Peelable liner for protecting optical sheet

Abstract

A peelable liner for protecting an optical sheet or a multilayer film from which an optical sheet can be cut, the liner comprising: a film A comprising one or more liner layers A each comprising a polymer A independently selected from polymers having a melting point (Tm) of from 100 DEG C to 135 DEG C; and a film B comprising one or more liner layers B each comprising a polymer B independently selected from polymers having a melting point of 140 DEG C to 170 DEG C, the film A comprising a first face configured to be in direct contact with the optical sheet when the liner is adhered to the optical sheet, and a second face configured to be in direct contact with the optical sheet when the liner is adhered to the optical sheet. The film A is placed on the first face, the second face is opposite the first face, and the film B is placed on the second face of the film A wherein the total thickness of the one or more liner layers A is at least 5 [mu] m and the total thickness of the one or more liner layers B is at least 30 [mu] m.

Description

Technical Field

[0001] This disclosure relates to an improved peelable liner for protecting an optical sheet. This disclosure also relates to an optical sheet protected by the improved peelable liner. This disclosure also relates to the use of the improved peelable liner for protecting an optical sheet, thereby allowing the avoidance of forming defects on the sheet during sheet formation. Background Art

[0002] Optical sheets (hereinafter simply referred to as "sheets") can be included in ophthalmic lenses to provide functions to the ophthalmic lenses. Sheets typically consist of a functional film or layer protected by one or two protective films or layers. The functions provided by the sheets can be, for example: a light absorption function (e.g., for absorbing UV light, visible light, and / or IR light), a photochromic function, a polarization function, or a color enhancement function.

[0003] Thus, sheets are films that have optical and thermomechanical properties that make them suitable for inclusion in ophthalmic lenses and include a functional film (or layer) that provides one or more desired functions to the lens. In some cases, the sheet can be used directly as an ophthalmic lens.

[0004] Sheets can be included in ophthalmic lenses by inserting the sheet into a lens mold and injection molding (in the case of a thermoplastic lens substrate) or casting (in the case of a thermosetting lens substrate) the lens substrate against the sheet in the lens mold. Thus, the sheet can be included on the front of the lens substrate, on the back of the lens substrate, or embedded in the lens substrate.

[0005] Sheets can also be included in ophthalmic lenses by laminating the sheet onto the lens substrate. In this case, an adhesive can be used to ensure strong adhesion of the sheet to the lens substrate.

[0006] Typically, sheets are produced by cutting them from a film having the same layer structure as the sheet to the desired size. In addition, it is necessary to form the sheet, i.e., to give the sheet the desired curvature before including the sheet in the ophthalmic lens. This step of forming the sheet is carried out using a former that heats and presses the sheet to give it the desired curvature.

[0007] When manufacturing an ophthalmic lens including a sheet, the sheet or the film used to produce the sheet is subjected to various process steps (e.g., cutting the sheet to a desired size, forming the sheet to a desired curvature). During this process, it is important to protect the sheet or the film used to produce the sheet to avoid appearance defects in the final lens. For example, it is necessary to protect the sheet or the film used to produce the sheet from possible contamination or scratches. For this purpose, the sheet or the film used to produce the sheet is covered with a peelable liner on one or both of its major surfaces. The liner is removed (by peeling) in the final step of the method when needed (e.g., before an injection molding or casting step or before laminating the sheet onto a lens substrate).

[0008] The use of a protective peelable liner is currently essential for making the lens obtained via a method involving the use of a sheet acceptable to consumers.

[0009] However, for it to be acceptable for mass production, in addition to efficiently protecting the sheet, the liner must meet many requirements, which include:

[0010] - being easy to cut without leaving residues at the edges,

[0011] - not peeling off in an unwanted manner at the edges of the sheet when handling the protected sheet,

[0012] - not leaving any molten residues in the former used to give the sheet the desired curvature,

[0013] - not sticking to the operator's gloves,

[0014] - having excellent peelability, which includes easy start of peeling, no tearing of the liner during peeling, and no residues left after peeling,

[0015] In addition, the inventors behind the present disclosure have found that the wavy pattern observed on an ophthalmic lens obtained via a method involving the use of a sheet is caused by the use of an inappropriate liner. In fact, it has been found that such a wavy pattern initially exists on the liner (usually when the liner includes a polypropylene layer) and is transferred to the sheet during the step of forming the sheet to the desired curvature (during which step it is necessary to keep the liner on the sheet to avoid other problems related to melting and contamination of the sheet and / or the former). Thus, the wavy pattern transferred to the sheet remains in the final ophthalmic lens. Summary of the Invention

[0016] To solve these problems, the present invention provides a peelable liner for protecting an optical sheet or a multilayer film from which an optical sheet can be cut, the liner comprising

[0017] Membrane A, the membrane comprising one or more backing layers A, each of the backing layers comprising polymer A, the polymers independently selected from polymers having a melting point (T m ) of 100°C to 135°C, and

[0018] Membrane B, the membrane comprising one or more backing layers B, each of the backing layers comprising polymer B, the polymers independently selected from polymers having a melting point of 140°C to 170°C,

[0019] The membrane A includes a first side and a second side, the first side being configured to be in direct contact with an optical sheet when the backing adheres to the optical sheet, the second side being opposite the first side, and

[0020] The membrane B is placed on the second side of the membrane A,

[0021] wherein the total thickness of the one or more backing layers A is at least 5 μm, and the total thickness of the one or more backing layers B is at least 30 μm. Detailed Description

[0022] As defined herein, an ophthalmic lens is a lens designed for use in a monocle or glasses (including sunglasses, goggles, and safety glasses). As defined herein, a contact lens is not an ophthalmic lens. Ophthalmic lenses are typically used to protect the eyes and / or correct vision. Ophthalmic lenses can be non-corrective ophthalmic lenses (also referred to as plano or afocal lenses) or corrective ophthalmic lenses. Corrective lenses can be single-focus lenses, bifocal lenses, trifocal lenses, or progressive lenses. As defined herein, an ophthalmic lens can be a finished lens or a semi-finished lens. A semi-finished lens undergoes various processing steps, such as surface finishing, coloring, coating, and edging, before ultimately being included in glasses or a monocle. A finished lens is ready to be included in glasses or a monocle.

[0023] As defined herein, a membrane is a stack of one or more layers.

[0024] A layer corresponds to the thickness of a given material between two interfaces. As defined herein, a stack of two or more layers is not a layer.

[0025] Typically, the interface between two consecutive layers can be observed with a microscope.

[0026] Layers can be assembled by coextrusion or by pressing the layers against each other. In some cases, inserting an adhesive layer between two layers before pressing the two layers together aids in the assembly of the two layers. In some cases, the electrostatic forces between the layers are sufficient to assemble them with only minimal pressure. As defined herein, an adhesive layer is considered a layer.

[0027] As defined herein, a film or layer "placed on" a surface is defined as a film or layer that: (a) is placed above the surface, (b) does not need to be in direct contact with the surface, i.e., one or more intermediate layers can be provided between the surface and the film or layer in question, and (c) does not need to completely cover the surface. However, preferably, a film or layer "on" a surface completely covers the surface.

[0028] As defined herein, the outer surface of a film or layer is the surface of the film or layer on which no other layer is placed. As defined herein, a film or layer has zero, one, or two outer surfaces.

[0029] The releasable liner for protecting an optical sheet or a multilayer film from which an optical sheet can be cut, disclosed in the present invention, comprises

[0030] Film A, the film comprising one or more cushion layers A, each of the cushion layers comprising polymer A, the polymers being independently selected from polymers having a melting point (T m ) of 100 °C to 135 °C, and

[0031] Film B, the film comprising one or more cushion layers B, each of the cushion layers comprising polymer B, the polymers being independently selected from polymers having a melting point of 140 °C to 170 °C,

[0032] Film A includes a first surface and a second surface, the first surface being configured to be in direct contact with the optical sheet when the liner adheres to the optical sheet, the second surface being opposite to the first surface, and Film B is placed on the second surface of Film A,

[0033] wherein the total thickness of the one or more cushion layers A is at least 5 μm, and the total thickness of the one or more cushion layers B is at least 30 μm.

[0034] For example, polymer A can be selected from polymers having a melting point (T m ) of 115 °C to 135 °C.

[0035] For example, polymer B can be selected from polymers having a melting point of 150 °C to 170 °C.

[0036] For example, the releasable liner for protecting an optical sheet or a multilayer film from which an optical sheet can be cut, disclosed in the present invention, can comprise

[0037] Film A, the film comprising one or more cushion layers A, each of the cushion layers comprising polymer A, the polymers being independently selected from polymers having a melting point (T m ) of 115 °C to 135 °C, and

[0038] Membrane B, said membrane comprising one or more backing layers B, each of said backing layers comprising polymer B, said polymers independently selected from polymers having a melting point of 150°C to 170°C,

[0039] Said membrane A includes a first side and a second side, said first side being configured to be in direct contact with the optical sheet when the backing adheres to the optical sheet, said second side being opposite to the first side, and said membrane B is placed on the second side of membrane A,

[0040] wherein the total thickness of said one or more backing layers A is at least X5 μm, and the total thickness of said one or more backing layers B is at least 30 μm.

[0041] In the present disclosure, the melting point of the polymer can be measured by modulated differential scanning calorimetry according to ISO 11357-3 standard using the following parameters:

[0042] - A first equilibration step at -90.00°C,

[0043] - Applying a modulation of + / -0.80°C every 60 seconds,

[0044] - At a first slope of 5.00°C / min to 250.00°C,

[0045] - At a second slope of 10.00°C / min to -90.00°C,

[0046] - At a third slope of 5.00°C / min to 250.00°C.

[0047] It is believed that the backing layer B protects the underlying backing layers (including backing layer A) from heat and improves the peelability of the backing. In the case where the total thickness of the backing layer B is insufficient, defects in the form of residues or pits are left on the formed sheet after peeling the backing.

[0048] It is believed that the backing layer A provides both good adhesion and peelability, and provides a cushioning effect that helps to avoid imprinting unwanted patterns (which may be present on the backing layer B) on the sheet during formation. In addition, compared with other types of backing layers that provide good adhesion, the backing layer A also reduces the amount of residues or defects left on the formed sheet after peeling the backing.

[0049] The backing disclosed in the present invention can be used with various types of sheets, and compared with the backing of the prior art, the appearance of wavy patterns is greatly reduced when forming the sheet. In addition, the backing disclosed in the present invention generally has excellent properties, making it suitable for use in mass production.

[0050] In the gasket disclosed herein, each gasket layer A may be free of polymers having a melting point below 100 °C. For example, in the gasket disclosed herein, each gasket layer A may be free of polymers having a melting point below 115 °C.

[0051] In the gasket disclosed herein, each gasket layer A may comprise at least 90% by mass of polymer A, based on the mass of gasket layer A.

[0052] In the gasket disclosed herein, each gasket layer A may comprise polymer A as the only polymer present in the gasket layer A. In such a case, non-polymeric additives may be present in gasket layer A.

[0053] In the gasket disclosed herein, each gasket layer B may comprise at least 90% by mass of polymer B, based on the mass of gasket layer B.

[0054] In the gasket disclosed herein, each gasket layer B may comprise polymer B as the only polymer present in the gasket layer B. In such a case, non-polymeric additives may be present in gasket layer B.

[0055] In the gasket disclosed herein, polymer A may be a polymer comprising at least 80 mol% of ethylene monomers, compared to the total amount of monomers in the polymer. For example, polymer A may be polyethylene (defined as a polymer comprising 100 mol% ethylene monomers, compared to the total amount of monomers in the polymer) or a copolymer of ethylene and methacrylic acid, which copolymer comprises at least 90 mol% ethylene monomers, compared to the total amount of monomers in the polymer.

[0056] In the gasket disclosed herein, polymer B may be polypropylene.

[0057] In the gasket disclosed herein, the first side of film A may provide static adhesion on an optical sheet, or the gasket may be adhered to the optical sheet through an adhesive layer.

[0058] For example, the first side of film A may be the side of the adhesive layer in direct contact with gasket layer A, or may be the side of gasket layer A. In particular, gasket layer A to which the first side of film A belongs or gasket layer A in direct contact with the adhesive layer to which the first side of film A belongs may have a thickness ranging from 10 μm to 150 μm, such as from 10 μm to 130 μm, such as from 10 μm to 70 μm, such as from 15 μm to 50 μm.

[0059] In the gasket disclosed herein, film A may be free of layers having a melting point exceeding 135 °C.

[0060] In the gasket disclosed herein, film A may be free of polypropylene layers.

[0061] In the liner disclosed herein, film A may comprise only one or more liner layers A, or may comprise only one or more liner layers A and one or more adhesive layers.

[0062] In the liner disclosed herein, film B may not contain a layer having a melting point below 140 °C.

[0063] In the liner disclosed herein, film B may comprise only one or more liner layers B, or may comprise only one or more liner layers B and one or more adhesive layers.

[0064] In the liner disclosed herein, the thickness of each layer A or B may be from 1 μm to 150 μm, such as from 1 μm to 100 μm or from 10 μm to 150 μm.

[0065] In the liner disclosed herein, the total thickness of one or more liner layers A may be at least 10 μm, such as from 10 μm to 150 μm, such as from 10 μm to 130 μm, such as from 10 μm to 70 μm, such as from 10 μm to 50 μm.

[0066] In the liner disclosed herein, film A may have a thickness of at least 10 μm, such as being included between 10 μm and 150 μm, such as from 10 μm to 130 μm, such as from 10 μm to 70 μm, such as from 10 μm to 50 μm.

[0067] In the liner disclosed herein, the total thickness of one or more liner layers B may be at least 35 μm, such as from 35 μm to 100 μm, or at least 40 μm, such as from 40 μm to 60 μm.

[0068] In the liner disclosed herein, film B may have a thickness of at least 35 μm, such as being included between 35 μm and 100 μm, or at least 40 μm, such as being included between 40 μm and 60 μm.

[0069] In the liner disclosed herein, film A may be in direct contact with film B.

[0070] In the liner disclosed herein, liner layer A may be co-extruded with liner layer B.

[0071] In the liner disclosed herein, film B may comprise only two liner layers B separated by an adhesive layer. In particular, film B may consist only of two liner layers B separated by an adhesive layer.

[0072] This disclosure also relates to a multilayer film suitable for manufacturing an optical sheet, the multilayer film comprising the following items stacked on top of each other in the following order:

[0073] A first peelable liner according to any one of the preceding claims;

[0074] Optionally, a front primer layer;

[0075] A front layer in direct contact with the front primer layer;

[0076] A functional layer;

[0077] A back layer;

[0078] Optionally, a back primer layer in direct contact with the back layer;

[0079] Optionally, a second peelable liner according to any one of the preceding claims

[0080] Wherein the outer surface of the first liner is the outer surface of the multilayer film, and wherein the first side of film A of the first liner is in direct contact with:

[0081] The front layer, or

[0082] When applicable, the front primer layer,

[0083] And wherein, when applicable, the outer surface of the second liner is the outer surface of the multilayer film, and wherein the first side of film A of the first liner is in direct contact with:

[0084] The back layer, or

[0085] When applicable, the back primer layer.

[0086] In the multilayer films disclosed herein, the front layer and the back layer can be regarded as the outermost layer of a protective film protecting the functional layer or the protective layer of the functional layer.

[0087] When casting a polymeric material on a sheet, a primer layer can be used to increase the adhesion of the polymeric material of the lens to one or both of the protective film or layer of the sheet. For example, KR 993596B1, WO 2018 / 052454 and WO2019175354 A1 describe primer coatings that are used to improve the adhesion between a triacetyl cellulose (TAC) protective layer of a sheet and a cast CR-39 plastic lens in which the sheet is embedded. WO 2021 / 170702 describes a primer coating for improving the adhesion of a polarizing sheet having a TAC protective film or layer, the film or layer being placed on and cast on top of a poly(thio)urethane lens (such as an ultra-high refractive index UHI Mitsui lens). In lenses with TAC on TOP, there is only one adhesion interface between the TAC film or layer and the lens.

[0088] The primer composition can be applied to either surface of the sheet or to both surfaces of the sheet.

[0089] The primer composition can be applied to the sheet by any method, including but not limited to spraying or roll coating. The primer composition can be air dried or dried in an air oven and can be cured by UV irradiation or exposure to heat.

[0090] In the multilayer films disclosed herein, the front layer and the back layer can each comprise a thermoplastic polymer.

[0091] In the multilayer films disclosed herein, the thermoplastic polymer contained in the front layer and the thermoplastic polymer contained in the back layer can be independently selected from the list consisting of: polycarbonate, poly(methyl methacrylate), polyethylene terephthalate, cycloolefin copolymer, polyamide, and cellulose acetate butyrate.

[0092] In the multilayer films disclosed herein, both the front layer and the back layer can each comprise at least 90% by mass of the thermoplastic polymer relative to the mass of the front layer and the back layer, respectively.

[0093] In the multilayer films disclosed herein, both the thermoplastic polymer contained in the front layer and the thermoplastic polymer contained in the back layer can be polycarbonate, poly(methyl methacrylate), polyethylene terephthalate, cycloolefin copolymer, polyamide, or cellulose acetate butyrate.

[0094] The multilayer films disclosed herein can further comprise an adhesive layer between the functional layer and the front layer, the adhesive layer being in direct contact with the functional layer and the front layer.

[0095] The multilayer films disclosed herein can further comprise an adhesive layer between the functional layer and the back layer, the adhesive layer being in direct contact with the functional layer and the back layer.

[0096] This disclosure also relates to an optical sheet made from the multilayer films disclosed herein.

[0097] The optical sheet can be made from the multilayer films disclosed herein by cutting the film to a suitable size.

[0098] This disclosure also relates to the use of the gasket as disclosed herein for protecting the optical sheet when forming the optical sheet while avoiding or limiting the imprinting of a pattern on the optical sheet during formation.

[0099] In the use disclosed herein, the optical sheet can be the optical sheet as disclosed herein.

[0100] Example

[0101] In the example, gasket 1 (which is a gasket according to this disclosure) comprises the following items stacked directly on top of each other:

[0102] - A polyethylene layer with a melting point of 120°C and a thickness of 25 μm co-extruded with a polypropylene layer having a melting point of 160°C and a thickness of 5 μm,

[0103] - An adhesive layer with a thickness of approximately 5 μm, and

[0104] - A polypropylene layer with a melting point of 160°C and a thickness of 40 μm.

[0105] Figure 1 Two commercial polarizing sheets with a protective layer made of triacetyl cellulose that have been formed are shown. On the left, the liner used (not according to the present invention) is a single-layer polypropylene with a melting point of 163°C and a thickness of 45 μm directly adhered to the sheet. Liner 1 is used on the left. The texture visible on the left does not exist on the right.

[0106]

[0107] Table 1

[0108] In Table 1, the patterns observed when forming various types of sheets with a protective layer made of polycarbonate are reported. Compared with the original liner, the liner of the present invention significantly reduces the occurrence of wavy patterns and the number of defects. The original liner is made of a layer of a copolymer containing ethylene and methacrylic acid with a melting point of 96°C and a thickness of 5.5 μm, which is co-extruded with a polypropylene layer having a melting point of 161°C and a thickness of 45 μm.

Claims

1. A peelable liner for protecting an optical sheet or a multilayer film from which the optical sheet can be cut, the liner comprising Membrane A, said membrane comprising one or more cushioning layers A, each of said cushioning layers comprising polymer A, said polymers independently selected from polymers having a melting point (T m ) of 100 °C to 135 °C, and film B, the film comprising one or more liner layers B, each liner layer comprising polymer B, the polymers independently selected from polymers having a melting point of 140 °C to 170 °C, film A includes a first side and a second side, the first side being configured to be in direct contact with the optical sheet when the liner adheres to the optical sheet, the second side being opposite the first side, and film B is placed on the second side of film A, wherein the total thickness of the one or more liner layers A is at least 5 μm, and the total thickness of the one or more liner layers B is at least 30 μm.

2. The liner according to claim 1, wherein, each liner layer A comprises at least 90% by mass of the polymer A relative to the mass of the liner layer A.

3. The liner according to claim 1 or 2, wherein, each liner layer B comprises at least 90% by mass of the polymer B relative to the mass of the liner layer B.

4. The liner according to any one of the preceding claims, wherein, the polymer A is a polymer: the polymer comprises at least 80 mol% of ethylene monomers compared to the total amount of monomers in the polymer.

5. The liner according to any one of the preceding claims, wherein, the polymer B is polypropylene.

6. The liner according to any one of the preceding claims, wherein, the first side of film A is the side of the adhesive layer in direct contact with liner layer A or the side of liner layer A.

7. The liner according to any one of the preceding claims, wherein, the total thickness of the one or more liner layers A is at least 10 μm.

8. The liner according to any one of the preceding claims, wherein, the total thickness of the one or more liner layers B is at least 35 μm.

9. A multilayer film suitable for manufacturing an optical sheet, the multilayer film comprising the following items stacked on top of each other in the following order: A first peelable liner according to any one of the preceding claims; Optionally, a primer layer; A front layer in direct contact with the primer layer; A functional layer; A back layer; Optionally, a back primer layer in direct contact with the back layer; Optionally, a second peelable liner according to any one of the preceding claims wherein the outer side of the first liner is the outer side of the multilayer film, and wherein the first side of film A of the first liner is in direct contact with: The front layer, or When applicable, the primer layer, and wherein, When applicable, the outer side of the second liner is the outer side of the multilayer film, and wherein the first side of film A of the first liner is in direct contact with: The back layer, or When applicable, the back primer layer.

10. The multilayer film according to claim 9, wherein, the front layer and the back layer each comprise a thermoplastic polymer.

11. The multilayer film according to claim 10, wherein, The thermoplastic polymer comprised in the front layer and the thermoplastic polymer comprised in the rear layer are independently selected from the list consisting of: polycarbonate, poly(methyl methacrylate), polyethylene terephthalate, cycloolefin copolymer, polyamide, and cellulose acetate butyrate.

12. The multilayer film according to claim 10 or 11, wherein, both the front layer and the rear layer comprise at least 90% by mass of the thermoplastic polymer, based on the mass of the front layer and the rear layer, respectively.

13. The multilayer film according to any one of claims 10 to 12, wherein, both the thermoplastic polymer comprised in the front layer and the thermoplastic polymer comprised in the rear layer are polycarbonate, poly(methyl methacrylate), polyethylene terephthalate, cycloolefin copolymer, polyamide, or cellulose acetate butyrate.

14. An optical sheet made from the multilayer film according to any one of claims 9 to 13.

15. Use of the liner according to any one of claims 1 to 8 for protecting the optical sheet when forming the optical sheet while avoiding or limiting imprinting a pattern on the optical sheet during the forming.

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