Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-08-24
2002-06-25
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000
Reexamination Certificate
active
06410648
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a tacky film. More particularly, the invention relates to a tacky film which is self-tacky, has a satisfactory tack strength when adhered to itself, can have any desired tack strength, and has satisfactory blocking resistance. The invention further relates to a tacky film suitable for use as one or more tacky layers (the innermost tacky layer and/or the outermost tacky layer) of a pallet stretch film.
BACKGROUND ART
A typical layer constitution of pallet stretch films is a three-layer structure employing a “copolymer of ethylene and vinyl acetate (hereinafter abbreviated as “EVA”)” containing a pressure-sensitive adhesive as the inner layer and the outer layer and a “linear low-density polyethylene (hereinafter abbreviated as “LLDPE”) as the interlayer. For example, in forming a blown film having the multilayer structure, both edges of the film are cut off to separate the film into two sheets, which are wound on paper tubes. The film which has been thus cut off is pelletized again and then blended with an LLDPE and this blend is introduced as it is into the hopper of a molding machine for the interlayer and used in film production. The incorporation of the reclaimed pellets into the LLDPE results in a film strength decrease of about 20%. This is because an EVA has come into the reclaimed pellets. There is hence a desire for a film not containing an EVA, i.e., a multilayer film in which all the layers are constituted of an LLDPE.
The tacky layers comprising an EVA contain a pressure-sensitive adhesive, and expensive materials are currently used, such as a liquid polybutene, sorbitan oleate, diglycerol dioleate, and the like. The degree of tackiness varies depending on applications, ranging from “strong tackiness” through “ordinary tackiness” to “weak tackiness”. Although the pressure-sensitive adhesives shown above are used in combination in order to obtain a target tack strength, it is necessary in this case to change the incorporation amounts of the pressure-sensitive adhesives, etc. There has hence been a problem that various pressure-sensitive adhesive masterbatches should be used. Besides having this problem, these pressure-sensitive adhesives are expensive. Consequently, there also is a desire for the development of a tacky film to which a target tack strength can be easily imparted without using any of those pressure-sensitive adhesives.
Objects of the invention are to provide a tacky film satisfying the desire. Specifically, a first object of the invention is to provide a tacky film containing none of the pressure-sensitive adhesives enumerated above, i.e., to provide a tacky film which is a film having self-tackiness, has a satisfactory tack strength when adhered to itself, can be easily made to have any desired tack strength, and has satisfactory blocking resistance. A second object is to provide a tacky film which is especially suitable for use as one or more tacky layers (the innermost tacky layer and/or the outermost tacky layer) of a pallet stretch film.
The present inventors made intensive studies in order to obtain the desired tacky film. As a result, they have found that the desired tacky film is obtained
by using a linear low-density polyethylene having specific properties and forming it into a film, or
by using a composition which is a resin composition obtained by blending in a specific proportion two linear low-density polyethylenes having specific properties and which has a density within a specific range and forming the composition into a film.
The invention has thus been completed.
DISCLOSURE OF THE INVENTION
Namely, a feature of the invention (a matter specifying the invention) resides in
“a tacky film comprising a linear low-density polyethylene having an MFR of from 0.1 to 10 g/10 min and a density of from 0.884 to 0.910 g/cm
3
”.
Another feature of the invention (another matter specifying the invention) resides in
“a tacky film comprising a polyethylene resin composition which is a composition obtained by blending ingredient A shown below with ingredient B shown below and which has an ingredient B content of 80% by weight or lower and a density of from 0.884 to 0.910 g/cm
3
,
ingredient A: a linear low-density polyethylene having the following properties (1) and (2);
(1) to have an MFR of from 0.1 to 10 g/10 min,
(2) to have a density of from 0.890 to 0.940 g/cm
3
,
ingredient B: a linear low-density polyethylene having the following properties (3) and (4);
(3) to have an MFR of from 0.1 to 50 g/10 min,
(4) to give, in differential scanning calorimetry (DSC), a melting peak whose extrapolated melting termination temperature is 98° C. or lower”.
REFERENCES:
patent: 4793956 (1988-12-01), Nogiwa et al.
patent: 0 298 700 (1989-01-01), None
patent: 0681 914 (1995-11-01), None
patent: 0 721 967 (1996-07-01), None
patent: 0 735 090 (1996-10-01), None
patent: 0 848 048 (1998-06-01), None
S. Bensason, et al., “Blends of Homogenous Ethylene-Octene Copolymers”,Polymer, 1997 vol. 38, No. 14, pp. 3513-3520.
Sasaki Yoshihiko
Takenaka Kazutoshi
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