Multi-layered lightly-laminated films and methods of making the same
Apparatus and methods for creating multi-layered lightly-laminated provide films with increased or maintained strength. An increased level of strength is achieved by bonding adjacent layers of the multi-layer film together in a manner that the bond strength of the laminated layers is less than a strength of a weakest tear resistance of the individual first and second film layers. The inventors have surprisingly found that such a configuration of light bonding provides increased and unexpected strength properties to the multi-layer film as compared to a monolayer film of equal thickness or a multi-layer film in which the plurality of layers are tightly bonded together.
1. A multi-layered lightly-laminated film, comprising:
a first thermoplastic film layer;
a second thermoplastic film layer;
a plurality of discrete non-adhesive bonded regions in which the first and second thermoplastic film layers are cold bonded directly together; and
a plurality of unbonded regions alternating with the plurality of bonded regions, the unbonded regions including discrete areas in which the first and second thermoplastic film layers are not bonded to one another;
wherein a bond strength of the bonded regions is less than a weakest tear resistance of either the first or second thermoplastic film layers;
wherein a machine direction of the first thermoplastic film layer is parallel to a machine direction of the second thermoplastic film layer.
2. The film as recited in claim 1 , wherein a bond strength of the bonded regions is less than a weakest MD tear resistance of either the first or second thermoplastic film layers.
3. The film as recited in claim 1 , wherein the multi-layered lightly-laminated film exhibits greater strength than a monolayer film having the same thickness as the multi-layered lightly-laminated film.
4. The film as recited in claim 1 , wherein the bonded regions comprise ultrasonic bonds.
5. The film as recited in claim 1 , wherein a tear resistance of the multi-layered lightly-laminated film is greater than a sum of a tear resistance of the first thermoplastic film layer and a tear resistance of the second thermoplastic film layer.
6. The film as recited in claim 5 , wherein an MD tear resistance of the multi-layered lightly-laminated film is greater than a sum of MD tear resistances of the first thermoplastic film layer and the second thermoplastic film layer.
7. The film as recited in claim 1 , wherein the first thermoplastic film layer comprises a tackifier that increases a tackiness of the first thermoplastic film layer.
8. A multi-layered lightly-laminated film, comprising:
a first layer of thermoplastic material;
a second layer of thermoplastic material; and
a plurality of discrete cold-formed non-adhesive bonds directly securing the first layer of thermoplastic material to the second layer of thermoplastic material;
wherein the bonds provide less resistive force to an applied strain than molecular-level deformation of either the first layer or the second layer;
wherein a machine direction of the first layer of thermoplastic material is parallel to a machine direction of the second layer of thermoplastic material.
9. The film as recited in claim 8 , wherein a bond strength of the bonded regions is less than a weakest tear resistance of the individual first and second layers.
10. The film as recited in claim 8 , wherein the bonds are non-continuous.
11. The film as recited in claim 8 , wherein the bonds comprise one or more of mechanical pressure or ultrasonic bonds.
12. The film as recited in claim 8 , wherein the bonds are joined at incrementally-stretched regions of the first and second layers.
13. A multi-layered lightly laminated film, comprising:
a first layer of thermoplastic material;
a second layer of thermoplastic material; and
a plurality of discrete cold-formed non-adhesive bonds directly securing the first layer of thermoplastic material to the second layer of thermoplastic material;
wherein the bonds have a bond strength less than a force required to fail either the first layer or the second layer;
wherein a machine direction of the first layer of thermoplastic material is parallel to a machine direction of the second layer of thermoplastic material.
14. The film as recited in claim 13 , wherein the bonds are non-continuous.
15. The film as recited in claim 13 , wherein the bonds comprise one or more of mechanical pressure or ultrasonic bonds.
16. The film as recited in claim 13 , wherein the bonds are joined at incrementally-stretched regions of the first and second layers.
17. The film as recited in claim 13 , further comprising varying one or more of a pattern, size, or number of the bonds to control bond strength.