Polyimide resin, coating composition, coating, and 3c product cover plate

Abstract

The application relates to the technical field of materials, and discloses a polyimide resin, a coating composition, a coating and a 3C product cover plate. The polyimide resin is obtained by polycondensation of at least one dianhydride monomer and at least one diamine monomer; the diamine monomer is an olefin diamine with aryl groups on side groups; and the dianhydride monomer is a compound shown in formula (I); wherein, in formula (I), R1 and R2 are each independently selected from -H, C 1‑3 alkyl. The polyimide resin provided by the application can be used to prepare a coating suitable for the surface of a 3C product glass fiber cover plate, and the coating can endow the glass fiber surface with a smooth and flat texture, high hardness, scratch resistance and high light transmittance.

Description

Technical Field

[0001] This invention relates to the field of materials technology, specifically to a polyimide resin, a coating composition, a coating, and a cover plate for 3C products. Background Technology

[0002] Fiberglass cover plates differ from glass and ceramic cover plates. Due to their suitable strength, light weight, and high processability, they are widely used in the back covers of 3C products.

[0003] To enhance the aesthetics of 3C products, decorative layers are often added to fiberglass covers. Common decorative methods include spray painting and OMR film lamination. However, these two methods result in poor surface hardness of the cover, making it impossible to achieve a smooth and delicate texture.

[0004] Therefore, in order to improve the surface hardness of fiberglass cover plates, a hardening coating is applied to the surface of the decorative layer. Commonly used hardening coatings include epoxy resin, acrylic ester, and polyurethane resin hardening layers. However, these materials cannot maintain good transparency while improving hardness, which will affect the decorative effect of the fiberglass cover plate surface.

[0005] In the prior art, transparent polyimide is suitable for coating the appearance of fiberglass cover plates due to its good transparency and certain hardness. However, when polyimide is used as an ultra-hard coating, in order to improve its material hardness, the polymer molecular chains are prone to extrusion displacement during the curing process. As the hardness increases, the degree of cross-linking increases, and the internal stress generated is greater, which manifests as poor film leveling effect and coating shrinkage and curling phenomenon, resulting in poor flatness of the cover plate.

[0006] Therefore, there is an urgent need to develop a polyimide resin that combines transparency, hardness, and smoothness to meet the application requirements of fiberglass covers for 3C products. Summary of the Invention

[0007] The purpose of this invention is to solve the problem that the transparency, hardness and surface smoothness of polyimide resin used in the appearance coating of fiberglass cover plates cannot be achieved simultaneously.

[0008] To achieve the above objectives, a first aspect of the present invention provides a polyimide resin formed by polycondensation of at least one dianhydride monomer and at least one diamine monomer;

[0009] The diamine monomer is an olefinic diamine with an aryl side group; the dianhydride monomer is a compound represented by formula (I);

[0010]

[0011] In equation (I), R1 and R2 are each independently selected from -H and C.1-3 Alkyl groups.

[0012] A second aspect of the present invention provides a coating composition comprising a polyimide resin and a photoinitiator; wherein the polyimide resin is the polyimide resin described in the first aspect.

[0013] The content of the photoinitiator is 2-6 parts by weight relative to 100 parts by weight of the polyimide resin.

[0014] A third aspect of the invention provides a coating prepared by applying a coating composition comprising the second aspect.

[0015] A fourth aspect of the present invention provides a cover plate for a 3C product, comprising a substrate layer and a protective layer disposed sequentially from the inside out; the protective layer comprising the coating described in the third aspect.

[0016] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects:

[0017] (1) The polyimide resin provided by the present invention is formed by the condensation polymerization of a dianhydride monomer and a diamine monomer with a specific structure, so that the polyimide molecular chain has a bicyclic [2.2.2]octene structure and a large-volume side double bond containing aryl groups. In this way, the bicyclic [2.2.2]octene structure can change the conjugated characteristics of the polyimide molecular chain, thereby inhibiting the movement of electron cloud and improving the flexibility of the polyimide molecular main chain. The large-volume side group containing aryl groups can weaken the close packing of polymer chains, restrict the movement of the polyimide molecular main chain, and reduce the formation of intermolecular CTC. At the same time, both the main chain and the side chain contain double bonds. The double bonds of the side chain can directly interpenetrate and intertwine near the main chain. The double bond groups of the main chain and the double bond groups of the side chain react with each other at multiple sites, which can form a dense cross-linked network, improve the hardness of the film layer, and reduce the displacement of the main chain and reduce the generation of internal stress. Thus, the polyimide resin has excellent hardness, thermal stability and optical transparency when applied to the glass fiber surface after polymerization.

[0018] (2) The coating provided by the present invention is made of polyimide resin with a specific structure under the action of a photoinitiator. Because the double bonds on the main chain and side chain of the polyimide resin undergo free radical polymerization under the action of the photoinitiator, it forms a dense cross-linked network structure. At the same time, the main chain has a non-rigid structure, which can improve the flexibility of the polyimide molecular chain, improve the crystallization performance of the polyimide main chain, and reduce the overall solubility parameter of the resin molecule. Thus, the coating has good flatness and presents a smooth, delicate, hard, and glass-like texture.

[0019] (3) The coating made of polyimide resin in this invention can be applied to the surface of the glass fiber cover of 3C products. Compared with existing glass cover and ceramic cover, it is lighter, stronger and harder, and has broad application prospects. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] As previously described, a first aspect of the present invention provides a polyimide resin formed by polycondensation of at least one dianhydride monomer and at least one diamine monomer;

[0022] The diamine monomer is an olefinic diamine with an aryl side group; the dianhydride monomer is a compound represented by formula (I);

[0023]

[0024] In equation (I), R1 and R2 are each independently selected from -H and C. 1-3 Alkyl groups.

[0025] It should be noted that in this invention, "C" 1-3 "alkyl" refers to an alkyl group with a total number of carbon atoms of 1-3 (e.g., 1, 2, 3).

[0026] The polyimide resin provided by this invention is formed by the condensation polymerization of a dianhydride monomer with a specific structure and a diamine monomer. The diamine monomer is an olefinic diamine with aryl side groups, and the dianhydride monomer contains a bicyclic [2.2.2]octene structure. Thus, the polyimide chain formed by the condensation polymerization of dianhydride and diamine has a bicyclic [2.2.2]octene structure and large-volume aryl side double bonds. The bicyclic [2.2.2]octene structure can alter the conjugated properties of the polyimide molecular chain, thereby inhibiting electron cloud movement and improving the flexibility of the polyimide molecular backbone. Large-volume side groups can weaken the tight packing of polymer chains, restrict the movement of the polyimide molecular backbone, and reduce the formation of intermolecular CTCs. At the same time, both the backbone and the side chains contain double bonds, and the double bonds of the side chains can directly interweave and intersect near the backbone. The double bond groups of the backbone and the double bond groups of the side chains react with each other at multiple sites, which can form a dense cross-linked network, improve the hardness of the film, and reduce the displacement of the backbone and reduce the generation of internal stress. As a result, the polyimide resin has excellent hardness, thermal stability and optical transparency when applied to the surface of glass fiber after polymerization.

[0027] In some embodiments, the olefin diamine with aryl side groups is selected from at least one of olefin diamines with phenyl side groups, olefin diamines with biphenyl side groups, and olefin diamines with naphthyl side groups. Through inventive research, this invention has discovered that, in this preferred embodiment, introducing bulky phenyl, biphenyl, or naphthyl groups onto the diamine side chain further weakens the tight packing of polymer chains, restricts molecular chain movement, reduces the formation of intermolecular CTCs, and further improves the thermal stability and optical transparency of the polyimide resin after condensation with dianhydride. Simultaneously, the ethylene structure on the diamine side chain can further increase the density of active double bonds in the polyimide. When applied in coating formulations, under the action of an initiator, it can undergo a crosslinking reaction with the bicyclic [2.2.2]octene structure on the polyimide backbone, increasing the crosslinking density and improving the problems of low photosensitivity and long curing time in polyimide resins, further enhancing photosensitivity.

[0028] In some preferred embodiments, the aryl-side olefinic diamine is selected from at least one of 4,4'-diamino-4"(2,3,5,6-tetrafluoro-4-ethylenephenoxy)triphenylmethane, 4,4'-diamino-4"(4-ethylenephenoxy)triphenylmethane, 4,4'-([1,1'-biphenyl]-4-vinyl)bis(2,6-dimethylaniline), and 4,4'-((2,3,5,6-tetrafluoro-4-ethylenephenoxy)phenyl)methylene)bis(2-methylaniline). In this preferred embodiment, the selection of at least one of 4,4'-diamino-4"(2,3,5,6-tetrafluoro-4-ethylenephenoxy)triphenylmethane, 4,4'-diamino-4"(4-ethylenephenoxy)triphenylmethane, 4,4'-([1,1'-biphenyl]-4-vinyl)bis(2,6-dimethylaniline), and 4,4'-((2,3,5,6-tetrafluoro-4-ethylenephenoxy)phenyl)methylene)bis(2-methylaniline) is chosen from considerations of economy and ease of acquisition.

[0029] In some embodiments, in formula (I), R1 and R2 are each independently selected from -H and -CH3.

[0030] In some preferred embodiments, in formula (I), R1 and R2 are both -H and / or both R1 and R2 are -CH3. Through inventive research, this invention has discovered that, in some specific embodiments, R1 and R2, independently selected from -H and -CH3, which are connected to the bicyclic [2.2.2]octene structure, can further alter the conjugated properties of the polyimide molecular chain, thereby suppressing electron cloud movement and achieving a transparent effect. On the other hand, it can prevent the polyimide molecular chain from becoming excessively twisted, maintaining its transparency while improving the problems of low elastic modulus and low surface hardness of traditional transparent polyimides. Simultaneously, when applied in coating formulations, it can be better initiated by the initiator to undergo cross-linking reactions, better improving the degree of curing. It can also undergo cross-linking reactions with the double bonds on the polyimide side chains under photo-initiated conditions, providing more photocurable active sites, thereby further improving the degree of curing and increasing the coating hardness.

[0031] According to a preferred embodiment, the molar ratio of the dianhydride monomer to the diamine monomer is 1:0.905-0.955. This preferred embodiment ensures complete monomer reaction while preventing excessive cross-linking during the reaction, which could lead to large molecular weight and reduced solubility.

[0032] In some embodiments, the number-average molecular weight Mn of the polyimide resin is 12,000-30,000, preferably 12,000-20,000. In this preferred embodiment, controlling the number-average molecular weight Mn of the polyimide resin to 12,000-30,000 is beneficial for controlling the solubility of the polyimide resin, thereby facilitating the control of subsequent free radical reactions under the action of the photoinitiator, and thus further adjusting the coating hardness.

[0033] The present invention also provides, by way of example, a method for preparing the aforementioned polyimide resin, comprising:

[0034] In the presence of a catalyst, a dehydrating agent, and solvent I, dianhydride monomers and diamine monomers are subjected to a one-step polycondensation reaction, and the product is then dried to obtain the polyimide resin.

[0035] The amount of catalyst is 2-9 parts by weight relative to 100 parts by weight of the dianhydride monomer, the amount of dehydrating agent is 20-40 parts by weight, the amount of solvent I is 100-120 parts by weight, and the molar ratio of the amount of diamine monomer to the amount of dianhydride monomer is (0.905-0.955):1.

[0036] In some embodiments, the catalyst is selected from isoquinoline; the dehydrating agent is selected from toluene; and the solvent I is selected from resorcinol.

[0037] As previously described, a second aspect of the present invention provides a coating composition comprising a polyimide resin and a photoinitiator; wherein the polyimide resin is the polyimide resin described in the first aspect above.

[0038] The content of the photoinitiator is 2-6 parts by weight relative to 100 parts by weight of the polyimide resin.

[0039] In some preferred embodiments, the photoinitiator is an acylphosphine oxide initiator or a benzoylcarbamate initiator. Preferably, the photoinitiator is selected from at least one of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and diethyl 2,4,6-trimethylbenzoyl acid. In this preferred embodiment, the acylphosphine radicals and benzoyl radicals generated by thermal decomposition are more stable, less prone to yellowing, and can rapidly decompose even when the polyimide resin contains uniminated carboxyl groups, thus improving the initiation efficiency.

[0040] In some embodiments, the coating composition further includes a silane coupling agent;

[0041] The content of the silane coupling agent is 2-10 parts by weight relative to 100 parts by weight of the polyimide resin.

[0042] In this preferred embodiment, the addition of the silane coupling agent can improve the surface properties between interfaces and enhance the operability of the coating composition during the dispensing and roller coating process.

[0043] In some embodiments, the coupling agent is selected from at least one of γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane. In this preferred embodiment, these silane coupling agents also contain reactive groups, resulting in better compatibility and the ability to participate in subsequent reactions without causing pollution.

[0044] As previously described, a third aspect of the present invention provides a coating prepared by applying a coating composition comprising the coating composition described in the second aspect.

[0045] The coating provided by this invention is made from a polyimide resin with a specific structure under the action of a photoinitiator. Because the double bonds on the main chain and side chains of the polyimide resin undergo free radical polymerization under the action of the photoinitiator, it forms a dense cross-linked network structure. At the same time, the main chain has a non-rigid structure, which can improve the flexibility of the polyimide molecular chain, improve the crystallization performance of the polyimide main chain, and reduce the overall solubility parameter of the resin molecule. As a result, the coating has good smoothness and presents a smooth, delicate, hard, and glass-like texture.

[0046] In some embodiments, the coating has a hardness ≥7H and a visible light transmittance ≥91.5%.

[0047] In some embodiments, the method for preparing the coating includes: mixing and curing material I containing polyimide resin, coupling agent and photoinitiator in the presence of solvent II.

[0048] In some preferred embodiments, solvent II is selected from at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and tetrahydrofuran. The inventors have found that excessively rapid solvent evaporation can disrupt the uniformity of the system's curing process, leading to differences in local composition and physical properties, and causing defects in flow and curing, such as bubbles and surface unevenness due to poor leveling. In this preferred embodiment, the solvent volatility and evaporation temperature are beneficial for controlling the leveling performance and thickness uniformity of the coating, reducing the formation of pores.

[0049] In some embodiments, the amount of solvent II may be 80-120 parts by weight relative to 100 parts by weight of polyimide resin.

[0050] As previously described, a fourth aspect of the present invention provides a cover plate for a 3C product, comprising a substrate layer and a protective layer disposed sequentially from the inside out; the protective layer comprising the coating described in the third aspect.

[0051] In some embodiments, the substrate layer includes a fiberglass layer, and the protective layer has a thickness of 25-40 μm.

[0052] The 3C product cover provided by this invention is lighter, stronger, and harder than existing glass and ceramic covers, and has broad application prospects.

[0053] In some embodiments, the step of setting the protective layer on the substrate layer includes:

[0054] (1) Mix material I containing solvent II, polyimide resin, coupling agent and photoinitiator, and apply it to the starting section of the substrate surface through an automatic dotting machine;

[0055] (2) The substrate with material I applied to it is fed into a rolling mechanism for rolling coating, so that the average thickness of material I applied to the substrate is 25-40 μm; then it is baked at 100-140℃ for 8-12 min, and material I forms a pre-cured coating on the surface of the substrate.

[0056] (3) The substrate with the pre-cured coating is subjected to ultraviolet irradiation to obtain the coating.

[0057] According to one specific embodiment, the coating has a hardness of not less than 7H, a friction resistance of not less than 2000 cycles, and a light transmittance of not less than 91.5%.

[0058] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials used are commercially available products.

[0059] raw material:

[0060] Bicyclic [2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride: The structural formula is: Both R1 and R2 are -H; CAS number: 1719-83-1;

[0061] Bicyclic [2.2.2]oct-7-en-7,8-dimethyl-2,3,5,6-tetracarboxylic acid dianhydride: The structural formula is: R1 and R2 are both -CH3; CAS number: 32251-35-7;

[0062] 1,2,3,4-Cyclobutanetetramethyl dianhydride: CAS number: 4415-87-6;

[0063] 4,4'-Diamino-4"(2,3,5,6-tetrafluoro-4-vinylphenoxy)triphenylmethane: CAS No.: 2495164-60-6;

[0064] 4,4'-((2,3,5,6-tetrafluoro-4-ethylenephenoxy)phenyl)methylene)bis(2-methylaniline): CAS No.: 3075472-43-1;

[0065] 2,2'-Bis(trifluoromethyl)benzyldiamine: CAS No.: 341-58-2;

[0066] Polyurethane-type UV-curable superhard resin: Grade AH-1502E, purchased from Anhui Dawei Huatai New Materials Co., Ltd.

[0067] Epoxy-type UV-curable superhard resin: grade SJ-509P, purchased from Guangdong Shanjin New Materials Co., Ltd.

[0068] Polyacrylic acid type light-curing superhard resin: grade SJ-2001A, purchased from Guangdong Shanjin New Materials Co., Ltd.;

[0069] Preparation Example 1

[0070] This preparation example illustrates that the polyimide resin of the present invention is prepared according to the formulation in Table 1 and the method described below:

[0071] According to the mass fraction, dianhydride monomer, diamine monomer, isoquinoline, toluene, and resorcinol were stirred and mixed at 30°C for 4 hours, and then reacted at 150°C and 180°C for 3 hours and 8 hours respectively. During the process, a separation device was used to separate the water and toluene azeotrope from the reaction solution. The obtained product was washed with methanol 5 times and then dried (130°C, 10 hours) to obtain the polyimide resin Z1.

[0072] Unless otherwise specified, the remaining preparation examples were carried out using a similar process to that of Preparation Example 1. The difference is that the formulations used in each preparation example are different, as detailed in Table 1 (Note: Parameters not listed in Table 1 are the same as those in Preparation Example 1).

[0073] Table 1

[0074]

[0075] Example 1

[0076] This embodiment illustrates that the coating provided by the present invention is prepared according to the formula in Table 2 and the method described below:

[0077] (1) Mix material I containing solvent II, polyimide resin, coupling agent and photoinitiator, and apply it to the starting section of the substrate surface through an automatic dotting machine;

[0078] (2) The substrate with material I applied to it is fed into a rolling mechanism for rolling coating, so that the average thickness of material I applied to the substrate is 30 μm; then it is baked at 120°C for 10 min, and material I forms a pre-cured coating on the surface of the substrate.

[0079] (3) The substrate with the pre-cured coating is subjected to ultraviolet irradiation (energy of 1000MJ) to obtain the coating;

[0080] The substrate is an epoxy fiberglass board.

[0081] Unless otherwise specified, the remaining examples follow a similar process to Example 1, except that the formulations used in each example are different, as detailed in Table 2 (Note: Parameters not listed in Table 2 are the same as those in Example 1).

[0082] Table 2

[0083]

[0084] Table 2 (continued)

[0085]

[0086]

[0087] The coating was subjected to performance testing, and the test items and methods are as follows:

[0088] The test method for pencil hardness is as follows: refer to the test method of the national standard GB / T 6739-2022 "Determination of Hardness of Paint and Varnish Film by Pencil Method", and use the test conditions of (1±0.05) kg pressure and 1 mm / s.

[0089] Test method for steel wool friction: Refer to standard ASTM F2496-05 "Standard implementation procedure for determination of scratch hardness and scratch viscosity of printed matter and coatings", use a load of (1±0.05) kg, a speed of 40-50 reciprocating / minute, and a stroke of about 40 mm to conduct the friction test;

[0090] Test method for light transmittance: The test method shall be determined in accordance with the national standard GB / T 2410-2008 "Determination of light transmittance and haze of transparent plastics";

[0091] Roughness test method: The roughness is determined according to the test method of GB / T 14234-1993 "Surface Roughness of Plastic Parts";

[0092] Flatness test method: The flatness is determined according to the test method of the national standard GB / T 43059-2023 "flatness control requirements for printed circuit boards and printed circuit board assemblies";

[0093] The test method for the cross-cut test is as follows: Refer to the test method of GB / T 9286-2021 "Paints and Varnishes Cross-cut Test". Immerse the coating in hot water at 85℃ for 30 minutes and then conduct the cross-cut test. Judge the cross-cut grade and record it.

[0094] The test results are shown in Table 3.

[0095] Table 3

[0096]

[0097] As can be seen from the results in Table 3, the polyamide resin provided by the present invention can be used to prepare a special ultra-hard layer suitable for the surface of fiberglass cover plates, giving the fiberglass surface a smooth and flat texture and excellent properties such as high hardness, scratch resistance, and high light transmittance.

[0098] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polyimide resin, characterized in that, The polyimide resin is formed by polycondensation of at least one dianhydride monomer and at least one diamine monomer; The diamine monomer is an olefinic diamine with an aryl side group; the dianhydride monomer is a compound represented by formula (I); Equation (I), In equation (I), R1 and R2 are each independently selected from -H and C. 1-3 Alkyl groups; The aryl-containing olefinic diamine is selected from at least one of 4,4'-diamino-4''(2,3,5,6-tetrafluoro-4-ethylenephenoxy)triphenylmethane, 4,4'-diamino-4''(4-ethylenephenoxy)triphenylmethane, 4,4'-([1,1'-biphenyl]-4-vinyl)bis(2,6-dimethylaniline), and 4,4'-((2,3,5,6-tetrafluoro-4-ethylenephenoxy)phenyl)methylene)bis(2-methylaniline); The molar ratio of the dianhydride monomer to the diamine monomer is 1:0.905-0.

955.

2. The polyimide resin according to claim 1, characterized in that, In equation (I), R1 and R2 are each independently selected from -H and -CH3.

3. The polyimide resin according to claim 1, characterized in that, The number-average molecular weight (Mn) of the polyimide resin is 12,000-30,000.

4. A coating composition, characterized in that, The coating composition comprises a polyimide resin and a photoinitiator; the polyimide resin is the polyimide resin according to any one of claims 1-3; The content of the photoinitiator is 2-6 parts by weight relative to 100 parts by weight of the polyimide resin.

5. The coating composition according to claim 4, characterized in that, The photoinitiator is an acylphosphine oxide initiator or a benzoyl carboxylate initiator.

6. The coating composition according to claim 5, characterized in that, The photoinitiator is selected from at least one of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and diethyl 2,4,6-trimethylbenzoyl acid.

7. The coating composition according to claim 4, characterized in that, The coating composition further includes a silane coupling agent, wherein the content of the silane coupling agent is 2-10 parts by weight relative to 100 parts by weight of the polyimide resin.

8. The coating composition according to claim 7, characterized in that, The silane coupling agent is selected from at least one of γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane.

9. A coating, characterized in that, The coating is prepared by using a coating composition comprising any one of claims 4-8.

10. The coating according to claim 9, characterized in that, The coating has a hardness ≥7H and a visible light transmittance ≥91.5%.

11. A cover plate for 3C products, characterized in that, The 3C product cover plate includes a substrate layer and a protective layer arranged sequentially from the inside out, wherein the protective layer includes the coating as described in claim 9.

12. The 3C product cover plate according to claim 11, characterized in that, The substrate layer includes a fiberglass board, and the protective layer has a thickness of 25-40 μm.

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