阅读说明：本技术 用于垃圾袋的改进弹性和刚度性能的塌缩泡拉带膜 (Collapse blister strip film with improved resiliency and stiffness properties for trash bags ) 是由 F·G·哈马德 M·比尔根 J·E·鲁伊斯 J·W·霍布森 于 2018-12-05 设计创作，主要内容包括：本公开的实施方案针对用于垃圾袋的拉带,其中所述拉带包含具有改进刚度的多层聚合物膜。(Embodiments of the present disclosure are directed to a draw tape for a trash bag, wherein the draw tape comprises a multi-layer polymeric film having improved stiffness.)

1. A draw tape comprising a multilayer film, wherein the multilayer film comprises:

at least two outer layers, and at least two core layers disposed between the two outer layers, wherein:

each core layer comprising a density less than 0.905g/cc and a melt index (I)₂) An ultra low density polyolefin in the range of 0.2 to 5.0 grams per 10 minutes; and

each outer layer comprising a density of 0.940 to 0.970g/cc and a melt index (I)₂) From 0.01 to 5.0 g/10 min of a high density ethylene-based polymer.

2. The draw tape of claim 1 wherein the draw tape is a two layer multilayer film comprising at least 4 layers, the two layer multilayer film comprising two outer layers and two core layers, the two core layers being adhered to each other.

3. The draw tape of claim 1 wherein each outer layer comprises a skin layer and a sub-skin layer disposed between the skin layer and the core layer, wherein the sub-skin layer comprises a high density ethylene-based polymer and the skin layer comprises a linear low density ethylene-based polymer having a density of 0.905 to 0.920g/cc when measured according to ASTM D792 and a melt index (I) when measured according to ASTM D1238₂) From 0.2 to 10.0 g/10 min.

4. The draw tape of claim 3 wherein the draw tape is a two layer multilayer film comprising at least 6 layers, the two layer multilayer film comprising two skin layers, two core layers and two sub-skin layers, the two core layers being adhered to each other.

5. The draw tape of claim 4 wherein the two layer multilayer film comprising at least 6 layers comprises less than 35% high density ethylene based polymer.

6. The draw tape of any one of the preceding claims, wherein the multilayer film comprises less than 35 weight percent of a high density ethylene-based polymer.

7. The draw tape of any one of claims 3 to 6 wherein the multilayer film comprises greater than 65 weight percent linear low density ethylene-based polymer.

8. The draw tape of any one of claims 3 to 7 wherein the linear low density vinyl polymerThe density of the compound is 0.910 to 0.920g/cc and the melt index (I)₂) From 0.2 to 2.0 g/10 min.

9. The draw tape as claimed in any one of the preceding claims, wherein the density of the ultra low density polyolefin is less than 0.900 g/cc.

10. The draw tape as claimed in any one of the preceding claims, wherein the melt index of the high density ethylene-based polymer is from 0.01 to 1.0 grams/10 minutes.

11. The draw tape as set forth in any one of the preceding claims, wherein said ultra low density polyolefin comprises an ultra low density propylene based polymer, an ultra low density ethylene based polymer, or combinations thereof.

12. A thermoplastic bag, comprising:

a first panel and a second panel joined together at a first side edge, a second side edge, and a bottom edge, wherein the first panel and the second panel define an opening along respective top edges of the first panel and the second panel and a closed end along the bottom edge;

a hem defining a channel, the hem formed along the top edges of the first and second panels;

wherein the channel comprises the draw tape of any one of claims 1 to 11.

13. A process for making a collapsed blown film, the process comprising:

forming a multilayer blown film bubble, wherein the multilayer blown film bubble comprises at least one outer layer and at least one core layer, wherein:

the core layer comprises a density of less than 0.905g/cc and a melt index (I)₂) An ultra low density polyolefin in the range of 0.2 to 5.0 grams per 10 minutes; and

the outer layer comprises a density of 0.940 to 0.970g/ccAnd melt index (I)₂) From 0.01 to 5.0 g/10 min of a high density ethylene-based polymer.

Collapsing the multilayer blown film bubble to form a collapsed blown film, wherein the collapsed blown film comprises a two-layer multilayer film having at least 4 layers, the two-layer multilayer film comprising two outer layers and two core layers, the two core layers adhered to each other.

14. The process of claim 13, wherein the outer layer comprises a skin layer and a sub-skin layer disposed between the skin layer and the core layer, wherein the sub-skin layer comprises the high density ethylene-based polymer and the skin layer comprises a linear low density ethylene-based polymer having a density of 0.905 to 0.920g/cc when measured according to ASTM D792 and a melt index (I) when measured according to ASTM D1238₂) From 0.2 to 10.0 g/10 min.

15. The process of claim 14 wherein the two-layer, multilayer film comprises at least 6 layers, the two-layer, multilayer film comprising two skin layers, two core layers, and two sub-skin layers, the two core layers adhered to each other.

Technical Field

Embodiments described herein relate generally to trash bags having a draw tape, and in particular to trash bags having a collapsed draw tape.

Background

Two types of draw tapes are commonly found in commercial consumer trash bags: standard draw tapes and elastic draw tapes. Both types of draw tapes found in commercial liner bags have drawbacks due to insufficient tensile strength. For example, typical standard pull straps are difficult to open and often fail to grasp the trash can, which results in the bag collapsing into the container when weights are placed in the bag. At the same time, typical elastic pull straps can grip the trash can and support weight; however, their elasticity causes additional problems due to the imbalance between tensile strength and elastic recovery. For example, most elastic pull straps are extensively overextended when the trash bag reaches a certain weight. Consequently, the elastic pull straps also cause inconvenience to the consumer due to this imbalance.

Thus, there is a need for both standard draw tapes having improved tensile strength and elastic draw tapes having improved tensile strength while maintaining a balance of sufficient elastic recovery.

Disclosure of Invention

Embodiments of the present disclosure address those needs by providing a draw tape comprising a multilayer film, which helps to improve stretch performance by causing more Machine Direction (MD) orientation in the film by collapsing the structure. This increase in MD orientation allows for improved tensile properties or stiffness.

In addition, for embodiments of the draw tape that include an elastic component, this allows for improved stretch performance with minimal degradation of elastic recovery properties. These results can be achieved by adding a greater amount of elastomeric material in the form of a linear low density ethylene-based polymer (LLDPE), which induces a greater elastic recovery without affecting the stiffness of the material.

In accordance with at least one embodiment of the present disclosure, a draw tape comprising a multilayer film is provided. The multilayer film comprises at least two outer layers and at least two core layers disposed between the two outer layers. Each core layer comprising a density less than 0.905g/cc and a melt index (I)₂) An ultra low density polyolefin of 0.2 to 5.0 grams/10 minutes and each outer layer comprises a density of 0.940 to 0.970g/cc and a melt index (I)₂) From 0.01 to 5.0 g/10 min of a high density ethylene-based polymer.

According to another embodiment, the draw tape is a two layer multilayer film comprising at least 4 layers, wherein the two layer multilayer film comprises two outer layers and two core layers, and the two core layers are adhered to each other.

According to yet another embodiment, the outer layer of the draw tape comprises a skin layer and a sub-skin layer disposed between the skin layer and the core layer, wherein the sub-skin layer comprises a high density ethylene-based polymer and the skin layer comprises a linear low density ethylene-based polymer having a density of 0.905 to 0.920g/cc when measured according to ASTM D792 and a melt index (I) when measured according to ASTM D1238₂) From 0.2 to 10.0 g/10 min. Furthermore, according to this embodiment, the draw tape is a two-layer multilayer film comprising at least 6 layers, wherein the two-layer multilayer film comprises two skin layers, two core layers and two sub-skin layers, and the two core layers are adhered to each other.

According to another embodiment, a process for making a collapsed blown film is provided. The process comprises forming a multilayer blown film bubble, wherein the multilayer blown film bubble comprises an outer layer and a core layer. The core layer comprises a density of less than 0.905g/cc and a melt index (I)₂) An ultra low density polyolefin of 0.2 to 5.0 grams/10 minutes and the outer layer comprises a density of 0.940 to 0.970g/cc and a melt index (I)₂) From 0.01 to 5.0 g/10 min of a high density ethylene-based polymer.The process further comprises collapsing the multilayer blown film bubble to form a collapsed blown film, wherein the collapsed blown film comprises a two layer multilayer film having at least 4 layers. Further, according to this embodiment, the two-layer multilayer film comprises two outer layers and two core layers, and the two core layers are adhered to each other.

These and other embodiments are described in more detail below in the detailed description and in conjunction with the following figures.

Drawings

The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

fig. 1 is a schematic view of a film 1 of the present invention, which is a draw tape having a two-layer collapsed configuration.

Fig. 2 is a schematic view of a film 2 of the present invention, which is a draw tape having a three-layer collapsed structure.

Fig. 3 is a schematic view of a trash bag according to one or more embodiments of the present disclosure.

Fig. 4 is a schematic view of a comparative film 1, which is a draw tape having a two-layer separation structure.

Fig. 5 is a schematic view of a comparative film 2, which is a draw tape having a three layer separation structure.

Fig. 6 is a graph comparing the tensile curves of comparative film 1 and inventive film 1.

Fig. 7 is a graphical representation comparing the tensile curves of comparative film 2 and inventive film 2.

Fig. 8 is a graph comparing the elastic recovery curves of comparative film 2 and inventive film 2.

Figure 9 is a graph showing the effect of HDPE resin on the elastic recovery of collapsed bubble films.

Fig. 10 is a graphical representation showing the effect of HDPE on tensile properties of a collapsed film.

Detailed Description

Specific embodiments of the present application will now be described. The present disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth in the present disclosure. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art.

The term "polymer" refers to a polymeric compound prepared by polymerizing monomers of the same or different types. Thus, the generic term polymer encompasses the term "homopolymer", which generally refers to polymers prepared from only one type of monomer, and "copolymer", which refers to polymers prepared from two or more different monomers. As used herein, the term "interpolymer" refers to a polymer prepared by the polymerization of at least two different types of monomers. Thus, the generic term interpolymer includes copolymers, or polymers, prepared from two or more different types of monomers, such as terpolymers.

"polyethylene" or "vinyl polymer" shall mean a polymer comprising greater than 50 weight percent of units derived from ethylene monomers. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers).

As used herein, "polypropylene" or "propylene-based polymer" refers to a polymer that is contained in polymerized form, meaning a polymer that contains greater than 50 mole percent of units derived from propylene monomers. This includes propylene homopolymers, random copolymer polypropylenes, impact copolymer polypropylenes, propylene/alpha-olefin copolymers, and propylene/alpha-olefin copolymers.

As used herein, "multilayer draw tape" refers to a structure having multiple layers, typically formed via coextrusion. In contrast, a "single layer draw tape" is a single layer film.

Reference will now be made in detail to embodiments of various draw tapes comprising the multilayer film. Referring to fig. 1, the multilayer film 100 includes at least two outer layers 110 and at least two core layers 120 disposed between the two outer layers 110. Each core layer 120 comprises a density less than 0.905g/cc and a melt index (I)₂) An ultra low density polyolefin in the range of 0.2 to 5.0 grams per 10 minutes.

As described below, the ultra low density polyolefin needs to be sufficiently tacky so that when the blown film bubble collapses, the two layers of ultra low density polyolefin will adhere to each other upon contact. Various compositions are believed to be suitable for use with ultra low density polyolefins. In one embodiment, the ultra low density polyolefin comprises an ultra low density propylene based polymer. In further embodiments, the ultra low density polyolefin comprises an ultra low density ethylene-based polymer. In some embodiments, the ultra low density polyolefin comprises a combination of an ultra low density propylene-based polymer and an ultra low density ethylene-based polymer. In further embodiments, the ultra low density polyolefins may include elastomers and plastomers.

Various methods for producing ultra low density polyolefins are contemplated. For example, ultra low density ethylene based polymers may use ziegler-natta catalysts; single-site catalysts (including but not limited to dual metallocene catalysts and constrained geometry catalysts); and a post-metallocene molecular catalyst.

Although the ultra low density polyolefins disclosed above have densities less than 0.905g/cc, the ultra low density polyolefins may have densities less than 0.900 g/cc. In some embodiments, the ultra low density polyolefin has a density of from 0.850g/cc to 0.905g/cc, or from 0.880 to 0.900 g/cc. Further, in some embodiments, the ultra low density polyolefin has a melt index (I)₂) From 0.2 to 2.0 g/10 min. In some embodiments, the ultra low density polyolefin has a melt index (I)₂) From 0.2 to 1.5 g/10 min.

Referring again to FIG. 1, each outer layer 110 may comprise a density of 0.940 to 0.970g/cc and a melt index (I)₂) From 0.01 to 5.0 g/10 min of a high density ethylene-based polymer. In further embodiments, the high density ethylene-based polymer may have a density of from 0.940 to 0.960 g/cc. In some embodiments, the high density ethylene-based polymer may have a density of 0.940 to 0.950 g/cc. Further, the melt index (I) of the high-density ethylene-based polymer₂) And may be 0.01 to 1.0 g/10 min. In some embodiments, the melt index (I) of the high density ethylene-based polymer₂) And may be 0.01 to 0.5 g/10 min.

Various methods for producing high density ethylene-based polymers are contemplated. For example, high density ethylene-based polymers are typically prepared using ziegler-natta catalysts, chromium catalysts, or single-site catalysts (including, but not limited to, bi-metallocene catalysts and constrained geometry catalysts).

It is also contemplated that the multilayer film includes less than 35 weight percent of the high density ethylene-based polymer. In some embodiments, the multilayer film comprises less than 30 weight percent of the high density ethylene-based polymer. Further, in some embodiments, the multilayer film includes less than 25 weight percent of the high density ethylene-based polymer. Without being limited by theory, the use of a high density ethylene-based polymer of less than 35% results in an improvement in elongation (%), as will be further explained below.

Referring again to fig. 1, multilayer film 100 is a two-layer multilayer film comprising two outer layers 110 and two core layers 120. The two core layers 200 are adhered 130 to each other.

Referring to fig. 2, other embodiments are directed to a two layer multilayer film 200 comprising at least 6 layers. Like the multilayer film of fig. 1, the two core layers 120 are adhered 130 to each other. In this embodiment, each outer layer 110 comprises a skin layer 112 and a sub-skin layer 114 disposed between the skin layer 112 and the core layer 120. According to this embodiment, sub-skin 114 comprises the high density vinyl polymer mentioned above.

In one or more embodiments, skin layer 112 comprises a linear low density ethylene-based polymer having a density of 0.905 to 0.920g/cc when measured according to ASTM D792 and a melt index (I) when measured according to ASTM D1238₂) From 0.2 to 10.0 g/10 min. In another embodiment, the linear low density ethylene-based polymer has a density from 0.910 to 0.920g/cc, or from 0.915g/cc to 0.920 g/cc. Also contemplated is the melt index (I) of the linear low density ethylene-based polymer₂) May be 0.2 to 2.0 g/10 min, or 0.2 to 1.5 g/10 min.

Various methods for producing linear low density ethylene-based polymers are contemplated. For example, linear low density ethylene-based polymer resins may be prepared using ziegler-natta catalyst systems, resins prepared using single-site catalysts (including, but not limited to, dual metallocene catalysts and constrained geometry catalysts), and resins prepared using post-metallocene molecular catalysts. The linear low density ethylene-based polymer resin may comprise linear, substantially linear, or heterogeneous ethylene-based polymer copolymers or homopolymers. Linear low density ethylene-based polymer resins may contain less long chain branching than LDPE and include substantially linear ethylene-based polymers, which are further defined in U.S. patent No. 5,272,236, U.S. patent No. 5,278,272, U.S. patent No. 5,582,923, and U.S. patent No. 5,733,155; homogeneously branched linear ethylene polymer compositions such as those in U.S. Pat. No. 3,645,992; heterogeneously branched ethylene polymers such as those prepared according to the process disclosed in U.S. Pat. No. 4,076,698; and/or blends thereof (such as those disclosed in U.S. patent No. 3,914,342 or U.S. patent No. 5,854,045). The linear low density ethylene-based polymer resin may be prepared via gas phase, solution phase, or slurry polymerization, or any combination thereof, using any type of reactor or reactor configuration known in the art.

In one or more embodiments, the multilayer film comprises greater than 65 weight percent of the linear low density ethylene-based polymer. In some embodiments, the multilayer film comprises greater than 70 wt% of the linear low density ethylene-based polymer. Further, in some embodiments, the multilayer film comprises less than 80 weight percent of the high density ethylene-based polymer.

Reference will now be made in detail to various thermoplastic bag embodiments of the present disclosure. Referring to fig. 3, the thermoplastic bag 10 comprises a first panel 12 and a second panel 22. The first panel 12 and the second panel 22 are joined together at a first side edge 18, a second side edge 28, and a bottom edge 29. The first and second panels 12, 22 define an opening 25 along respective top edges 19 of the first and second panels 12, 22. Further, the first panel 12 and the second panel 22 define a closed end as the first panel 12 and the second panel 22 are joined along the bottom edge 29.

Referring again to fig. 1, thermoplastic bag 10 includes a hem 16 formed along a top edge 19. As shown, the flap 16 is a thermoplastic flap extending from the top edge 19 of the first and second panels 12, 22 and sealed to the first and second panels 12, 22 such that a channel is formed between the first flap 16 and the first and second panels 12, 22.

The thermoplastic bag 10 includes a draw tape 40 disposed within the channel, the draw tape including a multilayer film as described above, such as multilayer film 100 or multilayer film 200. In addition, the first panel 12 has a first draw tape access hole 17 located along a top edge 19 of the first panel 12. The first draw tape access hole 17 allows access to the draw tape 40 from the outside. The second panel 22 has a second draw tape access hole 27 located along the top edge 23 of the second panel 22. The second draw tape inlet hole 27 allows access to the draw tape 40 from the outside.

Various methods of producing thermoplastic bags are familiar to those of ordinary skill in the art. For example, the first panel 12, the second panel 22, and the draw tape 40 may undergo surface modification, such as ring rolling, Machine Direction Oriented (MDO) stretching, or embossing.

Reference will now be made in detail to various embodiments of the present disclosure of processes for making these multilayer films. In one or more embodiments, the process comprises forming a multilayer blown film bubble, and collapsing the multilayer blown film bubble to form a collapsed blown film. The collapsed blown film comprises a two layer multilayer film comprising the 4 layer structure of figure 1 or the 6 layer structure of figure 2.

For the 4-layer, two-layer, multilayer film of fig. 1, the process of making the collapsed blown film comprises forming a multilayer blown film bubble, wherein the multilayer blown film bubble comprises an outer layer 110 and a core layer 120. Next, the process comprises collapsing the multilayer blown film bubble to form a collapsed blown film, wherein the collapsed blown film comprises a two-layer multilayer film comprising at least 4 layers. Further, according to this embodiment, the two-layer multilayer film comprises two outer layers and one two-layer core layer, and the two core layers are adhered to each other. The process for the two-layer film of fig. 2 is similar to the process for the two-layer film of fig. 1, except that the 3-layer film is collapsed to produce a 6-layer film.

More details regarding the collapse technique in the blown film process are described below. During the blown film process, a plastic film extruded from the extruder die is formed and pulled up the tower above the nip. At the nip, the bubble collapses into two flat sheets. In contrast, in conventional blown film processes, the sides of the two-layer film are trimmed away to separate the film into two separate single-layer films prior to winding the film onto the core. In a collapsed blown film process, as in the process embodiments of the present disclosure, the films do not separate — meaning that both films remain collapsed. Therefore, the blown film needs to be half the thickness of the final article, as the two layer technique will give the required gauge. The tackiness of the ultra low density polyolefin on the inside of the bubble ensures adhesion once the bubble collapses. This makes the two films difficult to separate, which is important for these applications. Without being bound by theory, this collapsing process for producing the two-layer film imparts improved tensile strength. Furthermore, for embodiments that also include an elastic component, this collapsing process for producing the two layer film imparts an improved balance between tensile strength or stiffness and elastic recovery, which is highly desirable in draw tape applications.

In other embodiments, the blown film bubble is formed via a blown film extrusion line having a blow-up ratio of from 1 to 4 or from 1 to 3. Further, the formation of the multilayer blown film bubble step can be conducted at a temperature of 350 to 500 ° F or 375 to 475 ° F. The output speed may be 10 to 50 lbs/hr/inch, or 10 to 30 lbs/hr/inch.

Test method

The test method comprises the following steps:

₂melt index (I)

In order to test the melt index (I)₂) Vinyl polymer samples were measured at 190 ℃, 2.16kg according to ASTM D1238. These values are reported in grams per 10 minutes, corresponding to grams eluted every 10 minutes. Propylene based polymers measured at 230 ℃ and 2.16kg according to ASTM D1238

Density of

To test density, samples were prepared and measured according to ASTM D4703 and in grams per cubic centimeter (g/cc or g/cm)³) And (6) reporting. Measurements were made within one hour of sample pressing using ASTM D792, method B.

Rigidity and rigidity

To test the stiffness and rigidity of the membrane, a standard tensile test was performed according to ASTM D882, and the load was calculated from the strain gauges. To obtain good load carrying capacity, the draw tape requires high yield and breaking stresses. Tensile properties in both the Machine Direction (MD) and the cross-machine direction (CD) were determined according to ASTM D882 at a cross-head speed of 20 inches per minute (in/min). The width of the sample was 1 inch and the width of the initial grip spacing was 5 inches. The sample was pulled continuously in the MD on an Instron instrument at a rate of 20 inches/minute until breaking. The breaking stress is recorded as tensile strength.

Elastic recovery rate

To test the elastic recovery of the draw tape, a modified StretchHooder 60/40 experiment (astm d4649) was conducted and the elastic recovery was calculated using the collected data. The modified Stretch Hooder60/40 experiment included changing the percent strain from 60/40 to 12/6 and the hold time from 15 to 2 seconds. In conducting the experiment, 1 inch strips of the sample were first pulled longitudinally on the Instron at 5 inch intervals. Next, the sample was pulled to 12% strain at 20 inches/minute and held for 2 seconds. The crosshead then recovered to 6% strain and held for 100 seconds. Third, the strain returns to 0%. The elastic recovery of the film was then calculated using the data collected from this experiment.

Free shrinkage rate

To test the unconstrained biaxial thermal shrinkage of the films, a hot oil bath test was used. The hot oil bath contained silicone oil and was maintained at a temperature of 140 ℃. Free shrinkage measures the amount of polymer orientation in the amorphous regions of a semi-crystalline polymer. The results of the hot oil bath test are reported and the Machine Direction (MD) and Cross Direction (CD) dimensional changes of the pre-cut samples are compared.