MXPA04000740A

MXPA04000740A - Biaxially oriented polyolefin slip films with improved flatness and adhesion properties.

Info

Publication number: MXPA04000740A
Application number: MXPA04000740A
Authority: MX
Inventors: John Waywood William
Original assignee: Applied Extrusion Technologies
Priority date: 2001-07-26
Filing date: 2002-04-23
Publication date: 2004-07-08
Also published as: WO2003011593A1; CA2452026C; CA2452026A1

Abstract

A biaxially oriented multilayer film usable to form adhesive labels to be attached to containers, such as bottles and cans. The film includes a core layer comprising polypropylene and a migratory slip agent and an outer slip layer on one side of the core layer. The slip layer includes primarily polypropylene, by weight, and a minor percent, by weight, of an additive, with the additive and the migratory slip agent being present in amounts to provide a COF on the surface of the slip layer of no greater than 0.45 and to provide an adhesion of the adhesive employed on the formed label for the slip layer of at least 50%.

Description

BIOXIALALLY ORIENTED POLYOLEFINE SLIDING FILMS WITH ACCESSION AND PLAQUE PROPERTIES IMPROVED FIELD OF THE INVENTION This invention relates generally to polyolefin films; more particularly to biaxially oriented polyolefin films, preferably polypropylene films, having a desired plain to minimize the processing problems during printing and / or lamination, sliding properties desired to make films in labeling apparatus and properties of adhesion desired to adhere to adhesives, in particular hot melt adhesives, used in labeling applications.

BACKGROUND OF THE ART Biaxially oriented polypropylene films have been employed in the label and roll-fed label industries. One of the key product attributes that these films should have is a coefficient of friction (low enough COF) to allow the film to easily slide across various machine surfaces, resulting in efficient film processing. In addition, a second key attribute is that the surface having desired slip properties must also have sufficient adhesion properties to adhere effectively to adhesives used in label applications. Because the COF of the polypropylene film is generally greater than that desired for effective processing in labeling applications, various additives have been incorporated into the film to reduce COF. The two common additives used to reduce COF are organosilicon particulate materials, such as TospearI T120, which is supplied by G.E. Toshiba Sales Americas in Waterford, New York, and fatty acid amides. When an organosilicon particulate material such as Tospearl is used, the particles are usually included in a thin coextruded surface layer of a multilayer film. The particles tend to reduce the degree of contact between the polypropylene film and the machine surface which couples the skin layer, and generally act as ball supports to reduce the drag of the film on the machine surfaces. Although this technology works well to reduce the degree of contact between the film and the machine surfaces, as well as to lower the measured COF, the resulting film surface has a roughness, or uneven contour, that has been shown to have a negative impact. in certain labeling applications. As noted above, fatty acid amides have also been used as slip agents to reduce COF. These amides are generally formed in compound with the polymer of polyolefin and thus are contained within the matrix of the polymer throughout the process of orientation of the film. Because the polyolefin and amide polymer are generally chemically incompatible, over time the amide will migrate to the surface of the film, thereby providing the desired sliding properties for the film. However, due to other spherical, thermodynamic and practical considerations, the diffusion process frequently needs to be accelerated through the use of heat. Although heating the film provides a faster and more effective migration of the amide to the film surface, thereby decreasing the COF, exposure of the film to elevated temperatures often causes uneven shrinkage of the film. This can have an adverse effect on the desired plainness of the sheet, thereby creating problems during the printing and / or lamination processes. Moreover, excessive migration of the fatty acid amides to the surface of the film can adversely affect the adhesion properties of the film surface. This can present problems to use the film in labeling applications. Although co-extruded polyolefin films have included an antistatic additive in an outer skin layer and a migratory amide in the core layer, as far as the applicant is aware, these additives have not been used for the purpose of reducing the COF of the skin layer against the metal machine surfaces, such as metal surfaces in carving machines, and of providing desired adhesion properties to adhesives. employees on labels. The applicant is not aware of any prior art film, in which the types and amounts of an antistatic additive in the outer skin and a migratory amide in the core, achieve the desired COF and the desired adhesion properties for label applications adehsiva , as in the present invention. In view of the state of the art, there is a need in the art for labeling by a biaxially oriented polyolefin film having a desired plain to reduce, or minimize, problems during printing and / or lamination in the manufacture of labels, properties of Sliding desired to make the film workable without the use of particulate materials, such as particulate organosilicon materials, in the surface layer to reduce the COF, and also without the need to heat the film to intensify the migration speed of an amide of fatty acid from the core to the surface of the film to provide the desired COF, and with the desired "adhesion" (defined below) to adhesives used in labeling applications, such as hot melt adhesives. It is to such an improved multilayer polyolefin film that the present invention is directed.

BRIEF DESCRIPTION OF THE INVENTION The foregoing and other objects of this invention are achieved in a biaxially oriented, multilayer polyolefin film, including a core layer and at least one outer skin layer. The skin layer adheres preferably to the core layer and has desired slip properties and adhesion properties in accordance with this invention. The outer skin layer preferably includes a blend which is predominantly polypropylene homopolymer, by weight, with a minor weight percentage of an additive resulting in the films of this invention having the desired slip and adhesion properties as specified. in more detail later in the present. In the most preferred embodiments of this invention, the additive includes an antistatic agent. Most preferably, the antistatic agent includes an ethoxylated alkylamine and / or an ethoxylated alkylamide, each by itself, or each possibly either physically mixed with an ester or esterified by a chemical reaction with a suitable acid (e.g., stearic acid) ) or with another ester, for example, glycerol monostearate, sorbitol-based esters, etc. Most preferably, the antistatic agent includes an ethoxylated alkylamine which is esterified with another ester or with a suitable acid, an ethoxylated alkylamine mixed with an ester, or an ethoxylated alkylamine, by itself. It is also within the scope of the broader aspects of this invention to employ a glycerol monostearate, by itself, as the antistatic additive. However, the benefits achieved with this last antistatic additive are not as good as the benefits achieved with an antistatic agent in the form of an ethoxylated alkylamine which is esterified with another ester or with a suitable acid, an ethoxylated alkylamine mixed with an ester, or an ethoxylated alkylamine, by itself. The core layer is predominantly a polypropylene homopolymer, by weight, including a minor percentage by weight of the core layer of a migratory amide. The additive in the skin layer, preferably including an antistatic agent, and the migratory amide in the core layer, are present in amounts that provide a film / metal COF of less than 0.45 and preferably less than 0.35, and a adhesion of at least 50% to hot melt adhesives usable in the products of this invention; more preferably, an adhesion of at least 70%; even more preferably an adhesion of at least 90% and most preferably, an adhesion in excess of 90%. In order to achieve these adhesion and COF properties, the additive in the skin layer needs to be of a type that provides the desired slip properties without undesirably affecting the adhesion properties and needs to be present in an amount to prevent The migratory amide in the core migrates to the surface of the skin layer in an amount that deteriorates the adhesion properties on that surface. Similarly, the migratory amide needs to be of a type and amount that does not prevent the additive in the skin layer from providing its desired slip and adhesion properties. In a preferred embodiment of this invention, the additive in the skin layer is an antistatic agent that is included in a particulate masterbatch based on polypropylene homopolymer, with about 87-88% of the masterbatch and the antistatic agent being about 12 - 13% of the master lot. The preferred master batch is POLYBATCH ASPA 2485, manufactured by A. Schulman, Inc., of Akron, Ohio. The weight percent of the master batch POLYBATCH ASPA 2485 employed in the skin layer of preference is at least 4% by weight of said skin layer; more preferably in excess of 4% and even more preferably approximately 8% or even more. Thus, the percentage by weight of the antistatic agent in the skin layer of preference is at least about 0.48%, more preferably in excess of 0.48% and even more preferably in the range of 0.96% to 1.04%, or even more. As an alternative to employing the masterbatch identified above, the antistatic agent may be an ethoxylated amine, such as a synthetic ethoxylated amine, for example, Atmer 163 sold by Uniquema in New Castle, Delaware. This ethoxylated amine may be employed by itself or in combination with a small amount of an ester, such as glycerol monostearate, for example, Atmer 129 sold by Uniqema in New Castle, Delaware. Moreover, for some applications it may be possible to employ an ester, such as glycerol monostearate, by itself as the antistatic agent. In a preferred embodiment of this invention, the migratory amide in the core is behenamide and preferably is present in the core in an amount greater than 0.10% by weight of the core layer and more preferably approximately 25% or more. Most preferably, behenamide is present in a range of about 0.25% to about 0.50%. At a level of approximately 1 .00%, adhesive performance is diminished, and in some cases it is unacceptable. In a preferred embodiment of this invention, the migratory amide is a behenamide of the type supplied as Kemamide B by Witco, based in Greenwich Connecticut, and is included in the commercially available polypropylene homopolymer, Aristech FF038A2.

In accordance with the preferred embodiments of this invention, the adhesives employed in the labels are hot melt adhesives having varying levels of aggressiveness. In this invention, these hot melt adhesives have a desired level of adhesion to the surface of the outer skin layer including the antistatic agent therein, even if the film is exposed to adverse environmental conditions, for example, as a result of be stored and / or transporatadas in a hot environment for long periods. Under these adverse conditions, the surface of prior art films including behenamide both in the core and in the outer skin layer of a multilayer structure, or in a single monolayer structure, will not retain its desired adhesion properties. As noted above, the adhesion of the hot melt adhesives according to this invention is at least 50%; more preferably, at least 70%, even more preferably, at least 90% and most preferably in excess of 90%.

According to the preferred embodiment of this invention, the film surface including the antistatic agent herein is free from direct oxidative treatment, such as flame or corona treatment. However, when the opposite surface of the film is subjected to direct oxidative treatment, for example, to improve its properties of ink receptivity or adhesive receptivity, there is a spill, or "backside treatment" of the film surface including the antistatic agent that inherently occurs. The opposite surface is preferably treated oxidatively. This back treatment is substantially less than the direct treatment of the opposite surface, and still results in the formation of an acceptable product. It has been found that direct corona treatment of the film surface, including the antistatic agent therein, tends to decrease the adhesion of the hot melt adhesive to the surface layer, resulting in poor or reduced label performance. The reason for this phenomenon is not clearly understood. However, in some products within the scope of this invention, the film surface including the additive herein can be directly oxidized. In fact, it has been determined that the "light", direct corona treatment of the sliding layer also results in the formation of an acceptable product, although the best results are achieved when the film surface including the antistatic agent therein, It is not treated directly.

D ISSUE OF THE PRE-RIDE MODEL OF THE I NVE NTION When referred to herein as "polypropylene", it is meant to mean a crystalline propylene homopolymer or a copolymer of propylene with another olefin having from 2 to 5 atoms of carbon in an insufficient amount to have a significant effect on the crystallinity of polypropylene. Typically, this is ethylene in an amount up to about 2% by weight. The polypropylene used in this invention is preferably the homopolymer. Most preferably, the polypropylenes employed in this invention are catalyzed by Ziegler-Natta and are commercially available isotactic polypropylenes having a melt flow rate between about 2 and 10 g / 10 min at 230 ° C and 2.16 kg load and a point DSC melt from about 1 60 to 166 ° C. Suitable polypropylene homopolymers are available from numerous sources, such as Sunoco of Philadelphia, Pennsylvania, Basell, which is located in the Netherlands, Exxon Chemical Company of Baytown, Texas, and Fina Oil and Chemical Company of Deerpark, Texas. The specific polypropylene employed in this invention is not considered a limitation in the broader aspects of this invention. For example, and not by way of limitation, the polypropylene can be catalyzed by metallocene, or a mixture of polypropylene catalyzed by metallocene and catalyzed by Ziegler-Natta. In a preferred embodiment of this invention, the polyolefin film is a biaxially oriented, multilayer polypropylene film having a central core and at least one outer skin layer, and preferably opposed outer skin layers. Preferably, the central core is the thickest component of the multilayer film and is thick enough to be self-supporting or supported, without the inclusion of one or more outer skin layers. In a representative non-limiting embodiment of this invention, the film has a gauge thickness of 48, with the core layer being 42 gauge and each of the outer skin layers being opposite in gauge 3. At least one of the layers of Outer skin includes a desired low COF in accordance with this invention. In accordance with the broader aspects of this invention, the multilayer film includes at least two layers; a thick core layer and a thin outer skin layer having low, desired metal / film COF sliding properties in accordance with this invention. For ease of description, this outer skin layer will sometimes be referred to as the "slip layer" or "outer slip layer". Moreover, the reference throughout this application to "coefficient of friction" or "COF" refers to a coefficient of friction of metal / film determined in a manner to be described later. Most preferably, the multilayer film includes at least three (3) layers. In particular, for printed label applications, a coextruded three (3) layer film is clear, or transparent, and includes the slip layer and core layer, as described above, and, in addition, a bottom skin layer, outside, in the form of a printable or assurance layer, which is on the side of the core layer opposite the slip layer. In printed labels employing the clear or transparent three-layer structure described in the preceding just paragraph, the lower skin layer is generally laminated through a suitable adhesive to another multilayer film or single layer, which may be either clear or opaque. The construction and / or use of this last single layer or multilayer film does not constitute a limitation in the broader aspects of this invention. If the clear co-extruded film of this invention is printed on the lower skin layer, a reverse printing process is employed, so that the printed indicia will be readable across the upper surface of the sliding layer, and the adhesive used for Laminating the upper layer of the additional film to the reverse printed label surface is compatible with the ink and the surfaces bonded by the adhesive. If the clear co-extruded film of this invention is not printed on the lower skin layer, a direct printing process is employed to include indicia printed on the upper surface of the additional film, which is the surface that is laminated to the film layer. lower skin through a suitable adhesive. Therefore, if the lower skin layer is printed reverse, or the upper surface of the additional film is printed directly, the print is inside the stock of labels, and: therefore is protected. Moreover, in order to enhance or enhance the visibility of the printed indicia, either indirect or direct, the additional film laminated to the multilayer film of this invention is preferably an opaque multilayer film or single layer; thereby providing a white support for the printed material. However, if you really want to see the color or appearance of an edible product or beverage held within a bottle or clear can, then the printed label used on that bottle or can needs to be transparent. Therefore, the additional film laminated to the lower skin layer of a transparent film of this invention also needs to be transparent, whether or not the additional film is a single layer or multiple layer film. In the compiled label construction, which includes both a clear or transparent multilayer film of this invention and an additional film laminated to the multilayer film to protect the indicia printed on the label, an adhesive is applied to the bottom surface exposed from the additional film for use in attaching the label to a container, such as a bottle or can. Preferably, the adhesive is included in vertical edges of the label and most preferably is applied adjacent each vertical edge in the form of a strip of narrow adhesive, as is well known in the art. In the most preferred embodiment of this invention, one of the vertical adhesive strips on the label is adhered directly to the container, and the label is then wrapped over the container with the other strip of vertical adhesive overlapping and adhesively attached to the edge of the outer slip layer of the label in a resting region on said first strip of vertical adhesive that adheres directly to the bottom surface of the label to the container. In this most preferred embodiment, it is extremely important that the vertical adhesive strip secured to the slide layer provide effective adhesion to prevent the label from separating in the overlapped, joined region. Thus, the slip layer of the film of this invention, in addition to having a desired low coefficient of friction to allow the film to be handled in commercial labeling equipment, must be able to effectively adhere the lower surface by overlapping the label. to her through the strip of adhesive used for that purpose. According to this invention, the sliding layer of the multilayer film has a metal / film COF of less than 0.45 and more preferably less than 0.35, as determined by a modified form of ASTM D1 894. Specifically, In the standard ASTM procedure, a piece of film is placed both on the sled and on the stainless steel platform, and the COF that is determined is a film / film COF. In accordance with this invention, the film of this invention is placed only on the sled, and the COF is determined between the slip layer of this film and the stainless steel platform of the test apparatus, using all other steps specified in ASTM. D1894. Most preferably, the adhesives employed in the labels of this invention are hot melt adhesives, which may have various levels of aggressiveness. In accordance with this invention, the slip layers need to allow "adhesion" of the hot melt adhesives at a level of at least 50%; more preferably at least 70%; even more preferably at least 90% and most preferably in excess of 90%. The test used to determine the "adhesion" for the hot melt adhesives to the slip layers of the films of this invention is as follows: A labeling machine is used rums to adhere a label to a metal can with a type of hot melt adhesive. Krones, Inc., the Krones packaging equipment supplier in the United States, is located at 9600 South 58th Street, Franklin, Wl. The adhesive is applied as a strip to the inner, or lower, surface of the label (which will contact the can) at the recommended application temperatures using the standard operating procedures for the labeller. The amount of glue applied corresponds to a setting of 1.5 on the glue application wheel of the Krones labeling machine. Visually, this corresponds to a point where the full length (ie, vertical height) of the label (5-7 / 8 inches), in this case) is covered with adhesive, but less than the point where the excess adhesive is squeezed out of the overlap seal that is formed between the upper sliding layer of the film of this invention and the innermost, or lower, surface of the label. The labeller is run at an operating speed of 120 labels per minute (LP). According to a test procedure, the label is a lamination of adhesive of an outer film according to this invention to an internal film, opaque, emptied, printed. Both are oriented, coextruded, multi-layer polypropylene films. The structure of the internal film can be varied; however, it is important that the hot melt adhesive that is employed adhere firmly to the lower surface of the inner film in a manner that will not allow the hot melt adhesive to separate from this lower surface during the peel test. for "adhesion". In other words, the peeling test is for the purpose of determining the adhesion of the adhesive to the sliding layer, and therefore the adhesive can not be separated from the lower surface of the inner film before being separated from the sliding layer or before the movie fails in some other way, as described later.

After reaching steady state conditions, the labeller is run to the conditions described above and the labels are applied to new clean metal cans. As the can leaves the machine, it is removed and the adhesion is evaluated in the manner described later. As noted above, the adhesion being investigated is the overlap seal of the adhesive to the slip layer of the film of this invention. An attempt is made to strip the overlap seal apart by lifting the outer edge that overlaps the label by hand along the length or vertical dimension of the can. If the adhesion of the hot melt adhesive. to the surface of the sliding layer is 100%, then the overlap seal will remain intact and the label will tear or destroy at some other interface. If the adhesion of the hot melt adhesive to the surface of the sliding layer is 0%, then the hot melt adhesive will peel cleanly from the surface of the sliding layer. If the adhesion pattern is intermittent, with remaining portions of the adhesive adhering to the slip layer and other portions peeling cleanly, then the adhesion percentage is the fraction of the total length of portions of the overlapping edges of the label that remain adhered , as evidenced by the length of the portions of the overlap edges that tear or destroy at an interface different to the slip-adhesive layer interface, to the total length of the overlap stamp, reported as a percentage. It is desirable to have an adhesion degree as close to 1 00% as possible. However, as noted above, adhesion of at least 50% is considered acceptable with the hot melt adhesives used in this invention. More preferably, the level of adhesion is at least 70%; even more preferably at least 90% and most preferably in excess of 90%. If the level of adhesion falls below 50%, then the degree of adhesion should be considered a failure.

It should be noted that the adhesion test is generally performed within one (1) minute of removal from the can of the labeller, and the percentage of adhesion reported for the multiple films of this invention refers to the adhesion determined in this way . If the time is prolonged, then the degree of adhesion generally increases. However, due to the chemical nature of certain hot melt adhesives, the failure mode can be cohesive (through the thickness of the hot melt by itself) . This may tend to cloud the adhesion results. In these latter cases, it has been determined that the period of time between the production and evaluation of the seal must be altered to a point that is significantly greater than 1 minute. The exact time is dependent on the specific hot melt adhesive being used and it is that time that prevents the cohesive failure. In a preferred embodiment of this invention, the outer skid layer is a mixture of a polypropylene homopolymer and a minor weight percentage of an additive resulting in the films of this invention having the desired slip and adhesion properties specified above in the I presented. In the most preferred embodiments of this invention, the additive includes an unsightly agent.

Most preferably, the antistatic agent includes an ethoxylated alkylamine and / or an ethoxylated alkylamide, each by itself, or each possibly either physically mixed with an ester or esterified by a chemical reaction with a suitable acid (e.g., stearic acid) ) or with another ester, for example, glycerol monostearate, esters based on sorbitol, etc. Most preferably, the antistatic agent includes an ethoxylated alkylamine that is esterified with another ester or with a suitable acid, an ethoxylated alkylamine mixed with an ester, or an ethoxylated alkylamine, by itself. It is also within the scope of the broader aspects of this invention to employ a glycerol monostearate, by itself, as the antistatic additive. However, the benefits achieved with this last antistatic additive are: not as good as the benefits achieved with an antistatic agent in the form of an ethoxylated alkylamine that is esterified with another ester or with a suitable acid, an ethoxylated alkylamine mixed with an ester , or an ethoxylated alkylamine, by itself. In the most preferred embodiment of this invention, the additive is an antistatic agent including an ethoxylated alkylamine included in a particulate masterbatch, or pelletized, which is predominantly a polypropylene homopolymer, by weight, with a minor percentage, by weight, of the ethoxylated alkylamine. In a representative embodiment, the additive is a blend including 87-88% by weight of polypropylene homopolymer and 12-13% by weight of an antistatic agent including an ethoxylated alkylamine that is possibly either physically mixed with an ester or esterified by reacting chemically with another ester, for example, glycerol monostearate, esters based on sorbitol, etc. , or with a suitable acid, for example, stearic acid. The antistatic agent may be an ethoxylated amine, such as a synthetic ethoxylated amine, for example, Atmer 163 sold by Uniquema in New Castle, Delaware. This ethoxylated amine can be used in small amounts by itself or in combination with a small amount of an ester, such as glycerol monostearate, for example, Atmer 129 sold by Uniquema in New Castle, Delaware. For example, excellent results have been achieved by using as additive either 0.50% Atmer 163 or 1.00% Atmer 163, by itself. In addition, excellent results have been achieved when using mixtures including 0.50% ~ of Atmer 129 with 0.50% of Atmer 16.3; 0.25% of Atmer 129 with 0.50% of Atmer 163 and 0.50% of Atmer 129 - with 0.25% of Atmer 163. All percentages in the present are percentages by weight, based on the weight of the skin layer. Although with less satisfactory results, 1.00% of Atmer 129 (a glycerol monostearate) can be employed by itself as the antistatic agent in the slip layer. For some applications this may be acceptable; however, it is not a preferred formulation in this invention. It has been determined that using 0.50% of Atmer 129 by itself as the antistatic agent in the slip layer does not provide a satisfactory product in accordance with this invention. In accordance with the broader aspects of this invention, other additives to achieve the desired slip and adhesion properties may be employed; provided that the additives, in conjunction with the other components of the film, provide the desired slip and adhesion properties specified above in this application. The present invention will be described hereinafter in connection with the preferred embodiments including an antistatic agent as the desired additive to the slip layer. The Applicant has determined that in order to obtain the desired sliding effect, or metal / low film COF, on the outer surface of the sliding layer according to this invention, the core layer needs to include a migratory amide in the I presented. In a preferred embodiment, the migratory amide is behenamide, which is supplied as Kemamide B by Witco, based in Greenwich, Connecticut. However, it is believed that other migratory amides are usable in this invention to achieve the desired COF within the scope of this invention. According to a preferred embodiment of this invention, the application has found that the core layer is preferably a polypropylene homopolymer containing at least 0.1% of the migratory amide, such as behenamide; more preferably, a migratory amide in the range of about 0.2-0.5%, and more preferably a migratory amide in the range of about 0.2-0.3% based on the total weight of the core layer. In the most preferred embodiment, behenamide is present in an amount of about 0.25% of the total weight of the core layer. Although higher percentages of behenamide may be usable, there does not seem to be any reason to use such higher percentages. Furthermore, it has been determined that a level of behenamide as high as 1.00% adversely affects adhesion, and therefore the films employing the latter level of behenamide may be unacceptable for several label applications. Although some reduction in the coefficient of friction was observed when the percentage of behenamide was as low as 0.1% by weight of the total weight of the core layer, more desirable coefficients of friction were achieved with the level of behenamide being approximately 0.25% and higher . Interestingly, it has been determined that Croda EBS, which is an ethylene bistearamide, when used in the core layer at 0.25% and 0.50% of the total weight of the core layer, did not provide the same reduction. desired in the coefficient of friction as behenamide, which is classified as a primary amide. In addition, it has been determined that Erucamide, when used in the core layer at a level of 0.25%, did not provide desirable results in terms of processing capacity in Krones labeling equipment. However, the Erucamide test has been quite limited, and therefore it is possible that this amide may work in an acceptable manner for certain applications and / or at higher concentrations. Although Erucamide is not a preferred glidant for use in the most preferred embodiment of this invention, its use is within the scope of the broader aspects of this invention.

As noted hereinabove, according to the most preferred aspects of this invention, the antistatic additive is an ethoxylated alkylamine and / or an ethoxylated alkylamide; most preferably an ethoxylated alkylamine. The ethoxylated alkylamine and / or the ethoxylated alkylamide can be used individually, either alone, or physically mixed with an ester or esterified by a chemical reaction with another ester or a suitable acid, as discussed in detail earlier in this application. In a preferred embodiment of this invention, the antistatic additive is included in a particulate masterbatch, or pelletized, identified as POLYBATCH ASPA 2485, which is supplied as a concentrate pelletized by A. Schulman, Inc. of Akron, Ohio. POLYBATCH ASPA 2485 comprises an antistatic agent including an ethoxylated alkylamine that is either mixed with an ester or is esterified by a chemical reaction with another ester or with a suitable acid. POLYBATCH ASPA 2485 is a master batch including approximately 87-88% polypropylene homopolymer and approximately 12-13% antistatic agent. Most preferably, the master batch POLYBATCH ASPA 2485 is present in the slip layer in a range of at least 4% by weight of said skin layer; more preferably in excess of 4% and even more preferably approximately 8% or even more. Therefore, the antistatic agent in the slip layer, which constitutes 12-13% by weight of the masterbatch, is present in the range of at least about 0.48% by weight based on the total weight of the slip layer polymeric; more preferably in excess of 0.48%; more preferably in the range of about 0.96% to 1.04%, or even more. Although greater percentages by weight of the antistatic agent can be used, the Applicant has not perceived any desired benefit of lower, improved coefficient of friction, when employing, for example, 12% by weight of the particulate masterbatch, ie 1.44% in weight of the antistatic agent. Thus, although higher percentages of the antistatic agent may be employed, there is no practical reason to use such higher percentages. On the other hand, lowering the level of the POLYBATCH ASPA 2485 to 4% by weight of the total weight of the sliding layer, although it does not provide a significant adverse effect on the coefficient of friction of the sliding layer, did reduce the window of operation in the Krones labeling team. That is, when it was used. 4% by weight of the POLYBATCH ASPA 2485 in the sliding layer, a closer control must be achieved on the vacuum level employed in the cutting drum and on the position of the cutting knife in order to provide an effective operation of the cutting equipment. labeled. According to this invention, the sliding layer is capable of receiving hot melt adhesives having various levels of aggressiveness with a desired level of adhesion, thereby making the films highly desirable for use in adhesive labeling applications. Such hot melt adhesives are available from H. B. Fuller Company of St. Paul, MN, as well as from other sources. When Fuller CLARITY HL-4157 hot melt adhesive was used on films containing behenamide, both in the core and on the surface of the film (ie, prior art films), there was a low level of nearness of about 0% immediately after the application of the adhesive. However, with a biaxially oriented, co-extruded polypropylene film having an outer skid layer containing 8% of the POLYBATCH ASPA 2485 according to this invention, the behenamide in the core was effectively blocked from the surface of the skid layer exterior and the level of adhesion increased from about 0% in the prior art film to 70% -98%. When the film was heated to 55 ° C for twenty-four (24) hours before the application of the hot melt adhesive Fuller CLARITY HL-4157 (to accelerate the migration of the fatty acid amide to the surface), the level of adhesion of the film without the outer sliding layer of the present invention remained poor, at about 0%, while the modified film according to the present invention had high levels of adhesion in the range of 60% - 98 %. With other Fuller hot melt adhesives having more aggressiveness than Fuller CLARITY HL-4157, ie Fuller CLARITY HL-4164 and Fuller CLARITY HL-4165, the adhesion levels of the prior art "single amide" film were from 70% - 75%, without heating, up to 0% - 5% after heating under the conditions stated above (ie at 55 ° C for twenty-four (24) hours). However, with these latter adhesives, the films modified in accordance with the present invention exhibited adhesion levels of 98% to 100% regardless of the thermal history of the film.

Quite surprisingly, the Applicant determined that direct oxidatively treating the outer slip layer of the films of the present invention, such as by corona treatment, actually reduces the adhesion level of the hot melt adhesive to the surface of the sliding layer. This was somewhat surprising in view of the fact that corona treatment is very commonly employed to improve the adhesion characteristics of a surface layer of a film to both print inks and adhesives. Thus, according to the most preferred embodiments of the present invention, the outer sliding layer is free from direct oxidative treatment, although it is believed that for some applications the direct oxidative treatment of the outer sliding layer, particularly if the treatment is "light", it will still result in the formation of an acceptable product. Therefore, films in which the outer skid layer is directly oxidized are within the scope of the broader aspects of the invention.

EXAMPLE 1 A biaxially oriented, multilayer, co-extruded polyolefin film according to this invention is a biaxially oriented polypropylene film of 48 gauge thickness, having a 3-gauge outer skid layer with the antistatic agent therein. , a core layer of 42-gauge thickness adhered to the slip layer and a skin layer of thickness 3 gauge on the surface of the core opposite that of the slip layer and being receptive to printing and / or securing applications . In this exemplary embodiment, the skid layer included 92% polypropylene homopolymer (Aristech FF035C) combined with 8% concentrate A. Schulman POLYBATCH ASPA 2485. The core layer is a polypropylene homopolymer (Aristech FF038A2) containing 0.25% Behenamide (Kemamide B) The print layer opposite the slip layer is a sotactic polypropylene homopolymer containing 0.25% Tospearl T120 and 0.15% Sylobloc 45, and sold under the trade name Aristech FF035W. Tospearl included functions both as a slip and anti-blocking agent in the printing layer, while Sylobloc 45 functions predominantly as an anti-blocking agent. J, All polymers used in this invention are polypropylene homopolymers containing 0.068% sodium benzoate nucleator and 0.25% Irganox B225 stabilizer. The inclusion of the sodium benzoate nucleator helps maintain the crystallinity of the polypropylene, thereby providing improved optical and strength properties in the films of this invention. It should be noted that the POLYBATCH ASPA 2485 is announced by A. Schulman, Inc., as usable to control dust and optimize antistatic properties. There is no recognition in any of the literature of the product known to the applicant, that this additive can or will work in any way to improve the sliding properties of a film, set aside that it should or could be employed as in the present invention. In accordance with this invention, the POLYBATCH ASPA 2485 including the antistatic agent herein, in a minor amount, is mixed with polypropylene homopolymer to form an outer skin layer, and it is believed that the migration of the antistatic agent out of the layer of skin is prevented, or at least minimized, by the presence of a migratory amide in the nucleus. At the same time, the composition of the sliding layer prevents the migrating amide in the core from migrating to the surface of the sliding layer in an amount that adversely affects the ability of the sliding layer to receive hot melt adhesives with the desired degree of adhesion to the film, moreover, due to the construction of the films of this invention, ', the films do not need to be heated to achieve migration of the slip agent to the film surface. Thus, the possible adverse effect on the plain of the film resulting from heating of the film is avoided. Moreover, if the films of the invention are exposed to hot environments, for example, during storage or shipping, the adhesion properties of the slip layer for hot melt adhesives commonly employed in label applications in accordance with this invention. they will not be adversely affected. The above examples are given by way of illustration only, and the invention should be limited only in accordance with the terms of the appended claims. It should be understood that the present invention can be employed to form a wide range of multilayer films of varying thickness and employing alternating polymer types and a variety of different additives. The types of specific additives that can be employed can be determined by routine experiments performed by individuals skilled in the art. Without further elaboration, the foregoing will thus fully illustrate my invention that others may, by applying current or future knowledge, easily adopt it for use under various conditions of service.

Claims

CLAIMS 1 . A biaxially oriented multilayer film usable to form adhesive labels to be attached to the containers, such as bottles and cans, said film includes a core layer comprising polypropylene and a migratory slip agent and an outer slip layer on one side of the core layer, said slip layer comprising mainly polypropylene, by weight, and a minor percentage, by weight, of an additive, said additive and said migratory slip agent being present in amounts to provide a COF on the surface of the sliding layer of not more than 0.45 and to provide adhesion of the adhesive employed in the label formed by the sliding layer of at least 50%. 2. The biaxially oriented multilayer film of claim 1, wherein said migratory slip agent in the core layer is an amide. 3. The biaxially oriented multilayer film of claim 2, wherein the amide is behenamide. 4. The biaxially oriented multilayer film of claim 2, wherein said migratory amide is present in a percentage, by weight, of at least 0.10%, based on the weight of the core layer. The biaxially oriented multilayer film of claim 4, wherein the percentage, by weight, of the migratory amide is about 0.25% or greater based on the weight of the core layer. The biaxially oriented multilayer film of claim 4, wherein the percentage, by weight, of the migrating amide is in the range of about 0.2 - 0.5% based on the weight of the core layer. The biaxially oriented multilayer film of claim 4, wherein the percentage, by weight, of the migratory amide is in the range of about 0.2 - 0.3% based on the weight of the core layer. 8. The biaxially oriented multilayer film of claim 1, wherein said additive in the slip layer is an antistatic agent. 9. The biaxially oriented multilayer film of claim 8, wherein the antistatic agent includes an ethoxylated alkylamine and / or an ethoxylated alkylamide. 10. The biaxially oriented multilayer film of claim 8, wherein the antistatic agent is an ethoxylated alkylamine. eleven . The biaxially oriented multilayer film of claim 8, wherein the antistatic agent includes an ethoxylated alkylamine. The biaxially oriented multilayer film of claim 9, wherein said ethoxylated ethoxylated alkylamine and / or alkylamide is either physically blended with an ester or esterified by chemical reaction with an ester or an acid. 3. The biaxially oriented multilayer film of claim 11, wherein said ethoxylated alkylamine is either physically mixed with an ester or esterified by chemical reaction with an ester or an acid. The biaxially oriented multilayer film of claim 8, wherein said antistatic agent comprises glycerol monostearate. 15. The biaxially oriented multilayer film of claim 1, wherein said multilayer film includes an additional outer layer on the side of the core layer opposite said slip layer, said additional outer layer having a surface to receive indicia, printed on it and / or being bondable to a surface of an additional film used to form labels. 16. The biaxially oriented multilayer film of claim 1, wherein said outer skid layer is free of direct oxidizing treatment. 17. The biaxially oriented multilayer film of claim 8, wherein said outer skid layer is free of direct oxidizing treatment. 1 8. The biaxially oriented multilayer film of claim 9, wherein said outer sliding layer is free of direct oxidizing treatment. 19. The biaxially oriented multilayer film of claim 10, wherein said outer sliding layer is free of direct oxidative treatment. 20. The biaxially oriented multilayer film of claim 1, wherein said outer sliding layer is free of direct oxidative treatment. twenty-one . The biaxially oriented multilayer film of claim 12, wherein said outer sliding layer is free of direct oxidative treatment. 22. The biaxially oriented multilayer film of claim 1, wherein said outer sliding layer is free of direct oxidizing treatment. 23. The biaxially oriented multilayer film of claim 14, wherein said outer sliding layer is free of direct oxidative treatment. 24. The biaxially oriented multilayer film of claim 15, wherein said outer sliding layer is free of direct oxidative treatment. 25. The biaxially oriented multilayer film of claim 1, wherein the adhesion is at least 70%. 26. The biaxially oriented multilayer film of claim 1, wherein the adhesion is at least 90%. 27. The biaxially oriented multilayer film of claim 1, wherein the adhesive employed in the formed label is a hot melt adhesive. 28. The biaxially oriented multilayer film of claim 27, wherein the adhesion is at least 70%. 29. The biaxially oriented multilayer film of claim 27, wherein the adhesion is at least 90%. 30. The biaxially oriented multilayer film of claim 1, wherein the COF is not greater than 0.35. 31 The biaxially oriented multilayer film of claim 25, wherein the COF is not greater than 0.35. 32. The biaxially oriented multilayer film of claim 26, wherein the COF is not greater than 0.35. 33. The biaxially oriented multilayer film of claim 27, wherein the COF is not greater than 0.35. 34. The biaxially oriented multilayer film of claim 28, wherein the COF is not greater than 0.35. 35. The biaxially oriented multilayer film of claim 29, wherein the COF is not greater than 0.35. 36. A multi-layered biaxially oriented label to be attached to containers, such as bottles and cans, said label including a core layer comprising polypropylene and a migrating slip agent, an outer slip layer on one side of the core, said slip layer comprising mainly polypropylene, by weight, and a minor percentage, by weight, of an additive, an inner layer on the side of the core layer opposite the outer slip layer, and an additional film having an internal surface adhered to an outer surface of the inner layer and an outer, opposite surface, which includes an adhesive therein, indicia printed on the outer surface of the inner layer or on the inner surface of the additional film, one end of said outer surface of said additional film being unible to a container surface through the adhesive therein, and an opposite end of said The outer surface of said additional film which overlaps and is adhesively bondable to an outer surface of the sliding layer when the label is attached to a container, said additive and said migratory amide being present in amounts to provide a COF in the surface of the sliding layer of not more than 0.45 and to provide an adhesion of the adhesive for the sliding layer of at least 50%. 37. The biaxially oriented multilayer label of claim 36, wherein said migratory slip agent in the core layer is an amide. . :: > 38. The biaxially oriented multilayer label of claim 37, wherein the amide is behenamide. 39. The biaxially oriented multilayer label of claim 37, wherein said migratory amide is present in a percent, by weight, of at least 0.10%, based on the weight of the core layer. 40. The biaxially oriented multilayer label of claim 39, wherein the percentage, by weight, of the migratory amide is about 0.25% or greater based on the weight of the core layer. 41 The biaxially oriented multilayer label of claim 39, wherein the percentage, by weight, of the migratory amide is in the range of about 0.2 - 0.5% based on the weight of the core layer. 42. The biaxially oriented multilayer label of claim 36, wherein said additive in the slip layer is an antistatic agent. 43. The biaxially oriented multilayer label of claim 42, wherein the antistatic agent includes an ethoxylated alkylamine and / or an ethoxylated alkylamide. 44. The biaxially oriented multilayer label of claim 43, wherein the antistatic agent comprises an ethoxylated alkylamine. 45. The biaxially oriented multilayer label of claim 43, wherein said ethoxylated alkylamine and / or ethoxylated alkylamide is either physically blended with an ester or esterified by chemical reaction with an ester or an acid. 46. The biaxially oriented multilayer label of claim 44, wherein said ethoxylated alkylamine is either physically mixed with an ester or esterified by chemical reaction with an ester or an acid. 47. The biaxially oriented multilayer label of claim 36, wherein said additive in the slide layer comprises glycerol monostearate. 48. The biaxially oriented multilayer label of claim 36, wherein said outer sliding layer is free of direct oxidative treatment. 49. The biaxially oriented multilayer label of claim 36, wherein the adhesion is at least 70%. 50. The biaxially oriented multilayer label of claim 36, wherein the adhesion is at least 90%. 51 The biaxially oriented multilayer label of claim 36, wherein the adhesive is a hot melt adhesive. 52. The biaxially oriented multilayer label of claim 51, wherein the adhesion is at least 70%. 53. The biaxially oriented multilayer label of claim 51, wherein the adhesion is at least 90%. 54. The biaxially oriented multilayer label of claim 36, wherein the COF is not greater than 0.35. 55. The biaxially oriented multilayer label of claim 49, wherein the COF is not greater than 0.35. 56. The biaxially oriented multilayer label of claim 50, wherein the COF is not greater than 0.35. 57. The biaxially oriented multilayer label of claim 51, wherein the COF is not greater than 0.35. 58. The biaxially oriented multilayer label of claim 52, wherein the COF is not greater than 0.35. 59. The biaxially oriented multilayer label of claim 53, wherein the COF is not greater than 0.35.