Patent Application
20150376467
The present invention relates to new water activated paper adhesive tapes having a film reinforcement extrusion laminated to the paper thereof, which is particularly useful as a carton or box sealing tape.
Adhesive tapes for sealing cartons or carton flaps during manufacture or after the carton is filled are well known. One of the most common constructions is a standard Kraft paper tape which includes a water soluble or water activated adhesive on one side. Rolls of this tape can be dispensed through machines which rely on the longitudinal stiffness of the tape to unwind it from the roll and force it through a tape moisturizing component. This component includes a water reservoir which moistens the adhesive surface of the tape and readies it for application to the carton.
Various improvements to this type of tape have been tried over the years to meet differing requirements in the manufacture and sealing of cartons. For example, multiple layered tapes using reinforcing fibers generally made of fiberglass and extending longitudinally and/or angularly across this tape to increase its strength are conventionally used for higher closure strength requirements. Although the tape is harder to tear due to the reinforcing fibers, this construction results in the somewhat rough and uneven surface both along the top and bottom of the tape, as well in a tape construction that is somewhat thicker than the conventional Kraft tape. This uneven surface and thicker tape causes a standard size roll to be of a shorter length for any given diameter compared to conventional tapes.
Previous attempts to add plastic films to tapes have been inadequate. In one aspect, the plastic film was used as the layer to carry the water activated adhesive. The problem with this attempt is that the plastic film cannot hold a water soluble or water activatable adhesive very effectively. In another aspect, plastic film was cold laminated to a paper backing using an adhesive to develop a tape where the plastic could be stripped away after application because of the low bond strength provided by the adhesive between the plastic film and the paper backing Neither are desired characteristics for the water activated paper tape disclosed herein. Thus, the disclosed water activated paper tapes are an improvement over these previous attempts to use a plastic film in a water activated tape.
One aspect of the invention is a water activated paper tape, and, more particularly, a carton sealing tape including a film reinforcement extrusion laminated to the paper backing thereof. The water activated tapes have a paper backing having a top surface and a bottom surface, a water activated adhesive applied to the bottom surface of the paper backing, and a film reinforcement structure applied to the top surface of the paper backing The film reinforcement structure results in a hand-tearable water activated tape and includes an outermost oriented polyolefin film, and a lamination layer comprising one or more of an enhanced polyethylene resin, a polyolefin plastomer, a very low density polyethylene, a nylon, a polyester, and a co-polyester laminating the outermost polyolefin film to the paper backing These two layers are coextruded onto the paper backing, such as Kraft paper.
In one embodiment, the outermost oriented polyolefin film is a biaxially oriented polypropylene film. In another embodiment, the outermost oriented polyolefin film is a biaxially oriented polyethylene terephthalate. In either case, the outermost polyolefin film may have a thickness of about 0.5 mil to about 2 mil.
The lamination layer likewise has a thickness of about 0.5 mil to about 2 mil, or more preferably about 1 mil to about 1.3 mil. In one embodiment, the lamination layer includes, as the majority thereof, an enhanced polyethylene resin, and may include one or more other polyethylene resins. In one embodiment, low density polyethylene resin is included in the lamination layer composition with the enhanced polyethylene resin and the enhanced polyethylene resin is about 60% w/w to 99% w/w of the lamination layer.
In another aspect, methods of making such a water activated tape are disclosed herein. The methods include providing a water activated paper tape comprising a paper backing having a water activated adhesive defining a bottom major surface thereof, and extrusion laminating to the paper backing, opposite the water activated adhesive, a film reinforcement structure. The film reinforcement structure includes an outermost oriented polyolefin film, and an innermost lamination layer comprising one or more of an enhanced polyethylene resin, a polyolefin plastomer, a very low density polyethylene, a nylon, a polyester, and a co-polyester. The extrusion laminating places the innermost lamination layer contiguous to the paper backing and includes coextruding the outermost polyolefin film and the innermost lamination layer, and thereafter reducing the temperature of the tape. In one embodiment, coextruding includes extruding the outermost polyolefin film to have a thickness of about 0.5 mil to about 2.0 mil and extruding the innermost lamination layer to have a thickness of about 0.5 mil to about 2.0 mil.
In one embodiment, the method may also include providing the paper backing and applying the water activated adhesive to a bottom major surface thereof. The lamination layer composition is as described above and the oriented polyolefin film may be a biaxially oriented polypropylene film or a biaxially oriented polyethylene terephthalate.
The following detailed description will illustrate the general principles of the invention, examples of which are additionally illustrated in the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.
The film reinforcement 116 includes an oriented film as an outermost film layer 124 extrusion laminated to the paper backing 112 by a lamination layer 122 containing one or more of an enhanced polyethylene resin, a polyolefin plastomer, a very low density polyethylene, a nylon, a polyester, and a co-polyester. The outermost film layer 124 may be a polyester film, nylon film, polyethylene film or a polypropylene film or any other polymer capable of being formed into a thin oriented film structure. In one embodiment, the oriented film is biaxially-oriented. In another embodiment, the oriented film is monoaxially oriented. The oriented film is present at a thickness of about 0.5 mil to about 2 mil. In another embodiment, the film is present at a thickness of about 1.0 mil (25 micron). In one exemplary embodiment, disclosed in Example 1, the film layer 124 is a biaxially-oriented polypropylene, in particular a biaxially-oriented polypropylene homopolymer. In another exemplary embodiment, disclosed in Examples 2-4, the film layer 124 is a biaxially-oriented polyethylene terephthalate, which is a polyester film.
The lamination layer 122 includes a material that can be softened or melted for extrusion lamination and will adhere the selected oriented film layer 124 to the paper backing 112. Typically, the lamination layer 122 will have at least one material therein that is capable of forming a bond to both the paper backing and the oriented film layer. For example, when the oriented film includes a polyethylene, then the lamination layer likewise can include a polyethylene, such as an enhanced polyethylene resin, a polyolefin plastomer, and/or a very low density polyethylene. In another embodiment, the lamination layer 122 may be a nylon or polyester or co-polyester material. If a film such as an oriented polyester is used, then the laminating layer can be a polyester and/or other materials such as one or more plastomers. An embodiment with an oriented polyester as the film and a laminating layer comprising one or more plastomers without a polyester present will require the surface of the film being laminated with the laminating layer to be treated using such methods as corona or flame treatment to ensure proper adhesion.
Example suitable enhanced polyethylene resins are available from Dow Chemical Company under the brand ELITE™. These are ethylene alpha-olefin resins. In one embodiment, the enhanced polyethylene resin has a melt mass flow rate of greater than 3.5 g/10 min, more preferably greater than 5 g/10 min, and has a melting temperature (thermal, not extrusion) of greater than 200° F., more preferably greater than 250° F. In one embodiment, the lamination layer 122 consists of an ELITE™ enhanced polyethylene resin having a density of about 0.91 g/cm3, a melt index of about 15 g/10 min, and a melting temperature of about 255° F. In another embodiment, the lamination layer 122 comprises about 40% to about 99% w/w of an ELITE™ enhanced polyethylene resin having a density of about 0.91 g/cm3, a melt mass flow rate of about 15 g/10 min, and a melting temperature of about 255° F., the balance being one or more other polyethylene resins having a density greater than 0.91 g/cm3, a melting temperature within about plus or minus 5° F. of the melting temperature of the enhanced polyethylene resin, and/or a melt index of greater than 5 g/10 min.
In another embodiment, the lamination layer comprises about 70% to 85% w/w of the enhanced PE resin, about 10% to 25% w/w of one or more other polyethylene resins, and the balance being additives. The enhanced PE resin will preferably be present at a percentage of about 20% to 100% w/w, and most preferably from about 30% to 80% w/w. The one or more “other” polyethylene resins, may include linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), metallocene variations of any of the forgoing that are available, etc. In one embodiment, LDPE is added to the enhanced PE resin to improve extrusion processability such as reducing neck-in and improving melt strength. It is typically added at about 10%-40% w/w to achieve these improvements. The preferable melt index for the LDPE in a cast extrusion coating process is about 1-20 g/10 min, preferably 3-10 g/10 min.
Suitable polyolefin plastomers are available from Dow Chemical Company under the brand AFFINITY™ and from Exxon Mobile Corporation under the brand EXACT™. The AFFINITY™ polyolefin plastomers have densities in the range of 0.870 g/cm3 to 0.878 g/cm3, a melting point per Dow Chemical's own test method of 154° F. to 158° F., and a melt index of 500 g/10 min to 1250 g/10 min at 190° C. with a 2.16 kg weight. The EXACT™ plastomers are metallocene catalyzed ethylene alpha olefin copolymers. Suitable metallocene catalyzed ethylene alpha olefin copolymers for the applications disclosed herein include those having a density in the range of 0.870 g/cm3 to 0.905 g/cm3, a melt index in the range of 1-30 g/10 min, and 2-20 g/10 min.
Suitable very low density polyethylenes are available from Dow Chemical Company under the brand FLEXOMER™, and have a density in a range of about 0.905 to about 0.910 g/cm3 and a melt mass flow rate in a range of 0.5 g/10 min to 2.5 g/10 min.
The lamination layer 122 is present at a thickness of about 0.5 mil to about 2 mil. In another embodiment, the lamination layer 122 is present at a thickness of about 1.0 mil (25 micron) to about 1.3 mil (32.5 micron).
Additives for inclusion in the lamination layer may include one or more of UV inhibitors, antioxidants, pigments, and antistatic agents, but are not limited thereto.
The water activated tape 130 as a result of the extrusion lamination of the outermost film layer 124 to the paper backing 112 is not easily strippable therefrom. That is, once laminated, it is not easy to separate the outermost film layer 124 from the paper backing 112.
Paper backing 112 may be any type of paper including, but not limited to, creped paper, non-creped paper, or release paper. Preferably, the paper backing 112 is a Kraft paper. Creped NBSK (Northern Bleached Softwood Kraft) paper web is one suitable backing for use in this invention. In one embodiment, Kraft paper is used and is a 20 to 57 lb Kraft paper.
The water activated adhesive 114 may be applied to the paper backing 112 as a solvent-cast, aqueous, solventless, or molten film or as a coating layer using either extrusion, any manner of roll, knife, rod, or blade coating, curtain coating or any suitable method. In one embodiment, the water activated adhesive 114 is present at a thickness of about 0.1 mil to about 2.5 mil. The water activated adhesive 114 may be any conventional water activated adhesive or hereinafter developed adhesive suitable for box sealing or carton sealing tapes (also referred to as packaging tapes). In one embodiment, the water activated adhesive 114 is based on a starch from corn, sorghum, wheat, sago, tapioca, legumes, barley, rice, and/or potatoes. In another embodiment, the water activated adhesive 114 may be a polyvinyl alcohol-based, remoistenable adhesive.
A continuous method of manufacturing the film laminated water activated tapes includes providing a water activated paper tape comprising a paper backing having a water activated adhesive defining a bottom major surface thereof, and extrusion laminating to the paper backing, opposite the water activated adhesive, a film reinforcement structure. The film reinforcement structure includes an outermost oriented polyolefin film, and an innermost lamination layer comprising one or more of an enhanced polyethylene resin, a polyolefin plastomer, a very low density polyethylene, a nylon, a polyester, and a co-polyester. The extrusion laminating disposes the innermost lamination layer contiguous to the paper backing and includes coextruding the outermost polyolefin film and the innermost lamination layer together onto the paper backing on a surface opposite the adhesive layer. The method may also include reducing the temperature of the tape after the coextruding of the outermost polyolefin film and the innermost lamination layer and thereafter winding the tape onto a roll and slitting the rolled tape into a plurality of rolls of film laminated water-activation tape.
In one embodiment, coextruding includes extruding the outermost polyolefin film to have a thickness of about 0.5 mil to about 2.0 mil and extruding the innermost lamination layer to have a thickness of about 0.5 mil to about 2.0 mil.
In another embodiment, the continuous method of manufacturing a film laminated water activated tape may also include providing the paper backing and applying the water activated adhesive to a bottom major surface thereof before coextruding the outermost polyolefin film and lamination layers onto the paper backing. The lamination layer composition is as described above and the oriented polyolefin film may be a biaxially oriented polypropylene film or a biaxially oriented polyethylene terephthalate.
The water activated paper tapes described above eliminate the need for a filament scrim reinforcement layer and only require one layer of paper. This results in a tape product with uniform puncture and tear properties at a similar or lower total cost to commercially available carton sealing tapes today as well as producing a thinner tape that will provide more length for a given roll diameter, requiring fewer roll changes on applicating equipment. For example, rolls with an outer diameter of 6″ wound on a 1″ core would have approximately 420′ for a 5.5 mil thick tape of the invention compared to approximately 290′ of an 8 mil thick filament reinforced, water activated tape. Examples of film laminated water activated tapes, made according to the methods described above, are included below.
For the data presented below, a 140 grade water activated paper tape (already having the adhesive applied thereto in an independent manufacturing process) was extrusion laminated with a 25 micron biaxially-oriented polypropylene (BOPP) film using approximately 30 gsm of an enhanced polyethylene resin, Dow ELITE™ 5815 enhanced polyethylene resin, as the lamination layer connecting the BOPP film to the paper backing of the water activated paper tape. The water activated paper tape and the BOPP film are relatively stiff structures. In contrast, the Dow ELITE™ 5815 enhanced polyethylene resin is a soft resin having a density of 0.91 g/cm3, a melt index of 15 g/10 min, a relatively low modulus, but high melting point (melting temperature of 255° F.).
In Table 1 below, “MD” stands for the machine direction, and “TD” stands for the transverse direction relative to the machine direction.
For the Trapezoidal tear tests, these were conducted as notched or un-notched trials. For the notched trials, the samplers were notched and torn at the notch, and the failure was observed to be mostly a function of the failure of the lamination layer 122. For the unnotched trials, the tear propagated under the polyolefin film 124 until the polyolefin film 124 failed.
For this example, there was skepticism that a biaxially oriented polypropylene would provide enough strength for sufficient tear. It was originally thought that a monoaxially oriented polypropylene would be required. However, surprisingly, the film laminated, water activated paper tape had a significant increase in the transverse direction (TD) tear initiation strength. The unnotched TD tear strength (Trapezoidal Tear TD) in Table 1 above is representative of the force required to initiate the transverse direction tearing of a tape. Once the tear is initiated, it propagates much more easily as seen by the notched tear. This is beneficial in that the tape can withstand forces that would break it on a box in transport but is relatively easily hand tearable. No brittle tear was experienced.
For the data presented below, a 140 grade water activated paper tape (already having the adhesive applied thereto in an independent manufacturing process) was extrusion laminated with a 25 micron biaxially-oriented polyethylene terephthalate (BOPET) film using approximately 1.2 mil thickness of a lamination layer composition. The lamination layer composition included Dow ELITE™ 5815 enhanced polyethylene resin and a low density polyethylene resin as the lamination layer, and successfully connected the BOPET film to the paper backing of the water activated paper tape. The water activated paper tape and the BOPET film are relatively stiff structures. In contrast, the Dow ELITE™ 5815 enhanced polyethylene resin is a soft resin having a density of 0.91 g/cm3, a melt index of 15 g/10 min, a relatively low modulus, but high melting point (melting temperature of 255° F.). The linear low density polyethylene (LDPE), DOW™ LDPE 722, has a density of about 0.92 g/cm3 and a melt index of about 8 g/10 min, and a melting temperature of about 224° F.
The Trapezoidal Tear Strength, ASTM 4533, test was used, i.e., a trapezoidally-shaped sample, to evaluate the transverse direction (TD) tear initiation strength of the disclosed laminated film-WAT. The data in Table 2 shows that the unnotched TD tear strength (Trapezoidal Tear TD), representative of the force required to initiate the transverse direction tearing of a tape, is sufficient such that the tape can withstand forces that would break it on a box in transport. However, once the tear is initiated, based on the lower value for the notched Trapezoidal Tear TD, it propagates much more easily through the tape, evidencing that the tape is relatively easily hand tearable.
The examples in Table 3 were also made with a lamination layer composition of Dow ELITE™ 5815 enhanced polyethylene resin and a low density polyethylene resin that successfully connected the film to the paper backing of the water activated paper tape.
The comparative example in Table 3 is VENOM reinforced water-activated tape, a natural Kraft, 3-way reinforced, light duty, economy grade, water-activated carton sealing tape manufactured with a starch based adhesive. The three trial film laminated water activated tapes have generally similar adhesive layers and adhesive weight, generally similar paper backings and total caliper. However, the laminated water activated tapes of Trials 5-7 perform differently with respect to tear initiation strength, represented by the Finch Tear (ASTM D824) data in Table 3 above. The Finch Test is tear initiation in the cross or transverse direction. Here, all three Trials have a higher Finch Test value, which shows that the tape can withstand forces that would break it on a box in transport. Yet, the Elmendorf Tear (ASTM D9122) in the cross or transverse direction is much lower for the three Trials compared to the comparative example. This shows that the film laminated water activated tapes of Trials 5-6 are relatively easily hand tearable after the tear is initiated in the tape, and that the initial tear is not so easily initiated that the tape would fail during transport of a carton to which the tape was applied.
Other tests conducted using 100% HDPE as the lamination layer with a BOPP film and with a BOPET film had poor adhesion, such that it does not make a useful carton sealing tape.
Having described the invention in detail and by reference to preferred embodiments, it will be apparent that modifications and variations thereof are possible without departing from the scope of this invention. The tape is preferably a masking tape, but is not limited thereto.
This application claims the benefit of U.S. Provisional Application No. 62/016,685, filed Jun. 25, 2014, the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62016685 | Jun 2014 | US |
