Patent Application
20100272975
1. Technical Field
The present techniques generally relate to lamination films. More particularly, the present techniques relate to new lamination films incorporating styrenic polymers and methods of producing the same.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art which may be related to various aspects of the present techniques which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present techniques. Accordingly, it should be understood that these statements are to be read in this light, and not as any indication of what subject matter may constitute prior art to the present techniques.
Lamination is a process through which one or more sheets or coatings of a laminating material may be applied to an object to protect the surface of, or printing on, the object. The laminating material (e.g., a lamination film or coating) may be stronger and/or more durable than the object being protected. The lamination material may be a clear plastic or polymer designed to permit printing or graphics on the protected surface of the object to be seen, while shielding the surface from damage (e.g., from the environment) and, thus, extending the useful life of the object. Depending on the application, a lamination material or film may be applied to one or more sides of the object or item being protected.
Items typically laminated include educational items, restaurant menus, photographs, historical documents, interior and outdoor signage, posted policies, marketing or sales literature, and so on. In certain applications, the lamination film may prevent the printing and graphics on the protected item from being modified. In other words, attempts to remove or peel the lamination to access the graphics may result in the destruction of the protected surface, and therefore, prevent an unauthorized modification of the graphics or printing. This latter application may be beneficial, for example, with corporate or government issued identification cards, such as identification cards, driver's licenses, and the like.
Two lamination techniques are hot lamination and cold lamination. In hot lamination, the object or surface to be protected may be placed between layers of a lamination film. The combination may be passed through heated rollers, which melt an adhesive disposed on a portion or all of one side of each lamination film facing the surface(s) of the object to be protected. The melted adhesive may adhere to the protected surface and also bind to overlapping portions of the opposing lamination film layers. This overlap results in a final product in which the protected surface or object may be partially or totally encased between two or more layers of lamination film. Full enclosure may better protect the object or item from damage caused by liquids, and environmental conditions, for example.
In cold lamination, the object or surface to be protected may be placed between the lamination films (e.g., between two sheets of lamination film) that may have a pressure sensitive adhesive protected by a release liner, e.g., “peel and stick” adhesives, disposed on a portion or all of one side of each lamination. Shortly before the layers of lamination film are pressed together over the surface of the object or item, the release liner over the adhesive is removed, exposing the pressure sensitive adhesive facing the surface to be protected and allowing the adhesive to bind to the protected surface. Again, as for hot lamination, the two layers of lamination film may overlap (e.g., at the edges of the laminated layers or structure), partially or totally encasing the weaker object or surface to be protected. Cold lamination may be used for surfaces that are heat sensitive, or for convenience.
The thickness of the lamination film selected may be determined by the application needs. For example, single use or short term protection, such as posters advertising an event, may be protected by a lamination film having a thickness of about 1.5 mils (wherein a mil is 1/1000 of an inch). For materials needing a stiffer feel or longer term protection, such as menus or advertising brochures, and so forth, a lamination film of about 3 mils in thickness may be more useful. In cases where very long term protection is needed, such as with identification cards or signage, a lamination film having a thickness of about 6 mils, or even higher, may be beneficial.
Various types of materials may form the lamination film, which may be constructed of multiple layers of the same or different material. One protective layer currently used in lamination films is a biaxially-oriented polyester film which may be pretreated, such as by corona discharge, flame treatment, chemical surface treatment, or sanding, to improve its surface adhesion to other layers of the lamination film. An adhesive layer may be applied to the pretreated surface of the external polyester layer to improve adhesion of the polyester to a subsequent inner layer of a hot-melt adhesive, for example. The adhesive layer improves the adhesion of the polyester film to the inner adhesive layer. The application of the middle and inner layers may be performed using extrusion coating techniques, for example. This type of multilayer lamination film structure may be used in hot lamination.
In other examples with biaxially-oriented polyester film the sealing layer may be a pressure sensitive adhesive instead of a hot-melt adhesive. A release liner is generally placed over the pressure-sensitive adhesive. This type of multilayer lamination film structure may be used in cold lamination. Again, the application of the middle and inner layers may be performed using extrusion coating techniques.
In general, the types of lamination films discussed above that may be used for hot and/or cold lamination are durable and provide beneficial long-term protection to the protected object. Unfortunately, these types of lamination films may have significant associated production costs due to multiple process steps which can be energy intensive. For example, producing a biaxially oriented polyester film generally requires several energy intensive steps. The polyester resin must be pre-dried prior to extrusion to avoid breaking of the polyester chains and a loss of physical and/or optical properties for the lamination film. Further, after the polyester resin is extruded, the biaxial orientation process is performed using a tentering frame, which may be both expensive and energy intensive. In addition, following the orientation process, the pretreatment to improve the surface adhesion of the polyester layer may damage the film surface or otherwise generate scrap material. These techniques require multiple adjustments and may add significant cost and complexity.
Advantages of the techniques may become apparent upon reading the following detailed description and upon reference to the drawings in which:
One or more specific embodiments of the present techniques will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
The present techniques include lamination films that may be made from single or multiple layers that include one or more styrenic polymers. In contrast to other types of lamination films, previously discussed, these new films may provide lower-cost lamination materials, due to lower cost production processes and materials. Embodiments of the present techniques may be used in protective structures for numerous items, from single use individual sheets, such as, for example, advertisements for special events, to long term use items, such as photographic identification cards. The decrease in costs may allow for wider use of lamination films. Further, these films could be used in either cold or hot lamination systems and with either small scale, individual laminations or in large scale lamination machines. Moreover, the lamination films of the present techniques may be produced in simple film or sheet co-extrusion process, and may include one, two, or three layers, or more. While not needed, the production of the lamination films may use additional processes, such as extrusion coating, to apply other materials, e.g., water activated adhesives, to the films.
As discussed in more detail below, the present techniques provide for a lamination film including a protective layer (i.e., an external layer) containing at least one styrenic polymer (e.g., about 35% to about 90% of the total lamination film thickness) and a sealing layer containing at least one sealing material (e.g., about 10% to about 65% of the total lamination film thickness). In an embodiment, the protective layer may make up 100% of the protective layer in monolayer films. In another embodiment, the protective layer may make up about 35% to about 90% of the total thickness of the lamination film.
The protective layer is an outermost layer in the lamination film, while the sealing layer may generally be an external layer. The lamination film has a thickness that may be in the range of about 1 mils to about 20 mils, about 3 mils to about 15 mils, about 3 mils to about 6 mils, or about 7 mils to about 12 mils, among others. The sealing material may include any number of materials that may adhere to themselves and/or other materials. For example, such resins may include ethylene vinyl acetate, low density polyethylene, or a combination thereof. This ethylene vinyl acetate may have a vinyl acetate content of about 5% to about 35% by weight, 10% to about 30% by weight, 15% to about 25% by weight, among others. In one example, the styrenic polymer of the protective layer may be a styrene butadiene block copolymer having a styrene content of about 50% to about 95% by weight, about 60% to about 90% by weight, about 70% to about 85% by weight, among others. The protective layer may also contain more than one styrenic polymer. In one example, the styrenic polymer of the protective layer may be a blend of a styrenic polymer with polystyrene, and wherein the styrenic polymer is about 20% to about 98%, about 30% to about 95%, about 40% to about 93%, about 50% to about 90%, of the blend in the protective layer by weight. An adhesive layer (e.g., low density polyethylene) may be disposed between the protective layer and the sealing layer. The adhesive layer may be about 25% to about 55% of the total lamination film thickness.
A schematic of a two layer lamination film 10 is shown in
For example, an SBC may be blended with numerous other polymers to modify various properties. Styrenic polymers that may be used in these blends include, for example, styrene acrylonitrile (SAN), styrene methyl methacrylate (SMMA), styrene butyl methyl methacrylate (SBMA), and styrene butadiene elastomers, among others. The selection of a polymer blend depends on the final properties desired. For example, the use of styrene acrylonitrile in a blend with an SBC may increase the stiffness and scratch resistance of the protective material, but may also lower the impact resistance and flexibility of the protective material.
The sealing material may be any appropriate material capable of sealing with itself and the underlying substrate to be protected. For example, the sealing material may be ethylene vinyl acetate, with the vinyl acetate content chosen to control the strength of the seal formed. Such an ethylene vinyl acetate material is available from DuPont Chemical Corporation of Wilmington, Del., as the brand Elvax® 3165. Other materials may be used for the sealing material such as low density polyethylene (LDPE). One of ordinary skill in the art will recognize that any number of materials may be used as the sealing material, including combinations of the polymers discussed above.
The thickness of the two layer lamination film 10 may be determined by the properties desired for the final protective laminated structure. In various applications, the thickness may range from about 3 mils up to about 20 mils, while in other applications, the thickness may range from about 4 to 10 mils, or from 6 to 9 mils. The thickness of the individual layers may also control the final properties of the lamination films or laminated structure. In certain embodiments, the styrenic layer may range from 40 to 75 percent of the final thickness of the lamination film or structure.
The use of these lamination films in protecting a surface is shown by the cross-section of a laminated structure 20 in
The formation of a laminated structure 20 is not limited to the use of two layer lamination films 10. The laminated structures 20 may be formed using a single layer, having a styrenic polymer, or multiple polymer layers, of which a protective layer may contain a styrenic polymer. For example, the use of single layer lamination films formed using only styrenic polymers may provide advantages in single use items having a shorter lifespan, such as single-event advertising posters. In other examples, a three layer lamination film 24 as shown in the cross-section in
As for the two layer lamination film 10 discussed above, the three layer lamination film 24 shown in
In the three layer lamination film 24, the composition of the sealing layer 16 may be chosen as described with respect to
More complex layer structures may be used in the present techniques, as illustrated by the cross sectional views shown in
The thickness of the three layer lamination film 24, four layer lamination film 26, or five layer lamination film 28 may be determined by the properties desired for the final protective laminated structure. In various applications, the thickness may range from about 3 mils up to about 20 mils, while in other applications, the thickness may range from about 4 to 10 mils, or from 6 to 9 mils. The thickness of the individual layers may also control the final properties of the lamination films or laminated structure. In certain embodiments, the styrenic layer may range from 40 to 75 percent of the final thickness of the lamination film or structure.
The lamination films discussed above may be used in any number of different lamination processes. For example, a single sheet lamination process 36 is shown in the perspective view in
Other lamination systems and processes applicable with present techniques may include, for example, large scale commercial laminators where lamination films are stored on rolls that are continuously fed into the lamination machine. Further, the top and bottom layers of the laminated structure do not have to be identical. In some instances, thicker lamination films may be combined with thinner lamination films. In other instances this may provide improved readability of the graphics along with the desired stiffness. In some embodiments a clear lamination film may be used in combination with an opaque lamination film. In other embodiments, a lamination film may be used as a top or transparent layer over a layer of another polymer, such as polyethylene, polypropylene, or other protective opaque or translucent polymer.
The temperature used for the heated rollers 46 depends on the structure of the lamination film selected. For example, the heated rollers may be between about 120° F. and 240° F., between about 140° F. and 220° F., or between about 150° F. and 220° F. for the two layer lamination film 10 discussed with reference to
In addition to the hot lamination techniques discussed above with respect to
The lamination films of the present techniques may be produced by any number of techniques. For example, the two layer lamination film 10 discussed with respect to
The sealing material 62 may be fed into a second extruder 64. In the second extruder 64, the sealing material 62 is partially melted in a second feed zone 66, before being forced into the melt zones 68 of the second extruder 64. In the melt zones 68 of the second extruder 64, the sealing material 62 is melted and pressurized, prior to being forced into the co-extrusion film die 58 as a second melt. As for the first extruder 52, the second extruder 64 may be directly connected to the co-extrusion film die 58 or may be connected by a heated transfer line 70, which may be maintained at about the same temperature as the melt zones 68.
In the co-extrusion film die 58, the protective material 50 of the first melt and the sealing material 62 of the second melt are co-extruded into a film structure having a protective layer and a sealing layer. The thickness of the individual layers may be controlled by adjustment screws 72. The molten two-layer film structure 74 is forced out of a co-extrusion die head 76 onto a chill roll 78. An air knife 80 blows a stream of cool air opposite the chill roll 78 to help solidify the molten two layer structure. The film may be kept tight to avoid wrinkles by one or more tension rollers 82. The final solidified lamination film 84 may be fed into a slitter 86. In the slitter 86, the lamination film 84 may be slit into the final sizes required by the customers prior to being rolled up on take-up rolls 88.
The production of three layer lamination films 24, 25, and 26, discussed with respect to
In the three layer coextrusion die 100, the molten adhesive material 94 from the third extruder 92 is combined into a layered structure with the molten protective material 50 from the first extruder 52 and the molten sealing material 62 from the second extruder 64. The layered structure is forced out of the three layer co-extrusion die 100 through a three layer co-extrusion die head 104 which may be pointed downwards, as shown in
The four and five layer lamination film structures 26 and 28, discussed with respect to
The following examples are set forth to provide those of ordinary skill in the art with a detailed description of how the methods disclosed herein are evaluated, and are not intended to limit the scope of the present techniques.
A number of lamination film samples were produced to determine the properties of lamination films that may be made using styrenic polymers. These samples included monolayer lamination films including only styrenic polymers, two layer films that included styrenic polymers and a sealing material, and some three layer films that included a center adhesive material. The two and three layer lamination films were made using the procedures discussed with respect to
A commercially produced lamination film was used as a control (hereinafter referred to as “OPET Control Film”) for comparison to the experimental lamination films, as shown in the tables below. The commercial sample was made up of three layers, a protective layer of about 1.4 mil in thickness, made from oriented polyethylene terphthalate (PET), an adhesive layer of about 0.6 mil in thickness, made from a low density polyethylene (LDPE), and a sealing material of about 0.85 mil in thickness, made from an poly(ethylene vinyl acetate) (EVA) having a vinyl acetate content of at least about 12%, by weight. The construction of the OPET Control Film indicates that it was likely produced using an extrusion coating operation, in which an oriented PET is coated with a LDPE/EVA extrudate. Since LDPE does not adhere well to PET, the PET may need to be primed to increase the adhesion. This process provides a very strong protective film layer, but has significant costs associated with the complexity of the production process.
The styrenic polymer used for the examples was a styrene butadiene copolymer (SBC) made of sequential blocks of styrene and butadiene. The SBC contains about 50% to about 95% styrene by weight and about 50% to about 5% butadiene by weight. One such material may be available as K-Resin® DK11, which is an SBC available from Chevron Phillips Chemical Company LP of the Woodlands, Tex. One skilled in the art will recognize that any number of other commercially available SBCs may be used in embodiments of the present technique. Such additional SBCs include K-Resin® SBC grades KR05, KR01, KK38, and others available from Chevron Phillips Chemical Company LP, as well as similar SBCs available from other suppliers.
The poly(ethylene vinyl acetate) (EVA) used in the examples was a random copolymer of polyethylene and vinyl acetate having around 18% vinyl acetate, by weight. Such material may be commercially available as Elvax® 3165 Resin from E.I. du Pont de Nemours and Company, Inc. One skilled in the art will recognize that other suppliers provide similar grades, such as Evatane® 18-150 Resin, available from Arkema Company of Philadelphia, Pa. Further, grades having other levels of vinyl acetate may be used, depending on the properties desired.
The low density polyethylene (LDPE) used in the examples was a film grade LDPE, which may be commercially available as MarFlex® PE 4517 Polyethylene from Chevron Phillips Chemical Company LP. This material has a density of about 0.923 g/cm3 (measured using ASTM D1505) and a melt index of about 5.1 g/10 min (under ASTM D1238, Condition E). One of ordinary skill in the art will recognize that other commercially available LDPE grades, of varying densities and melt indices may be used in embodiments the present techniques.
The polystyrene (PS) used in the examples was a general purpose PS with a melt flow rate of 7 g/10 min (measured by ASTM D1238, Condition G). Such a grade may be commercially available as MC3200 from Chevron Phillips Chemical Company LP. One of ordinary skill in the art will recognize that other commercially available PS grades may be used in the current techniques.
A small amount of high impact polystyrene (HIPS) may optionally be used as an antiblocking agent to decrease the tendency of the lamination film to adhere to itself. The grade used in the examples was EA8100, commercially available from Chevron Phillips Chemical Company LP. One of ordinary skill in the art will recognize that other commercially available HIPS may also be used in the current techniques.
Surface and optical properties of the lamination films were measured using the following ASTM testing procedures. The haze was measured using ASTM D1003-00: “Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics.” The gloss was measured using ASTM D2457-03: “Test Method for Specular Gloss of Plastic Films and Solid Plastics,” using a 60% incidence angle. The coefficient of friction was measured using ASTM D1894-06: “Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting,” using a 200 g weight to hold the surfaces together.
The physical properties of the lamination films were measured using the following test procedures. Shrinkage was measured using ASTM D2732-03: “Standard Test Method for Unrestrained Linear Thermal Shrinkage of Plastic Film and Sheeting.” Elmendorf tear was measured using D 1922-06a: “Standard Test Method for Propagation Tear Resistance of Plastic Film and Thin Sheeting by Pendulum Method.” The tensile strength, elongation, and 1% secant modulus (i.e., stiffness) were measured using ASTM D882-02: “Standard Test Method for Tensile Properties of Thin Plastic Sheeting.”
The vapor transmission rates of the lamination films were measured using the following test procedures. The water vapor transmission rates were measured using ASTM F 1249-06: “Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor.” The oxygen transmission rates were measured using ASTM D3985-05: “Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor.”
The curl of the lamination films was measured using an internal technique that provided relative comparisons between samples. This value was merely used to determine comparisons between the operational characteristics of the lamination film samples. The technique used a glass plate with a marked grid as a support for a lamination film sample. The lamination film sample was laid over the glass plate and held in place by a metal frame that was entirely outside of the area of the marked grid. A razor blade was then used to cut diagonal lines in the lamination film sample between opposing corners of the grid. The lamination film would then curl both across the processing (e.g., flow) direction of the film sample (designated TD for transverse direction) and in the processing direction of the film sample (designated MD for machine direction). After 30 seconds, the location of the leading edge of each section of the curled lamination film was measured by vertically observing its position on the grid. A corresponding measurement was taken from the center (i.e., the intersection of the perpendicular cuts in the lamination film) to the edge of the grid. The curl was then calculated as a percentage ratio of the location of the leading edge of the curl to the length from the edge of the grid to the center point.
Monolayer lamination films were prepared using a single extruder in a cast film process, analogous to that discussed with respect to
The properties that may be obtained from monolayer lamination films made from an SBC with various amounts of added polystyrene are shown in Table 2. As tabulated, a first run containing no polystyrene was tested, and then a series of samples were made, wherein the amount of polystyrene was set to 20%, 30%, and 40%, by weight of the polymer.
As shown by the results in Table 2, the addition of increasing levels of polystyrene blended into the SBC may have a significant effect on lamination film stiffness. Over the polystyrene addition range studied of 0% through 40%, the lamination film stiffness, as measured by 1% secant modulus, increased by approximately 44% in the machine direction of the film and by over 100% in the transverse or cross direction of the lamination film. Further, the addition of polystyrene to the SBC at levels below 30% had little or no effect on lamination film haze or gloss. However, at an addition level of 40% of polystyrene into the SBC, both the film haze and film gloss may show a small level of improvement. Moreover, the addition of polystyrene to the SBC across the levels studied had little or no effect on tear strength. However, as seen from the data, the addition of polystyrene enhanced the tensile properties of the lamination film and impacted the elongation of the film. As these results show, the stiffness of the final product may be generally adjusted by the selection of the styrenic polymer blend. This stiffness could be selected to match the application.
1Values normalized for film thickness.
2MD stands for machine direction, or parallel to the direction of processing.
3TD stands for transverse direction, or perpendicular to the direction of processing.
Exemplary two layer lamination film structures that included an SBC in a protective layer 12 and an adhesive polymer in a sealing material 62 were generated using a blown film line, following the conditions in Table 3. The extruder setup was similar to that discussed with respect to
The properties obtained for lamination films made using these techniques are shown in Table 4, below. One property that may be more problematic is the increased shrinkage that may be seen for films produced by a blown film process. This shrinkage may be due to increased orientation introduced into the polymers in these films versus a cast film process. As shown in Table 4, this may be more significant for these lamination films than for the OPET Control Film. Accordingly, the current techniques have focused more on cast film techniques, as shown in
Although the stiffness and shrinkage of the two layer lamination films were not as good as the OPET Control Film, the easier production techniques may give lamination films produced by the current techniques a significant cost advantage. Further, the lower stiffness may provide advantages in applications in which higher stiffness may actual be a problem, such as, for example, in the lamination of architectural drawings, posters, or other items that may need to be rolled up for storage.
The heat sealing properties of the lamination films were comparable to that of the OPET Control Film, with initiation around 200° F. This property is controlled by the sealing material, or EVA, in both the OPET Control and test films. As shown in Table 4, all of the experimental lamination films had higher Elemendorf tear strength than the OPET Control Film. This indicates that the experimental lamination films may be less likely to tear during use.
1MD stands for machine direction, or parallel to the direction of processing.
2TD stands for transverse direction, or perpendicular to the direction of processing.
The results obtained for the two layer and monolayer lamination films indicated that a three layer lamination film may provide even more cost savings. In this type of construction, an adhesive layer 30 which may include lower cost materials is included between the protective layer 12 and the sealing layer 16. Two sets of three layer lamination films, using two different layer thicknesses, were generated to test the properties. The conditions used for extruding the films were identical and are shown in Table 5.
The first set of three layer lamination films tested were three mils thick, and used a layer distribution of 35% for the protective layer 12, 45% for the adhesive layer 30, and 20% for the sealing layer 16, each a percentage of the total thickness of the lamination film. The results obtained from tests on these films are shown in Table 6. Another set of lamination films were produced at a five mil layer thickness, using the same layer thickness ratios. The results obtained from tests on these films are shown in Table 7.
As shown in Tables 6 and 7, all of the test films were less stiff than the existing lamination film used in the market. However, the lower cost of the films may allow the gauge of the films to be increased to adjust the stiffness while retaining the benefits. A comparison of the 1% secant modulus of the test films and the OPET Control Film indicates that even the stiffest construction would need to be increased by a factor of 2 to 2.5 to achieve the same stiffness (lbf) as the OPET Control Film.
Fortunately, as previously noted, the stiffness of the experimental lamination films may not limit their use in certain applications, such as in page protection and posters, where stiffness may be not as highly valued and the surface of the item being protected may be relatively smooth. In some applications, such as blueprint protection where the lamination may be rolled-up for storage, the lower stiffness of the films of the present techniques may actually be beneficial.
Further, as shown in Tables 6 and 7, the three layer structures demonstrated similar outermost surface gloss as the OPET Control Film. The test lamination films may also show lower haze than the OPET Control Film. The low haze of the sealing surface 18 of the OPET Control Film may be caused by embossing of the sealing surface. In commercially produced films, the sealing surface 18 may be embossed to allow air to escape during the lamination process. For the same reasons, it may be beneficial to emboss certain embodiments of the present lamination films in commercial production. Accordingly, any difference in haze between the OPET Control Film and test films would be substantially mitigated or would disappear.
1Values normalized for film thickness.
2MD stands for machine direction, or parallel to the direction of processing.
3TD stands for transverse direction, or perpendicular to the direction of processing.
1Values normalized for film thickness.
2MD stands for machine direction, or parallel to the direction of processing.
3TD stands for transverse direction, or perpendicular to the direction of processing.
While the Elmendorf tear and tensile properties of the test lamination films may be lower than the OPET Control Film, the values are likely to be sufficient for many applications. However, one property that may negatively affect the final use of a film is curl. Curl is a measure of a film's ability to remain flat in an unrestrained state. During usage a film having a high degree of curl would be more difficult to handle and could interfere with the lamination process.
The OPET Control Film exhibits a low level of curl. All of the test lamination films using the first three layer structure showed a relatively large amount of curl as indicated in Tables 6 and 7. Based on the results obtained, the degree of curl may be dependent on the amount of polystyrene blended into the protective layer blend and the amount of LDPE used in the adhesive layer blend. The amount of curl may be able to be reduced by lowering the amount of polystyrene in the protective layer and the amount of LDPE in the adhesive layer. To test this proposition, a second set of three layer structures were tested, using different layer compositions and distributions.
Using a second composition and layer structure, a second set of three layer lamination films were prepared. These films used a layer distribution of 50% for the protective layer 12, 30% for the adhesive layer 30, and 20% for the sealing material 62, each percentage based on the total thickness of the lamination film. The compositions tested and results obtained from tests on these films are shown in Table 8. Additionally, a second set of films were produced at a five mil film thickness, using the same layer thickness ratios. The results obtained from tests on these films are shown in Table 9. In order to compare the results obtained for these layer structures with the results for the blend compositions of Tables 6 and 7, a final structure was made using the blend composition of Tables 6 and 7 and the layer structure of Tables 8 and 9. This structure is labeled as Film A in Tables 8 and 9.
The increase in protective layer thickness and the reduction in adhesive layer thickness had a positive effect on lamination film stiffness. On average the approximate 40% increase in protective layer thickness resulted in a 25% increase in machine direction stiffness and a 35% increase in cross direction stiffness. Although the increase in protective layer thickness of the experimental films did not achieve the stiffness seen for the OPET Control Film, they are believed to be sufficient for numerous applications considering the lower cost.
An increase in the thickness of the protective layer 12 may also improve the lamination film curl. As shown by Films 3-6, 3-10, in Table 8, and Film 5-9, in Table 9, adjustment of the layer distribution and composition allows films to be made that have a similar curl to the OPET Control Film, shown in Tables 6 and 7. As expected from the results of the previous structure, the lowest curl values were obtained when the level of polystyrene in the protective layer 12 and of the LDPE in the adhesive layer 30 were lowest. At the lowest PS and LDPE levels studied, for structure 5-9, the curl values obtained on the film were lower than that determined for the OPET Control Film.
The tensile properties of the experimental lamination films using this structure were not generally as good as those of the OPET Control Film, but were better that those measured for films using the first structure. The tear properties of the films made using the second three layer structure were comparable with those of the OPET Control Film and slightly lower than the tear properties of films made using the first three layer structures.
Conclusions from Experimental Results
Based on the data obtained for the test lamination films, a three layer lamination film structure including a styrenic polymer as a protective, layer 14, an adhesive layer 30 made of an adhesive material including a LDPE/EVA blend and an EVA sealing layer 16 may provide a low cost structure for lamination applications. Such a film would not be as stiff as the OPET Control Film at the same film thickness, which may preclude its use in some segments of the market, but the material cost savings may widen its use in other applications.
For certain embodiments, the data collected during the study indicated that very favorable properties may be obtained for a three layer structure in which the polystyrene in the protective layer 12 may be limited to about 57%, the LDPE in the adhesive layer 30 may be limited to about 50% and the thickness of the adhesive layer may be limited to less than about 30%. Structures corresponding to these conditions are indicated as “3-9” and “5-9” in Tables 8 and 9.
1Values normalized for film thickness.
2MD stands for machine direction, or parallel to the direction of processing.
3TD stands for transverse direction, or perpendicular to the direction of processing.
1Values normalized for film thickness.
2MD stands for machine direction, or parallel to the direction of processing.
3TD stands for transverse direction, or perpendicular to the direction of processing.
While the techniques disclosed above may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings. However, it should be understood that the techniques are not intended to be limited to the particular forms disclosed. Rather, the techniques encompass all modifications, equivalents and alternatives falling within the spirit and scope of the techniques as defined by the following appended claims.
