A multilayer double-color PI composite reinforcing plate and a preparation method thereof

Abstract

The application discloses a kind of multilayer double-color PI composite reinforcing plate and preparation method thereof, from top to bottom including at least one white PI film layer, at least two yellow PI film layers, first adhesive layer is equipped between the white PI film layer and the yellow PI film layer, second adhesive layer is equipped between adjacent yellow PI film layer;The thickness of the white PI film layer is 5-75um;The thickness of the yellow PI film layer is 5-75um;The thickness of the first adhesive layer is 5-50um;The thickness of the second adhesive layer is 5-50um;The total thickness of the reinforcing plate is greater than or equal to 3 mil.The application is realized high light shielding, high heat resistance, high dimensional stability and strong bonding reliability by white PI, modified yellow PI two different formula PI, special glue + structural epoxy glue two different functional glue layers are matched, without ink layer, without metal layer.

Description

Technical Field

[0001] This invention pertains to FPC (Flexible Printed Circuit) reinforcement materials, primarily used for reinforcing FPCs in mobile phones, cameras, and automotive electronics. It is particularly suitable for reinforcing FPCs in high-end electronic devices such as mobile phones, camera modules, and automotive electronics, where high levels of light shielding, heat resistance, and dimensional stability are required. Background Technology

[0002] Currently, FPC reinforcing plates are mainly made of PI materials. Common structures include single-color PI with a single adhesive layer and double-layer PI of the same color with the same adhesive layer. Some also incorporate steel sheets, copper foil, or PET substrates. They are widely used in various electronic devices. However, as electronic devices develop towards miniaturization, high temperature, and high precision, existing products can no longer meet high-end demands.

[0003] Core defects of existing technology: (1) Light-shielding and heat resistance cannot be achieved simultaneously: the light-shielding rate of existing monochrome PI reinforcing plates is mostly below 90%, which cannot be adapted to scenarios such as camera modules; products containing PET substrate or ordinary PI have a temperature resistance of mostly below 260℃, which cannot be adapted to the high temperature environment of automotive electronics.

[0004] (2) High risk of patent infringement: The existing PI reinforcement plate structure design is simple (single color, same glue, simple stacking), and the patent protection is dense. New designs are likely to fall into the scope of existing patent protection.

[0005] (3) Poor structural stability: Single adhesive layer design is prone to high temperature overflow and delamination problems; products containing metal materials have poor insulation, which can easily lead to FPC short circuits; PET substrate has poor dimensional stability, which affects the assembly accuracy of FPC.

[0006] (4) Insufficient inventiveness: Existing technologies are mostly simple color or layer replacements, without functional layering, which cannot meet the inventiveness requirements of substantive examination of invention patents, and have limited practical performance.

[0007] For example, the classic patented structure of existing white cover film is: white PI + white adhesive + release layer, a simple structure with only three layers, and a single function, which can only meet basic light blocking requirements; Most commercially available white and black reinforcing boards are simply multiple layers of the same color and adhesive, which has the following defects: Its simple structural hierarchy is fully covered by a large number of existing patents, making it easy to infringe on patents. White reinforcing boards cannot simultaneously provide light blocking, temperature resistance, and dimensional stability, and are prone to delamination and yellowing at high temperatures. It only involves simple layering, lacks functional layering design, and has low innovation. Summary of the Invention

[0008] The main technical problem solved by this invention is to provide a PI-based reinforcing plate with a novel structure and balanced performance (high light-blocking, high heat resistance, and high stability). It utilizes two different PI formulations—white PI and modified yellow PI—combined with two different functional adhesive layers: a white special adhesive and a structural epoxy adhesive. It has no ink layer and no metal layer. This achieves high light-blocking, high heat resistance, high dimensional stability, and strong adhesive reliability.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a multi-layer dual-color PI composite reinforcing plate, comprising at least one white PI film layer and at least two yellow PI film layers from top to bottom, wherein a first adhesive layer is provided between the white PI film layer and the yellow PI film layer, and a second adhesive layer is provided between adjacent yellow PI film layers; The thickness of the white PI film layer is 5-75 μm; The thickness of the yellow PI film layer is 5-75 μm; The thickness of the first adhesive layer is 5-50 μm; The thickness of the second adhesive layer is 5-50 μm; The total thickness of the reinforcing plate is ≥3mil.

[0010] Furthermore, the first adhesive layer is an epoxy adhesive layer containing white filler.

[0011] Furthermore, the white filler is at least two of rutile titanium dioxide, precipitated barium sulfate, and fine talc; the amount of the white filler added is 15-25 wt%.

[0012] To elaborate further, the second adhesive layer is an epoxy adhesive layer.

[0013] Furthermore, the epoxy value of the second adhesive layer is 0.4 to 0.6 eq / 100g.

[0014] Furthermore, the white PI film layer is a polyimide layer containing rutile titanium dioxide and zinc oxide.

[0015] Furthermore, the amount of rutile titanium dioxide added is 3-8 wt%, and the amount of zinc oxide added is 0.5-1.5 wt%.

[0016] Furthermore, the yellow PI film layer is a polyimide layer with a temperature resistance rating of ≥280℃, a glass transition temperature of ≥300℃, a tensile strength of ≥200MPa, an elongation at break of ≥30%, and a CTE of 10-23ppm / ℃.

[0017] Furthermore, the reinforcing plate also includes an outer adhesive layer and a release layer, the outer adhesive layer being formed on the other side of the yellow PI film layer, and the release layer being formed on the other side of the adhesive layer.

[0018] A method for preparing a multilayer dual-color PI composite reinforcing plate includes the following steps: S1. After coating a yellow PI film with a second adhesive layer, place it in an oven to dry, and then press it with another yellow PI film using a hot roller to obtain semi-finished product 1; or continue to coat the yellow PI film with a second adhesive layer, press semi-finished product 1 to obtain semi-finished product 2; repeat this step n times (n=1, 2, ...). S2. After coating the white PI film with the first adhesive layer, place it in an oven to heat and dry, and then press it with the semi-finished product 1 / semi-finished product 2 obtained in S1 using a hot roller. S3. The semi-finished product obtained in S2 is cured at a high temperature of 160-180℃ to obtain a two-color composite film. S4. Apply an outer layer adhesive to the surface of the yellow PI film of the two-color composite film obtained in S3, and then bond the release layer to the outer layer adhesive layer to obtain a white reinforcing plate.

[0019] The beneficial effects of this invention are: 1. The first adhesive layer of this invention provides a white interface, enhances adhesion, and improves light blocking. The specific functions of the first adhesive layer are as follows: 1) Main bonding: Bonds white opaque PI to high-temperature resistant yellow PI, adaptable to the interface bonding of two different modified PIs, with high temperature resistance and strong adhesion; 2) Excellent resistance to yellowing: When combined with the white PI system, it is not easy to discolor under long-term high temperature and ultraviolet environment, ensuring the consistency of overall appearance and light blocking; the white filler continues the light blocking effect of the upper white PI, eliminates the light transmission gap between layers, and further improves the overall light blocking rate; 3) Interface buffer: Flexible resin system to alleviate the material stress difference between white PI and yellow PI and avoid interlayer warping.

[0020] 4) This adhesive layer is free of halogens and polyurethane, has a glass transition temperature of 40-100℃, a peel strength of ≥1.0N / mm at 180°, provides light shielding, is resistant to high temperatures, and has strong adhesion.

[0021] 2. The second adhesive layer of this invention connects two layers of yellow PI, providing stress buffer and solving the problems of high-temperature delamination and warping. The crosslinking density of the second adhesive layer is high (GEL > 90%), possessing excellent high-temperature resistance, creep resistance, and structural strength; it is specifically designed for bonding two layers of high-temperature resistant PI of the same material, and is not prone to softening or slippage under reflow soldering and high-temperature operating environments, thus improving the structural stability and process resistance of the entire reinforcing plate.

[0022] 3. The white PI film layer of this invention is a polyimide layer containing rutile titanium dioxide and zinc oxide. Rutile titanium dioxide is the main light-shielding pigment, ensuring high whiteness and high hiding power of the film; trace amounts of zinc oxide form a synergistic system with titanium dioxide, on the one hand filling the gaps between fillers to improve the film's density, and on the other hand achieving full-band ultraviolet absorption, inhibiting the oxidative yellowing of the PI matrix under high temperature and ultraviolet conditions. The combined use of these two fillers overcomes the defects of poor yellowing resistance and strong reflectivity of titanium dioxide alone, while avoiding the problems of decreased insulation and mechanical properties caused by high zinc oxide content, giving the white PI layer comprehensive properties of high light shielding, yellowing resistance, low glare, and high strength.

[0023] 4. This invention features a novel structure and balanced performance, and can be used for reinforcement of FPCs in mobile phones, cameras, and automotive electronics, demonstrating excellent novelty and inventiveness. It also possesses characteristics such as high light shielding, high temperature resistance, high adhesion, high dimensional stability, high insulation, optically friendly design, no conductive layer, and low cost. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of the dual-color composite film of the present invention; Figure 2 This is a schematic diagram of the structure of the white reinforcing plate of the present invention. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0026] Example: A multilayer dual-color PI composite reinforcing plate 100, comprising at least one white PI film layer 101 and at least two yellow PI film layers 102 from top to bottom, wherein a first adhesive layer 103 is provided between the white PI film layer and the yellow PI film layer, and a second adhesive layer 104 is provided between adjacent yellow PI film layers; the white PI layer provides high whiteness, high light blocking, and surface protection; the yellow PI layer provides high strength, high temperature resistance, and dimensional stability; The thickness of the white PI film layer 101 is 5-75 μm; preferably 12.5-50 μm. The thickness of the yellow PI film layer 102 is 5-75 μm; preferably 12.5-50 μm. The thickness of the first adhesive layer 103 is 5-50 μm; preferably 10-25 μm. The thickness of the second adhesive layer 104 is 5-50 μm; preferably 10-35 μm. The total thickness of the reinforcing plate 100 is ≥3 mil. The reinforcing plate can be a single or multiple layers formed by coating and curing one layer at a time or by curing multiple layers. Multiple coatings are beneficial to reducing surface defects, and multiple layers are beneficial to changing the composition balance and mechanical properties.

[0027] The first adhesive layer 103 is an epoxy adhesive layer containing white filler. The epoxy adhesive layer containing white filler provides a white interface, enhances adhesion, and improves light blocking.

[0028] The function of the first adhesive layer: 1. Main bonding: Bonds white opaque PI to high-temperature resistant yellow PI, adaptable to the interface bonding of two different modified PIs, with high temperature resistance and strong adhesion; 2. Excellent resistance to yellowing: When combined with a white PI system, it is not prone to discoloration under long-term high temperature and ultraviolet environment, ensuring the consistency of overall appearance and light blocking; the white filler continues the light blocking effect of the upper white PI, eliminates light transmission gaps between layers, and further improves the overall light blocking rate; 3. Interface buffer: Flexible resin system to alleviate the material stress difference between white PI and yellow PI and avoid interlayer warping.

[0029] This adhesive layer is halogen-free, polyurethane-free, has a glass transition temperature of 40–100℃, a 180° peel strength ≥1.0N / mm, provides light shielding, is heat resistant, and has strong adhesion.

[0030] The white filler is at least two of rutile titanium dioxide, precipitated barium sulfate, and fine talc; the amount of white filler added is 15~25wt%. Rutile titanium dioxide is the main light-shielding component, precipitated barium sulfate improves the density and insulation of the adhesive layer, and fine talc improves the flexibility of the adhesive layer. The three fillers have a synergistic effect.

[0031] The amount of filler added should be strictly controlled between 15 and 25 wt%. If the amount added is too low, it will not be able to achieve auxiliary light blocking, and if the amount added is too high, it will lead to an increase in the viscosity of the adhesive layer, difficulty in coating, and a decrease in the bonding strength.

[0032] This design is not simply about color matching, but rather a customized solution to address two major pain points in two-color composite structures: light leakage between layers and interfacial stress. On the one hand, it continues the light-blocking effect of white PI to eliminate light transmission through the gaps between layers; on the other hand, it improves the toughness of the adhesive layer to alleviate the material stress difference between white PI and yellow PI and reduce warping of the composite board.

[0033] The second adhesive layer 104 is an epoxy adhesive layer. The epoxy adhesive layer connects the two yellow PI layers, providing stress buffer and solving the problems of high-temperature delamination and warping.

[0034] The second adhesive layer 104 has an epoxy value of 0.4 to 0.6 eq / 100g. It has a high crosslinking density (GEL > 90%), excellent high temperature resistance, creep resistance, and structural strength. It is specifically designed for bonding two layers of high-temperature resistant PI of the same material. It is not easy to soften or slip in reflow soldering or high-temperature operating environments, thus improving the structural stability and process resistance of the entire reinforcing plate.

[0035] The white PI film layer 101 is a polyimide layer containing rutile titanium dioxide and zinc oxide. Rutile titanium dioxide is the main light-shielding pigment, ensuring high whiteness and high hiding power of the film. A trace amount of zinc oxide forms a synergistic system with the titanium dioxide, filling the gaps between fillers to improve film density and achieving full-band UV absorption, thus inhibiting oxidative yellowing of the PI matrix under high temperature and UV conditions. The combined use of these two fillers overcomes the shortcomings of single titanium dioxide, such as poor yellowing resistance and strong reflectivity, while avoiding the problems of decreased insulation and mechanical properties caused by high zinc oxide content. This allows the white PI layer to possess comprehensive properties including high light shielding, yellowing resistance, low glare, and high strength.

[0036] The amount of rutile titanium dioxide added is 3-8 wt%, and the amount of zinc oxide added is 0.5-1.5 wt%.

[0037] The yellow PI film layer 102 is a polyimide layer with a temperature resistance rating of ≥280℃, a glass transition temperature of ≥300℃, a tensile strength of ≥200MPa, an elongation at break of ≥30%, and a CTE of 10-23ppm / ℃.

[0038] The reinforcing plate also includes an outer adhesive layer 105 and a release layer 106, wherein the outer adhesive layer is formed on the other side of the yellow PI film layer and the release layer is formed on the other side of the adhesive layer.

[0039] A method for preparing a multilayer dual-color PI composite reinforcing plate includes the following steps: S1. After coating a yellow PI film with a second adhesive layer, place it in an oven to dry, and then press it with another yellow PI film using a hot roller to obtain semi-finished product 1; or continue to coat the yellow PI film with a second adhesive layer, press semi-finished product 1 to obtain semi-finished product 2; repeat this step n times (n=1, 2, ...). S2. After coating the white PI film with the first adhesive layer, place it in an oven to heat and dry, and then press it with the semi-finished product 1 / semi-finished product 2 obtained in S1 using a hot roller. S3. The semi-finished product obtained in S2 is cured at a high temperature of 160-180℃ to obtain the two-color composite film. Figure 1 ); S4. Apply an outer layer adhesive to the surface of the yellow PI film of the two-color composite film obtained in S3, and then bond the release layer to the outer layer adhesive to obtain a white reinforcing plate. Figure 2 ).

[0040] Comparative Examples 1, 2, and 3 are commercially available yellow composite film / reinforcing plate products of different specifications from Kunshan Yasen Electronic Materials Co., Ltd. The outermost layer of the reinforcing plate is commercially available yellow polyimide, while the outermost layer of the examples is white polyimide. Table 1 shows the specific stacked structures of the embodiments and comparative examples of the present invention.

[0041] Table 1 The relevant physical property tests of the embodiments and comparative examples of the present invention are shown in Table 2.

[0042] Test method: 1. Gloss test method: Prepare a sample measuring 25*25cm. Measure the gloss using a gloss meter along the longitudinal direction (MD direction) of the sample, and read the value at 60°. Gloss test on a white polyimide surface (example).

[0043] Commonly used inspection standards are found in ASTM D523.

[0044] 2. L / a / b value test: Standard test samples were prepared, and measurements were taken on the samples using a spectrophotometer. The L / a / b values ​​were then recorded as measured values. The L / a / b value was tested on the white polyimide surface (example).

[0045] Commonly used inspection standards are found in ASTM E 308.

[0046] 3. Flatness test method: The reinforcing plate was cut into 25cm×25cm sizes and pressed onto a 74.5±1um adhesive double-sided flexible copper foil substrate at 180℃. It was then cured at 160℃. The samples of each embodiment and the control sample were placed on a smooth surface and left to stand for 20 minutes. The warping height of the four corners was measured to perform a flatness test.

[0047] Table 2 As shown in Table 2, the relevant performance of the embodiments, especially the whiteness of the appearance, remained above 91 (≥85) and ΔL≤1.5 after rigorous testing during the high-temperature process, with no obvious visual difference. After high-temperature pressing and curing, and standing for 20 minutes to release thermal stress, the curling height was ≤1cm, indicating a super-flat reinforcing plate. The overall performance of the embodiments of the present invention is significantly better than that of the comparative examples.

[0048] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A multilayer dual-color PI composite reinforcing plate, characterized in that: From top to bottom, it includes at least one white PI film layer and at least two yellow PI film layers. A first adhesive layer is provided between the white PI film layer and the yellow PI film layer, and a second adhesive layer is provided between adjacent yellow PI film layers. The thickness of the white PI film layer is 5-75 μm; The thickness of the yellow PI film layer is 5-75 μm; The thickness of the first adhesive layer is 5-50 μm; The thickness of the second adhesive layer is 5-50 μm; The total thickness of the reinforcing plate is ≥3mil.

2. The multilayer dual-color PI composite reinforcing plate according to claim 1, characterized in that: The first adhesive layer is an epoxy adhesive layer containing white filler.

3. The multilayer dual-color PI composite reinforcing plate according to claim 2, characterized in that: The white filler is at least two of rutile titanium dioxide, precipitated barium sulfate, and fine talc; the amount of white filler added is 15~25wt%.

4. The multilayer dual-color PI composite reinforcing plate according to claim 1, characterized in that: The second adhesive layer is an epoxy adhesive layer.

5. The multilayer dual-color PI composite reinforcing plate according to claim 1, characterized in that: The epoxy value of the second adhesive layer is 0.4 to 0.6 eq / 100g.

6. The multilayer dual-color PI composite reinforcing plate according to claim 1, characterized in that: The white PI film layer is a polyimide layer containing rutile titanium dioxide and zinc oxide.

7. The multilayer dual-color PI composite reinforcing plate according to claim 6, characterized in that: The amount of rutile titanium dioxide added is 3-8 wt%, and the amount of zinc oxide added is 0.5-1.5 wt%.

8. The multilayer dual-color PI composite reinforcing plate according to claim 1, characterized in that: The yellow PI film layer is a polyimide layer with a temperature resistance rating of ≥280℃, a glass transition temperature of ≥300℃, a tensile strength of ≥200MPa, an elongation at break of ≥30%, and a CTE of 10-23ppm / ℃.

9. The multilayer dual-color PI composite reinforcing plate according to claim 1, characterized in that: The reinforcing plate also includes an outer adhesive layer and a release layer, wherein the outer adhesive layer is formed on the other side of the yellow PI film layer and the release layer is formed on the other side of the outer adhesive layer.

10. A method for preparing a multilayer dual-color PI composite reinforcing plate, characterized in that: Includes the following steps: S1. After coating a yellow PI film with a second adhesive layer, place it in an oven to dry, and then press it with another yellow PI film using a hot roller to obtain semi-finished product 1; or continue to coat the yellow PI film with a second adhesive layer, press semi-finished product 1 to obtain semi-finished product 2; repeat this step n times (n=1, 2, ...). S2. After coating the white PI film with the first adhesive layer, place it in an oven to heat and dry, and then press it with the semi-finished product 1 / semi-finished product 2 obtained in S1 using a hot roller. S3. The semi-finished product obtained in S2 is cured at a high temperature of 160-180℃ to obtain a two-color composite film. S4. Apply an outer layer adhesive to the surface of the yellow PI film of the two-color composite film obtained in S3, and then bond the release layer to the outer layer adhesive layer to obtain a white reinforcing plate.

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