Patent Application
20140106096
1. Field
Embodiments of the present invention relate to packaging films and bags formed by packaging films.
2. Background
Items are often enclosed in packaging for distribution and handling. Packaging can, for example, be designed to provide physical protection of the item, aesthetic appeal to the consumer, and convenience during distribution and handling.
Plastic films are often used in packaging. For example, sheets of film or bags formed from one or more sheets of film can be used to contain or protect items. The film can also be contained within other packaging, such as a box or clamshell container, which can provide additional protection or containment of an item. For items having a heightened susceptibility to scratches, such as certain polycarbonate surfaces, it can be especially desirable to develop packaging film that does not visibly scratch the item during normal distribution and handling. In some cases, it can be desirable for such packaging film to also exhibit other characteristics, such as a desired texture, color, or other mechanical or material properties.
In broad terms, a packaging film can include one or more layers of film, such as bi-axially oriented polypropylene (BOPP) film having one or more additives, such as certain antiblocking additives. The type and amount of additives used in the film can be selected such that the film does not visibly scratch the surface of an item in contact with the film during normal distribution and handling. For example, the film can be tailored to reduce or eliminate scratches on a polycarbonate polymer surface, such as those found on certain computer accessories. In some embodiments, the film is clear and transparent. In some embodiments, the film is thin and rigid, which can result in the film having a crinkly feel. One or both sides of the film can also be heat sealable which can, for example, allow the film to form an enclosure. Additional additives or treatments can be used to realize other desired effects or properties.
Additional features of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. Both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention.
The accompanying figures, which are incorporated herein, form part of the specification and illustrate exemplary embodiments of the present invention. Together with the description, the figures further serve to explain the principles of, and to enable a person skilled in the relevant art(s) to make and use the exemplary embodiments described herein.
The following detailed description refers to the accompanying figures, which illustrate exemplary embodiments of the present invention. Other embodiments are possible. Modifications may be made to the exemplary embodiments described herein without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not meant to be limiting. The operation and behavior of the embodiments presented are described with the understanding that modifications and variations may be within the scope of the present invention.
Some existing packaging films can undesirably scratch the surface of items in contact with the film. Scratches can occur, for example, during transportation or handling of the packaging. The material of the film is one factor that can affect the amount of scratching caused by the film. For example, some polypropylene (PP) films with embedded hard particles such as certain silica additives can cause scratches on soft surfaces. The particles can cause scratches due to the creation of high and low points on the film's surface. In some cases, particles protruding from a first side of the film can scratch adjacent opposite sides of the film while the film is being wound or unwound.
In addition, scratched surfaces of a film can potentially act as stress points or abrasive points. That is, even if there are no hard particles in or on the film, the previously scratched surface of the film can itself cause scratches. In some films, scratches can be caused by the film itself even if it does not contain embedded particles. As a result, attempting to remove all particles from such a film may not entirely eliminate scratches. For at least the above reasons, it can be desirable to develop a film that does not visibly scratch an item in contact with the film during normal distribution and handling. In some cases, it can be desirable for such packaging to also exhibit other characteristics, such as a desired texture, color, or other mechanical or material properties.
As described further herein, the properties of base polypropylene can be tailored by mixing the base polypropylene with certain additives. The additives can be mixed with the base polypropylene using one or more conventional thermoplastic processes, such as for example during compounding in an extruder or dry blending at a feed hopper during sheet extrusion. Film can then be created by extrusion to produce a cast sheet of film having a desired shape and thickness. The extrusion process can be continuous, which can produce an indefinitely long material, or it can be semi-continuous, which can produce multiple discrete extrusions. The extrusion process can include the use of heated or non-heated stock material.
The cast sheet of film can then be converted to bi-axially oriented polypropylene (BOPP) film to increase its strength and clarity. The conversion process includes extruding the cast sheet of film and then stretching it in both the machine direction and an across-machine direction. Film 10 can, for example, be produced in large rolls which can then be slit on slitting machines into smaller rolls for use on packaging machines. Trade names for BOPP and other films include MOPLEN™ (e.g., MOPLEN™ HP522H, which is also known as LyondellBasell HP 522 H by LyondellBasell Industries of Rotterdam, Netherlands), DOWLEX™ SC 2108G Polyethylene Resin (by The Dow Chemical Company of Midland, Mich.), and NAN YA 2020S (YUNGSOX 2020S) (by Formosa Plastics Corporation of Taiwan, R.O.C.).
MOPLEN™, for example, is a polypropylene homopolymer without slip additives or antiblocking additives. With respect to its material properties, MOPLEN™ is a semi-crystalline and stiff polymer having a melt flow rate (MFR) of approximately 10 g/10 min (230° C./2.16 Kg) and a tensile modulus of approximately 1500 MPa (1 mm/min). After biaxial orientation, MOPLEN™'s tensile modulus increases to about 1700-2000 MPa in machine direction and about 2800-3800 MPa in transverse direction.
In some embodiments, the thickness of film 10 can range from about 20 microns (0.78 mils) to about 250 microns (9.84 mils). Suitable uses for films having a thickness of approximately 1 mil can include, for example, dust protection, grocery store produce bags, and packaging for small parts and items having an irregular shape. Suitable uses for films having a thickness of approximately 1.5 mil to approximately 2 mil can include, for example, moisture protection, plastic sandwich bags, and packaging for certain clothing or food items, such as nuts or candy. Suitable uses for films having a thickness of approximately 3 mil can include packaging for items requiring added strength, such as tools, hardware, metal fasteners, and furniture. Suitable uses for films having a thickness of approximately 4 mil can include, for example, packaging for items such as gears, bolts, auto parts, and heavy items with sharp corners. Suitable uses for films having thicknesses of above approximately 4 mil can include, for example, extra heavy duty packaging applications. In some embodiments, film 10 has a varying thickness.
Film 10 can include additives that affect the material and mechanical properties of the film. The amount of additives used in the film can depend, for example, on the desired film thickness, the presence of other additives within the film, and desired subsequent film treatments. In some embodiments, film 10 can include multiples additives having different sizes in shapes. In some embodiments, the additives are substantially spherical.
Film 10 can include certain antiblocking additives that can, for example, facilitate winding and unwinding of a roll of film by creating a spacing effect that allows air flow between layers of film. Once compounded into a plastic, antiblocking additives can create a microrough surface that reduces adhesion between film layers thereby lowering blocking tendency between the layers. The antiblocking additives can also affect the Coefficient of Friction (COF) of the film. This can, for example, allow for smooth transport of the film web over rollers during converting and bag making operations.
Two factors that can determine the effect of an antiblocking additive are the number of particles of antiblock at the film surface and the size of the antiblock particles, in general, the greater the concentration of antiblock particles within the film, the rougher the film surface produced. In some embodiments, the antiblocking particles on the layer of film facing the inside of the bag are spherical. Such spherical particles can serve to minimize scratches during roll winding operations. In some embodiments, antiblocking particles can be lubricated with silicone oil or silicone gum which can reduce scratches formed by the film. Examples of antiblock additives include synthetic silica, limestone, natural silica, talc, zeolites, organic additives, such as certain hard waxes and fatty acid amides. Trade names for certain antiblock additives include: CONSTAB™ AB 06064 PPR (by CONSTAB™ Polyolefin Additives GmbH of Rüthen, Germany), CONSTAB™ SAB 06564 (antiblock and slip), and Shantou Best Polybatch ABPP905A (by Guangdong Meilian New Materials Technology Co., Ltd, of Shantou China, formerly known as Shantou Meilian Chemical Co., Ltd.).
In some embodiments, certain migratory slip and antistatic additives can be included that can provide a lubrication layer on the surface of the film. Such migratory additives can bloom to the surface of the film to create a lubricating layer between the surface of the film and the surface of the item. Slip additives can be used to reduce the surface coefficient of friction of the film, which can substantially prevent the film from sticking to itself and other surfaces such as converting equipment. Antistatic additives can be used to resist dust and dirt on the surface of the film by migrating to the surface of the film to dissipate static charge. Slip and antiblock additives can be used together to provide a desired balance between slip and antiblock performance. One or more of the migratory additives described herein can have a controlled solubility, which can provide a reservoir of material that continuously migrates to the surface. Trade names for certain slip and antistat additives include: CONSTAB™ SL 0581 (slip), CONSTAB™ SL 05095 PPR (slip), CONSTAB™ SL 05077 PPR (slip), and CONSTAB™ SAT 04551 PP (antistat and slip).
Film 10 can also include processing aid additives. The processing aid additives can, for example, enhance flow characteristics of the film. In some embodiments, film 10 includes anti-fog additives. The anti-fog additives can, for example, migrate to the surface of the film to substantially prevent the formation of visible condensation on the film.
A large number of end-use applications for film 10 can be realized by tailoring the properties of film 10 with the above or additional additives during its manufacture. For example, film 10 can include certain desired functional, tactile, cosmetic, or other effects. For example, certain embodiments can have smooth surfaces or rough surfaces. In addition, the film can be soft or crinkly.
In addition, film 10 can be tailored to demonstrate certain visual aesthetics. For example, film 10 can be completely opaque, completely transparent, or any desired degree of transparency. Film 10 can be any desired color, such as for example, clear, white, blue, or black. Film 10 can have a glossy finish or a matte finish.
Film 10 can also be tailored to demonstrate enhanced resistance to environmental factors. For example, film 10 can be resistant to certain chemical solvents, such as certain bases or acids. Film 10 can be substantially resistant to ultraviolet (UV) light. Film 10 can provide good abrasion or scuff resistance. Film 10 can provide a protective barrier against moisture, vapors, and bacteria. Film 10 can provide substantial heat resistance.
Film 10 can demonstrate one or more material characteristics on one or more sides. For example, film 10 can have one or more anti-fogging, antistatic, and moisture resistance properties on one or more sides. Film 10 can be configured to allow for metallizing on one or more sides. Film 10 can be easy to coat, print and laminate one or more sides. Film 10 can be configured to be heat sealable on one or more sides.
Beyond adjusting the properties of polypropylene through additives, film 10 can also be specially treated to achieve desired effects. For example, one or more surface treatments can be applied to the film to impart a desired functional, tactile, cosmetic, or other effect to the surface. For example, in some embodiments, the surface treatment can promote adhesion of printing ink and/or paints.
In some embodiments, film 10 includes one or more coatings, such as for example silicone, adhesive, premask, or print treatments. The coatings can, for example, be used for purposes such as labeling, printing, physical protection, or other purposes. One or more sides of the film can be treated with corona or flame, which can improve ink adhesion and roll winding. In some cases, migratory additives within the film will migrate preferentially to a treated film surface. As a result, in some cases a non-treated surface of film 10 will experience diminished effects from additives embedded within the film. In some embodiment, the treatment is configured to optimize the blooming of the additive to the outside layers of film 10.
In some embodiments, such as the embodiments shown in
An inside layer of film 10 (e.g., the layer on the inside of a bag formed by film 10) can be made of a softer, less stiff terpolymer resin. In some embodiments, an outside layer (that is, a layer on the outside of the bag) can be made of a high-crystallinity polypropylene, which can prevent the film from being scratched, marred or scuffed during bag making operations. In some embodiments, a layer of a softer polymer having a lower modulus, such as medium-density polyethylene (MDPE) can be coextruded with another layer of film 10. Such a softer inner layer can serve to substantially prevent scratching of the item by the film.
For multiple-layer films, additives can be blended into any of the layers. In some embodiments, a migratory slip additive is blended into a layer of the film that does not form one of the outer surfaces of film 10 (for example, a core or intermediate layer). The additive can then migrate to a surface of the film and create a thin layer that can act as a lubricant to prevent scratches. In some embodiments, certain migratory additives can be chosen to optimize the speed and stability of blooming while minimizing haze in the film. Film 10 can have a single set of properties or can have separate portions with one or more different sets of properties.
Bag 12 can be formed from a single piece of film 10 or multiple pieces of the same or different types of film. In embodiments where bag 12 is formed from a single piece of film 10, film 10 can have a single set of properties or can have separate portions with one or more different sets of properties. In embodiments where bag 12 is formed from multiple pieces of the same or different types of film 10, the multiple pieces of film 10 can have the same or different sets of properties. Bag 12 can be used by itself or within other packaging, such as a box or clamshell container, to provide additional protection of the item.
Several examples of films are described below.
The coefficient of friction between second side 38 of the film and second side 38 of another piece of the film is about 0.47 μs. The coefficient of friction between first side 36 of the film and second side 38 of another piece of the film is about 0.40 μs. The coefficient of friction between first side 36 of the film and first side 36 of another piece of the film is about −0.37 μs. The haze of the film ranges from about 0.83% to about 1.27%. Film 28 can be made of any combination of the base films or surface treatments described herein.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.45 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.32 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.23 μs. The haze of the film ranges from about 1.52% to about 1.92%.
In another embodiment, first layer 42 is made from a master batch having about 95% MOPLEN™ and about 5% organic antiblock and slip additive 52 (CONSTAB™ SAB 06564). Second layer 44 and third layer 46 are made of MOPLEN™.
Additive 52 is a spherical size of about 3.5 micron particles with very narrow particle size distribution. The particle size for additive 52 can range from about 4 to about 4.5 microns, compared with about 8 to about 9 micron silica particles that can be found in a master batch of about 4 micron silica. Additive 52 is thermally stable up to about 850° C. The slip additive is Ultra High Molecular Weight (about 25 million centi-Stokes) silicon.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.38 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.28 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.18 μs. The haze of the film ranges from about 1.34% to about 1.62%.
In another embodiment, first layer 42 is made from a master batch having about 95% MOPLEN™ and about 5% slip additive 52 (Behenamide or CONSTAB™ SL 0581). Second layer 44 and third layer 46 are made of MOPLEN™.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.46 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.40 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.30 μs. The haze of the film ranges from about 1.09% to about 1.92%.
In another embodiment, first layer 42 is made from a master batch having about 90% MOPLEN™, about 5% slip additive (Behenamide or CONSTAB™ SL 0581), and about 5% organic antiblock additive CONSTAB™ AB 06064 PPR. The slip additive and antiblock additive are combined in the figure as additive 52. Second layer 44 and third layer 46 are made of MOPLEN™.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.42 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.32 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.24 μs. The haze of the film ranges from about 1.50% to about 1.84%.
In another embodiment, first layer 42 is made from a master batch having about 97.5% MOPLEN™ and about 2.5% slip additive 52 (silicone oil, CONSTAB™ SL 05095 PPR). Second layer 44 and third layer 46 are made of MOPLEN™.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.48 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.40 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.32 μs. The haze of the film ranges from about 0.71% to about 1.30%.
In another embodiment, first layer 42 is made from a master batch having about 92.5% MOPLEN™, about 2.5% slip additive (silicone oil, CONSTAB™ SL 05095 PPR), and about 5% organic antiblock (CONSTAB™ AB 06064 PPR). The slip additive and antiblock additive are combined in the figure as additive 52. Second layer 44 and third layer 46 are made of MOPLEN™.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.49 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.30 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.18 μs. The haze of the film ranges from about 1.34% to about 1.81%.
In another embodiment, first layer 42 is made from a master batch having about 95% MOPLEN™ and about 5% silicone gum additive 52 (CONSTAB™ SL 05077 PPR). Second layer 44 and third layer 46 are made of MOPLEN™.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.54 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.38 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.27 μs. The haze of the film ranges from about 0.63% to about 1.57%.
In another embodiment, first layer 42 is made from a master batch having about 90% MOPLEN™, about 5% silicone gum additive (CONSTAB™ SL 05077 PPR), and about 5% additive 52 (organic antiblock CONSTAB™ AB 06064 PPR). Second layer 44 and third layer 46 are made of MOPLEN™.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.49 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.30 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.20 μs. The haze of the film ranges from about 1.31% to about 2.32%.
In another embodiment, first layer 42 and second layer 44 are made of MOPLEN™ Third layer 46 is made of DOWLEX™ SC 2108G Polyethylene Resin. This resin was selected due to its processability on BOPP manufacturing equipment. For example, alternative polyethylene resins can be difficult to stretch and transport on heated rolls as the layer softens and sticks to heated rolls.
For a first batch of this film, the coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.37 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.23 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.40 μs. The haze of the film ranges from about 1.11% to about 2.59%.
For a second batch of this film, the coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.42 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.27 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.41 μs. The haze of the film ranges from about 1.18% to about 1.43%.
In another embodiment, first layer 42 is made from a master batch having about 95% MOPLEN™ and about 5% additive 52 (organic antiblock CONSTAB™ AB 06064 PPR). Second layer 44 is made of MOPLEN™. Third layer 46 is made of DOWLEX™ SC 2108G Polyethylene Resin.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.41 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.31 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.22 μs. The haze of the film ranges from about 1.90% to about 2.25%.
In another embodiment, first layer 42 is made from a master batch having about 95% MOPLEN™ and about 5% organic antiblock and slip additive 52 (CONSTAB™ SAB 06564). Second layer 44 is made of MOPLEN™. Third layer 46 is made of DOWLEX™ SC 2108G Polyethylene Resin.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.38 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.29 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.20 μs. The haze of the film ranges from about 2.91% to about 3.26%.
In another embodiment, first layer 42 is made from a master batch having about 95% MOPLEN™ and about 5% silicone gum additive 52 (CONSTAB™ SL 05077 PPR). Second layer 44 is made of MOPLEN™. Third layer 46 is made of DOWLEX™ SC 2108G Polyethylene Resin.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.37 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.21 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.24 μs. The haze of the film ranges from about 2.06% to about 3.18%.
In another embodiment, first layer 42 is made from a master batch having about 90% MOPLEN™, about 5% silicone gum additive (CONSTAB™ SL 05077 PPR), and 5% additive (organic antiblock CONSTAB™ AB 06064 PPR). The slip additive and antiblock additive are combined in the figure as additive 52. Second layer 44 is made of MOPLEN™. Third layer 46 is made of DOWLEX™ SC 2108G Polyethylene Resin.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.46 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.30 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.19 μs. The haze of the film ranges from about 2.00% to about 2.79%.
In another embodiment, first layer 42 is made from a master batch having about 95% MOPLEN™ and about 5% additive 52 (Shantou Best Polybatch ABPP905A). Second layer 44 is made of MOPLEN™. Third layer 46 is made of NAN YA 2020S. One or both first side 48 and second side 50 are treated with corona or flame, which improves ink adhesion and roll winding.
The coefficient of friction between second side 50 of the film and second side 50 of another piece of the film is about 0.83 μs. The coefficient of friction between first side 48 of the film and second side 50 of another piece of the film is about 0.35 μs. The coefficient of friction between first side 48 of the film and first side 48 of another piece of the film is about 0.33 μs. The haze of the film ranges from about 1.50% to about 1.65%.
The coefficient of friction between second side 68 of the film and second side 68 of another piece of the film is about 0.33 μs. The coefficient of friction between first side 66 of the film and second side 68 of another piece of the film is about 0.33 μs. The coefficient of friction between first side 66 of the film and first side 66 of another piece of the film is about 0.33 μs. The haze of the film ranges from about 2.12% to about 2.28%.
The particular grade of additive 78 was chosen because it migrates fast and remains stable on the surface of the film. The grade was also chosen because unlike other slip additives, it does not cause hazy build up on the film surface with increased storage time. The master batch was incorporated into an inner layer, but has the ability to migrate to an outer layer of the film.
The coefficient of friction between second side 82 of the film and second side 82 of another piece of the film is about 0.44 μs. The coefficient of friction between first side 80 of the film and second side 82 of another piece of the film is about 0.39 μs. The coefficient of friction between first side 80 of the film and first side 80 of another piece of the film is about 0.38 μs. The haze of the film ranges from about 0.83% to about 1.26%.
The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. For example, films can be made of any combination of the base films, additives, or surface treatments described herein.
In addition, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
