Films including solvent barrier and primer layers

Abstract

A film comprising a solvent barrier and a primer layer is described. Specifically, the film includes a substrate, the substrate comprising polylactic acid, a primer layer disposed on the substrate, a barrier layer disposed on a surface of the primer layer opposite the substrate, and an adhesive layer disposed on a surface of the barrier layer opposite the primer layer. The barrier layer comprises an amorphous aliphatic polyamide having a glass transition temperature of at least 40°C. Such a film can provide acceptable adhesion and barrier performance for polylactic acid-based graphic film systems.

Description

[Background technology]

[0001] Certain films are used to display graphics and other visual information when adhered to a surface. These films can be made in part by printing ink onto the ink-receptive surface of such films. When the ink is typically solvent-based, some of these solvents can penetrate through the thickness of the film and into the adhesive layer, causing undesirable tack and poor peelability. Certain pressure-sensitive adhesives can have poor adhesion to the film substrate, making the film prone to delamination without an intermediate layer that has adequate adhesion to both the adhesive and the substrate. Summary of the Invention

[0002] In one aspect, the present disclosure relates to a film. The film includes a substrate comprising polylactic acid, a primer layer disposed on the substrate, a barrier layer disposed on the surface of the primer layer opposite the substrate, and an adhesive layer disposed on the surface of the barrier layer opposite the primer layer. The barrier layer includes a polyamide, the polyamide being an amorphous aliphatic polyamide, and the polyamide having a glass transition temperature of at least 40°C.

[0003] In another aspect, the present description relates to a method, comprising providing a substrate comprising polylactic acid, coating a primer layer on the substrate, and coating a barrier layer on the primer layer, wherein the barrier layer comprises an amorphous aliphatic polyamide having a glass transition temperature of at least 40°C. [Brief explanation of the drawings]

[0004] [Figure 1] FIG. 1 is a schematic cross-sectional side view of a film including a solvent barrier and primer layer. DETAILED DESCRIPTION OF THE INVENTION

[0005] Graphic films, including large-format graphics for use in displaying information on vehicles, walls, and signs, are typically provided as adhesive films for easy temporary, semi-permanent, or permanent (whether peelable or not) positioning on a substrate. Such films may be unpigmented (transparent), white, or any other suitable color. Often, the films may be designed to be printable (i.e., may be inherently ink-receptive or may include an ink-receptive coating) so that images or other information can be transferred onto the film. For example, a brand owner may want to provide advertising, logos, or other information on the film to be adhered to a truck or van.

[0006] Ink is typically applied by printing. Large-format printing is widely available using solvent-based inks. Water-based latex inks exist but are not commonly used. Ink is typically applied only to the top surface of such films, and the solvents used in most common ink systems permeate through the layer and ultimately migrate to the adhesive layer. Solvent migration into the adhesive layer can alter the otherwise carefully tuned properties of the adhesive layer, potentially making application and removability difficult. In some applications, contaminant migration in other ways (i.e., from the adhesive to the ink-receiving substrate) can also be an issue.

[0007] Films formed from polylactic acid or polylactide can present challenges in some cases because a suitable primer that adheres well to a PLA film substrate may not adhere well to a suitable barrier layer, resulting in unintended and undesirable delamination.

[0008] The structures and related methods described herein utilize polyamides in the barrier layers, specifically amorphous aliphatic polyamides having a glass transition temperature of at least 40° C. These barrier layers can provide suitable solvent penetration resistance and also have acceptable adhesion to other layers of the film, making them useful in a variety of applications and environments. In addition to the embodiments, the following aspects will be noted. (Appendix 1) a substrate comprising polylactic acid; a primer layer disposed on the substrate; a barrier layer disposed on a surface of the primer layer opposite the substrate; an adhesive layer disposed on a surface of the barrier layer opposite the primer layer; A film comprising: the barrier layer comprises a polyamide; the polyamide is an amorphous aliphatic polyamide, the polyamide has a glass transition temperature of at least 40°C; film. (Appendix 2) 2. The film of claim 1, wherein the polyamide has a glass transition temperature of 70° C. or less. (Appendix 3) 10. The film of claim 1, wherein the film includes a release liner disposed on the surface of the adhesive layer opposite the barrier layer. (Appendix 4) 10. The film of claim 1, wherein the polyamide comprises secondary amine units resulting in tertiary amide bonds. (Appendix 5) 10. The film of claim 1, wherein the polyamide comprises piperazine. (Appendix 6) 2. The film of claim 1, wherein the adhesive is a pressure-sensitive adhesive. (Appendix 7) 10. The film of claim 1, wherein the polyamide of the barrier layer is extrudable. (Appendix 8) 10. The film of claim 1, wherein the polyamide of the barrier layer is soluble in a polar solvent. (Appendix 9) 9. The film of claim 8, wherein the polar solvent comprises 1-propanol. (Appendix 10) 9. The film of claim 8, wherein the polar solvent comprises 1-butanol. (Appendix 11) 2. The film of claim 1, further comprising an ink-receiving layer on a surface of the substrate opposite the primer layer. (Appendix 12) providing a substrate, the substrate comprising polylactic acid; coating a primer layer on the substrate; coating a barrier layer over the primer layer, the barrier layer comprising an amorphous aliphatic polyamide having a glass transition temperature of at least 40°C; A method comprising: (Appendix 13) 13. The method of claim 12, wherein the amorphous aliphatic polyamide has a glass transition temperature of 70° C. or less. (Appendix 14) 13. The method of claim 12, further comprising applying an adhesive layer carried by a release liner to the barrier layer. (Appendix 15) 13. The method of claim 12, further comprising applying heat to one or more of the primer layer and the barrier layer. (Appendix 16) 13. The method of claim 12, wherein coating the barrier layer is a solvent coating process. (Appendix 17) 13. The method of claim 12, wherein coating the barrier layer is an extrusion process. (Appendix 18) 13. The method of claim 12, wherein the extrusion of the barrier layer is performed simultaneously with the extrusion of at least one other layer.

[0009] 1 is a schematic side view of a film 100 including a solvent barrier and primer layer. The film includes a substrate 110, a primer layer 120, a barrier layer 130, an adhesive 140, and a liner 150.

[0010] Substrate 110 can be any suitable substrate, which can have any suitable shape or size. For example, substrate 110 can be formed from or as a cast, calendered, or extruded film substrate. In some embodiments, substrate 110 can be or include polylactic acid. PLA substrates can be formed, at least in part, from renewable or bio-based resources, including otherwise commonly grown crops such as corn, sugarcane, or beets. Substrate 110 can include or contain additives, plasticizers, other polymers, or stabilizers in addition to PLA to make such substrates suitable for long-term or outdoor use. Suitable PLA-based films are described in U.S. Pat. No. 10,577,494 (Zhou et al.), which is incorporated herein by reference in its entirety. Substrate 110 can be of any suitable thickness, which may, in fact, depend on the method by which it is manufactured. For example, the substrate can have a thickness of 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 125 μm, 150 μm, 175 μm, or 200 μm, or a range between any two of the previously listed values. In some embodiments, the substrate 110 can include a pigment or other colorant. In some embodiments, the substrate 110 can include, for example, carbon black or titanium dioxide (white), although any pigment system or blend can be selected for a desired application.

[0011] In some embodiments, the substrate 110 may include an ink-receiving layer, or the surface of the substrate 110 may be treated or configured to make it ink-receptive. Such an ink-receiving layer may be useful when the film 100 is used as a printable or digitally printable graphic film.

[0012] Primer layer 120 can be any suitable primer coated at any suitable thickness. Primer layer 120 can be selected for its adhesive ability to the PLA in substrate 110. Suitable primers include 3M VHB TAPE UNIVERSAL PRIMER UV (available from 3M Company, St. Paul, Minn.). Primer layer 120 can be solvent coated or extruded. In some embodiments, the thickness of the primer layer can be less than 10 μm, less than 8 μm, less than 6 μm, less than 4 μm, less than 3 μm, less than 2 μm, less than 1 μm, or even less than 0.5 μm. In some embodiments, the thinness of the primer layer is limited only by the minimum thickness necessary to provide the desired adhesive performance. In some embodiments, if the primer layer is extruded, there may be a higher practical thickness due to the need to maintain the integrity of the web through the die.

[0013] The barrier layer 130 may be selected for compatibility with the adhesive and primer layers. In some embodiments, the barrier layer 130 may be solvent coated or extruded. In some embodiments, the thickness of the barrier layer may be less than 10 μm, less than 8 μm, less than 6 μm, less than 4 μm, less than 3 μm, less than 2 μm, less than 1 μm, or even less than 0.5 μm. In some embodiments, the thinness of the barrier layer is limited only by the minimum thickness necessary to provide the desired barrier performance. In some embodiments, if the barrier layer is extruded, there may be a higher practical thickness due to the need to maintain the integrity of the web through the die.

[0014] The barrier layer 130 may be or include at least one polyamide in some embodiments. In some embodiments, the polyamide may be an amorphous aliphatic polyamide. In some embodiments, the polyamide may have a glass transition temperature of at least 40°C. In some embodiments, the polyamide may have a glass transition temperature of 40°C to 70°C. In some embodiments, the polyamide includes secondary amine units that result in the formation of tertiary amide bonds. Polyamides are often synthesized from at least one diacid and at least one diamine. In some embodiments, polyamides including at least one of 2,2,4(2,4,4)-trimethyl-1,6-hexanediamine or 2,2,4(2,4,4)-trimethyl-1,6-hexanedioic acid may be used. In some embodiments, the polyamide may include piperazine or bipiperazine repeat units.

[0015] In some embodiments, the barrier layer may comprise a polyamide soluble in a polar solvent, hi some embodiments, the barrier layer may comprise a polyamide soluble in a polar solvent, including 1-propanol or 1-butanol.

[0016] Application of the primer layer or barrier layer may include applying heat to one or both of the layers. Heat can drive off solvents or crosslink polymers within the layer. In some embodiments, one or more of the layers may be UV curable.

[0017] Adhesive layer 140 can be made from or include a variety of adhesives, including pressure-sensitive adhesives. A suitable adhesive may be selected by one skilled in the art and is often selected based on the type of substrate to which the adhesive will be adhered. Classes of pressure-sensitive adhesives include acrylic, tackified rubber, tackified synthetic rubber, ethylene vinyl acetate, and silicone. Suitable acrylic adhesives are disclosed, for example, in U.S. Patent Nos. 3,239,478, 3,935,338, 4,952,650, 4,181,752, and 5,169,727.

[0018] A particular class of pressure-sensitive adhesives that may be useful for this particular application is the reaction product of at least one alkyl acrylate and at least one reinforcing comonomer. Suitable alkyl acrylates have a homopolymer glass transition temperature of less than about -10°C, such as n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, and octadecyl acrylate. Suitable reinforcing monomers have a homopolymer glass transition temperature of more than about -10°C, such as acrylic acid, methylidenesuccinic acid, isobornyl acrylate, N,N-dimethylacrylamide, N-vinylcaprolactam, and N-vinylpyrrolidone.

[0019] The thickness of adhesive layer 130 can be selected for a particular application based on several factors, including, for example, the adhesive composition, whether the adhesive includes a microstructured surface, the type of substrate, and the thickness of the film. One of ordinary skill in the art, based on the disclosure herein, can adjust the thickness to address the factors of a particular application. Adhesive layer 130 can be coated onto a liner and applied to the remainder of film 100, or it can be coated directly onto the remainder of film 100, or it can be co-extruded with the remainder of film 100.

[0020] The liner 150 is optional in construction and is typically a paper or polymer liner with a coating to provide easy release from the adhesive layer. In some cases, the liner 150 can have a very uniform, smooth, or glossy surface. In other examples, the liner can have a surface texture created by methods such as embossing or printing. In some embodiments, the liner includes a structured pattern, such as channels, ridges, or grooves. Such a structured pattern can impart an inverse structure to the adhesive layer. This pattern can help apply the adhesive to the surface and facilitate easy air release, for example, during initial installation.

[0021] The terms and expressions used are used as terms of description rather than limitation, and the use of such terms and expressions is not intended to exclude any equivalents or portions of the features shown and described, but it is understood that various modifications are possible within the scope of the embodiments of the present invention. Thus, although the present invention has been specifically disclosed by certain embodiments and optional features, it should be understood that modifications and variations of the concepts disclosed herein may be resorted to by those skilled in the art, and such modifications and variations are considered to be within the scope of the embodiments of the present invention. [Example]

[0022] Polylactide (PLA)-based graphic film structures were fabricated containing a polyamide barrier layer and a primer layer. The films were tested for ink solvent barrier properties and adhesion.

[0023] These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and elsewhere herein are by weight unless otherwise indicated. The following abbreviations are used herein: " = inches, cm = centimeter, mmol = millimole, °C = degrees Celsius, min = minutes, s = seconds, h or hr = hours, g = grams, ml = milliliters, % = percent, RPM = revolutions per minute, mmHg = millimeters of mercury.

[0024] material:

[0025] [Table 1]

[0026] Test Method: Adhesiveness Polyamide-coated, primed PLA film samples were selected for this analysis. Samples were referenced by polyamide selection and coating thickness. 0.5" (1.3 cm) strip test samples were cut to 3" (2.6 cm) lengths, and the side opposite the coated surface was first supported by a layer of SCOTCH 3750 tape (3M Company, St. Paul, MN). A layer of 3M CONTROLTAC Graphic Film IJ180 (3M Company, St. Paul, MN) was then applied to the polyamide-coated side in two passes using a 3M Hand Applicator PA-1 (3M Company, St. Paul, MN). The test samples were then conditioned at 25°C for 30 minutes, and the applied IJ180 film was finally peeled off the coated PLA substrate. If the polyamide coating remained on the primed PLA side and the adhesive on the test tape remained exposed and tacky, the sample passed the adhesion test. If the polyamide coating transfers to the adhesive side and becomes non-tacky, the sample fails the adhesion test.

[0027] MEK Permeability Gravimetric Cup Test The test was adapted from Society of Automotive Engineers (SAE) J2665, "Test Procedure to Measure the Fuel Permeability of Materials by the Cup Weight Loss Method." The test is performed by filling a cup with solvent and then sealing it using a barrier-coated film. The cup was placed in an oven and weighed over time. The amount of solvent lost from the cup is a measure of barrier performance. After filling the cup with MEK or EtOAc (ink simulation), the coated film sample was placed on the cup with the polyamide-coated side facing up. A PTFE gasket was used to seal the film. A fine wire mesh screen, followed by a coarsely perforated aluminum plate, was used to cover the film. Finally, a ring was placed on the aluminum plate and screwed tightly. By limiting the expansion of the film, the coating thickness remained unstretched and constant. The cup was placed in a 40°C oven and weighed at time = 0 and over time thereafter. The data was plotted as % weight loss as a function of time. The low MEK loss rate (% solvent loss / hour) indicated good barrier performance of the polyamide coating.

[0028] Working Example: Preparation of polyamide (C6DA-co-C9DAm) (PE1) Adipic acid (69.48 g, 468.7 mmol), 2,2,4-(2,4,4)-trimethyl-1,6-hexamethylenediamine (73.18 g, 462.3 mmol), and phosphoric acid (85%, 2 drops) were placed in a 250 mL three-neck round-bottom flask equipped with an overhead stirrer, an insert thermocouple, and a condenser. The reagents were placed under a N blanket overnight. The following day, the reaction temperature was initially set to 100°C. When the reagents began to melt, manual stirring was added. The reaction temperature was then set to slowly increase from 100°C to 200°C over 1 hour under a N atmosphere. The overhead stirring rate was also slowly increased from 0 RPM to 60 RPM. During this stage of the reaction, condensed distillate was refluxed back into the reaction vessel, increasing the melt temperature from 100°C to 190°C, with the distillate temperature reaching 104°C. The reaction set temperature was further gradually increased to 240°C. Then, distillate (15.15 g) was collected over 1 hour. The polymer melt temperature reached 240°C, and the distillate temperature decreased to 70°C. The polymer melt was finally subjected to a vacuum of 200 mmHg for 1 hour, and the reaction product (PE1) was discharged onto a Teflon sheet in air.

[0029] Preparation of polyamide (C6DA-co-C9DAm / C6DAm / Pip 100-co-60 / 20 / 20) (PE2) PE2 was synthesized under the same conditions as PE1, except that adipic acid (74.69 g, 511.1 mmol), hexamethylenediamine (11.68 g, 100.7 mmol), 2,2,4-(2,4,4)-trimethyl-1,6-hexamethylenediamine (47.99 g, 303.2 mmol), piperazine (8.70 g, 101.0 mmol), and phosphoric acid (85%, 2 drops) were added to the reaction vessel. The reaction product was finally treated at 260 °C under a vacuum of 200 mmHg and then discharged.

[0030] Table 2 compares the compositions of a series of custom polyamides prepared using the process disclosed above. An amine / acid molar ratio of 0.988 was targeted for all compositions.

[0031] [Table 2]

[0032] Thermal analysis of polyamides Table 3 compares the glass transition temperatures and melting temperatures (where detectable) for PE1, PE1, and two commercially available polyamides. Thermal transitions were measured using a TA Q2000 differential scanning calorimeter (TA Instruments, New Castle, DE). Samples were first heated from ambient temperature to 180°C at a heating rate of 10°C / min, then cooled to -60°C at a cooling rate of 20°C / min, and finally heated to 280°C at a heating rate of 10°C / min. For samples that did not exhibit a melting transition, the glass transition temperature was reported from the second heat. For samples that did exhibit a melting transition, the glass transition temperature, crystallization temperature (if observed), and melting temperature were reported from the first heat.

[0033] [Table 3]

[0034] Preparation of Primed PLA Film (PE3) The UPUV primer solution was coated onto the PLA film using an RDS06 Meyer rod (RD Specialties, Webster, NY), and the coating was then dried in a convection oven at 70°C for 10 minutes.

[0035] Preparation of polyamide coating solutions (PE4-8) Polyamide coating solution PE4 was prepared by dissolving PE1 in 1-propanol / water (75 / 25) at 15% solids for 6 hours in a 70°C water bath. Polyamide coating solutions PE5-7 were prepared by dissolving PE2 in 1-propanol / water (75 / 25) at 5%, 10%, and 15% solids, respectively, for 6 hours in a 70°C water bath. PE8 was prepared in 1-propanol / water (90 / 10) instead. The detailed compositions of PE4-8 are shown below.

[0036] [Table 4]

[0037] Preparation of a comparative polyamide (C6DA-co-C9DAm)-coated primed PLA film (CE1) Primed PLA film (PE3) was selected as the coating substrate. Polyamide (C6DA-co-C9DAm) coating solution PE4 was coated onto PE3 using an RDS05 Mayer rod. The coating was then dried in a convection oven at 70 °C for 10 min and annealed in a convection oven at 135 °C for 30 s.

[0038] Preparation of a comparative polyamide (ULTRAMID 1C / PLATAMID HX2592 70 / 30) coated primed PLA film (CE2) Primed PLA film (PE3) was selected as the coating substrate. Polyamide (ULTRAMID 1C / PLATAMID HX2592 70 / 30) coating solution PE8 was coated onto PE3 using an RDS05 Meyer rod. The coating was then dried in a convection oven at 70 °C for 10 minutes and annealed in a convection oven at 135 °C for 30 seconds.

[0039] Preparation of Example Polyamide (C6DA-co-C9DAm / C6DAm / Pip 100-co-60 / 20 / 20) Coated Primed PLA Films (E1-3) E1-3 were prepared similarly to CE1, except that polyamide coating solution PE5 was used for E1, PE6 for E2, and PE7 for E3. The coatings were again prepared using an RDS05 Mayer rod, dried in a 70 °C convection oven for 10 min, and annealed in a 135 °C convection oven for 30 s.

[0040] result:

[0041] Table 5

[0042] Table 6

Claims

1. a substrate comprising polylactic acid; a primer layer disposed on the substrate; a barrier layer disposed on a surface of the primer layer opposite the substrate; an adhesive layer disposed on a surface of the barrier layer opposite the primer layer; A film comprising: the barrier layer comprises a polyamide; The polyamide (i) an amorphous aliphatic polyamide; (ii) having a glass transition temperature of at least 40°C and no greater than 70°C; (iii) containing a tertiary amide bond derived from piperazine; film.

2. 10. The film of claim 1, wherein the film comprises a release liner disposed on a surface of the adhesive layer opposite the barrier layer, and optionally an ink-receiving layer on a surface of the substrate opposite the primer layer.

3. The film of claim 1 , wherein the adhesive is a pressure sensitive adhesive.

4. The film of claim 1 , wherein the polyamide of the barrier layer is extrudable.

5. The film of claim 1 , wherein the polyamide of the barrier layer is soluble in a polar solvent.

6. The film of claim 5, wherein the polar solvent comprises 1-propanol or 1-butanol.

7. providing a substrate, the substrate comprising polylactic acid; coating a primer layer on the substrate; coating a barrier layer on the primer layer, the barrier layer comprising an amorphous aliphatic polyamide having a glass transition temperature of at least 40°C and no more than 70°C and containing tertiary amide bonds derived from piperazine; A method comprising:

8. The method of claim 7 further comprising applying an adhesive layer carried by a release liner to the barrier layer.

9. The method of claim 7 further comprising applying heat to one or more of the primer layer and the barrier layer.

10. The method of claim 7 , wherein coating the barrier layer is a solvent coating process.

11. The method of claim 7 , wherein the extrusion of the barrier layer is performed simultaneously with the extrusion of at least one other layer.

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