected to a surface treatment to form the tape backing film of the invention. The surface treatment improves the surface adhesion of the film to subsequently formed adhesives. Non-limiting examples of suitable surface treatments include corona treatment (for example, 1000 to 5000 volt/cm2) or chemical treatment (for example, coating a primer). The tape backing film may have a thickness of about 0.02 to 0.30 mm, or 0.08 to 0.20 mm.
The PE layer or the mixing layer of the tape backing film disclosed may be uniformly coated with a layer of polymeric pressure sensitive adhesive (PSA), such as acrylic adhesive or rubber adhesive, for instance with a thickness of about 0.01 to 0.05 mm and adhesive force of about 1.4 to 5.8 kgf/19 mm, similar to conventional PVC tape, while remaining halogen free. Other adhesives known in the art may also be employed. Note that if adhesive is coated on the first layer (PE layer), the surface treatment needs a primer coating after corona treatment. On the other hand, if adhesive is coated on the second layer (mixing layer), the primer coating can be ignored. Because the primer coating contains high ratio solvent, adhesive coated on the second layer is free of solvent problems such as industrial safety and environment protection.
100 parts by weight of PE (C7100, produced by Asia Polymer Co., Taiwan), 80 parts by weight of EPDM rubber (Nordel 1070, produced by DuPont), 10 parts by weight of a filler, 4 parts by weight of a colorant, and 0.5 parts by weight of an antioxidant were placed in a mixer and mixed at high speed, and then pelletized by a twin screw extruder at 190° C. The resulting pellets were placed in a single screw extruder with a screw of 90 mm in diameter, ratio of screw length to screw diameter (L/D) of 30, and a die of 400 mm in diameter at 220 to 280° C. to undergo extrusion to form a mixing film. A PE layer was coated on the mixing film and then molded to form a thick film (double layer). The thick film was drawn at a stretch ratio of 1:3 in a longitudinal direction and at a stretch ratio of 1:4 in a transverse direction to form a thin film of 0.15 mm thickness. The thin film was subjected to corona treatment at 2000 v/cm2 to form the tape backing film of the invention.
Comparison 1
100 parts by weight of PE (C7100, produced by Asia Polymer Co., Taiwan), 118 parts by weight of EPDM rubber (Nordel 1070, produced by DuPont), 4 parts by weight of a processing aid, and 2 parts by weight of a colorant were placed in a mixer and mixed at high speed, and then pelletized by a twin screw extruder at 190° C. The resulting pellets were placed in a single screw extruder with a screw of 90 mm in diameter, ratio of screw length to screw diameter (L/D) of 30, and a die of 400 mm in diameter at 220 to 280° C. to undergo extrusion to form a mixing film (single layer). The mixing film was drawn at a stretch ratio of 1:3 in a longitudinal direction and at a stretch ratio of 1:4 in a transverse direction to form a thin film of 0.15 mm thickness. The thin film was subjected to corona treatment at 2000 v/cm2 to form a tape backing film.
Test
Tensile strength, elongation at break, breakdown voltage, deformation set, and heat resistance of Example 1 and Comparison 1 were respectively tested according to the UL-510 standard, with results shown in Table 1.
As shown, the physical properties of Example 1 (double layer) are better than that of Comparison 1 (single layer of EPDM rubber/PE). In particular, Comparison 1 exhibits cracking and corrosion after heating for extended periods. Compared to Comparison 1, the tensile strength of Example 1 is more similar to PVC backing film. In addition, the breakdown voltages of Example 1 exceed that of the PVC backing film. Accordingly, Example 1 has better physical properties than the EPDM rubber/PE single layer backing film of Comparison 1.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 95131084 | Aug 2006 | TW | national |
