Foaming Agent Composition, Light Diffusion Plate and Preparation Method Thereof

Abstract

The present invention provides a foaming agent composition, a light diffusing plate and a preparation method thereof. The foaming agent composition includes a first foaming agent and a second foaming agent. The first foaming agent is used to form first pores in the foaming layer, and the second foaming agent is used to form second pores in the foaming layer. The average diameter of the second pores is smaller than that of the first pores. Wherein, the mass of the first foaming agent does not exceed 3 / 4 of the total mass of the foaming agent composition. This foaming agent composition can generate two types of pores with different diameters in the foaming layer of the light diffusing plate, so as to reduce the density of the light diffusing plate on the premise of meeting the requirements of haze and light transmittance.

Description

Technical Field

[0001] The present invention relates to the technical field of light diffusing plates, and particularly to a foaming agent composition, a light diffusing plate and a preparation method thereof. Background Art

[0002] A light diffusing plate is an optical plate with a certain haze and light transmittance, and is widely used in the fields of LCD TVs and LED lighting. The working principle of the light diffusing plate is as follows: light passes through a diffusion layer made of materials such as polycarbonate (PC) / polymethyl methacrylate (PMMA) / polystyrene (PS) as a substrate, and when it encounters a medium (diffusion particles or bubble holes) with a refractive index different from that of the substrate, refraction, reflection or scattering occurs, thereby changing the propagation route of the light and achieving sufficient divergence of the incident light to produce an optical diffusion effect. The light diffusing plate can effectively convert a point or line light source into a soft and uniform surface light source, and has good shielding properties for the light source dot matrix or line array while achieving a good light transmittance. The foaming diffusing plate is a type of light diffusing plate, which uses bubble holes as the medium for light diffusion to achieve the light diffusion function, and is widely used because of its advantages such as low density, high haze, high light transmittance, and low cost.

[0003] The most core process of the foaming diffusing plate is the foaming process. Currently, the main foaming processes include chemical foaming (i.e., adding a chemical foaming agent for foaming) and physical foaming (such as supercritical fluid foaming). Among them, the preparation method of the chemical foaming method is relatively convenient, and the requirements for equipment are relatively low, and it can be widely used in industrial production.

[0004] There are two main factors that determine the performance indicators of the chemical foaming diffusing plate: the size of the bubble pore diameter (hereinafter referred to as: pore size), and the density distribution of the bubbles (referred to as: pore density, that is, the number of pores per unit volume). For example: for a foaming diffusing plate with the same thickness, when the pore density is constant, the larger the pore size, the relatively higher the light transmittance, but the worse its diffusion effect (i.e., haze), that is, the light homogenization effect of the diffusing plate will become worse; when the pore size is constant, the larger the pore density, the better its diffusion effect (i.e., haze), and the light transmittance will be reduced; therefore, to make the foaming diffusing plate have both a high light transmittance and a good light homogenization effect, it is necessary to control the pore size and pore density of the foaming diffusing plate.

[0005] When the existing chemical foaming diffusing plate is made, generally a single type of chemical foaming agent is added to generate a plurality of pores with similar sizes. Although the haze and light transmittance of this chemical foaming diffusing plate with a single pore size can also meet the requirements, the density of the chemical foaming diffusing plate is relatively large, which is not conducive to the lightweight design of the chemical foaming diffusing plate. Summary of the Invention

[0006] The object of the present invention is to provide a foaming agent composition which can generate two types of pores with different diameters in the foaming layer of a light diffusing plate, so as to reduce the density of the light diffusing plate on the premise of meeting the requirements of haze and light transmittance.

[0007] The present invention provides a foaming agent composition for preparing a foaming layer in a light diffusing plate. The foaming agent composition includes a first foaming agent and a second foaming agent. The first foaming agent is used to form first pores in the foaming layer, and the second foaming agent is used to form second pores in the foaming layer. The average diameter of the second pores is smaller than that of the first pores. Wherein, the mass of the first foaming agent does not exceed 3 / 4 of the total mass of the foaming agent composition.

[0008] In an achievable manner, the mass of the first foaming agent is 1 / 4 to 3 / 4 of the total mass of the foaming agent composition.

[0009] The present invention further provides a light diffusing plate, which includes a foaming layer, a plurality of first pores and a plurality of second pores dispersed in the foaming layer. The plurality of second pores are dispersed among the plurality of first pores. Wherein, the average diameter of the second pores is smaller than that of the first pores; the difference between the average diameter of the first pores and the average diameter of the second pores is greater than 0 μm and less than or equal to 500 μm.

[0010] In an achievable manner, the raw materials for preparing the foaming layer include a foaming agent composition. The foaming agent composition includes a first foaming agent and a second foaming agent. The first pores are formed by foaming of the first foaming agent, and the second pores are formed by foaming of the second foaming agent.

[0011] In an achievable manner, the average diameter of the first pores is a, and the average diameter of the second pores is b. Wherein, 450 μm < a ≤ 700 μm, 200 μm ≤ b ≤ 450 μm.

[0012] In an achievable manner, the density ρ of the light diffusing plate < 0.900 g / cm 3 .

[0013] In an achievable manner, the density ρ of the light diffusing plate > 0.810 g / cm 3 .

[0014] The present invention further provides a preparation method of the light diffusing plate as described above, including the following steps:

[0015] S10: Weigh polystyrene and a foaming agent composition. The foaming agent composition includes a first foaming agent and a second foaming agent; mix the polystyrene and the foaming agent composition evenly to obtain a premix.

[0016] S20: Add the premix into a screw extruder, conduct melt mixing, and then extrude through the die head of the screw extruder to obtain a foamed layer.

[0017] In an implementable manner, in the above S10 step, a mixer is used to weigh and mix the polystyrene and the foaming agent composition; wherein, the specific steps for weighing the polystyrene and the foaming agent composition include:

[0018] (1) Set multiple sequentially increasing weight thresholds for the mixer, and the multiple sequentially increasing weight thresholds are M1, M2... M n-1 、M n ; wherein, M n is equal to the total weight M of the material to be weighed, n≥2; the material is the polystyrene or the foaming agent composition;

[0019] (2) Add the material into the mixer through the feed inlet of the mixer, and use the weighing device in the mixer to weigh the cumulative added weight of the material;

[0020] When the cumulative added weight of the material in the mixer reaches M1, reduce the opening diameter of the feed inlet of the mixer;

[0021] When the cumulative added weight of the material in the mixer reaches M2, reduce the opening diameter of the feed inlet of the mixer again;

[0022] ……

[0023] When the cumulative added weight of the material in the mixer reaches M n , close the feed inlet of the mixer and stop feeding.

[0024] In an implementable manner, in the above S20 step, the screw extruder is a twin-screw extruder, and the stirring speed of the screw of the twin-screw extruder is 100 RPM to 150 RPM.

[0025] The foaming agent composition provided by the present invention adopts a combination of a first foaming agent and a second foaming agent. The first foaming agent foams in the foaming layer to form first pores, and the second foaming agent foams in the foaming layer to form second pores. Moreover, the average diameter of the second pores is smaller than that of the first pores. That is, two types of pores with different diameters (i.e., large pores and small pores) are generated by the foaming agent composition to form a foaming layer doped with large and small pores. At the same time, by limiting the mass ratio of the first foaming agent and the second foaming agent, the number of the first pores and the second pores is limited. Among them, the first pores (i.e., large pores) are mainly used to ensure that the foaming layer has sufficient light transmittance, and the second pores (i.e., small pores) are mainly used to improve the haze of the foaming layer. Through the combination of the first pores and the second pores, the light diffusing plate meets the requirements of haze and light transmittance.

[0026] At the same time, due to the different pore sizes, the second pores with smaller pore sizes can fill the voids between the first pores with larger pore sizes, making it easy for the foaming layer to be fully filled with pores, increasing the volume occupancy ratio of the pores, reducing the density of the foaming layer, and further reducing the density of the light diffusing plate, which is beneficial to the lightweight design of the light diffusing plate. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a schematic structural diagram of the foaming layer of the light diffusing plate in the prior art I.

[0029] Figure 2 It is a schematic structural diagram of the foaming layer of the light diffusing plate in the prior art II.

[0030] Figure 3 It is a schematic structural diagram of the light diffusing plate in the embodiment of the present invention.

[0031] Figure 4 For Figure 3 The schematic structural diagram of the foaming layer in

[0032] Figure 5 It is the actual measurement diagram of the product of the foaming layer in the embodiment of the present invention.

[0033] Figure 6 It is a schematic diagram of the measurement method of the diameter of the pores in the embodiment of the present invention.

[0034] Figure 7 It is a schematic diagram of the control logic of the mixer in the embodiment of the present invention. Detailed implementation manners

[0035] The following further describes in detail the specific implementation manners of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention. Terms such as "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present invention are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence.

[0036] As Figure 3 and Figure 4 shown, an embodiment of the present invention provides a foaming agent composition for preparing a foaming layer 11 in a light diffusing plate 1. The foaming agent composition includes a first foaming agent and a second foaming agent. The first foaming agent is used to form first pores 111 in the foaming layer 11, and the second foaming agent is used to form second pores 112 in the foaming layer 11. The average diameter of the second pores 112 is smaller than the average diameter of the first pores 111 (specifically, as Figure 6 shown, the diameter of the pore refers to the diameter D of the circumscribed sphere of the pore); wherein, the mass of the first foaming agent does not exceed 3 / 4 of the total mass of the foaming agent composition. The foaming agent composition is formed by uniformly mixing the first foaming agent and the second foaming agent.

[0037] Specifically, when the thickness of the foaming layer is constant, the smaller the pore size, the greater the pore density. When light passes through the foaming layer, the more times of reflection or refraction occur in the foaming layer, which is beneficial to diffusing light, that is, the higher the haze of the light diffusing plate; however, due to the increase in the number of times of reflection or refraction of light, light energy loss will occur due to the interface effect, resulting in a decrease in light transmittance. When the thickness of the foaming layer is constant, the larger the pore size, the smaller the pore density, then the fewer times of reflection or refraction occur when light passes through the foaming layer, and the interface loss of light energy will be reduced. At this time, the light transmittance is relatively high, but the haze is low.

[0038] When manufacturing existing chemical foaming diffusing plates, generally a single type of chemical foaming agent is added to generate multiple pores with similar sizes. As Figure 1 shown, some existing light diffusing plates generate multiple small pores in the foaming layer by adding a single type of chemical foaming agent. The small pores can improve the haze of the light diffusing plate, but will reduce the light transmittance of the light diffusing plate; in order to improve the light transmittance of the light diffusing plate, the pore density of the small pores needs to be relatively reduced (when the pore size is constant, the smaller the pore density, the higher the light transmittance), so that the volume occupancy ratio of the pores (the total volume of the pores in a unit volume, that is, the ratio of the total volume of the pores to the total volume of the foaming layer) is reduced, increasing the density of the light diffusing plate. As Figure 2As shown in the figure, some existing light diffusing plates generate multiple large pores in the foaming layer by adding a single type of chemical foaming agent. The large pores can improve the light transmittance of the light diffusing plate. However, due to the large volume of the large pores, the gaps between adjacent large pores are large, resulting in a low volume occupancy ratio of the pores and an increase in the density of the light diffusing plate. Therefore, whether it is a light diffusing plate with a single large pore structure or a single small pore structure, under the premise of meeting the relevant requirements of haze and light transmittance, the volume occupancy ratio of the pores is relatively low, and the density of the light diffusing plate is relatively large.

[0039] The foaming agent composition provided by the embodiment of the present invention uses a combination of a first foaming agent and a second foaming agent. The first foaming agent is used to form first pores 111 in the foaming layer 11, and the second foaming agent is used to form second pores 112 in the foaming layer 11. The average diameter of the second pores 112 is smaller than that of the first pores 111, that is, two types of pores with different diameters are generated by the foaming agent composition to form a foaming layer 11 doped with large and small pores. At the same time, by limiting the mass ratio of the first foaming agent to the second foaming agent, the number of the first pores 111 and the second pores 112 is limited. Among them, the first pores 111 are mainly used to ensure that the foaming layer 11 has sufficient light transmittance, and the second pores 112 are mainly used to improve the haze of the foaming layer 11. Through the combination of the first pores 111 and the second pores 112, the light diffusing plate 1 meets the requirements of haze and light transmittance.

[0040] At the same time, as Figure 4 and Figure 5 shown in Figure 4 (only schematically showing the distribution of large and small pores, not representing the actual pore arrangement of the product; Figure 5 FIG. Figure 5 is the actual measured figure of the foaming layer product. Specifically, Figure 5 is the pore distribution diagram observed after magnifying the foaming layer under a microscope), since the average diameter of the second pores 112 is smaller than that of the first pores 111, the second pores 112 can fill the gaps between the first pores 111, so that the foaming layer 11 is fully filled with pores, the volume occupancy ratio of the pores is increased, the density of the foaming layer 11 is reduced, and further the density of the light diffusing plate 1 is reduced, which is beneficial to the lightweight design of the light diffusing plate.

[0041] As an implementation manner, the mass of the first foaming agent is 1 / 4 to 3 / 4 of the total mass of the foaming agent composition. Specifically, the mass of the first foaming agent can be 1 / 4, 1 / 3, 2 / 5, 1 / 2, 2 / 3, 3 / 4, etc. of the total mass of the foaming agent composition, or any combination range of the above values.

[0042] As an implementation manner, the difference between the foaming temperature of the first foaming agent and the foaming temperature of the second foaming agent does not exceed 20°C, for example, both are about 220°C.

[0043] As an implementation manner, both the first foaming agent and the second foaming agent are pre-mixed foaming agent masterbatches. The first foaming agent is selected from one or more of the LSPS-203 natural color foaming agent of Kingfa Sci. & Tech. Co., Ltd., the HYD2016 foaming agent of Suzhou Chixunjia Electronic Materials Co., Ltd., the Z201 foaming agent of Guangyuxing Intelligence (Nantong) Technology Co., Ltd., and the polystyrene foaming masterbatch of Wuzhi New Materials Technology Co., Ltd. The second foaming agent is selected from one or more of the CE-3152C foaming agent of Guangzhou Benqi New Materials Co., Ltd., the HC-C3152E foaming agent of Xinfu Electromechanical Co., Ltd., and the PS356 foaming agent of Zhejiang Jieshangjie New Materials Co., Ltd. The first foaming agent and the second foaming agent are different foaming agents.

[0044] As Figure 3 and Figure 4 shown, an embodiment of the present invention further provides a light diffusing plate 1, including a foaming layer 11, a plurality of first pores 111 and a plurality of second pores 112 dispersed in the foaming layer 11, and the plurality of second pores 111 are dispersed among the plurality of first pores 112; wherein, the average diameter of the second pores 112 is smaller than the average diameter of the first pores 111.

[0045] Specifically, when measuring the average diameters of the first pores 111 and the second pores 112, a plurality of (for example, 30-100) pores in a plurality of regions of the light diffusing plate 1 can be randomly selected, the diameters of each pore are measured respectively, the pores with a diameter greater than 450 μm are recorded as the first pores 111, the pores with a diameter less than or equal to 450 μm are recorded as the second pores 112, and then the measured values of the diameters of each first pore 111 are averaged to obtain the average diameter of the first pores 111. The measurement method of the average diameter of the second pores 112 is the same as that of the first pores 111, and will not be elaborated here.

[0046] As an implementation manner, the average diameter of the first pores 111 is a, and the average diameter of the second pores 112 is b, wherein, 450 μm < a ≤ 700 μm, 200 μm ≤ b ≤ 450 μm.

[0047] As an implementation manner, the difference between the average diameter of the first pores 111 and the average diameter of the second pores 112 is greater than 0 μm and less than or equal to 500 μm.

[0048] As an implementation manner, the sum of the volumes of all the first pores 111 and all the second pores 112 accounts for 16.3% - 22.7% of the total volume of the foaming layer 11 (i.e., the volume occupancy ratio of the pores is 16.3% - 22.7%).

[0049] As Figure 3As shown, as an embodiment, the light diffusing plate 1 further includes a first protective layer 12 and a second protective layer 13, and the first protective layer 12 and the second protective layer 13 are respectively disposed on opposite sides of the foaming layer 11. The thickness ratio of the first protective layer 12 to the foaming layer 11 and the thickness ratio of the second protective layer 13 to the foaming layer 11 are both about 1:9. The first protective layer 12 and the second protective layer 13 can protect the foaming layer 11, prevent the internal bubbles of the foaming layer 11 from overflowing or the cell structure from being damaged during production, ensure the flatness of the surface of the light diffusing plate 1, and improve the weather resistance of the light diffusing plate 1, etc. Since no cell structure needs to be formed inside the first protective layer 12 and the second protective layer 13, the first protective layer 12 and the second protective layer 13 can be made of a single material such as polystyrene or polymethyl methacrylate.

[0050] As an embodiment, the density ρ of the light diffusing plate 1 < 0.900 g / cm 3 .

[0051] As an embodiment, the density ρ of the light diffusing plate 1 > 0.810 g / cm 3 .

[0052] As an embodiment, the density ρ of the light diffusing plate 1 is 0.877 g / cm 3 ~0.879 g / cm 3 .

[0053] As an embodiment, the haze of the light diffusing plate 1 is 98% ± 1%, and the light transmittance of the light diffusing plate 1 is 30% ± 1%.

[0054] As an embodiment, the preparation raw materials of the foaming layer 11 include the above-mentioned foaming agent composition. The foaming agent composition includes a first foaming agent and a second foaming agent. The first cell 111 is formed by foaming with the first foaming agent, and the second cell 112 is formed by foaming with the second foaming agent.

[0055] As an embodiment, the preparation raw materials of the foaming layer 11 further include polystyrene. The mass fraction of polystyrene is 84.0 - 99.8 parts, and the mass fraction of the foaming agent composition is 0.2 - 1 part. Specifically, the mass fraction of polystyrene can be 99.6 parts, and the mass fraction of the foaming agent composition can be 0.4 part.

[0056] The embodiment of the present invention also provides a preparation method of a light diffusing plate, including the following steps:

[0057] S10: Weigh polystyrene and the foaming agent composition in proportion. The foaming agent composition includes a first foaming agent and a second foaming agent; mix the polystyrene and the foaming agent composition evenly to obtain a premix;

[0058] S20: Add the premix into a screw extruder, conduct melting and mixing, and then extrude through the die head of the screw extruder to obtain the foaming layer 11.

[0059] As an implementation manner, in the above S10 step, a mixer is used to weigh and mix polystyrene and the foaming agent composition; wherein, the specific steps of separately weighing polystyrene and the foaming agent composition include:

[0060] (1) Set multiple successively increasing weight thresholds for the mixer, and the multiple successively increasing weight thresholds are M1, M2…M n-1 、M n ; wherein, M n is equal to the total weight M of the material to be weighed, n≥2; the material is polystyrene or the foaming agent composition;

[0061] (2) Add the material into the mixer through the feed port of the mixer, and use the weighing device in the mixer to weigh the cumulative added weight of the material;

[0062] When the cumulative added weight of the material in the mixer reaches M1, reduce the opening diameter of the feed port of the mixer;

[0063] When the cumulative added weight of the material in the mixer reaches M2, reduce the opening diameter of the feed port of the mixer again;

[0064] ……

[0065] When the cumulative added weight of the material in the mixer reaches M n , close the feed port of the mixer and stop feeding.

[0066] After both polystyrene and the foaming agent composition are weighed, then use the mixer to stir and mix polystyrene and the foaming agent composition to obtain the premix (it should be noted that polystyrene and the foaming agent composition are separately weighed according to the above method, rather than weighed simultaneously; after polystyrene and the foaming agent composition are separately weighed, then mix the two).

[0067] Specifically, the current conventional practice when weighing materials is as follows: After various materials are sequentially added into the mixer from different feed inlets, the materials fall onto the weighing platform (i.e., the weighing device) inside the mixer in the form of free fall. The weighing platform is connected with a pressure sensor (or other forms of weight detection and feedback devices). When the weight of the materials on the weighing platform reaches the set value, the main control end of the mixer outputs a command to close the feed inlet and stop feeding. However, there will inevitably be a delay phenomenon from when the main control end of the mixer outputs the closing command to when the feed inlet is completely closed, resulting in materials still entering the mixer during the closing process of the feed inlet, making the mixing ratio accuracy of the premix lower than the set value. Especially for the foaming agent, its proportion in the premix is very small, and the leakage of materials caused by the delay makes the actual addition ratio of the foaming agent deviate greatly from the standard addition ratio, thereby affecting the cell density, cell size, and uniformity of cell arrangement of the later light diffusing plate, etc.

[0068] In this embodiment, by improving the way of weighing materials, the opening diameter of the feed inlet is gradually reduced during the feeding process, which can not only ensure the feeding rate (if the opening diameter of the feed inlet always remains small, the feeding is very slow, greatly reducing the production efficiency), but also ensure that the opening diameter of the feed inlet is very small in the final stage of feeding, thus greatly reducing the leakage of materials caused by the delay during the closing process of the feed inlet and greatly improving the weighing accuracy of the materials (the weighing accuracy of the premix can reach 99.99% and above).

[0069] As an implementation manner, in the above step (1), the difference between every two adjacent weight thresholds is not greater than 20% of M, and the difference between M n and M n-1 is not greater than 5% of M.

[0070] As Figure 7 shown, the following is an example to illustrate the specific steps of using the mixer to weigh the polystyrene and foaming agent composition:

[0071] 1. Set multiple sequentially increasing weight thresholds at the main control end of the mixer. The multiple sequentially increasing weight thresholds are M1, M2, M3, and M4 respectively; among them, M4 is equal to the total weight M of the materials to be weighed, M1 = 80%M, M2 = 90%M, M3 = 99%M; the materials are polystyrene or foaming agent composition (i.e., both are weighed separately according to this method);

[0072] 2. After the feeding starts, the material falls onto the weighing platform inside the mixer. The weighing platform is connected to a pressure feedback device, which can transmit the weighing data of the weighing platform to the host control terminal in real time. The host control terminal compares the read data with the first weight threshold M1. If they are equal, the host control terminal outputs a first command to the valve control unit of the feeding port of the mixer (i.e., the travel distance of the valve. If the opening diameter of the feeding port is R, the control command is R / 2), causing the valve at the feeding port to execute the action of reducing the feeding port diameter; when the valve reaches the position of R / 2 set for the feeding port diameter, the action stops.

[0073] 3. During the execution of the above step 2, the material actually continues to enter. When the host control terminal receives that the data from the pressure feedback device reaches the second weight threshold M2, the host control terminal outputs a second command to the valve control unit of the feeding port of the mixer, causing the valve at the feeding port to execute the action of reducing the feeding port diameter again (such as making the valve travel another R / 4).

[0074] 4. During the execution of the above step 3, the material actually continues to enter. When the host control terminal receives that the data from the pressure feedback device reaches the third weight threshold M3, the host control terminal outputs a third command to the valve control unit of the feeding port of the mixer, causing the valve at the feeding port to execute the action of reducing the feeding port diameter again (such as making the valve travel another R / 8).

[0075] 5. During the execution of the above step 4, the material actually continues to enter. When the host control terminal receives that the data from the pressure feedback device reaches the fourth weight threshold M4, the host control terminal outputs a fourth command to the valve control unit of the feeding port of the mixer, causing the feeding port of the mixer to be completely closed, i.e., the feeding is completed.

[0076] In the above steps 2 to 5, the number of times the valve travels can be set according to actual production requirements, for example, according to the maximum throughput of the foam extruder. If the throughput of the foam extruder is large, the number of times the valve travels can be set more. With such a setting, as shown in Table 1 below, the weighing accuracy of the material can reach 99.99% and above.

[0077] Table 1. Comparison of weighing accuracy

[0078] Comparison item Weighing accuracy Accumulative material difference Before improvement of the feed inlet 99.32％-99.90％ 50g - 240g After improvement of the feed inlet ≥99.99％ 0g - 5g

[0079] As an implementation manner, the above step S10 can specifically be: adding polystyrene and the foaming agent composition into the mixer through different feeding ports, weighing and stirring and mixing the polystyrene and the foaming agent composition by using the mixer, and the stirring time is 30s - 40s to obtain a uniformly mixed premix.

[0080] As an implementation manner, in the above step S20, the screw extruder is a twin-screw extruder, and the stirring speed of the screws of the twin-screw extruder is 100 RPM to 150 RPM. Specifically, the twin-screw extruder can be a flat twin-screw with a length-diameter ratio of the screw of 40:1, and the total stroke of the twin-screw extruder is 3 meters.

[0081] Specifically, in the field of chemical foaming, the commonly used screw extruders are all single-screw extruders, and the total stroke of the screw extruder is 5 meters. Using a twin-screw for chemical foaming is something that the industry has not dared to attempt because during the chemical foaming process, gases are generated when the material is in a molten state. When the twin-screw stirs the material in the molten state, the two screws rotate simultaneously, generating more shear heat, which causes the local temperature inside the melt to rise, and thus easily leads to partial molecular carbonization, making the product turn yellow. However, the present invention attempts to use a twin-screw extruder with a total stroke of 3 meters and finds that by controlling the rotational speed between 100 RPM and 150 RPM, not only can the blowing agent foam more fully and the bubble distribution be more uniform, but also no carbonization phenomenon will occur.

[0082] As an implementation manner, in the above step S20, the pre-mixed material with uniform proportion is fed into the screw storage hopper in the form of free fall, and the screw storage hopper then feeds the pre-mixed material into the screw extruder through an automatic feeder, so that the pre-mixed material completes chemical foaming in the screw extruder. The screw extruder includes eight heating zones, which are the first heating zone, the second heating zone, the third heating zone, the fourth heating zone, the fifth heating zone, the sixth heating zone, the seventh heating zone, and the eighth heating zone from the feeding end to the discharging end. The heating temperature of the first heating zone is 195°C to 205°C, and the heating temperature of the second heating zone is 200°C to 210°C. The first heating zone and the second heating zone are used for feeding and pushing the material. The heating temperature of the third heating zone is 205°C to 215°C, and the heating temperature of the fourth heating zone is 210°C to 220°C. The third heating zone and the fourth heating zone are used for heating the material to raise the temperature and start plasticizing the material. The heating temperature of the fifth heating zone is 190°C to 200°C, and the heating temperature of the sixth heating zone is 213°C to 223°C. The fifth heating zone and the sixth heating zone are used to discharge the waste gases and oils generated during the plasticizing process of the material. The heating temperature of the seventh heating zone is 213°C to 223°C, and the heating temperature of the eighth heating zone is 213°C to 223°C. The seventh heating zone and the eighth heating zone are used to make the material fully melt and mix here, so that the blowing agent foams evenly and fully.

[0083] As an implementation manner, the light diffusing plate 1 further includes a first protective layer 12 and a second protective layer 13, and the first protective layer 12 and the second protective layer 13 are respectively disposed on opposite sides of the foaming layer 11. During production, in the above step S20, when adding the premix into the screw extruder for melting and mixing, the raw materials of the protective layer (such as PS, PMMA, etc.) can be added into the surface layer extrusion equipment (such as a single-screw extruder) at the same time. After the premix and the raw materials of the protective layer that have been melted and mixed enter the confluence device, the confluence device stacks the materials after uniformly melting and mixing the upper and lower protective layers (i.e., the first protective layer 12 and the second protective layer 13) and the foaming layer, and then sends them into a T-shaped die head to extrude a three-layer plate structure; then, after subsequent steps such as rolling, temperature reduction, cooling, and cutting, the light diffusing plate 1 with the required size is finally obtained.

[0084] Example 1

[0085] Weigh 99.6 parts by mass of polystyrene and 0.4 parts of a foaming agent composition; the foaming agent composition includes a first foaming agent and a second foaming agent. The first foaming agent is a white granular foaming agent of Zhejiang Jieshangjie New Materials Co., Ltd., and the second foaming agent is CE-3152C foaming agent of Guangzhou Benqi New Materials Co., Ltd. The mass fraction of the first foaming agent is 0.1 part, and the mass fraction of the second foaming agent is 0.3 part. Mix the polystyrene and the foaming agent composition evenly to obtain a premix.

[0086] Add the premix into a twin-screw extruder for melting and mixing, and control the rotation speed between 100 RPM and 150 RPM; add the raw materials of the protective layer (such as PS, PMMA, etc.) into the surface layer extrusion equipment (such as a single-screw extruder). After the premix and the raw materials of the protective layer that have been melted and mixed enter the confluence device, the confluence device stacks the materials after uniformly melting and mixing the upper and lower protective layers and the foaming layer, and then sends them into a T-shaped die head to extrude a three-layer plate structure; then, after subsequent steps such as rolling, temperature reduction, cooling, and cutting, the light diffusing plate with the required size is finally obtained.

[0087] Example 2

[0088] The difference between Example 2 and Example 1 is that: in Example 2, the mass fraction of the first foaming agent is 0.2 part, and the mass fraction of the second foaming agent is 0.2 part, that is, the mass of the first foaming agent is 1 / 2 of the total mass of the foaming agent composition.

[0089] Other process conditions and steps of Example 2 are the same as those of Example 1, and will not be elaborated here.

[0090] Example 3

[0091] Example 3 is different from Example 1 in that: in Example 3, the mass fraction of the first blowing agent is 0.3 parts, and the mass fraction of the second blowing agent is 0.1 part, that is, the mass of the first blowing agent is 3 / 4 of the total mass of the blowing agent composition.

[0092] Other process conditions and steps of Example 3 are the same as those of Example 1 and will not be elaborated here.

[0093] Comparative Example 1

[0094] Comparative Example 1 is different from Example 1 in that: Comparative Example 1 uses a single blowing agent, and the premix includes 99.6 parts by mass of polystyrene and 0.4 parts by mass of the blowing agent, and the blowing agent is CE-3152C blowing agent of Guangzhou Benqi New Materials Co., Ltd.

[0095] Other process conditions and steps of Comparative Example 1 are the same as those of Example 1 and will not be elaborated here.

[0096] Comparative Examples 2-4

[0097] Comparative Examples 2-4 are all commercially available light diffusing plates. Comparative Example 2 is a light diffusing plate for a 55-inch liquid crystal display model, purchased from Shenzhen Chengyuxing Optoelectronics Co., Ltd.; Comparative Example 3 is a light diffusing plate for a 55-inch liquid crystal display model, purchased from Qingdao Guoqi Optoelectronic Technology Co., Ltd.; Comparative Example 4 is a light diffusing plate for a 55-inch liquid crystal display model, purchased from Guangdong Ruijie Optoelectronics Co., Ltd. The light diffusing plates in Comparative Examples 2-4 are all prepared with a single blowing agent, so a single small bubble hole or a single large bubble hole is obtained.

[0098] The light diffusing plates in the above Examples 1-3 and Comparative Examples 1-4 are all light diffusing plates with a light transmittance of 30% and a plate thickness of 1.2T series.

[0099] Compare the technical indicators of the light diffusing plates in Examples 1-3 and Comparative Examples 1-4. The specific parameters are shown in Table 2:

[0100] Table 2. Technical indicators of light diffusing plates

[0101]

[0102] Regarding the data in Table 2 above, it should be noted that:

[0103] 1. The average bubble diameter of the light diffusing plates in Examples 1 to 3 in Table 2 is calculated based on the data in Table 3 below. The calculation method of the average bubble diameter of the light diffusing plate can be referred to the previous description and will not be elaborated here.

[0104] Table 3. Actually measured bubble diameters of the light diffusing plates in Examples 1 to 3

[0105]

[0106]

[0107] For the data measured in Example 1, among the 30 selected pores, 10 are large pores (450 μm < diameter ≤ 700 μm) and 20 are small pores (200 μm ≤ diameter ≤ 450 μm). The average diameter of the 10 large pores is about 525 μm, and the average diameter of the 20 small pores is about 376 μm.

[0108] For the data measured in Example 2, among the 30 selected pores, 13 are large pores (450 μm < diameter ≤ 700 μm) and 17 are small pores (200 μm ≤ diameter ≤ 450 μm). The average diameter of the 13 large pores is about 522 μm, and the average diameter of the 17 small pores is about 342 μm.

[0109] For the data measured in Example 3, among the 30 selected pores, 14 are large pores (450 μm < diameter ≤ 700 μm) and 16 are small pores (200 μm ≤ diameter ≤ 450 μm). The average diameter of the 14 large pores is about 529 μm, and the average diameter of the 16 small pores is about 361 μm.

[0110] It should be noted that the above data are only the values measured from some selected pores in the light diffusing plate, in order to combine the product parameters with the internal principle for explanation. Understandably, there will be a certain tolerance in the pore diameter and quantity in the actual light diffusing plate compared with the measured values.

[0111] 2. Generally speaking, for a light diffusing plate with a light transmittance of 30% and a plate thickness of 1.2T series, when the haze of the light diffusing plate reaches 98% and the light transmittance is between 29% and 31%, it is considered to meet the industry standard.

[0112] Analyzing the data in Table 2, it can be seen that:

[0113] 1. From Comparative Examples 1 to 4, it can be seen that the light diffuser plate prepared by using a single foaming agent, whether it is a light diffuser plate with a single large pore structure or a light diffuser plate with a single small pore structure, has a relatively low volume ratio of the pores under the premise of meeting the relevant requirements of haze and transmittance, and the density of the light diffuser plate is relatively large. This is because: (a) for a light diffuser plate with a single small pore structure, although the small pores can improve the haze of the light diffuser plate, it will reduce the transmittance of the light diffuser plate; in order to improve the transmittance of the light diffuser plate, it is necessary to reduce the pore density of the small pores, and the volume ratio of the pores is reduced, and the density of the light diffuser plate is relatively large; (b) for a light diffuser plate with a single large pore structure, although the large pores can improve the transmittance of the light diffuser plate, due to the large volume of the large pores, the gaps between adjacent large pores are large, and the gaps cannot be effectively filled by the large pores, so that the volume ratio of the pores is also low, and the density of the light diffuser plate is relatively large.

[0114] 2. By comparing Examples 1-3 with Comparative Examples 1-4, it can be seen that the doping ratio of large and small bubbles in the light diffuser plate prepared in Examples 1-3 is moderate, and the gaps between the large bubbles are properly filled with small bubbles, so that when the haze and transmittance meet the standards, the volume ratio of the bubbles is higher, the plate density is smaller, and the plate can be made lighter.

[0115] Among them, it should be noted that for Example 3, although the transmittance of the light diffuser plate in Example 3 is 26%-29.5%, for the light diffuser plate with a transmittance of 30% and a plate thickness of 1.2T series, its transmittance is on the lower limit, but it can still be used in industries such as industrial control that have relatively low requirements for display brightness; therefore, the light diffuser plate prepared in Example 3 is also within the protection scope of this application.

[0116] 3. By comparing Examples 1-3, it can be seen that as the mass proportion of the first foaming agent increases, the number of large cells increases, the volume proportion of the cells increases, and the density of the board decreases.

[0117] 4. According to Example 3, it can be seen that when the proportion of the first foaming agent that produces large cells reaches 3 / 4, the light transmittance of the light diffuser plate is reduced, and its light transmittance is only 26%-29.5%. This is because: although the proportion of large cells is increasing and the number of large cells is increasing, the proportion of small cells filling the gaps between the large cells is higher, and it is more difficult for light to pass through the gaps between the cells and then be emitted, that is, it is more difficult for light to pass through the light diffuser plate directly and emit, causing the light transmittance of some areas of the light diffuser plate to decrease, such as only reaching 26%. Therefore, this application stipulates that the mass ratio of the first foaming agent cannot exceed 3 / 4, otherwise the light transmittance of the light diffuser plate will be further reduced, and it will not meet the requirements of the client.

[0118] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A light diffusing plate, characterized in that, It includes a foaming layer, a plurality of first pores and a plurality of second pores dispersed in the foaming layer, and the plurality of second pores are dispersed among the plurality of first pores; wherein, the average diameter of the second pores is smaller than that of the first pores; the average diameter of the first pores is a, the average diameter of the second pores is b, 450μm < a ≤ 700μm, 200μm ≤ b ≤ 450μm; the difference between the average diameter of the first pores and the average diameter of the second pores is greater than or equal to 149μm and less than or equal to 500μm; the sum of the volumes of all the first pores and all the second pores accounts for 16.3% - 22.7% of the total volume of the foaming layer; The raw materials for preparing the foaming layer include a foaming agent composition, and the foaming agent composition is composed of a first foaming agent and a second foaming agent. The first pores are formed by foaming with the first foaming agent, and the second pores are formed by foaming with the second foaming agent; the mass of the first foaming agent is 1 / 4 - 3 / 4 of the total mass of the foaming agent composition; Both the first foaming agent and the second foaming agent are pre-formulated foaming agent masterbatches; the first foaming agent is selected from one or more of the LSPS-203 natural color foaming agent of Kingfa Science & Technology Co., Ltd., the HYD2016 foaming agent of Suzhou Chixunjia Electronic Materials Co., Ltd., the Z201 foaming agent of Guangyuxing Intelligence (Nantong) Technology Co., Ltd., and the polystyrene foaming masterbatch of Wuzhi New Materials Technology Co., Ltd., and the second foaming agent is selected from one or more of the CE-3152C foaming agent of Guangzhou Benqi New Materials Co., Ltd., the HC-C3152E foaming agent of Xinfu Electromechanical Co., Ltd., and the PS356 foaming agent of Zhejiang Jieshangjie New Materials Co., Ltd.; the first foaming agent and the second foaming agent are different foaming agents.

2. The light diffusing plate according to claim 1, wherein, The density ρ of the light diffusing plate < 0.900 g / cm 3 .

3. The light diffusing plate according to claim 2, wherein, The density ρ of the light diffusing plate is > 0.810 g / cm 3 .

4. A method for preparing a light diffusing plate according to any one of claims 1 to 3, characterized in that, It includes the following steps: S10: Weigh polystyrene and a foaming agent composition, and the foaming agent composition includes a first foaming agent and a second foaming agent; mix the polystyrene and the foaming agent composition evenly to obtain a premix; S20: Add the premix into a twin-screw extruder, carry out melt mixing, and then extrude it through the die head of the twin-screw extruder to obtain a foaming layer.

5. The method for preparing a light diffusing plate according to claim 4, characterized in that, In the above S10 step, a mixer is used to weigh and mix the polystyrene and the foaming agent composition; wherein, the specific steps for weighing the polystyrene and the foaming agent composition include: (1) Set multiple sequentially increasing weight thresholds for the mixer, and the multiple sequentially increasing weight thresholds are M1, M2... Mn respectively. n-1 、M n ; where Mn n is equal to the total weight M of the material to be weighed, n≥2; the material is the polystyrene or the foaming agent composition. (2) Add the materials into the mixer through the feed inlet of the mixer, and use the weighing equipment in the mixer to weigh the cumulative added weight of the materials; When the cumulative added weight of the materials in the mixer reaches M1, reduce the opening diameter of the feed inlet of the mixer; When the cumulative added weight of the materials in the mixer reaches M2, reduce the opening diameter of the feed inlet of the mixer again; …… When the cumulative added weight of the materials in the mixer reaches M n close the feed inlet of the mixer and stop feeding.

6. The method for preparing a light diffusing plate according to claim 4, characterized in that, In the above S20 step, the twin-screw extruder is a twin-screw extruder, and the stirring speed of the screw of the twin-screw extruder is 100 RPM - 150 RPM.

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