A low-side-view haze electrically controlled dimming film and its preparation method

Abstract

This invention discloses a low-side-view haze electrically controlled dimming film and its preparation method. A second conductive layer and a third conductive layer are respectively disposed on both sides of a second substrate layer to facilitate the subsequent stacking of a first PDLC layer and a second PDLC layer. By stacking the two PDLC layers (first and second PDLC layers), the thickness of a single PDLC layer can be reduced, effectively reducing side-view haze. Furthermore, due to the thinner PDLC, even with a lower liquid crystal ratio, the saturation voltage remains low, meeting the low-voltage requirements for automotive applications. Simultaneously, the haze of a single PDLC layer in the open state is low; the haze remains low after stacking the two PDLC layers, and anti-reflection is achieved through refractive index matching. By using low birefringence liquid crystal in the PDLC layer, the mismatch between the refractive index of the adhesive and the refractive index of the liquid crystal can be reduced during side-view observation, which is beneficial for reducing side-view haze in the transparent state of the dimming film. This preparation method can produce an electrically controlled dimming film with low side-view haze, low open-state haze, good transparency, and low driving voltage.

Description

Technical Field

[0001] This invention relates to the field of dimming film technology, specifically to a low-side-view haze electrically controlled dimming film and its preparation method. Background Technology

[0002] PDLC thin film is a novel type of functional optoelectronic thin film, also known as electrically controlled dimming film. By controlling an external electric field, it can rapidly switch between two states: colorless and transparent, and milky white and opaque. With advancements in dimming film technology and continuous performance improvements, electrically controlled dimming films have begun to be used in automobiles. However, when applied to automotive sunroofs, it has been found that side-view haze is relatively noticeable in the transparent state. Car owners are dissatisfied with this side-view haze phenomenon, resulting in a relatively poor user experience and hindering the widespread application of electrically controlled dimming films.

[0003] However, to ensure the shielding properties of PDLC films, liquid crystals with a relatively high Δn (refractive index) of ≥0.2 are typically selected. Due to their high birefringence, these liquid crystals exhibit a greater mismatch between the refractive indices of the adhesive and the liquid crystal when viewed from the side. Furthermore, to achieve a relatively low operating voltage for PDLC films, the liquid crystal content is usually 50%-65%. A higher liquid crystal content leads to insufficient solubility, resulting in slightly larger liquid crystal droplet sizes after curing, thus causing more noticeable haze when viewed from the side. Significantly reducing the liquid crystal ratio and using liquid crystal materials with relatively low birefringence Δn usually results in a higher saturation voltage and a corresponding decrease in shielding properties. Since automotive applications require low-voltage operation, it is necessary to consider how to balance various parameters and develop an electronically controlled dimming film product with low side-view haze and other good overall performance. Summary of the Invention

[0004] The present invention provides a low-side-view haze electrically controlled dimming film, which can overcome the technical defect of existing electrically controlled dimming films exhibiting obvious side-view haze when powered on; the present invention also provides a method for preparing a low-side-view haze electrically controlled dimming film, which can prepare a low-side-view haze electrically controlled dimming film to overcome the technical defect of existing electrically controlled dimming films exhibiting obvious side-view haze when powered on.

[0005] On one hand, a low-side-view haze electrically controlled dimming film includes an electrically controlled dimming film, characterized in that the electrically controlled dimming film comprises a first substrate layer, a first conductive layer, a first PDLC layer, a second conductive layer, a second substrate layer, a third conductive layer, a second PDLC layer, a fourth conductive layer, and a third substrate layer stacked sequentially, wherein the first PDLC layer and the second PDLC layer each contain a low birefringence liquid crystal and an acrylic adhesive cured by ultraviolet light.

[0006] Preferably, the thickness of both the first PDLC layer and the second PDLC layer is less than or equal to 7.5 μm, and the total thickness of the electro-controlled dimming film is less than or equal to 450 μm.

[0007] Preferably, the birefringence Δn of the low birefringence liquid crystal is ≤0.15.

[0008] Preferably, the acrylic adhesive is a UV adhesive, and the refractive index of the UV adhesive after curing is consistent with the normal refractive index n0 of the liquid crystal, and the liquid crystal droplet size is ≤1µm.

[0009] Preferably, the first PDLC layer and / or the second PDLC layer further include spacers, the thickness of which is ≤7.5µm.

[0010] Preferably, the first substrate layer, the second substrate layer, and the third substrate layer are gray-black PET base films. The PET base film has a transmittance of ≥40%, a haze of ≤1%, and under the condition of heating at 150°C for 30 minutes, the PET base film has a heat shrinkage rate of ≤1% in the MD direction and a heat shrinkage rate of ≤0.8% in the TD direction.

[0011] Preferably, the first conductive layer, the second conductive layer, the third conductive layer, and the fourth conductive layer are transparent conductive films, wherein the transparent conductive film has a resistance of 50-150 ohms, a visible light transmittance of ≥20%, and a haze of ≤1%.

[0012] On the other hand, a method for preparing a low-side-view haze electrically controlled dimming film, for preparing the above-mentioned low-side-view haze electrically controlled dimming film, includes the following steps:

[0013] S1. Provide a first substrate layer, a second substrate layer, and a third substrate layer. A conductive film is deposited / coated on one side of the first substrate layer to form a first conductive layer. A conductive film is deposited / coated on one side of the third substrate layer to form a fourth conductive layer. A conductive film is deposited / coated on both sides of the second substrate layer to form a second conductive layer and a third conductive layer.

[0014] S2. Provide PDLC material, coat the PDLC material on the surface of the first conductive layer away from the first substrate layer, then composite the second conductive layer on the PDLC material already coated on the surface of the first conductive layer, or coat the PDLC material between the first conductive layer and the second conductive layer by roller coating, and finally cure with ultraviolet light to obtain the first PDLC layer.

[0015] S3. Coat the PDLC material on the surface of the fourth conductive layer away from the third substrate layer, then laminate the third conductive layer onto the PDLC material already coated on the surface of the fourth conductive layer, or coat the PDLC material between the third and fourth conductive layers using a roller coating method, and finally cure with ultraviolet light to obtain the second PDLC layer.

[0016] Preferably, the UV curing conditions in steps S2 and S3 are: curing temperature 18-30℃, curing light intensity 4-50mw / cm². 2 .

[0017] Preferably, the method further includes the following steps: cutting the dimming film obtained in step S3 to a specified size, and fabricating electrodes on the two PDLC layers, as well as test data.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. This invention provides a low-side-view haze electrically controlled dimming film. A second conductive layer and a third conductive layer are respectively disposed on both sides of a second substrate layer to facilitate the subsequent stacking of a first PDLC layer and a second PDLC layer. By stacking the two PDLC layers (first and second PDLC layers), the thickness of a single PDLC layer can be reduced, effectively lowering side-view haze. Furthermore, due to the thinner PDLC, even with a lower liquid crystal ratio, the saturation voltage remains low, meeting the low-voltage requirements for automotive applications. Moreover, the haze of a single PDLC layer in the open state is low. Simultaneously, the haze remains low after stacking the two PDLC layers, and anti-reflection is achieved through refractive index matching. Furthermore, by using low birefringence liquid crystal in the PDLC layer, the mismatch between the refractive index of the adhesive and the refractive index of the liquid crystal can be reduced during side-view viewing, which is beneficial for reducing side-view haze in the transparent state of the dimming film. Therefore, it can improve user satisfaction for automotive users and promote the widespread application of electrically controlled dimming films.

[0020] 2. In this case, the thickness of both the first PDLC layer and the second PDLC layer is less than or equal to 7.5μm, which can reduce the thickness of the first PDLC layer and the second PDLC layer respectively. On the one hand, the liquid crystal ratio can be reduced by reducing the thickness. Although there are two PDLC layers, the saturation voltage is still low, which can meet the low voltage use in automobiles and effectively reduce side fog. On the other hand, it can ensure the shielding effect without increasing the thickness too much when two PDLC layers are subsequently stacked.

[0021] 3. The low birefringence liquid crystal described in this case has a birefringence Δn≤0.15, which enables the liquid crystal to have a low birefringence, reduces the mismatch between the refractive index of the adhesive and the refractive index of the liquid crystal when viewed from the side, and can appropriately reduce the haze when viewed from the side.

[0022] 4. The refractive index of the UV adhesive after curing is consistent with the normal refractive index n0 of the liquid crystal, which ensures that the dimming film has low haze and is highly transparent in the transparent state. The size of the liquid crystal microdroplets is ≤1µm, which can minimize side-view haze and meet the needs of automotive users.

[0023] 5. The preparation method described in this case can produce a dimming film with two relatively thin PDLC layers. By reducing the thickness of the single-layer PDLC and the refractive index of the PDLC material, it can effectively reduce side-view haze while meeting the requirements for low-voltage use in automobiles. It can also reduce the mismatch between the refractive index of the adhesive and the refractive index of the liquid crystal when viewed from the side. Therefore, an electrically controlled dimming film with low side-view haze, low open-state haze, good transparency, and low driving voltage can be obtained. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the dimming film in this case. Detailed Implementation

[0025] The following examples further illustrate the features and other related characteristics of the present invention in detail, to facilitate understanding by those skilled in the art:

[0026] Example 1

[0027] like Figure 1 As shown, a low-side-view haze electrically controlled dimming film includes an electrically controlled dimming film comprising, in sequence, a first substrate layer 1, a first conductive layer 2, a first PDLC layer 3, a second conductive layer 4, a second substrate layer 5, a third conductive layer 6, a second PDLC layer 7, a fourth conductive layer 8, and a third substrate layer 9. The first PDLC layer 3 and the second PDLC layer 7 each contain low birefringence liquid crystal and an acrylic adhesive cured by ultraviolet light. In a specific implementation, the first substrate layer 1, the second substrate layer 5, and the third substrate layer 9 can be PET base films made of PET material. The second conductive layer 4 and the third conductive layer 6 are respectively on both sides of the second substrate layer 5, forming a PET base film with double-sided conductive films. The first PDLC layer 3 and the second PDLC layer 7 have a smaller thickness than the PDLC layer of a conventional dimming film.

[0028] As described above, this invention provides a low-side-view haze electrically controlled dimming film. A second conductive layer 4 and a third conductive layer 6 are respectively disposed on both sides of the second substrate layer 5 to facilitate the subsequent stacking of the first PDLC layer 3 and the second PDLC layer 7. By stacking the two PDLC layers (first PDLC layer 3 and second PDLC layer 7), the thickness of a single PDLC layer can be reduced, effectively lowering side-view haze. Furthermore, due to the thinner PDLC, even with a lower liquid crystal ratio, the saturation voltage remains low, meeting the low-voltage requirements for automotive applications. Moreover, the haze of a single PDLC layer in the open state is low. Simultaneously, the haze remains low after stacking the two PDLC layers, and anti-reflection is achieved through refractive index matching. Furthermore, by using low birefringence liquid crystal in the PDLC layer, the mismatch between the refractive index of the adhesive and the refractive index of the liquid crystal can be reduced during side-view viewing, which is beneficial for reducing side-view haze in the transparent state of the dimming film. Therefore, it can improve user satisfaction for automotive users and promote the widespread application of electrically controlled dimming films.

[0029] The thickness of both the first PDLC layer 3 and the second PDLC layer 7 is less than or equal to 7.5 μm, and the total thickness of the electrically controlled dimming film is less than or equal to 450 μm. This reduces the thickness of the first PDLC layer 3 and the second PDLC layer 7, resulting in a smaller liquid crystal ratio. Although there are two PDLC layers, the saturation voltage remains low, meeting the low-voltage requirements for automotive applications and effectively reducing side-view haze. Furthermore, it ensures that the thickness does not increase significantly when two more PDLC layers are subsequently stacked, while maintaining the shielding effect. The total thickness of the electrically controlled dimming film, less than or equal to 450 μm, is consistent with conventional dimming film thicknesses, facilitating existing automotive installation requirements. In practice, the thicknesses of the first PDLC layer 3 and the second PDLC layer 7 can be the same or different.

[0030] The low birefringence liquid crystal has a birefringence Δn ≤ 0.15. This results in a lower birefringence, reducing the mismatch between the refractive index of the adhesive and the liquid crystal when viewed from the side, thus appropriately reducing haze when viewed from the side.

[0031] The acrylic adhesive is a UV adhesive. The refractive index of the cured UV adhesive is consistent with the normal refractive index n0 of the liquid crystal, and the liquid crystal droplet size is ≤1µm. In specific implementation, through a series of PDLC formulation and curing process experiments, the liquid crystal droplet size is preferentially controlled within the range of 0.5-1µm. The specific liquid crystal droplet size is obtained by controlling the ratio of liquid crystal to UV adhesive and adjusting the curing light intensity, curing temperature, and total curing energy. Typically, the adhesive components are selected based on the liquid crystal material, and the liquid crystal / UV adhesive ratio is controlled to be ≤1. During the curing process, a series of experiments are conducted on curing light intensity and curing temperature. By testing the microstructure and basic properties of the experimental samples, the optimal liquid crystal / adhesive ratio and curing process conditions are found. Through a series of experiments, it has been determined that liquid crystal droplets with uniform size and ≤1µm can minimize side-view haze.

[0032] As described above, the refractive index of the cured UV adhesive is consistent with the normal refractive index n0 of the liquid crystal, which ensures that the dimming film has low haze and is highly transparent in the transparent state. The liquid crystal microdroplets are ≤1µm in size, which helps to minimize side-view haze and meets the needs of automotive users.

[0033] The first substrate layer 1, the second substrate layer 5, and the third substrate layer 9 are gray-black PET base films. The PET base film has a transmittance ≥40% and a haze ≤1%, with a preferred haze ≤0.5%. Under heating at 150℃ for 30 minutes, the PET base film has a thermal shrinkage rate ≤1% in the MD direction and ≤0.8% in the TD direction. In specific implementations, the first substrate layer 1, the second substrate layer 5, and the third substrate layer 9 can be selected with different thicknesses as needed. In actual production, the total thickness of the first substrate layer 1 and the second substrate layer 5 is usually approximately equal to the thickness of the third substrate layer 9. This ensures that when the second PDLC layer 7 is coated for the second time, the production parameters are controllable due to the similar thickness on both sides of the second PDLC layer, resulting in a better appearance. The thicknesses of the first substrate layer 1 and the third substrate layer 9 can be 100μm, 125μm, 175μm, 188μm, etc., and the thickness of the second substrate layer 5 can be 50μm, 75μm, 100μm, 125μm, etc.

[0034] As described above, the first substrate layer 1, the second substrate layer 5, and the third substrate layer 9 are composed of PET base film to achieve high transparency, low haze, and high brightness. The PET base film is grayish-black, which, compared to conventional milky white, eliminates the appearance of white haze, thereby reducing side-view haze. The limitations on the transmittance, haze, thermal shrinkage rate in the MD direction, and thermal shrinkage rate in the TD direction of the PET base film ensure that each substrate layer has good transparency, is free from haze, is not easily deformed, and has good temperature resistance, thus presenting excellent optical effects.

[0035] The first conductive layer 2, the second conductive layer 4, the third conductive layer 6, and the fourth conductive layer are transparent conductive films. These transparent conductive films have a resistance of 50-150 ohms, a visible light transmittance of ≥20%, and a haze of ≤1%. In specific implementations, ITO thin films can be selected. This results in high conductivity, high transparency, high mechanical hardness, and good chemical stability.

[0036] Example 2

[0037] The difference between Example 2 and Example 1 is that the first PDLC layer 3 and / or the second PDLC layer 7 further include spacers, the thickness of which is ≤7.5µm. In actual production, a PDLC layer containing spacers is typically formed by roller coating and curing. Thus, the spacers facilitate control over the uniformity of the distance between the two substrates of the film material, and allow adjustment of the PDLC layer thickness by selecting spacers of different diameters, thereby adjusting the thickness of the dimming film. When the PDLC layer is formed by slot coating and curing, it may not include spacers.

[0038] Example 3

[0039] A method for preparing a low-side-view haze electrically controlled dimming film, used to prepare the low-side-view haze electrically controlled dimming film as described above, includes the following steps:

[0040] S1. Two rolls of 125µm thick PET base film are provided, namely, a first substrate layer 1 and a third substrate layer 9; one roll of 50µm thick PET base film is provided, namely, a second substrate layer 5. This dimming film is produced using a roll-to-roll continuous production method. First, a conductive film is deposited or coated on one side of the first substrate layer 1 by coating or magnetron sputtering to form a first conductive layer 2. A conductive film is deposited or coated on one side of the third substrate layer 9 by coating or magnetron sputtering to form a fourth conductive layer 8. A conductive film is deposited or coated on one side of the second substrate layer 5 to form a second conductive layer 4, and a conductive film is deposited or coated on the other side of the second substrate layer 5 to form a third conductive layer 6. The 125µm thick PET base film has a total light transmittance of 54% and a haze of 0.3%; the 50µm thick PET base film has a total light transmittance of 45% and a haze of 0.25%. The first conductive layer 2 and the fourth conductive layer 8 can be made of ITO film with a thickness of 125 μm, and the second conductive layer 4 and the third conductive layer 6 can be made of ITO film with a thickness of 50 μm.

[0041] S2. Provide PDLC material, coat the PDLC material on the surface of the first conductive layer 2 away from the first substrate layer 1, then composite the second conductive layer 4 on the PDLC material already coated on the surface of the first conductive layer 2, or coat the PDLC material between the first conductive layer 2 and the second conductive layer 4 by roller coating, and finally cure with ultraviolet light to obtain the first PDLC layer 3.

[0042] S3. The PDLC material is coated on the surface of the fourth conductive layer 8 away from the third substrate layer 9. Then, the third conductive layer 6 is laminated onto the PDLC material already coated on the surface of the fourth conductive layer 8, or the PDLC material is coated between the third conductive layer 6 and the fourth conductive layer 8 by roller coating. Finally, ultraviolet curing is performed to obtain the second PDLC layer 7.

[0043] The thickness of both the first PDLC layer 3 and the second PDLC layer 7 is less than or equal to 7.5 μm, and the birefringence Δn of the low birefringence liquid crystal is ≤0.15. The liquid crystal in this PDLC material can be a nematic liquid crystal with Δn of 0.12 and a normal refractive index n0 of 1.50. The UV-curable acrylic adhesive can be a conventional UV adhesive, and its refractive index after curing is consistent with the normal refractive index n0 of the liquid crystal. The liquid crystal / UV adhesive ratio can be 0.8:1, and the final PDLC material is obtained after thorough mixing and degassing. When the PDLC material contains spacers, the low birefringence liquid crystal, acrylic adhesive, and spacers are thoroughly mixed and degassed to obtain the PDLC material. When the PDLC material is coated using a slot coating method, it may not contain spacers.

[0044] In practice, the curing conditions for UV curing described in steps S2 and S3 are typically: UV / UV curing temperature 18-30℃, curing light intensity 4-50mw / cm². 2 In actual production, the following curing conditions can be used: UV light intensity of 15mW / cm². 2 The curing temperature is 22℃ and the curing time is 3 minutes.

[0045] In actual production, the preparation method of this case may also include the following steps: cutting the dimming film obtained in step S3 into a specified size, such as a sample of 1000*2000mm, and fabricating electrodes on two PDLC layers, as well as testing data. The dimming film prepared by the above method has a visible light transmittance of up to 52%, a haze of up to 1.8%, a viewing angle ≥160°, and a gray-black color. It appears very clear to the naked eye when powered on, and the haze is very slight when viewed from the side.

[0046] As described above, the preparation method of this invention can produce a dimming film with two relatively thin PDLC layers. By reducing the thickness of the single-layer PDLC and the refractive index of the PDLC material, it can effectively reduce side-view haze while meeting the requirements for low-voltage use in automobiles. It can also reduce the mismatch between the refractive index of the adhesive and the refractive index of the liquid crystal when viewed from the side. Therefore, an electrically controlled dimming film with low side-view haze, low open-state haze, good transparency, and low driving voltage can be obtained.

[0047] As stated above, this case protects a low-side-view haze electronically controlled dimming film and its preparation method. All technical solutions that are the same as or similar to this case should be considered to fall within the protection scope of this case.

Claims

1. A low-side-view haze electrically controlled dimming film, comprising an electrically controlled dimming film, characterized in that... The electro-dimming film comprises a first substrate layer (1), a first conductive layer (2), a first PDLC layer (3), a second conductive layer (4), a second substrate layer (5), a third conductive layer (6), a second PDLC layer (7), a fourth conductive layer (8), and a third substrate layer (9) stacked sequentially. The first PDLC layer (3) and the second PDLC layer (7) each contain low birefringence liquid crystal and an acrylic adhesive cured by ultraviolet light. The thickness of the first PDLC layer (3) and the second PDLC layer (7) is less than or equal to 7.5 μm, and the total thickness of the electro-dimming film is less than or equal to 450 μm. The first substrate layer (1), the second substrate layer (5), and the third substrate layer (9) are gray-black PET base films. The PET base film has a transmittance ≥40%, a haze ≤1%, and under the condition of heating at 150°C for 30 minutes, the thermal shrinkage rate of the PET base film in the MD direction is ≤1% and the thermal shrinkage rate in the TD direction is ≤0.8%.

2. The low-side-view haze electrically controlled dimming film according to claim 1, characterized in that... The birefringence of the low birefringence liquid crystal is Δn≤0.

15.

3. A low-side-view haze electrically controlled dimming film according to any one of claims 1-2, characterized in that... The acrylic adhesive is a UV adhesive. After curing, the refractive index of the UV adhesive is consistent with the normal refractive index n0 of the liquid crystal, and the liquid crystal droplet size is ≤1µm.

4. The low-side-view haze electrically controlled dimming film according to claim 1, characterized in that... The first PDLC layer and / or the second PDLC layer further include spacers with a thickness ≤ 7.5 μm.

5. A low-side-view haze electrically controlled dimming film according to claim 4, characterized in that... The first, second, third, and fourth conductive layers are transparent conductive films, and the transparent conductive films have a resistance of 50-150 ohms, a visible light transmittance of ≥20%, and a haze of ≤1%.

6. A method for preparing a low-side-view haze electrically controlled dimming film, used to prepare a low-side-view haze electrically controlled dimming film as described in any one of claims 1-5, characterized in that... Includes the following steps: S1. Provide a first substrate layer, a second substrate layer, and a third substrate layer. A conductive film is deposited / coated on one side of the first substrate layer to form a first conductive layer. A conductive film is deposited / coated on one side of the third substrate layer to form a fourth conductive layer. A conductive film is deposited / coated on both sides of the second substrate layer to form a second conductive layer and a third conductive layer. S2. Provide PDLC material, coat the PDLC material on the surface of the first conductive layer away from the first substrate layer, then composite the second conductive layer on the PDLC material already coated on the surface of the first conductive layer, or coat the PDLC material between the first and second conductive layers by roller coating, and finally cure with ultraviolet light to obtain the first PDLC layer. S3. Coat the PDLC material on the surface of the fourth conductive layer away from the third substrate layer, then laminate the third conductive layer onto the PDLC material already coated on the surface of the fourth conductive layer, or coat the PDLC material between the third and fourth conductive layers using a roller coating method, and finally cure with ultraviolet light to obtain the second PDLC layer.

7. The method for preparing a low-side-view haze electrically controlled dimming film according to claim 6, characterized in that... The UV curing conditions described in steps S2 and S3 are: curing temperature 18-30℃, curing light intensity 4-50mw / cm². 2 .

8. The method for preparing a low-side-view haze electrically controlled dimming film according to claim 7, characterized in that... It also includes the following steps: The dimming film obtained in step S3 is cut to the specified size, and electrodes are fabricated on the two PDLC layers, along with test data.

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