US20050063622A1

US20050063622A1 - Blended polymeric draw tapes

Info

Publication number: US20050063622A1
Application number: US10/938,902
Authority: US
Inventors: Rengan Kannabiran
Original assignee: Tyco Plastics LP
Current assignee: Covalence Specialty Materials Corp
Priority date: 2003-09-12
Filing date: 2004-09-10
Publication date: 2005-03-24
Also published as: WO2005028551A3; WO2005028551A2

Abstract

The present invention relates to a draw tape bag having a draw tape made of a polymeric blend of first and second polymeric components having varying densities. The polymeric blend is formed into a film by a blown process known in the art. The film is oriented providing strength and reduced elongation allowing the draw tape bag to be held without sagging or failure under load during usage. The polymeric blend imparts to the draw tape material a sealability and tensile strength that is not achievable by the multi-layer films or single layer films used in the prior art.

Description

RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application No. 60/502,814 entitled Blended Polymeric Draw Tapes filed on Sep. 12, 2003, the entirety of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The instant invention relates to draw tape bags wherein an oriented blended polymeric draw tape is provided to improve the performance and ease of use of the draw tape bag.

BACKGROUND OF THE INVENTION

Draw tape bags have been commercially available for many years. For example, draw tape or draw cord bags are generally described in U.S. Pat. Nos. 2,798,523; 3,029,853; 3,506,048 and 3,687,357. Draw tape bags have been typically formed by employing two or more pliable layers joined together forming a draw tape that is fastened to the bag. Typically, a tubular hem is provided at the open edge of each sheet and contains a drawstring or tape made from a pliable thermoplastic strip. One or more access holes are provided in the tubular hem to expose the draw tape, so as to facilitate pulling the draw tape through the opening(s). The action of pulling the draw tape through the opening results in closing the open mouth of the bag and formation of a handle. The handle may further be tied to seal the contents of the bag. The drawstrings can be also used to carry bag.
Draw tapes have been constructed from the same polyethylene material as the bag materials have been used successfully with seal designs to support loads as high as 30 to 50 lbs as shown in U.S. Pat. No. 4,558,463. In order to improve the strength of drawstrings or tape and their sealability in relation to thin pliable bag forming materials, multi-layered structures have been used as shown in U.S. Pat. No. 5,006,380 (the '380 patent). In the '380 patent a draw tape is formed from at least two layers of two different thermoplastic materials having varying densities. The first layer of the draw tape comprises a material characterized by its ability to form strong heat seals with the thermoplastic film employed to form the panels of the draw tape bag and with itself and thus imparts to the multi-layer tape sealability. The second layer of the draw tape is characterized as a thermoplastic material having a higher density that has greater tensile strength than the first layer but disadvantageously is unable to form proper heat seals used in bag construction. Typically the sealability layer is formed from low-density polyethylene and the tensile strength layer is formed for high-density polyethylene. Unfortunately the use of multilayer films to impart both sealability and tensile strength increases the manufacturing costs and complexity of bag construction.
Another approach to a multilayer draw tape is disclosed in U.S. Pat. No. 4,390,573 (the '573 patent). The '573 patent discloses laminar thermoplastic films having a first layer of low density polyethylene bonded to a layer of a dissimilar polymer blend comprising high density polyethylene and polyethylene copolymers.
It was thought that multilayer draw tapes have several advantages over the use of draw tapes formed of a single material. However, while a multilayer draw tape permits the use of a layer of strong tape material to provide strength to the draw tape, without sacrificing the sealing strength of the heat seals to the bag panels, from a manufacturing prospective it would be more efficient and thus less costly if all requirements of drawstrings or tapes such as strength, sealability and high load bearing properties can be achieved with a singular tape structure. In all the multi-layer tapes and single layer tapes there is a maximum load that the tape can carry before total failure or elongation. Even when prior art draw tapes do not totally fail, they can elongate under the load causing the loaded bag to get closer to the floor or drag on the ground.
Typically draw tapes used in polymer bags are about 2 millimeters (“mil”) thick and 1 inch wide and carry a maximum load of approximately 10 lbs. Unfortunately, uses of polymer bags in heavy industries such as construction and in industries such as food services demand drawstrings or tapes that have much greater load strength. In addition, the tactile qualities of prior art strong thermoplastic materials tend to be unsatisfactory, since such stronger thermoplastic materials tend to have harder surfaces that cut into the hand of the user when the draw tape is used as a handle.
As is clear from the above discussion, there is a need from a manufacturing perspective of a draw tape having singular construction that combines both tensile strength and sealability.

SUMMARY OF THE INVENTION

The instant invention relates to a draw tape bag having at least one draw tape made of a polymeric blend that is oriented to provide strength and reduced elongation. The inventive polymeric blend allows the draw tape to be held without sagging under load during usage. According to the invention, the inventive draw tape is fashioned from a polymeric blend that imparts to the tape material sealability and tensile strength. This combined sealability and tensile strength are not achievable by prior art multi-layer or single layer films. As discussed above, prior art multi layer tapes are comprised of a core layer for strength and a skin layer for sealability. The sealability of the tape is required by typical polymer bag construction that is dependant upon heat-sealing. As with other parts of polymer bag construction, draw tapes are secured to the bag by heat-sealing methods known in the art.
It is an object of the invention to provide an oriented polymeric tape having a blend of polymeric components that is singular in construction. It is a further object of the inventive draw tape that the draw tape is made by blown process as known in the art. This blown tape is then further physically stretched or oriented in machine direction to impart higher strength and low elongation.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the present invention will be more fully understood from the following detailed description of illustrative embodiments, taken in conjunction with the accompanying drawing in which:
FIG. 1 is a diagrammatic view illustrating the polymeric bag having blended polymeric drawstrings that have been oriented providing sealability and tensile strength for a singular polymeric film.

DETAILED DESCRIPTION

As shown in FIG. 1, the draw tape of the present disclosure may be utilized in any type of bag, for example, refuse, product handling or shipping bags, requiring a draw tape component for at least partially sealing an open end of a bag 101. The bag 101 according to the present disclosure may include two or more panels 103 attached together by heat sealing, adhesive or other means to form a bag structure having three closed ends 105 and one open end 107. It is also contemplated that the bag 101 of the present disclosure may be fabricated from a tube of plastic having at least one sealed end and at least one open end.
The opening or top of the bag 101 is either internally or externally folded over onto itself to form a hem portion 109, which is then sealed onto the bag to define an opening between the bag 101 and hem portion 109. This hem portion 109 opening may run circumferentially around the perimeter of the bag 101 to thereby define a continuous opening around the perimeter or run along spaced discrete panel portions of the bag 101 to thereby define discrete hem portion opening 111 sections.
At least one draw tape 113 is placed within the hem portion opening 1 11 for use in at least partially sealing the bag 101. The draw tape 113 may run continuously around the perimeter of the bag opening or be placed in discrete sections along the panel sections 103. One or more cutout sections 115 may be incorporated into the hem portion 109 to aid in the use of the draw tape 113.
In one embodiment according to the present disclosure, the bag 101 contains two panel sections that are heat sealed together to form two heat sealed side sections, one heat sealed bottom section and one opening. At the opening of the bag 101, a separate hem portion 109 is defined along each panel. The hem portions 109 are discrete in that they extend along each panel from one heat sealed side section to the other heat sealed side section. A draw tape 113 is included in each discrete hem portion opening 1 11. The draw tapes 113 each include end portions that are attached to the panels of the bag by heat sealing, adhesive or other means. The attachment of the draw tapes 113 may be accomplished either contemporaneously or after the formation of the panels of the bag 101.
The instant invention overcomes problems associated with multi-layer prior art draw tapes by forming a draw tape having a selected polymeric blend. The selected polymeric blend gives the singularly constructed inventive draw tape both tensile strength and sealability. The inventive draw tape being configured from a singular polymeric film allows for a more efficient and cost effective manufacturing process. The polymeric film according to the invention is a blend of polymeric materials having varying densities that impart to the film both strength and sealability.
In one illustrative embodiment the draw tape is a selected blend of polymeric components. These polymeric components have varying densities to achieve desired properties of the draw tape. According to the invention, low density polymeric compounds such as but not limited to low density polyethylene (LDPE) allows for the sealing of draw tapes to thermoplastic bag material by known heat sealing methods. It is contemplated within the scope of the invention that other polymeric compounds may be used in place of the low-density polyethylene these include but are not limited to Metallocene, VLDPE, LLDPE, ethylene-vinyl acetate, ethylene-methyl acrylate, ethylene-ethyl acrylate, ultra low density polyethylene and mixtures thereof, and the like. It is further contemplated that other low density polymeric compounds known in the art may also be used in place of the low-density polyethylene.
In a first illustrative embodiment, the low density polyethylene has a density between 0.900 grams per cubic centimeter and up to 0.935 grams per cubic centimeter and most desirably 0.900 grams per cubic centimeter and about 0.930 grams per cubic centimeter. The low density polyethylene has a melt index of between about 0.05 and about 2.0 decigrams per minute.
The second polymeric component is high density polymeric compounds that are stronger than the first polymeric component. These high density polymeric compounds include but are not limited to high density polyethylene (HDPE). The high density polymeric compound imparts tensile strength to the draw tape. In a first illustrative embodiment the high density polyethylene has a density greater than about 0.935 grams per cubic centimeter up to about 0.965 grams per cubic centimeter and typically between 0.945 grams per cubic centimeter and 0.965 grams per cubic centimeter. The high density polyethylene has a melt index of between about 0.05 and about 6.0 decigrams per minute. According to the invention, tensile strength is imparted to the draw tape by the use of this high density polyethylene. It is contemplated within the scope of the invention that other polymeric compounds having good tensile strength may be used. These polymeric compounds include but are not limited to polyesters, polyamides, polypropylene, copolymers of polyethylene and mixtures thereof, and the like. It is further contemplated within the scope of the invention that other polymeric systems can be used to impart tensile strength such as inter penetrating network polymers, cross linkable systems, thermoplastic elastomers (TPE), reinforcement filler containing polymers and the like.
According to the invention, the HDPE and LDPE are blended in a ratio of about 5 to 1 to about 20 to 1. In a first illustrative embodiment the HDPE and LDPE are blended in a ratio of about 9 to 1. It is contemplated within the scope of the invention that different blended ratios of the HDPE and LDPE may be used. It is further contemplated that one component of the blend could be a mixture of two or more components consisting of LDPE, metallocene, metallocene polyethylene (mLDPE), LLDPE, HDPE and or the like. It is contemplated within the scope of the invention that the low density polymeric compound could be a major component of the polymeric blend up to approximately 95% to a minor component down to approximately 5%.
The blended polymeric compounds forming the inventive draw tape may further contain routinely employed materials including fillers, colorants such as pigments and dyes, slip agents, curing agents and the like. It is contemplated within the scope of the invention that the oriented draw tape may have a thickness from about 0.50 mil to 5.0 mils, although other thickness dimensions are hereby contemplated as dependent upon particular needs and uses of the draw tape.
The following example is provided to further illustrate the invention and is not intended to be limiting thereof:

EXAMPLE 1

A draw tape was constructed from a polymeric blend consisting of approximately 87.5% high-density polyethylene (HDPE), 10% low-density polyethylene (LDPE) and 2.5% of color concentrate. The HDPE used in this illustrative embodiment was a bimodal distribution high molecular weight material with an at least a density of approximately 0.952 and a melt index of approximately 0.055. The LDPE is a HPLD grade material having a melt index of 2.0 and a density of approximately 0.92. The addition of LDPE acts as a synergistic agent in improving the tensile performance of the draw tape. The color concentrate is pigment dispersed in a 2.0 MI LDPE carrier. The polymeric blend was made into a film by a blown process as known in the art. The blown film was made to approximately 9 mil thick and was then oriented in a machine direction yielding around 1.3 mil thick film. The orientation of the film imparts higher strength and lower elongation. In this particular illustrative embodiment the orientation reduced the elongation to approximately 40 from a value of approximately 400 or greater.

EXAMPLE 2

A draw tape was constructed from a polymeric blend consisting of approximately 75% high-density polyethylene (HDPE), 20% metallocene polyethylene (mLDPE) and 5% of color concentrate. The HDPE used in this illustrative embodiment was a bimodal distribution high molecular weight material having a density of approximately 0.952 and a melt index of approximately 0.055. The mLDPE used within the example had a melt index of approximately 1.0 and a density of approximately 0.92. The polymeric blend according to this example was made into a film by a blown process as known in the art. The blown film was made to approximately 6 mil thick and was then oriented in a machine direction to yield around 1.0 mil thick film.

EXAMPLE 3

A draw tape was constructed from a polymeric blend consisting of approximately 67.5% high-density polyethylene (HDPE), 30% metallocene polyethylene (mLDPE) and 2.5% of color concentrate. The HDPE used in this illustrative embodiment was a bimodal distribution high molecular weight material having a density of approximately 0.952 and a melt index of approximately 0.055. The mLDPE used within this illustrative example had a melt index of approximately 1.0 and a density of approximately 0.92. The polymeric blend according to this illustrative example was made into a film by a blown process as known in the art. The blown film was made to approximately 6 mil thick and was then oriented in a machine direction yielding around 1.0 mil thick film.

EXAMPLE 4

A draw tape was constructed from a polymeric blend consisting of approximately 78% high-density polyethylene (HDPE), approximately 10% metallocene polyethylene (mLDPE), approximately 10% filler concentrate and approximately 2% color concentrate. The HDPE used in this illustrative example was a bimodal distribution high molecular weight material with an at least a density of approximately 0.952 and a melt index of approximately 0.055. The mLDPE used in this illustrative example had a melt index of approximately 1.0 and a density of approximately 0.92. The polymeric blend was made into a film by a blown process as known in the art. The blown film was made to approximately 5 mil thick and was then oriented in a machine direction yielding around 1.0 mil thick film.
The foregoing has been a description of certain specific embodiments of the present disclosure. The present disclosure is not to be limited in scope by the illustrative embodiments described which are intended as specific illustrations of individual aspects of the disclosure, and functionally equivalent methods and components are within the scope of the invention. Indeed, various modifications of the disclosure, in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and all such modifications are included.

Claims

1. A draw tape bag comprising:

at least two panels formed from a thermoplastic material wherein said panels are sealed forming a bag;

a hem portion of each panel being folded over a top portion of said bag, said hem portion defining at least one opening;

at least one draw tape being disposed within said hem portion opening, said at least one draw tape being formed from a blend of a first polymeric compound and a second polymeric compound forming a film, said film being oriented in a manner to improve strength and decrease elongation.

2. The draw tape bag according to claim 1 wherein said at least one draw tape is formed from at least two polymeric compounds.

3. The draw tape bag according to claim 1 wherein said first polymeric compound is high-density polyethylene and said second polymeric compound is low-density polyethylene.

4. The draw tape bag according to claim 1 wherein said first polymeric compound and said second polymeric compound are blended in a ratio between about 5 to 1 to about 20 to 1.

5. The draw tape bag according to claim 1 wherein said first polymeric compound and said second polymeric compound are blended and extruded forming said film.

6. The draw tape bag according to claim 1 wherein said film forming said at least one draw tape is oriented in a machine direction.

7. The draw tape bag according to claim 6 wherein said orientation is accomplished by physical stretching.

8. The draw tape bag according to claim 6 wherein said oriented film is about 0.50 to 5.0 mil thick.

9. The draw tape bag according to claim 1 wherein said polymeric blend imparts tensile strength and heat-sealing properties to said at least one draw tape.

10. The draw tape bag according to claim 1 wherein said second polymeric compound is selected from the group consisting of low density polyethylene, Metallocene, VLDPE, LLDPE, mLDPE, ethylene-vinyl acetate, ethylene-methyl acrylate, ethylene-ethyl acrylate, ultra low density polyethylene and mixtures thereof.

11. The draw tape bag according to claim 1 wherein said first polymeric compound is selected from the group consisting of high density polyethylene, polyesters, polyamides, and mixtures thereof.

12. The draw tape bag according to claim 1 where said film is made by a blown process.

13. The draw tape bag according to claim 1 wherein said first polymeric compound and said second polymeric compound are blended in a ratio of about 9 to 1.

14. The draw tape bag according to claim 1 wherein said first polymeric compound is a high density polyethylene having a melt index of between about 0.05 and about 6.0 decigrams per minute and a density of between about 0.945 and about 0.965 grams per cubic centimeter.

15. The draw tape bag according to claim 1 wherein said second polymeric compound is a low density polyethylene having a melt index of between about 0.05 and about 2.0 decigrams per minute and a density of between about 0.900 and about 0.965 grams per cubic centimeter.

16. The draw tape bag according to claim 1 wherein said second polymeric component is an ultra low density polyethylene having a density less than about 0.900.

17. The draw tape bag according to claim 1 wherein said film forming said at least one draw tape contains a colorant selected from the group consisting of a pigment, a dye and a mixture thereof.

18. The draw tape bag according to claim 1 wherein said film forming said at least one draw tape contains a blend of first polymeric compound selected from the group consisting of low density polyethylene, ultra low density polyethylene, ethylene methyl acrylate, ethylene-ethyl acrylate, ethylene-vinyl acetate and mixtures thereof, and a second polymeric compound selected from the group consisting of high density polyethylene, polyesters, polyamides, and mixtures thereof.

19. The draw tape bag according to claim 1 wherein said at least one draw tape is affixed to said bag by heating sealing.

20. The draw tape bag according to claim 1 wherein said at least one draw tape is not affixed to said bag.

21. The draw tape bag according to claim 1 wherein said at least one draw tape is secured within said hem portion by heat sealing.