Polaroid for improving weather resistance of polaroid and manufacturing process

Abstract

The invention discloses a polaroid for improving the weather resistance of the polaroid and a manufacturing process, and belongs to the technical field of polaroids. The manufacturing process comprises the following steps: providing an upper-layer membrane material and a lower-layer membrane material with hydrophobicity; a free radical type UV adhesive is adopted as an adhesive; coating one side of the membrane material with the UV glue through a honeycomb structure roller; laminating the film material and the stretched PVA film, and controlling the drying rate of the PVA film; irradiating and curing the UV adhesive by using ultraviolet light with the wavelength of 300-500nm, and performing heat treatment after curing to enhance the intermolecular permeation and anchoring effect of the resin, thereby forming the polaroid with a three-layer fitting structure; the free radical type UV glue is combined with the honeycomb structure coating process, the moisture content of the PVA film is accurately controlled, heat treatment is conducted after curing, interface stress concentration and glue layer shrinkage are effectively reduced, the structural stability of the polaroid in the high-temperature and high-humidity environment is improved, and the advantages that the interlayer delamination risk is reduced, and the binding force of the glue layer and the film material is enhanced are achieved.

Description

Technical Field

[0001] The present invention relates to a polarizer and a manufacturing process for improving the weather resistance of the polarizer, belonging to the technical field of polarizers. Background Art

[0002] Polarizers, also known as polarizing films, rely on polarized light for image formation in liquid crystal displays (LCDs). All LCDs have two polarizing films, front and back, attached tightly to the outside of the liquid crystal glass, forming a liquid crystal film approximately 1mm thick. Without either polarizer, the LCD cannot display an image. Therefore, polarizers are considered a crucial component of the display panel, second only to the backlight module and color filter. Currently, most polarizing films are iodine-based. These films are a composite material made by laminating, stretching, and coating polyvinyl alcohol (PVA) stretched film and cellulose acetate film (TAC). They enable high brightness and high contrast in LCD displays. For example, in TFT-LCDs, polarizers account for approximately 10% of the cost of a TFT-LCD panel. Polarizers possess a high level of technical expertise, as their production technology integrates diverse technologies, including polymer materials, microelectronics, optoelectronics, thin films, high-purity chemistry, and computer control.

[0003] UV adhesives are a type of adhesive that must be cured by ultraviolet light. Their main components are acrylate oligomers, some acrylate monomers, and a key component, photoinitiators. The curing mechanism is that the photoinitiators in UV-curable materials absorb ultraviolet light and generate active free radicals or cations, which trigger polymerization and cross-linking reactions, transforming the adhesive from a liquid to a solid state within seconds.

[0004] While existing UV-curable adhesives offer advantages such as fast curing and environmental friendliness, conventional UV adhesives in polarizer applications suffer from issues such as incomplete curing and high shrinkage stress caused by oxygen inhibition. In particular, during the lamination process between PVA film and hydrophobic film, differences in the thermal expansion coefficients of the materials and mismatched water evaporation rates can easily lead to interfacial stress concentration, which can cause delamination. Furthermore, traditional coating processes make it difficult to precisely control the thickness and uniformity of the adhesive layer, further exacerbating the polarizer's weatherability issues. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art. In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions: In a first aspect, a free radical UV adhesive process for improving the weather resistance of a polarizer is provided, comprising the following steps: Provide upper and lower membrane materials with hydrophobicity; Free radical UV adhesive is used as the adhesive, and the free radical UV adhesive includes: a main agent, a hydrophobic monomer, a hydrophilic monomer, a silane coupling agent, a photoinitiator and a tackifier; Applying the UV glue to one side of the film material through a honeycomb structure roller; Laminating the film material with the stretched PVA film and controlling the drying rate of the PVA film; The UV glue is cured by ultraviolet light with a wavelength of 300 to 500 nm, and heat treatment is applied after curing to enhance the penetration and anchoring effect between resin molecules to form a polarizer with a three-layer bonding structure.

[0006] Furthermore, the proportion of the hydrophobic monomer is higher than that of the hydrophilic monomer.

[0007] Furthermore, in the UV curing step, the irradiation wavelength of the ultraviolet light source is 300 to 500 nm.

[0008] Furthermore, in the laminating step, the moisture content of the PVA film is controlled to be 2% to 6% to reduce stress unevenness and interlayer delamination caused by water evaporation.

[0009] Furthermore, the step of coating the UV adhesive on one side of the film material by the honeycomb structure roller includes coating with a thickness of 5 to 25 μm and controlling the contact angle between the roller and the film material to be 30 to 60 degrees.

[0010] Furthermore, the UV adhesive layer is coated by a roller device provided with a honeycomb structure, and the honeycomb structure is a regularly arranged hexagonal groove structure.

[0011] In a second aspect, a polarizer with improved weather resistance is provided, which is prepared using the polarizer manufacturing process for improving weather resistance of the polarizer described in any one of the first aspects, comprising: an upper hydrophobic film material, a lower hydrophobic film material, an intermediate PVA film, and a free radical UV adhesive layer sandwiched therebetween and cured by ultraviolet light; Wherein: the UV adhesive layer contains a hydrophobic monomer, a small amount of hydrophilic monomer, a photoinitiator, a silane coupling agent and a tackifier.

[0012] Furthermore, the polarizer peeling width is 15 mm, the peeling rate is 300 mm / min, and the peeling force is not less than 98 gf / 15 mm.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts free radical UV adhesive combined with honeycomb structure coating process, accurately controls the moisture content of PVA film and heat treatment after curing, effectively reduces interfacial stress concentration and adhesive layer shrinkage, improves the structural stability of polarizer in high temperature and high humidity environment, and has the advantages of reducing the risk of interlayer delamination and enhancing the bonding strength between the adhesive layer and the film material. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The figure shows the intermolecular forces of the free radical UV glue provided by the present invention; Figure 2 The figure shows a schematic diagram of laminating different materials with the free radical UV adhesive provided by the present invention; Figure 3 Shown is a schematic diagram of UV glue coating provided by the present invention. DETAILED DESCRIPTION

[0015] The present invention will be described in further detail below with reference to specific embodiments and the accompanying drawings. Unless otherwise specified, the experimental methods described in the present invention are all conventional methods; and the materials used can be obtained from commercial sources. Example

[0016] This embodiment proposes a polarizer manufacturing process comprising the following steps: providing upper and lower film materials with hydrophobicity; using free radical UV glue as an adhesive, wherein the UV glue contains a main agent, a hydrophobic monomer, a hydrophilic monomer, a silane coupling agent, a photoinitiator and a tackifier; applying the UV glue to one side of the film material using a honeycomb structure roller; laminating the film material to a stretched PVA film and controlling the drying rate of the PVA film; and curing the UV glue with ultraviolet light and then applying heat treatment.

[0017] Hydrophobic membrane materials refer to polymer films with surface contact angles greater than 90 degrees, such as polyester or cycloolefin materials. Their low moisture permeability can reduce the erosion of PVA films by environmental water vapor. The proportion of hydrophobic monomers in free radical UV adhesives is higher than that of hydrophilic monomers. For example, isobornyl acrylate is used as the hydrophobic component. By adjusting the ratio of the two, the water absorption rate of the adhesive layer can be reduced. The surface of the honeycomb roller has regularly arranged hexagonal grooves. By controlling the roller speed and contact angle, the adhesive forms a uniformly distributed microstructure coating, reducing residual bubbles. The drying rate of the PVA film can be controlled by adjusting the ambient humidity or pre-drying time to maintain the moisture content within a specific range and avoid dimensional mutations caused by rapid water loss. The heat treatment after UV curing uses a gradient temperature increase method to promote the movement of resin molecular segments and enhance interfacial penetration and anchoring effects.

[0018] It is important to note that when implementing the process, a hydrophobic film with low moisture permeability is first selected as the upper and lower substrates, and the prepared UV glue is injected into the groove structure of the honeycomb roller. The roller contacts the film at a specific angle and transfers the glue to the film surface through rotation to form a coating with controllable thickness. The stretched PVA film is then aligned and bonded to the adhesive-coated substrate and pre-dried in a humidity-controlled environment to slowly release moisture from the PVA film. During the curing stage, a broadband ultraviolet light source is used to excite the photoinitiator to produce free radicals to initiate the polymerization reaction. The bonded body is then annealed using a hot plate or infrared radiation to encourage the resin molecules to penetrate the micropores on the substrate surface.

[0019] In this embodiment, a hydrophobic monomer refers to a polymeric unit with a low-polarity group in its molecular structure, specifically isobornyl acrylate or lauryl acrylate. Its hydrophobic properties can reduce the hygroscopicity of the adhesive layer. A hydrophilic monomer refers to a polymeric unit with a polar group such as a hydroxyl or carboxyl group in its molecular structure, specifically hydroxyethyl acrylate or acrylic acid. Its hydrophilic properties can adjust the wettability of the adhesive layer and the substrate.

[0020] like Figure 1 As shown in the figure, by increasing the proportion of hydrophobic monomers and reducing the proportion of hydrophilic monomers in the formulation of free radical UV adhesives, the number of polar groups within the adhesive layer is reduced, and the intermolecular hydrophobic interaction is enhanced. In high temperature and high humidity environments, the adhesive layer's reduced hygroscopicity reduces water intrusion, preventing stress concentration at the interface between the PVA film and the upper and lower film layers caused by water molecule penetration. At the same time, the hydrophobic monomers and silane coupling agents work synergistically to form a dense cross-linked network through hydrophobic association between molecular chains, further inhibiting water vapor diffusion pathways.

[0021] The irradiation wavelength range of the ultraviolet light source refers to the ultraviolet band used to trigger the photoinitiator to produce free radicals. Specifically, it can be achieved by using ultraviolet light emitted by a high-pressure mercury lamp, a metal halide lamp or an LED light source. This wavelength range covers the area where the photoinitiator absorption peak is located, ensuring that the initiator is fully decomposed and triggers the monomer polymerization reaction.

[0022] like Figure 2 As shown, after laminating the film material and PVA film, the UV adhesive is irradiated with ultraviolet light with a wavelength of 300-500nm. This allows the photoinitiator to efficiently absorb energy within this wavelength range, rapidly generating active free radicals, which promote a cross-linking reaction between the main agent and the monomer. This wavelength range can penetrate the surface of the film material, ensuring sufficient curing within the adhesive layer, while also preventing damage to the PVA film caused by short-wavelength UV rays. After curing, heat treatment further promotes the penetration and anchoring of the resin molecular chains, forming a stable three-dimensional network structure.

[0023] Controlling the moisture content of PVA film involves maintaining the film's moisture content within a specific range through pre-drying or ambient humidity adjustment. This can be achieved using a hot air circulation drying oven in conjunction with a humidity sensor. This approach balances the moisture distribution within the film. Uneven stress and delamination caused by water evaporation refer to internal stress concentrations in the film due to localized differences in water loss rates. This manifests as separation at the interlayer interfaces due to uncoordinated shrinkage. This phenomenon can be suppressed by controlling the evaporation rate gradient.

[0024] During the lamination process between the PVA film and the hydrophobic film, when the film's moisture content is between 2% and 6%, the water evaporation process becomes more gradual. This allows the film to maintain moderate flexibility while avoiding excessive shrinkage, and the upper and lower layers can maintain dimensional matching despite the difference in thermal expansion coefficients. By adjusting the drying oven temperature gradient, for example, using a three-stage temperature zone for gradual dehydration, water can be released at a controlled rate. This mechanism synchronizes the deformation of the PVA layer and the UV adhesive layer during the curing phase, thereby reducing interfacial shear stress.

[0025] like Figure 3 As shown, a honeycomb roller is a coating device with a regularly arranged hexagonal groove structure on its surface. The grooves are formed by laser engraving or machining and are used to carry and transfer UV adhesive to the film surface. This structural design reduces the formation of bubbles within the adhesive during the coating process while improving the uniformity of the adhesive layer. The coating thickness of 5-25μm refers to the vertical height range of the UV adhesive layer formed on the film surface before curing. This can be controlled, for example, by adjusting the roller speed, adhesive supply rate, or groove depth. This thickness range balances bonding strength and optical performance requirements, avoiding bonding failure due to excessive thinness or reduced light transmittance due to excessive thickness. The contact angle of 30-60 degrees refers to the angle formed by the roller axis and the direction of film travel. This can be achieved, for example, by adjusting the roller mounting position or the film feed path. This angle range optimizes the shear force distribution of the adhesive in the contact area between the roller and the film, ensuring continuous coverage and no overflow at the edges.

[0026] During the coating operation, the honeycomb structure roller is immersed in the UV glue and then rotates to bring the glue into the groove. When the roller contacts the film material, the glue in the groove is transferred to the surface of the film material under the action of pressure. By controlling the synchronization between the roller speed and the film material conveying speed, the hexagonal groove units continuously release the glue to form a uniform coating. The coating thickness is achieved through the synergistic effect of the groove depth and the viscosity of the glue. For example, a groove with a depth of 20μm and a UV glue with a viscosity of 500cps can obtain a coating thickness of about 15μm. Adjustment of the contact angle can change the residence time of the glue in the contact area between the roller and the film material. For example, a 45-degree angle can balance the glue spreading speed and shear force distribution to avoid local accumulation or glue breakage.

[0027] Compared to existing technologies, traditional coating processes often use flat rollers or blades, which are prone to thickness fluctuations due to insufficient adhesive leveling and pinhole defects caused by air entrapment during high-speed coating. The honeycomb roller uses grooves to quantitatively load the adhesive, creating a controllable adhesive film release mechanism in the contact area. Combined with a specific contact angle, this significantly reduces the surface defect rate of the adhesive layer. Existing technologies do not disclose a technical solution for achieving uniform adhesive coating through the coordinated control of the hexagonal groove structure and angle.

[0028] A honeycomb roller device is a coating roller with hexagonal grooves on its surface. Laser engraving or machining can be used to create evenly distributed hexagonal grooves on the metal roller surface. The roller's rotation transfers UV adhesive from the adhesive reservoir to the film surface. The hexagonal groove structure evenly disperses the adhesive flow path, reducing the generation of bubbles within the adhesive during the coating process. A regularly arranged hexagonal groove structure refers to grooves arranged at equal intervals and angles. Specifically, hexagonal units are used to form a periodic, repeating pattern on the roller surface. Geometric symmetry ensures even distribution of the adhesive during coating, preventing localized accumulation or loss.

[0029] As the roller rotates, hexagonal grooves on its surface carry UV adhesive from the adhesive reservoir. When the roller contacts the film, the adhesive in the grooves is transferred to the film surface under pressure. The regular arrangement of the hexagonal grooves ensures that the adhesive forms a continuous and uniform film in the contact area between the roller and the film. The geometric structure of the groove edges helps maintain a stable flow of the adhesive during the coating process, reducing coating defects caused by differences in the adhesive's surface tension. After coating, the adhesive layer thickness is uniform, providing stable interface conditions for subsequent lamination processes. Example

[0030] This embodiment provides a polarizer with improved weather resistance, which is prepared using a three-layer laminated structure including an upper hydrophobic film material, a lower hydrophobic film material, an intermediate PVA film, and a free radical UV adhesive layer sandwiched therebetween and cured by ultraviolet light; wherein the UV adhesive layer contains a hydrophobic monomer, a small amount of hydrophilic monomer, a photoinitiator, a silane coupling agent, and a tackifier.

[0031] Among them, hydrophobic monomers refer to acrylic ester substances with non-polar groups in the molecular chain, which can be specifically achieved by methyl methacrylate or isooctyl acrylate. The hydrophobic group reduces the water absorption of the adhesive layer to improve weather resistance. Hydrophilic monomers refer to acrylic esters containing hydroxyl or carboxyl groups, which can be specifically achieved by hydroxyethyl acrylate. A small amount of addition is used to adjust the interfacial wettability of the adhesive layer and the PVA film. Silane coupling agents refer to organic silicon compounds with alkoxy and vinyl groups, which can be specifically achieved by γ-methacryloyloxypropyltrimethoxysilane. The interfacial bonding force is enhanced by forming chemical bonds with the substrate surface through the silicon hydroxyl group. Tackifiers refer to acrylic ester oligomers with a long-chain structure, which can be specifically achieved by polyurethane acrylate. The cohesion of the adhesive layer is improved by increasing the entanglement of molecular chains.

[0032] Specifically, the upper and lower hydrophobic membrane materials are made of polyester or cycloolefin polymer with a moisture permeability of less than 5g / m²·24h, and the middle PVA film is biaxially stretched to form a uniformly oriented structure. The UV adhesive layer is applied to the surface of the hydrophobic membrane material by a honeycomb roller, and a free radical polymerization reaction occurs under ultraviolet light to form a three-dimensional cross-linked network structure. The hydrophobic monomer constitutes the main framework of the adhesive layer, a small amount of hydrophilic monomer promotes molecular diffusion between the adhesive layer and the PVA film, the silane coupling agent forms a chemical bond at the interface between the adhesive layer and the substrate, and the tackifier inhibits cohesive failure of the adhesive layer through molecular chain entanglement. The cured adhesive layer is bonded to the hydrophobic membrane material through the anchoring effect, and at the same time forms an interpenetrating network structure with the PVA film, forming a stable interlayer interface.

[0033] This embodiment further proposes a free radical UV adhesive for improving the weather resistance of the polarizer. The polarizer peeling width is 15 mm, the peeling rate is 300 mm / min, and the peeling force is not less than 98 gf / 15 mm.

[0034] The peel width refers to the lateral dimension of the peel area when testing the interlayer bonding strength of the polarizer. Specifically, a standard test fixture can be used to limit the width of the peel area to 15mm. By controlling the peel width, the comparability and repeatability of the test results can be ensured. The peel rate refers to the displacement per unit time of the peel test. Specifically, a uniform stretching device can be used to set the peel speed to 300mm / min. This rate can simulate the dynamic conditions of the polarizer in actual use. The peel force refers to the minimum unit width force required to separate the polarizer layers. Specifically, the ratio of tackifier and the content of silane coupling agent in the UV adhesive formula can be adjusted so that the cured adhesive layer can withstand a peel force of at least 98gf at a width of 15mm.

[0035] After the polarizer is cured, a peel test is performed at a 15mm width and 300mm / min rate to quantitatively assess the bond strength between the UV adhesive layer, the hydrophobic film, and the PVA film. During the test, the chemical bonds formed by the tackifier and silane coupling agent within the adhesive layer resist interlayer separation stress, while the low shrinkage of the UV adhesive during cure prevents interfacial failure due to internal stress concentration. The peel force threshold is set at 98gf / 15mm, ensuring effective adhesion of the polarizer even in high-temperature and high-humidity environments.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the embodiments of the present invention. It should be understood by those skilled in the art that any modifications, equivalent substitutions, and improvements based on the present invention, without departing from the inventive concept of the present invention, fall within the scope of protection claimed in the present invention.

Claims

1. A polarizer manufacturing process for improving the weather resistance of a polarizer, characterized in that: The following steps are involved: Provide upper and lower membrane materials with hydrophobicity; Free radical UV adhesive is used as the adhesive, and the free radical UV adhesive includes: a main agent, a hydrophobic monomer, a hydrophilic monomer, a silane coupling agent, a photoinitiator and a tackifier; Apply UV glue to one side of the membrane material through a honeycomb structure roller; Laminating the film material with the stretched PVA film and controlling the drying rate of the PVA film; The UV adhesive is cured by ultraviolet light with a wavelength of 300 to 500 nm, and heat treatment is applied after curing to enhance the penetration and anchoring effect between resin molecules to form a three-layer laminated structure polarizer.

2. The polarizer manufacturing process for improving the weather resistance of polarizer according to claim 1, characterized in that: The ratio of the hydrophobic monomer is higher than that of the hydrophilic monomer.

3. The polarizer manufacturing process for improving the weather resistance of polarizer according to claim 1, characterized in that: In the step of laminating the film material and the stretched PVA film, the moisture content of the PVA film is controlled to be 2% to 6% to reduce stress unevenness and interlayer delamination caused by water evaporation.

4. The polarizer manufacturing process for improving the weather resistance of polarizer according to claim 1, characterized in that: In the step of curing the UV glue, the wavelength of the ultraviolet light is 300 to 500 nm.

5. The polarizer manufacturing process for improving the weather resistance of polarizer according to claim 1, characterized in that: The UV glue is coated on one side of the film material by the honeycomb structure roller, wherein the coating thickness is 5 to 25 μm, and the contact angle between the roller and the film material is controlled to be 30 to 60 degrees.

6. The polarizer manufacturing process for improving the weather resistance of polarizer according to claim 1, characterized in that: The UV glue is applied by a roller device provided with a honeycomb structure, and the honeycomb structure is a regularly arranged hexagonal groove structure.

7. A polarizer with improved weather resistance, prepared by the polarizer manufacturing process for improving weather resistance of polarizer according to any one of claims 1 to 6, characterized in that: include: An upper hydrophobic film material, a lower hydrophobic film material, a middle PVA film, and a free radical UV adhesive layer sandwiched therebetween and cured by ultraviolet light; Wherein: the UV adhesive layer contains a hydrophobic monomer, a small amount of hydrophilic monomer, a photoinitiator, a silane coupling agent and a tackifier.

8. The polarizer for improving weather resistance of a polarizer according to claim 7, wherein: The polarizer peeling width is 15 mm, the peeling rate is 300 mm / min, and the peeling force is not less than 98 gf / 15 mm.

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