Patent Application
20130089685
The present invention relates to pressure sensitive labels based on oriented polypropylene, and, in particular, to oriented polypropylene labels having improved squeezability and low haze.
Pressure sensitive labels are used in a wide variety of labeling applications. Many of these labels are used on semi-rigid or plastic containers or tubes that would be frequently squeezed during consumer use. Such applications include containers used in health and beauty, and food packaging (shampoo, lotion, dressing, tubes, etc.). Conformable labels are also needed for smooth application to a contour container or rigid bottles, which may have irregular shapes.
Currently in the market, polyethylene films and modified polypropylene films are mostly used for this label application. The main problem with a polyethylene label is that it is usually soft and requires high thickness to compensate its low stiffness and modulus. For polypropylene based conformable labels, usually a high level of polyethylene or polypropylene block copolymers are added that could cause undesirable high haze and loss of physical properties.
We found that squeezable, conformable labels can be made by using polypropylene and a propylene-based copolymer (elastomer) in a 3 to 5-layer or more co-extruded film structure with copolymer skins. This film will have balanced properties of conformability, stiffness, and modulus. Stiffness and modulus properties are required for pressure-sensitive adhesive label converting operations, including die cutting and label dispensing.
Though there is general disclosure in the art of incorporating propylene-based copolymers and elastomers in polypropylene films, there is no disclosure of having a composition with the right balance of stiffness (e.g., for cutting) and conformability (e.g., for squeezability). Related patents and publications include U.S. Pat. Nos. 7,927,712; 7,537,829; 7,217,463; 7,052,750; 6,835,462; 6,663,947; 6,376,058; 5,709,937; 5,451,283; U.S. Application Publication Nos. 2009/0220757; 2009/0197022; 2009/0136698; 2008/248299; 2006/0178483; 2003/0143357; EP 1 423 408 and PCT Publication WO 2010/120295.
Described in one aspect is a squeezable oriented polypropylene adhesive film useful as a label comprising at least one core layer sandwiched between at least two skin layers, the layers comprising (or consisting essentially of):
(i) a core layer comprising polypropylene and within the range of from 20 wt % to 50 wt %, by weight of the materials in the core layer, of a propylene-α-olefin elastomer having within the range of from 5 wt % or 8 wt % or 10 wt % or 12 wt % to 18 wt % or 20 wt % or 22 wt % or 25 wt % α-olefin derived units, by weight of the elastomer;
(ii) a printable skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the printable skin layer, of an α-olefin copolymer comprising at least 30 wt % ethylene; and
(iii) an adhesive-accepting skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the adhesive-accepting skin layer, of a polypropylene;
wherein the polypropylene film has an MD Elastic Modulus (ASTM 882) of at least 80 kpsi (551 MPa); and a Haze (ASTM D 1003) value of less than 10%.
In another aspect is a method of forming an adhesive label comprising coextruding at least a three layer film comprising a core layer comprising (or consisting essentially of, or consisting of) polypropylene and within the range of from 20 wt % to 50 wt %, by weight of the materials in the core layer, of a propylene-α-olefin elastomer having within the range of from 5 wt % or 8 wt % or 10 wt % or 12 wt % to 18 wt % or 20 wt % or 22 wt % or 25 wt % α-olefin derived units, by weight of the elastomer; a printable skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the materials in the printable skin layer, or an α-olefin copolymer comprising at least 30 wt % ethylene; and an adhesive-accepting skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the materials in the adhesive accepting skin layer, of a polypropylene; orienting the film; attaching an adhesive to the adhesive-accepting skin layer; attaching a backing sheet to the film having the adhesive there between, thus forming an adhesive sheet of film; cutting the sheet in the form of a label with a cutting die at a die gap within the range of from 25 μm to 75 μm and a minimum die pressure of greater than 200 psi (1379 kPa); wherein the polypropylene film has an MD Elastic Modulus (ASTM 882) of at least 80 kpsi (551 MPa); and a Haze (ASTM D 1003) value of less than 10%.
The various descriptive elements and numerical ranges disclosed herein for the films and labels or method of making the films and labels can be combined with other descriptive elements and numerical ranges to describe the invention(s); further, for a given element, any upper numerical limit can be combined with any lower numerical limit described herein.
What is provided herein is a polypropylene-based, adhesive, multi-layered label formed from a film that will conform readily to the external (or internal) surface of round, oval, or otherwise irregularly shaped articles such as bottles, etc. The term “label” simply refers to the films described herein having adhesive bound thereto, and optionally a backing sheet, thus, the label should have the same properties as the base film as described herein. These labels are provided such that they are squeezable with the article to which it is attached without bubbling, tearing, or otherwise becoming permanently deformed. At the same time, the labels are also made to be readily cuttable so that during the process to cut and dispense the labels from a larger backing sheet, labels are not destroyed and lost. This is achieved by providing a polypropylene film having a soft polymer modifier in the core layer, and, in a particular embodiment, a medium to high density polyethylene as the upper print skin layer, that is, the layer that will contact the cutter first.
The labels have a desirable amount of strength and elasticity. For instance, the films that make up the labels having at least three-layers of materials can be described as having an MD Elastic Modulus (ASTM 882) of at least 80 kpsi (551 MPa) or 100 kpsi (689 MPa), or within the range of from 80 kpsi (551 MPa) or 100 kpsi (689 MPa) or 110 kpsi (758 MPa) to 150 kpsi (1034 MPa) or 160 kpsi (1103 MPa) or 180 kpsi (1241 MPa) or 200 kpsi (1379 MPa). Further, the films should be clear, such that they possess a Haze (ASTM D 1003) value of less than 5% or 7% or 10%. In yet another embodiment, the films have a TD Elastic Modulus (ASTM 882) of at least 200 kpsi (1379 MPa), or within the range of from 150 kpsi (1034 MPa) or 160 kpsi (1103 MPa) or 180 kpsi (1241 MPa) or 200 kpsi (1379 MPa) to 250 kpsi (1724 MPa) or 260 kpsi (1792 MPa) or 270 kpsi (1861 MPa) or 280 kpsi (1930 MPa) or 290 kpsi (2000 MPa) or 300 kpsi (2068 MPa).
Provided in one embodiment is a squeezable oriented polypropylene adhesive label comprising a film having at least one core layer sandwiched between at least two skin layers, the layers comprising (or consisting essentially of) a core layer comprising polypropylene and within the range of from 20 wt % to 50 wt %, by weight of the materials in the core layer, of a propylene-α-olefin elastomer having within the range of from 5 wt % or 8 wt % or 10 wt % or 12 wt % to 18 wt % or 20 wt % or 22 wt % or 25 wt % α-olefin derived units, by weight of the elastomer; a printable skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the materials in the printable skin layer, of an α-olefin copolymer comprising at least 30 wt % ethylene; and an adhesive-accepting skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the materials in the adhesive-accepting skin layer, of a polypropylene, preferably a polypropylene copolymer having within the range of from 1 to 2 or 3 or 4 of 5 wt % ethylene-derived units. Desirably, the polypropylene film, and hence the label made from the film, has an MD Elastic Modulus of at least 80 kpsi (551 MPa) or 100 kpsi (689 MPa), or within the range of from 80 kpsi (551 MPa) or 100 kpsi (689 MPa) or 110 kpsi (758 MPa) to 150 kpsi (1034 MPa) or 160 kpsi (1103 MPa) or 180 kpsi (1241 MPa) or 200 kpsi (1379 MPa); and a Haze value of less than 5% or 7% or 10%.
By “consisting essentially of,” what is meant is that the particular layer referred to does not have any more than 1 wt % or 2 wt % or 3 wt % of a polymer modifier, but does not exclude the possibility of the layer having other additives known in the art such as anti-slip agents, anti-blocking agents, anti-oxidants, pigments, whitening agents, cavitation agents, etc. In a very particular embodiment, no cavitation or whitening agents (such as titanium dioxide) are present. Thus, in one embodiment the polypropylene layer consists of one core layer; wherein the core layer consists essentially of the propylene-α-olefin elastomer and the polypropylene.
The films described herein can be of any number of layers that include at least one printable skin, at least one adhesive-accepting skin, and at least one core layer. The film can also be of any desirable thickness, though in specific embodiments it is desirable if the layers' skins and core layers have a thickness of at least 50 μm or 54 μm or 58 μm or 60 μm or 62 μm; and a maximum thickness of 80 μm or 90 μm or 100 μm or 120 μm in another embodiment. In certain embodiments, a thickness of at least 54 μm or 58 μm or 60 μm or 62 μm provides the best cuttability.
In one embodiment, the at least one core layer comprises polypropylene and within the range of from 25 wt % or 30 wt % to 40 wt % or 45 wt % or 50 wt %, by weight of the materials in the core layer, of a propylene-α-olefin elastomer. Desirably, the polypropylene of the core layer has a melting point of greater than 120° C. or 130° C. and the propylene-α-olefin elastomer has a melting point of less than 110° C.
The “polypropylene” is a homopolymer or copolymer comprising from 60 or 70 or 80 or 85 or 90 or 95 to 100 wt % propylene-derived units (and comprising within the range from 0 or 1 to 5 or 10 or 15 or 20 or 30 or 40 wt % C2 and/or C4 to C10 α-olefin derived units) and can be made by any desirable process using any desirable catalyst as is known in the art, such as a Ziegler-Natta catalyst, a metallocene catalyst, or other single-site catalyst, using solution, slurry, high pressure, or gas phase processes. In certain embodiments, the polypropylene has a melting point (ASTM D3418) of at least 120° C. or 130° C. or 140° C. or 150° C. or 160° C., or within a range of from 120° C. to 150° C. or 160° C.
In a particular embodiment the “polypropylene” is a polymer comprising from 96 wt % to 100 wt % propylene-derived units, and comprising from 0.1 or 0.2 or 0.5 to 1 or 2 or 4 or 6 wt % C2 or C4 to C10 α-olefin derived units, made by any catalyst or process. Preferably, the polypropylenes have a melting point as described above. A “highly crystalline” polypropylene is polypropylene useful in certain embodiments, and is typically isotactic and comprises 100 wt % propylene-derived units (propylene homopolymer) and has a relatively high melting point of from greater than (greater than or equal to) 140° C. or 145° C. or 150° C. or 155° C. or 160° C. or 165° C. as measured by ASTM D3418.
The term “crystalline,” as used herein, characterizes those polymers which possess high degrees of inter- and intra-molecular order. In certain embodiments, the polypropylene has a heat of fusion (Hf) greater than 60 J/g or 70 J/g or 80 J/g, as determined by DSC analysis. The heat of fusion is dependent on the composition of the polypropylene; the thermal energy for the highest order of polypropylene is estimated at 189 J/g, that is, 100% crystallinity is equal to a heat of fusion of 189 J/g. A polypropylene homopolymer will have a higher heat of fusion than a copolymer or blend of homopolymer and copolymer.
In any case, in certain embodiments, the polypropylene has a melt flow rate (“MFR”, 230° C., 2.16 kg, ASTM D1238) within the range of from 0.1 g/10 min or 0.5 g/10 min or 1 g/10 min to 4 g/10 min or 6 g/10 min or 8 g/10 min or 10 g/10 min or 12 g/10 min or 16 g/10 min or 20 g/10 min. Also, in any case, the polypropylene may have a molecular weight distribution (determined by GPC) of from 1.5 or 2.0 or 2.5 to 3.0 or 3.5 or 4.0 or 5.0 or 6.0 or 8.0. Suitable grades of polypropylene, and, in particular, highly crystalline polypropylenes that are useful in oriented films include those made by ExxonMobil, LyondellBasell, Total, Borealis, Japan Polypropylene, Mitsui, and other sources.
To improve the squeezability of polypropylene, especially highly crystalline polypropylene, it is desirable to add an agent that is miscible with the polypropylene but adds some softness. As used herein, a “propylene-α-olefin elastomer” refers to a random copolymer that is elastomeric, has moderate crystallinity and possesses propylene-derived units and one or more units derived from ethylene, higher α-olefins, and/or optionally diene-derived units. Added to the core compositions herein are so called propylene-α-olefin elastomers which are propylene-based polymers having an intermediate amount of α-olefin such as within a range of from 5 wt % or 8 wt % or 10 wt % or 12 wt % to 18 wt % or 20 wt % or 22 wt % or 25 wt % α-olefin derived units. In some embodiments, where more than one comonomer is present, the amount of a particular comonomer may be less than 5 wt %, but the combined comonomer content is greater than 5 wt %. The propylene-α-olefin elastomers may be described by any number of different parameters, and those parameters may comprise a numerical range made up of any desirable upper limit with any desirable lower limit as described herein.
In certain embodiments, the propylene-α-olefin elastomer comprises ethylene or C4-C10 α-olefin-derived units (or “comonomer-derived units”) within the range of 4 wt % or 7 wt % or 9 wt % to 13 wt % or 16 wt % or 18 wt % or 20 wt % or 25 wt % by weight of the elastomer. The propylene-α-olefin elastomer may also comprise two different comonomer-derived units. Also, these copolymers and terpolymers may comprise diene-derived units as described below. In a particular embodiment, the propylene-α-olefin elastomer comprises propylene-derived units and comonomer units selected from ethylene, 1-hexene, and 1-octene. And, in a more particular embodiment, the comonomer is ethylene and, thus, the propylene-α-olefin elastomer is a propylene-ethylene copolymer. When dienes are present, the propylene-α-olefin elastomer comprises less than 5 wt % or 3 wt %, by weight of the elastomer, of diene derived units, or within the range of from 0.1 wt % or 0.5 wt % or 1 wt % to 5 wt % in other embodiments. Suitable dienes include, for example: 1,4-hexadiene, 1,6-octadiene, 5-methyl-1,4-hexadiene, 3,7-dimethyl-1,6-octadiene, dicyclopentadiene (DCPD), ethylidiene norbornene (ENB), norbornadiene, 5-vinyl-2-norbornene (VNB), and combinations thereof.
These propylene-α-olefin elastomers may have some isotactic polypropylene sequences but they also have some amorphous regions in the polymer chains, thus imparting desirable qualities to them and the compositions in which they are blended. In certain embodiments, the propylene-α-olefin elastomers have a melting point of less than 110° C. or 100° C. or 90° C. or 80° C.; and within the range of from 10° C. or 15° C. or 20° C. or 25° C. to 65° C. or 75° C. or 80° C. or 95° C. or 105° C. or 110° C. in other embodiments. One or a mixture of propylene-α-olefin elastomers may be present in the core compositions, preferably only one.
In certain embodiments, the propylene-α-olefin elastomers have a heat of fusion (Hf), determined according to the Differential Scanning calorimetry (DSC) procedure described herein within the range of from 0.5 J/g or 1 J/g or 5 J/g to 35 J/g or 40 J/g or 50 J/g or 65 J/g or 75 J/g. In certain embodiments, the Hf value is less than 75 J/g or 60 J/g or 50 J/g or 40 J/g. In certain embodiments, the propylene-α-olefin elastomers have a percent crystallinity within the range of from 0.5% to 40%, and from 1% to 30% in another embodiment, and from 5% to 25% in yet another embodiment, wherein “percent crystallinity” is determined according to the DSC procedure described herein. The thermal energy for the highest order of polypropylene is estimated at 189 J/g (i.e., 100% crystallinity is equal to 189 J/g).
In certain embodiments, the propylene-α-olefin elastomers have a melt flow rate (“MFR,” ASTM D1238, 2.16 kg, 230° C.), within the range of from 0.5 g/10 min or 1 g/10 min or 1.5 g/10 min or 2 g/10 min to 4 g/10 min or 6 g/10 min or 12 g/10 min or 16 g/10 min or 20 g/10 min in other embodiments.
In certain embodiments, the molecular weight distribution (MWD) of the propylene-α-olefin elastomers is within the range of from 1.5 or 1.8 or 2.0 to 3.0 or 3.5 or 4.0 or 5.0. Techniques for determining the molecular weight (Mn, Mz, and Mw) and molecular weight distribution (MWD) are as follows and as in Verstate et al. in 21 M
(Showa-Denko America, Inc.) polystyrene gel columns 802, 803, 804 and 805 are used. This technique is discussed in L
The propylene-α-olefin elastomers described herein can be produced using any catalyst and/or process known for producing polypropylenes. In certain embodiments, the propylene-α-olefin elastomers can include copolymers prepared according to the procedures in WO 02/36651; U.S. Pat. No. 6,992,158; and/or WO 00/01745. Preferred methods for producing the propylene-α-olefin elastomers are found in U.S. Patent Application Publication 2004/0236042 and U.S. Pat. No. 6,881,800. Preferred propylene-α-olefin elastomers are available commercially under the trade names Vistamaxx™ (ExxonMobil Chemical Company, Houston, Tex., USA) and Versify™ (The Dow Chemical Company, Midland, Mich., USA), certain grades of Tafmer™ XM or Notio™ (Mitsui Company, Japan) or certain grades of Clyrell™ and/or Softel™ (LyondellBasell Polyolefins of the Netherlands).
The skin layers can comprise any desirable material, and each skin layer typically makes up from 1% or 2% to 4% or 5% or 6% of the entire skin/core/skin film. In a particular embodiment, the skin layer materials comprise an α-olefin copolymer comprising at least 30 wt % or 40 wt % or 50 wt % or 60 wt % or 70 wt % ethylene. These “polyethylenes” can be selected from LDPEs, LLDPEs, ethylene-butene copolymers, ethylene-hexene copolymers, ethylene-propylene-butene terpolymers, MDPE, and HDPE as are well known in the art. The printable and adhesive skin layers can be the same or different, preferably different.
In a particular embodiment, the printable skin layer comprises (or consists essentially of) within the range of from 60 wt % or 70 wt % or 80 wt % or 90 wt % to 100 wt % medium or high density polyethylene having a density within the range of from 0.930 g/cc or 0.935 g/cc to 0.945 g/cc or 0.950 g/cc or 0.955 g/cc or 0.960 g/cc or 0.970 g/cc; and a density of greater than 0.940 g/cc or 0.945 g/cc or 0.950 g/cc or 0.955 g/cc or 0.960 g/cc in other desirable embodiments. In desirable embodiments, the polyethylene making up the printable skin layer possess a melt index (“MI”, 190° C., 2.16 kg) within the range of from 5 g/10 min or 10 g/10 min or 15 g/10 min or 20 g/10 min or 25 g/10 min to 35 g/10 min or 40 g/10 min or 50 g/10 min.
In another particular embodiment, the adhesive-accepting skin layer comprises (or consists essentially of) within the range of from 60 wt % or 70 wt % or 80 wt % or 90 wt % to 100 wt % of a polypropylene, and in particular, a polypropylene copolymer. In a particular embodiment, the adhesive-accepting skin layer is a propylene-ethylene copolymer having within the range of from 0.5 or 1 to 2 or 3 or 4 or 5 wt %, by weight of the copolymer, of ethylene-derived units. This layer accepts an adhesive for use in the pressure sensitive label industry as is well known in the art. It is this face, having the adhesive thereon, which can make up a “matrix” sheet of film that is adhered to a backing sheet. Cutters will cut individual labels from the matrix that can be pulled off and adhered to an article. In any case, what results in certain embodiments is a hollow, squeezable container having the polypropylene label described herein adhered thereto.
The at least three-layer film or label can be made by any suitable method known, and is preferably made by co-extruding the three layers together in the desired compositions and thicknesses. In certain embodiments, the films (or labels) herein may also be characterized in certain embodiments as being biaxially oriented. Examples of methods of making the films for the labels include a tentered or blown process, LISIM™, and others. Further, the working conditions, temperature settings, lines speeds, etc. will vary depending on the type and the size of the equipment used. Nonetheless, described generally here is one method of making the labels described throughout this specification. In a particular embodiment, the films for the labels are formed and biaxially oriented using the “tentered” method. In the tentered process, line speeds of greater than 100 m/min to 400 m/min or more, and outputs of greater than 2000 kg/hr to 4000 kg/hr or more are achievable. In the tenter process, the various materials that make up the film layers are melt blended and coextruded, such as through a 3, 4, 5, 7-layer die head, into the desired label structure.
Downstream of the first cooling step in this embodiment of the tentered process, the unoriented film is reheated to a temperature of from 80° C. to 100° C. or 120° C. or 150° C., in one embodiment by any suitable means such as heated S-wrap rolls, and then passed between closely spaced differential speed rolls to achieve machine direction orientation. It is understood by those skilled in the art that this temperature range can vary depending upon the equipment, and in particular, upon the identity and composition of the components making up the label. Ideally, the temperature will be below that which will melt the film, or cause it to become tacky and adhere to the equipment, but high enough to facilitate the machine direction orientation process. The heating means for the film line may be set at any appropriate level of heating, depending upon the instrument, to achieve the stated film temperatures.
The lengthened and thinned film is cooled and passed to the tenter section of the line for TD orientation. At this point, the edges of the sheet are grasped by mechanical clips on continuous chains and pulled into a long, precisely controlled hot air oven for a pre-heating step. The film temperatures range of from 100° C. or 110° C. to 150° C. or 170° C. or 180° C. in the pre-heating step. Again, the temperature will be below that which will melt the film, or cause it to become tacky and adhere to the equipment, but high enough to facilitate the step of transverse direction orientation. Next, the edges of the sheet are grasped by mechanical clips on continuous chains and pulled into a long, precisely controlled hot air oven for transverse stretching. As the tenter chains diverge, a desired amount to stretch the film in the transverse direction, the film temperature is lowered by at least 2° C. but typically no more than 20° C. relative to the pre-heat temperature to maintain the film temperature so that it will not melt the film. After stretching to achieve transverse orientation in the film, the film is then cooled and the clips are released prior to edge trim, optional coronal, printing and/or other treatment can then take place, followed by winding. The steps are carried out for a sufficient time to affect the desired film properties as those skilled in the art will understand.
After forming the initial base multi-layer film or “sheet” which becomes the matrix with adhesive applied thereto, in certain embodiments, the film is treated on the printable skin layer to accept printing, the treatment selected from the group consisting of corona discharge, flame treatment, plasma treatment, chemical treatment (either permanent or temporary), polarized flame, and a combination thereof The film may also be treated on the adhesive-accepting side by the same or different methods as well.
Chemical treatment includes both sacrificial treatment, such as by peroxides, fluoriding agents, and other oxidants or reductants, and permanent treatments such as one, two or more layers of coatings to promote greater ink, adhesive, and/or metal adhesion. Coatings are well known in the art, and particularly useful coatings include those based on polyalkylamines and modified polyalkylamines (e.g., acetylacetonate or glycidyl condensation products), acrylic and modified acrylic coatings, polyurethane coatings, polyvinyl alcohol and polyvinyl chloride coatings, coatings comprising micron-sized particulate fillers, and combinations of these materials. These can be used in one, two or more layers. A first or “primer” layer may comprise any one or combination of these, and is preferably an epoxy resin, polyurethane and/or polyalkylimine (e.g., polyethyleneimine). Other coatings includes layers of metal such as aluminum, or metal oxides such as aluminum oxide or silicon oxide. A chemical coating may be used in conjunction with a metal coating.
Thus, in one particular embodiment is a method of forming an adhesive label comprising coextruding at least a three layer film comprising the components described herein, in a particular embodiment a core layer comprising polypropylene and within the range of from 20 wt % to 50 wt %, by weight of the materials in the core layer, of a propylene-α-olefin elastomer having within the range of from 5 wt % or 8 wt % or 10 wt % or 12 wt % to 18 wt % or 20 wt % or 22 wt % or 25 wt % α-olefin derived units, by weight of the elastomer; a printable skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the materials in the printable skin layer, or an α-olefin copolymer comprising at least 30 wt % ethylene; and an adhesive-accepting skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the materials in the adhesive-accepting skin layer, of a polypropylene; orienting the film; attaching an adhesive to the adhesive-accepting skin layer; attaching a backing sheet to the film having the adhesive there between, thus forming an adhesive sheet of film; and cutting the sheet in the form of a label with a cutting die at a die gap within the range of from 25 .im to 75 μm and a minimum die pressure of greater than 200 psi (1379 kPa) or 250 psi (1724 kPa), or within the range of from 200 psi (1379 kPa) or 220 psi (1517 kPa) to 250 psi (1724 kPa) or 280 psi (1930 kPa) or 300 psi (2068 kPa) or 350 psi (2413 kPa) or 400 psi (2758 kPa); wherein the polypropylene label has an MD Elastic Modulus of at least 80 kpsi (551 MPa) or 100 kpsi (689 MPa), or within the range of from 80 (551) or 100 (689) or 110 kpsi (758 MPa) to 150 (1034) or 160 (1103) or 180 (1241) or 200 kpsi (1379 MPa); and a Haze value of less than 5% or 7% or 10%. The base multi-layered film or “label” having adhesive bound thereto has all of the desirable properties described above.
Desirably, the label can be cut at a minimum die pressure of 200 psi (1379 kPa) or 250 psi (1724 kPa). The labels are further characterized in that they can be cut from the matrix sheet and peeled from the backing layer, wherein the loss to the matrix is less than 20% or 15% or 10%. Other desirable properties of the label include a desirable level of stiffness, wherein the Gurley Stiffness (MD) is less than 15 mg or 14 mg or 13 mg or 12 mg or 10 mg, or within a range of from 9 mg or 10 mg to 14 mg or 15 mg or 16 mg; and the Gurley Stiffness (TD) is less than 40 mg or 35 mg or 30 mg or 28 mg or 25 mg, or within a range of from 10 mg or 12 mg to 18 mg or 20 mg.
As mentioned, the multi-layered films or labels can be used for various purposes, especially as an adhesive label with printed material thereon for bottles, cans, boxes, bags, plastic articles and devices, metal articles and devices, glass, and other surfaces that require conformability and squeezability.
Having described desirable features of the films and labels, listed here are numbered embodiments of the films and process for making them:
Also envisioned is the use of a squeezable oriented polypropylene adhesive label for an article, the label comprising at least one core layer sandwiched between at least two skin layers, the layers comprising (or consisting essentially of) a core layer comprising polypropylene and within the range of from 20 wt % to 50 wt %, by weight of the materials in the core layer, of a propylene-α-olefin elastomer having within the range of from 5 wt % or 8 wt % or 10 wt % or 12 wt % to 18 wt % or 20 wt % or 22 wt % or 25 wt % α-olefin derived units, by weight of the elastomer; a printable skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the materials in the printable skin layer, of an α-olefin copolymer comprising at least 30 wt % ethylene; and an adhesive-accepting skin layer comprising within the range of from 60 wt % to 100 wt %, by weight of the materials in the printable skin layer, of an α-olefin copolymer comprising at least 30 wt % ethylene; wherein the polypropylene label has an MD Elastic Modulus of at least 80 kpsi (551 MPa) or 100 kpsi (689 MPa), or within the range of from 80 kpsi (551 MPa) or 100 kpsi (689 MPa) or 110 kpsi (758 MPa) to 150 kpsi (1034 MPa) or 160 kpsi (1103 MPa) or 180 kpsi (1241 MPa) or 200 kpsi (1379 MPa); and a Haze value of less than 5% or 7% or 10%.
What follows are non-limiting examples of the inventions) described above.
The different components of the films produced for the examples are described in Table 1. Unless otherwise stated, “MFR” is 230° C./2.16 kg (ASTM D1238) and “MI” is 190° C./2.16 kg; Flexural Modulus (“FM”) is measured per ASTM D 790; density (“D”) is measured per ASTM D 1505; melting point (“MP”) is measured by DSC, as is the heat of fusion OHO determined as described above.
The components in Table 1 are combined, as well known in the art, in the amounts shown for the “Core Compositions” in the Tables below. Each film also includes a skin layer adhered to both sides of the core layer, thus, forming a three-layer film having the core sandwiched there between. The skin layers are a co-extruded ethylene-propylene copolymer (Total 8573HB). The gauge ratios for the film layers are typically 2/96/2, where the total thickness is about 50 μm to 60 μm. Samples 1-27 were made on a “semiworks” line which includes a 3.5 inch (8.89 cm) extruder with L/D ratio of 32:1, single flight, double compression screw with a Maddock mixing head, smooth bore. Unless otherwise specified, the temperatures of the three zones in the TD tenter stretching unit are 355° F./320° F./315° F. (±5° F.), or 179° C./160° C./157° C. (±3° C.). The data for samples 1-9 in Table 2 are the initial, preliminary work to determine a target range for the materials; samples 10-27 in Tables 3 and 4 represent more refined sample films having desirable properties. Examples 28-34 in Table 5 are further refined examples. In Table 2, the “MFR” is for the additives. Data in Table 6 refers to selected examples of die-cutting. Blank spaces in the Tables mean that data was not recorded for those instances. The “Young's Modulus” is the equivalent of the Elastic Modulus or 1% Secant Modulus, measured per ASTM D 882; Gurley Stiffness measured per ASTM D6125-97 (2007); Gloss measured per ASTM D 2457; Handle-o-meter measured per ASTM D-2923.
Squeeze Testing Procedure:
6. The control K-Mart Head & Shoulders bottle is set up with the following process settings:
The squeeze results are based on the number of squeezes till failure. The operator will record the failure of the samples on a scale from 0-5 (0=bottle did not compress, 1=no defect, 2=slight defect, 3=minor defect, 4=unacceptable). The number of squeezes it takes for a sample to first receive a rating of a 3 is recorded, (for the No. 2 HDPE bottle). The test cycle consists of 75 squeezes, so if a sample receives a 1 or 2 for all 75 squeezes, the operator gives that sample a score of 80. The higher the number (rating) means the more squeezes the label was able to withstand before a defect was seen by the operator.
Die Cutting & Dispensing Test: Sheets of the polypropylene label adhered to a liner or “backing sheet” were tested for its ability to be cleanly cut without the label sticking to the surrounding “matrix” and without adhesive being pushed into the backing sheet and preventing or impeding removal of labels. The die gap is the gap set between the farthest downward point of the blade when cutting the labels from the sheet and the platen upon which the entire sheet moved upon. This allows, ideally, cutting of the label only and not the backing sheet. The “jog” speed is a speed of from 10-20 feet/min (“fpm”) that the sheet moves along the platen, while the “run” speed represents speeds closer to commercial runs, at 400 fpm. The “Labels Lost to Matrix” test is a test of pulling the matrix material away from the cut labels and backing sheet, leaving only the labels adhered to the backing sheet. The “Ticker Test” is a test of hand-pulling individual labels away from the backing sheet with the matrix still adhered. The “minimum die pressure” is simply the pressure placed on the cutting knife to cut the label.
More particularly, the die cut test performed using an Allied Gear Flexomaster 1B die cut machine. The dispensing test was done on Label-Aire Incorporated Model 2115-M label dispensing applicator. The face stock film to be tested was adhesive laminated to 1.5 mil PET release liner to form the pressure sensitive label stock. The adhesive coating weight was usually about 5-20 lbs per ream. The solvent based adhesive used was COVINAX™ 462 acrylic emulsion adhesive from Franklin Adhesive and Polymers.
The sandwiched structure was passed through the die cut machine with the cut gap set at 1.4 mil (liner is 1.5 mil thick), and cutting pressure set at 250 psi (1724 kPa) or 400 psi 2757 kPa). The face stock to be cut into individual labels was facing up toward the cutting die. After the die cut step, the matrix was stripped, leaving individual cut labels sitting on the release liner. The matrix was run at a stripping speed at jog speed (very low speed) or at high speed (400 fpm). Ideally, there would be no label lost during the matrix stripping step. If the cut is not complete, or cut too much, then, labels are lost during the stripping step. Then, the liner was stained after all labels removed. If the cut was too deep, dye will penetrate the release coating and stain the paper liner. When cutting too deep, the sticky adhesive could be pushed into the cut slit and the label may not strip off easily.
For the dispensing test, the roll of pressure sensitive label was run through the dispensing applicator at jog (low) speed, and at 150 labels per minute. The continuous liner was pulled downward at a sharp angle on the edge of the dispensing plate. The liner pulled away at the bending angle will leave the die-cut face stock to stick up and out in the air horizontally. Gravity will cause the stuck out label to bend down. The bending angle is related to the stiffness of the face stock (label film). The stiffer the film, the smaller the bending down angle. When the label's bending down angle is too big, the film will curl and cannot reach the object that will pick up the label at the dispensing plate area. Therefore, usually a smaller dispensing angle is preferred.
When the face stock is very stiff, it will have less bending down angle at the dispensing plate, making it easier to dispense. After applied to a plastic bottle, the stiff film may have a “darting” problem. The darting problem can occur when a label applied to a bottle separates from the bottle, leaving a dart shape gap (non-conformable), when the bottle is deformed or “squeezed” down. A balance of film softness/stiffness properties is sought that will provide acceptable label dispensing as well as conformability after applied to a plastic bottle. A lower rating is better with 1 as very good, 4 is average.
Tables 5a, 5b, and 6 are a summary of preliminary results of die cutting experiments on the inventive films, showing the failure rate is low for inventive films. Tables 6 and 7 are further experiments to show the advantageous properties of the inventive films. These results suggest that higher film gauge is better (2.5 mil vs. 2 mil).
L&W Stiffness Test. ISO 5628 (1991). A 1.5 inch wide specimen is bent at 15°, pushing 5 mm far from specimen holder. It is not said in the procedure, but the bending force measured in mN is calculated by the JBL PTM to express the rigidity in mN·m in the final extracted results table, following the relationship:
S=(60·F·L2)/(pi·a·b)
where
In the Tables, when “wt % additive” is mentioned, this means the weight percent of that component based on the total weight of materials for that layer, such as the core layer.
This application claims the benefit and priority to U.S. Ser. No. 61/545,612, filed Oct. 11, 2011 which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61545612 | Oct 2011 | US |
