CN115109223B

CN115109223B - Self-repairing and surface patterning cross-linked polyurethane elastomer

Info

Publication number: CN115109223B
Application number: CN202210833917.4A
Authority: CN
Inventors: 徐军; 史家昕; 郭宝华
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2022-07-14
Filing date: 2022-07-14
Publication date: 2023-08-25
Anticipated expiration: 2042-07-14
Also published as: CN115109223A

Abstract

The invention relates to a self-repairing surface patterning cross-linked polyurethane elastomer, a preparation method of the surface patterning cross-linked polyurethane elastomer, a circuit substrate comprising the surface patterning cross-linked polyurethane elastomer, a flexible circuit board and a manufacturing method of the flexible circuit board. The polyurethane elastomer has excellent mechanical properties, can realize self-repairing by heating and can laminate a patterned conductive layer. The flexible circuit board has excellent mechanical properties, can realize self-repair of mechanical and conductive properties by heating, has excellent shedding resistance of the conductive layer, and has high precision of the conductive layer.

Description

Self-repairing and surface patterning cross-linked polyurethane elastomer

Technical Field

The invention belongs to the technical field of flexible electronics, and particularly relates to a self-repairing and surface patterning crosslinked polyurethane elastomer.

Background

The flexible polymer elastomer is widely applied to the technical field of flexible electronics such as wearable equipment, soft robots, sensors and the like. The incorporation of high strength, high elasticity, conductivity, self-healing, etc. into a polymer is a great challenge in the field of flexible electronics. The polymer elastomer commonly used for the flexible substrate at present has poor mechanical properties, high printed circuit difficulty and poor stability of a conductive layer, and limits the application of related devices.

Because the flexible substrate is repeatedly bent for a plurality of times in use, damage is easy to occur, and if the self-healing performance is introduced into the flexible substrate, the service life of the flexible electronic device can be greatly prolonged. Accordingly, the development of high strength, self-healing, flexible substrates that can be patterned into printed circuits has become a necessary trend and need.

Patent document 1 discloses a preparation method of a self-healing polyurethane stretchable electrode and application of the self-healing polyurethane stretchable electrode in a flexible heater, which comprises the steps of firstly preparing a self-healing polyurethane elastomer by taking polytetrahydrofuran as a soft segment, isophorone diisocyanate as a hard segment and bis (2-hydroxyethyl) disulfide as a chain extender, coating an uncured self-healing polyurethane elastomer on a silver nanowire conductive layer on a PET substrate, and removing the bottom PET substrate after the self-healing polyurethane elastomer is cured to form the stretchable electrode with the silver nanowire layer embedded in the polyurethane surface.

Patent document 2 discloses a bisphenol-containing self-repairing thermoreversible crosslinked polyurethane obtained by mixing a bisphenol compound, a polyisocyanate compound, a polyol compound and a catalyst and curing.

Patent document 3 discloses a thermoreversibly crosslinked polyurethane obtained by mixing a dihydroxybenzophenone compound, a polyisocyanate compound, a polyol compound, and a catalyst and curing.

Citation literature:

patent document 1: CN113823440a;

patent document 2: CN110305293a;

patent document 3: CN113185644 a.

Disclosure of Invention

Problems to be solved by the invention

The method of patent document 1 casts an uncured polymer on a conductive layer for attachment, which does not obtain polyurethane or flexible substrate having a patterned transfer property that can be used for a printed circuit. Further, the polyurethane of patent document 1 is a linear structure, lacks the weatherability and stability possessed by a crosslinked structure, and is limited in creep resistance and rebound resilience.

The polyurethanes of patent document 2 and patent document 3, although having self-healing properties, also do not mention polyurethane elastomers useful for flexible circuit boards having patterning transfer properties.

Accordingly, there remains a need to develop a polyurethane elastomer having patterning transfer properties that can be used in flexible circuit boards, as well as flexible substrates.

Solution for solving the problem

The present inventors have conducted intensive studies to solve the above-mentioned problems, and have found that a portion of a surface of a polyurethane elastomer having a dynamic cross-linked structure between molecular chains, which has a dynamic cross-linked structure but does not have a permanent chemical cross-linked structure, can be laminated with a conductive layer to realize a patterned printed circuit by patterning the surface of the polyurethane elastomer to form a patterned surface.

Specifically, the present invention solves the problems of the present invention by the following means.

[1] A surface-patterned crosslinked polyurethane elastomer characterized by comprising a polyurethane having a dynamic crosslinked structure, and in a partial region of the surface thereof, the polyurethane having a dynamic crosslinked structure further having a permanent chemical crosslinked structure, the polyurethane having a dynamic crosslinked structure being obtained by polymerization of a raw material composition comprising a benzophenone compound, an isocyanate compound, and a polyol, the benzophenone compound comprising a compound having a phenolic hydroxyl group or an anilino group, and the isocyanate compound comprising a compound having 3 or more isocyanate groups.

[2] The surface-patterned crosslinked polyurethane elastomer according to [1], wherein, in the raw material composition, a benzophenone compound is present in mole: isocyanate compound: polyol = 1: (0.8-3): (0.3 to 3), preferably 1: (1-2.5): (0.5-2).

[3] The surface-patterned crosslinked polyurethane elastomer according to [1] or [2], wherein the benzophenone compound is one or more selected from the group consisting of 4,4 '-dihydroxybenzophenone, 2, 4-dihydroxybenzophenone, 4' -diaminobenzophenone and 2, 4-diaminobenzophenone.

[4] The surface-patterned crosslinked polyurethane elastomer according to [1] or [2], wherein the isocyanate-based compound further comprises a compound having 2 isocyanate groups;

preferably, the isocyanate compound has the following structure:

wherein R' is a hydrocarbon group having 2 to 30 carbon atoms, and n is an integer of 2 or more;

more preferably, the compound having 2 isocyanate groups is one or more selected from aliphatic diisocyanates, preferably one or more selected from hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, cyclohexylhexamethylene diisocyanate, tetramethylm-xylylene diisocyanate, 2, 4-trimethylhexamethylene diisocyanate, methylcyclohexyl diisocyanate; the compound having 3 or more isocyanate groups is a polymer of diisocyanate, preferably a trimer, and more preferably contains one or more selected from hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, dicyclohexylmethane diisocyanate trimer.

[5] The surface patterned crosslinked polyurethane elastomer according to [1] or [2], characterized in that the polyol is a polymer polyol, preferably having the following structure:

wherein R' is a polyester or polyether chain segment, and m is an integer of more than 2;

preferably, the polyol is one or more selected from the group consisting of polycaprolactone polyol and polybutylene adipate polyol.

[6] The surface patterned crosslinked polyurethane elastomer according to [1] or [2], characterized in that the raw material composition further comprises a catalyst; the catalyst is preferably an organic base, more preferably one or more selected from the group consisting of triethylenediamine and bis (dimethylaminoethyl) ether; in the raw material composition, the molar ratio of the diphenyl ketone compound to the catalyst is 1: (0.0001 to 0.01), preferably 1: (0.0005 to 0.01).

[7] The process for producing a surface-patterned crosslinked polyurethane elastomer according to any one of [1] to [6], characterized by comprising the steps of:

(1) Polymerizing a raw material composition comprising the benzophenone compound, the isocyanate compound, the polyol and an optional catalyst to obtain polyurethane with a dynamic cross-linking structure;

(2) And irradiating ultraviolet light to the polyurethane with the dynamic cross-linking structure through a patterned mask.

[8] The process according to [7], wherein the polymerization reaction temperature is 40 to 120℃and the reaction time is 6 to 48 hours; the ultraviolet light wavelength is 300-500 nm, preferably 365nm; the irradiation time of ultraviolet light is 5-60 minutes.

[9] A circuit board comprising the surface-patterned crosslinked polyurethane elastomer of any one of [1] to [6 ].

[10] A flexible circuit board comprising the circuit board of [9], and a conductive layer laminated on the circuit board; preferably, the conductive layer comprises one or more conductive fillers selected from metal nanowires, carbon nanotubes, graphene, liquid metals, metal particles.

[11] The method of manufacturing a flexible circuit board according to [10], characterized by comprising the steps of:

preparing a surface-patterned crosslinked polyurethane elastomer by the preparation method described in [7] or [8 ];

and laminating the conductive layer on the surface of the obtained surface patterned crosslinked polyurethane elastomer.

[12] The production method according to [11], characterized in that the conductive layer is laminated by a spray coating or transfer printing method; for example, a filter film deposited with a conductive filler is coated on the surface of the resulting surface-patterned crosslinked polyurethane elastomer, and the resulting laminate is heated, cooled, and then the filter film is removed to laminate the conductive layer

ADVANTAGEOUS EFFECTS OF INVENTION

The polyurethane elastomer has excellent mechanical properties, can realize self-repairing by heating and can laminate a patterned conductive layer.

The flexible circuit board has excellent mechanical properties, can realize self-repair of mechanical and conductive properties by heating, and has excellent shedding resistance and high precision.

Drawings

Fig. 1 (a) to (c) are experimental photographs of circuit tests of the flexible circuit board 1 obtained in example 1;

FIG. 2 is a graph showing the result of the test of the influence of the deformation of the flexible circuit board 1 on the conductivity obtained in example 1, wherein the plot is an enlarged display of the resistance data below 120% deformation rate;

FIG. 3 (a) is a photomicrograph of a 360 mesh stainless steel screen used in example 3. Fig. 3 (b) is a photomicrograph of the flexible circuit board 3 obtained in example 3.

Detailed Description

The following describes the present invention in detail. The following description of the technical features is based on the representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples.

< terms and definitions >

In the present specification, the "dynamic cross-linked structure" means that chemical bonds forming a cross-linked structure between polymer molecular chains can be dynamically broken and restored with changes in external conditions. For example, in a first condition, the polymer molecular chains are linked by chemical bonds to form a crosslinked structure, while in a second condition, the linked chemical bonds are broken, and when the first condition is restored, the broken chemical bonds are reformed.

In the present specification, "permanent chemical crosslinking" means that chemical bonds forming a crosslinked structure between polymer molecular chains cannot be dynamically broken and restored. For example, when the external conditions are changed such that the chemical bonds forming the crosslinked structure are broken, the broken chemical bonds cannot be reformed even if the external conditions are recovered.

In the present specification, the "circuit substrate" refers to a base material for manufacturing a circuit board on which a circuit pattern has not been formed.

In this specification, "patterned" means that the surface being described has portions of different structure or composition, and that the portions are arranged in a particular manner to form the desired pattern; by "patterned cross-linking" is meant that the surface is described as having portions of differing cross-linking patterns or cross-linking structures that are arranged in a particular manner to form the desired pattern.

In this specification, the term "alkyl" includes straight, branched or cyclic alkyl groups unless explicitly stated otherwise.

In the present specification, the numerical range indicated by the term "numerical value a to numerical value B" means a range including the end point numerical value A, B.

In the present specification, a numerical range indicated by "above" or "below" is a numerical range including the present number.

In the present specification, the meaning of "can" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

In this specification, the use of "optionally" or "optional" means that certain substances, components, steps of performing, conditions of applying, etc. may or may not be used.

In the present specification, unit names used are international standard unit names, and "%" used represent weight or mass% unless otherwise specified.

Reference in the specification to "a preferred embodiment," "an embodiment," and the like, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the elements may be combined in any suitable manner in the various embodiments.

< polyurethane elastomer >

An object of the present invention is to provide a surface-patterned crosslinked polyurethane elastomer (also simply referred to as "the polyurethane elastomer of the present invention") comprising a polyurethane having a dynamic crosslinked structure, and in a partial region of its surface, the polyurethane having a dynamic crosslinked structure further having a permanent chemical crosslinked structure, the polyurethane having a dynamic crosslinked structure being obtained by polymerization of a raw material composition comprising a benzophenone compound, an isocyanate compound and a polyol, the benzophenone compound comprising a compound having a phenolic hydroxyl group or an anilino group, the isocyanate compound comprising a compound having 3 or more isocyanate groups.

The polyurethane elastomer has a dynamic cross-linking structure, so that the polyurethane elastomer has self-repairing performance, and can realize self-repairing under the heating condition. The self-healing temperature, i.e., the heating temperature of the polyurethane elastomer of the present invention is 60℃or higher, preferably 70℃or higher. The heating temperature is 200 ℃ or lower, for example 180 ℃ or lower, and 160 ℃ or lower, for example, from the viewpoint of avoiding thermal degradation of the polyurethane elastomer due to excessive temperature and saving energy. The time required for self-repairing, i.e., the heating time, of the polyurethane elastomer of the present invention is 0.5 to 30 hours, for example, 1 to 20 hours, 1.5 to 16 hours. Too short a time, the self-repairing may be incomplete, the mechanical property and the electrical property of the repaired polyurethane elastomer are affected, the energy source may be wasted if the time is too long, and the too long heating time has the risk of thermal degradation.

The polyurethane elastomer of the present invention also has a permanent chemical crosslinking structure in a partial region of the surface thereof, for example, a permanent chemical crosslinking structure formed by a benzophenone group under irradiation of ultraviolet light. The patterned surface of the polyurethane elastomer includes a portion having a dynamic crosslinking structure but not having a permanent chemical crosslinking structure (hereinafter also simply referred to as a "surface portion having no permanent chemical crosslinking structure") and a portion having both a dynamic crosslinking structure and a permanent chemical crosslinking structure (hereinafter also simply referred to as a "surface portion having a permanent chemical crosslinking structure"). Wherein the surface portion having no permanent chemical cross-linked structure is subsequently capable of embedding the conductive filler, and the surface portion having a permanent chemical cross-linked structure is not capable of embedding the conductive filler, whereby a patterned circuit can be formed on the surface of the polyurethane elastomer. Therefore, the polyurethane elastomer of the present invention may be used for a flexible circuit substrate, or may be directly used as a flexible circuit substrate.

In one embodiment, the starting composition comprises, on a molar basis, a benzophenone compound: isocyanate compound: polyol = 1: (0.8-3): (0.3 to 3), preferably 1: (1-2.5): (0.5-2). The molar ratio within the above range is favorable for preparation of materials and improvement of properties. If the isocyanate content is too low, it will result in difficult curing, if the benzophenone content is too high, it will result in a material with a too high glass transition temperature, and if the polyol content is too high, it will result in a material that is too soft and has a low mechanical strength.

In one embodiment, the benzophenone compound is one or more selected from the group consisting of 4,4 '-dihydroxybenzophenone, 2, 4-dihydroxybenzophenone, 4' -diaminobenzophenone, and 2, 4-diaminobenzophenone.

In one embodiment, the isocyanate-based compound comprises a compound having 3 to 8 isocyanate groups, preferably a compound having 3 to 6 isocyanate groups. Preferably, the isocyanate-based compound comprises a polymer of a diisocyanate, preferably a trimer, for example comprising one or more selected from hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, dicyclohexylmethane diisocyanate trimer.

In one embodiment, the isocyanate-based compounds further include diisocyanate compounds having 2 isocyanate groups. The diisocyanate compound may be one or more selected from aliphatic diisocyanates, preferably one or more selected from hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, cyclohexyldimethylene diisocyanate, tetramethylm-xylylene diisocyanate, 2, 4-trimethylhexamethylene diisocyanate, methylcyclohexyl diisocyanate.

Specifically, the isocyanate compound has the following structure:

wherein, the liquid crystal display device comprises a liquid crystal display device,

r' is a hydrocarbon group having 2 to 30 carbon atoms, which may be an aliphatic or aromatic hydrocarbon group, wherein the aliphatic hydrocarbon group may be a cyclic hydrocarbon group or a chain hydrocarbon group; r' is preferably an aliphatic hydrocarbon group;

n is an integer of 2 or more, preferably 2 to 8, for example 3 to 6.

In one embodiment, the molar ratio of the diisocyanate compound to the compound having 3 or more isocyanate groups in the isocyanate compound is 1:1 to 8:1, preferably 2:1 to 6:1. Too high a proportion of diisocyanate results in poor mechanical strength and resilience of the material. Too low a proportion of diisocyanate compound may result in too high a glass transition temperature of the material and reduced toughness.

In one embodiment, the polyol compound is a polymer polyol, preferably one or more selected from polyester polyols and polyether polyols.

The number average molecular weight of the polyol compound is 200 to 10000, preferably 400 to 5000, more preferably 1000 to 3000.

In one embodiment, the polyol compound has the following structure:

wherein R' is a polyester or polyether segment, m is an integer of 2 or more, for example an integer of 2 to 10, and is, for example, 3, 4, 5 or 6, preferably 2.

The polyester segment may be a segment derived from an aliphatic lactone, a fatty acid dibasic acid, and an aliphatic diol. The polyether segment may be a segment derived from an aliphatic diol.

Preferably, the polyol may be one or more selected from polycaprolactone polyol and polybutylene adipate polyol.

In a preferred embodiment, a catalyst is also included in the feed composition to allow for smooth polymerization. The catalyst is not particularly limited in the present invention, and may be a catalyst known in the art to be suitable for the preparation of polyurethane. Specifically, the catalyst may be an organic base, preferably one or more selected from the group consisting of triethylenediamine and bis (dimethylaminoethyl) ether.

In this embodiment, the molar ratio of benzophenone compound to catalyst in the feed composition is 1: (0.0001 to 0.1), preferably 1: (0.0005 to 0.01).

It is another object of the present invention to provide a process for the preparation of the surface patterned crosslinked polyurethane elastomer of the present invention comprising the steps of:

For the kind and amount of the benzophenone compound, the isocyanate compound, the polyol and the catalyst, see the description of the polyurethane elastomer above.

In one embodiment, the temperature of the polymerization reaction in step (1) is from 40 to 120 ℃, preferably from 50 to 110 ℃; the reaction time of the polymerization reaction is 4 to 48 hours, preferably 6 to 24 hours.

In the step (1), since the reaction between the hydroxyl group or the amino group in the benzophenone compound and the compound having 3 or more isocyanate groups is reversible, a dynamic crosslinked structure is formed.

The polyurethane having a dynamic cross-linked structure obtained in the step (1) may have a desired shape, for example, a sheet shape, and a thickness of 0.01 to 10mm, for example, 0.1 to 8mm.

In one embodiment, the ultraviolet light in step (2) has a wavelength of 300 to 500nm, preferably 365nm; the time for irradiating the ultraviolet light is 5 to 60 minutes, preferably 8 to 30 minutes. In a more specific embodiment, the polyurethane having a dynamic cross-linked structure is irradiated with ultraviolet light in step (2) using an ultraviolet lamp having a power of 10 to 500W, preferably 50 to 200W.

In one embodiment, the patterned mask used in step (2) may have any desired patterned shape, for example, a mask having a shape corresponding to the circuit to be printed (a mask of a preset circuit pattern) may be used.

In the step (2), the patterning mask is only required to be placed between the polyurethane with the dynamic cross-linking structure obtained in the step (1) and an ultraviolet light source. From the aspect of pattern precision, a patterned mask may be placed over the polyurethane having a dynamic cross-linked structure obtained in step (1).

In the step (2), the photo-free radical initiation characteristic of the benzophenone group is utilized to realize the photo-self-crosslinking, so that a permanent chemical crosslinking structure is further formed on the surface part of polyurethane with a dynamic crosslinking structure, which is irradiated by ultraviolet light, and the two different crosslinking structures, namely the dynamic crosslinking structure and the permanent chemical crosslinking structure, are effectively concentrated together.

The invention also correspondingly relates to a flexible circuit substrate comprising a layer formed of the surface-patterned crosslinked polyurethane elastomer of the invention, optionally also comprising layers formed of other materials as desired.

The invention also correspondingly relates to the use of the surface-patterned crosslinked polyurethane elastomer according to the invention for producing flexible circuit substrates or flexible circuit boards.

< Flexible Circuit Board >

Another object of the present invention is to provide a flexible circuit board comprising the circuit substrate of the present invention, and a conductive layer laminated on the circuit substrate.

In one embodiment, the conductive layer has a pattern corresponding to the portion of the polyurethane elastomer surface of the present invention that does not have a permanent chemical cross-linked structure.

In one embodiment, the conductive layer comprises one or more selected from the group consisting of metal nanowires, carbon nanotubes, graphene, liquid metals, metal particles.

In one embodiment, the conductive layer has an areal density of 0.01 to 5mg/cm ² 。

In one embodiment, the line width of the conductive layer pattern is 10 to 5000 μm, for example, 20 to 1000 μm, 30 to 500 μm, 40 to 200 μm, etc.

The invention also correspondingly provides a manufacturing method of the flexible circuit board, which comprises the following steps:

(a) The surface patterned crosslinked polyurethane elastomer of the present invention is prepared by the method described above;

(b) And (3) overlaying a conductive layer on the surface of the obtained surface patterned crosslinked polyurethane elastomer.

In one embodiment, the stacked conductive layers are applied by spraying or transfer printing. In embodiments employing a spray coating process, a liquid containing a conductive filler may be sprayed onto the polyurethane elastomer surface. In particular, spraying may be performed by means of methods conventional in the art. The liquid containing the conductive filler contains water and/or an organic solvent as a medium. The conductive filler is one or more selected from metal nanowires, carbon nanotubes, graphene, liquid metal and metal particles.

In an embodiment employing a transfer method, a surface of a surface-patterned crosslinked polyurethane elastomer is covered with a filter film deposited with a conductive filler, and the resulting laminate is heated and then cooled and then the filter film is removed. In this embodiment, the filter membrane deposited with the conductive filler may be obtained by a conventional method, for example, by filtering a dispersion containing the conductive filler through the filter membrane, thereby depositing the conductive filler onto the filter membrane. The present invention is not limited to the filter membrane, and may be any conventional filter membrane, for example, a common filter paper, a polytetrafluoroethylene filter membrane, or the like.

In step (b), the conductive filler is embedded in the polyurethane elastomer surface by using the tackiness of the portion of the polyurethane elastomer surface that does not have permanent chemical crosslinking, thereby laminating the conductive layer to the polyurethane elastomer surface.

The invention also correspondingly relates to the use of the polyurethane elastomers and flexible circuit boards according to the invention in flexible electro-optical devices, for example in wearable devices, soft robots, brain-computer interfaces, sensors, display devices.

Examples

The invention is further illustrated by the following examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. Further, it is understood that various changes and modifications of the invention will become apparent to those skilled in the art upon reading the description herein, and such equivalents are intended to fall within the scope of the invention as defined by the appended claims.

Among the reagents used in the following examples: 4,4 '-dihydroxybenzophenone, 2, 4-dihydroxybenzophenone, 4' -diaminobenzophenone, 2, 4-diaminobenzophenone are produced as An Naiji reagent; polybutylene adipate diol produced by Jining Hongming chemical industry Co., ltd, molecular weight 1000; hexamethylene diisocyanate trimer manufactured by Wanhua chemical Co., product model HT100; isophorone diisocyanate trimer is produced by Yingchang company under the product model Vestanat T1890E; dicyclohexylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate were purchased from ala Ding Shiji; polycaprolactone diol produced by Jining Hongming chemical industry Co., ltd, molecular weight 2000; triethylene diamine, bis (dimethylaminoethyl) ether were purchased from Sigma-Aldrich reagent.

Example 1

1) Preparation of surface-patterned crosslinked polyurethane elastomer 1

4,4' -dihydroxybenzophenone, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate trimer, polycaprolactone diol and catalyst triethylene diamine are mixed according to the mole ratio of 1:1:1/3:0.5:0.002 to obtain the material composition. The raw material composition was poured into a square polytetrafluoroethylene mold, and polymerization was carried out at a temperature of 60℃for 18 hours to obtain a polymer elastomer sheet having a thickness of 2mm.

A mask of a predetermined circuit pattern was covered on the molded polymer elastomer sheet, and then irradiated under a 365nm, 100W ultraviolet lamp for 15 minutes, to obtain a surface-patterned crosslinked polyurethane elastomer 1.

2) Preparation of flexible circuit board 1

And depositing the silver nanowire dispersion liquid on a polytetrafluoroethylene filter membrane by a suction filtration method to obtain the filter membrane deposited with silver nanowires. Covering the surface of the obtained surface patterned cross-linked elastomer 1 with a filter membrane deposited with silver nanowires, heating at 100 ℃ for 1 hour, cooling to room temperature, and uncovering the filter membrane to obtain the flexible circuit board 1.

Example 2

1) Preparation of surface-patterned crosslinked polyurethane elastomer 2

2, 4-dihydroxybenzophenone, hexamethylene diisocyanate trimer, polybutylene adipate glycol and catalyst bis (dimethylaminoethyl) ether are mixed according to the mole ratio of 1:1.9:1/3:1:0.001 to obtain a raw material composition. The raw material composition was poured into a square polytetrafluoroethylene mold, and polymerization was carried out at a temperature of 80℃for a reaction time of 8 hours, to obtain a polymer elastomer sheet having a thickness of 0.5 mm.

A mask of a predetermined circuit pattern was covered on the molded polymer elastomer sheet, and then irradiated under a 365nm, 100W ultraviolet lamp for 10 minutes, to obtain a surface-patterned crosslinked polyurethane elastomer 2.

2) Preparation of flexible circuit board 2

And depositing the carbon nano tube dispersion liquid on the polytetrafluoroethylene filter membrane by a suction filtration method to obtain the filter membrane deposited with the carbon nano tubes. And covering the surface of the obtained surface patterned crosslinked elastomer 2 with a filter membrane deposited with carbon nano tubes, heating at 110 ℃ for 2 hours, cooling to room temperature, and uncovering the filter membrane to obtain the flexible circuit board 2.

Example 3

1) Preparation of surface-patterned crosslinked polyurethane elastomer 3

4,4' -diaminobenzophenone, 2, 4-diaminobenzophenone, isophorone diisocyanate trimer, polycaprolactone diol and catalyst bis (dimethylaminoethyl) ether in a molar ratio of 0.5:0.5:2.02:1/3:1:0.008 to obtain a raw material composition. The raw material composition was poured into a square polytetrafluoroethylene mold, and polymerization was carried out at a temperature of 100℃for 8 hours to obtain a polymer elastomer sheet having a thickness of 1 mm.

A 360 mesh stainless steel screen was covered on the molded polymer elastomer as a mask, and then irradiated under a 365nm, 100W uv lamp for 10 minutes to obtain a surface-patterned crosslinked polyurethane elastomer 3.

2) Preparation of flexible circuit board 3

And depositing the graphene and copper nanoparticle mixed dispersion liquid on a polytetrafluoroethylene filter membrane by a suction filtration method to obtain the filter membrane deposited with the graphene and copper nanoparticles. And covering the surface of the obtained surface patterned crosslinked elastomer 3 with a filter membrane deposited with graphene and copper nano particles, heating at 150 ℃ for 3 hours, cooling to room temperature, and uncovering the filter membrane to obtain the flexible circuit board 3.

< evaluation >

1. Evaluation of mechanical Properties

The flexible circuit boards 1 to 3 obtained in examples 1 to 3 were respectively subjected to tensile property test according to GB/T528-1998 standard using UTM-1432 type electronic universal tester (Maillard Jin Jian). The stretching speed is 50mm/min; the graticule spacing of the tensile specimen was 20.0.+ -. 0.2mm, the width was 4.0.+ -. 0.1mm, and the standard thickness was 2.0.+ -. 0.2mm.

Cutting off the flexible circuit boards 1-3 obtained in examples 1-3 respectively, then rapidly and tightly butting cut spline sections, heating the butted spline sections for a period of time, then fully cooling to room temperature, and carrying out tensile property test again. The self-healing conditions and the results of the tensile test are shown in table 1.

TABLE 1

As can be seen from the results in table 1, the flexible circuit board obtained from the surface-patterned crosslinked polyurethane elastomer of the present invention as a substrate has excellent mechanical properties. After the self-repair is cut off, the mechanical properties are maintained or only slightly reduced, which indicates that the polyurethane elastomers of the present invention as well as flexible circuit boards are capable of achieving near complete self-repair of mechanical properties.

2. Evaluation of conductive Properties

1) Self-healing test of conductivity

1-1) sheet resistance test

The sheet resistances of the flexible circuit boards 1 to 3 obtained in examples 1 to 3 were respectively tested by AN9605D electrical tester (Ai Nuo). The flexible circuit boards 1 to 3 obtained in examples 1 to 3 were cut off, cut-off spline sections were rapidly and tightly butted, and then the butted flexible circuit boards were heated for a period of time according to the conditions given in table 1, and then cooled sufficiently to room temperature, and sheet resistances were tested again, with the results shown in table 2.

TABLE 2

	Before cutting (omega/sq)	After self-repair (omega/sq)
			Example 1	5.87	5.92
Example 2	12.9	13.7
			Example 3	27.1	28.5

As can be seen from the results in table 2, the flexible circuit board obtained from the surface-patterned crosslinked polyurethane elastomer of the present invention as a substrate was excellent in electrical conductivity. After the self-healing is cut off, the conductivity is only slightly reduced, which indicates that the polyurethane elastomer of the invention and the flexible circuit board can achieve near complete self-healing of the conductivity.

1-2) Circuit testing

The flexible circuit board 1 obtained in example 1 was connected to a circuit, and the bulb was turned on as shown in fig. 1 (a). The flexible circuit board 1 is cut off and the bulb is extinguished as shown in fig. 1 (b). The flexible circuit board 1 was cut and allowed to self-repair according to the method and conditions given above, and it was observed that the bulb was lighted again with no significant difference in brightness from before the cut-off, as shown in fig. 1 (c).

2) Influence of deformation on conductivity

The flexible circuit board 1 obtained in example 1 was tested for resistance change during stretching. The flexible circuit board 1 was then cut and subjected to self-healing according to the methods and conditions given above, and the self-healed flexible circuit board 1 was tested for resistance change during stretching. The results are shown in FIG. 2.

As can be seen from fig. 2, the flexible circuit board 1 obtained in example 1 has almost no difference in resistance during the tensile deformation before and after the self-repairing, and has little resistance change below 120% deformation rate. This shows that the conductive properties of the flexible circuit board of the present invention are hardly affected by deformation.

The plot in fig. 2 is an enlarged display of resistance data below 120% deformation rate.

3. Evaluation of Circuit morphology

The shape of the flexible circuit board 3 obtained in example 3 was observed with a microscope as shown in fig. 3. Among them, fig. 3 (a) is a photomicrograph of a stainless steel screen, and fig. 3 (b) is a photomicrograph of the flexible circuit board 3 obtained in example 3, and it can be seen from a comparison of fig. 3 (a) and fig. 3 (b) that the mesh shape is substantially maintained before and after printing. This shows that circuits with a precision of tens of micrometers can be printed using the polyurethane elastomers of the present invention as a substrate.

4. Evaluation of drop resistance

1) Tape stripping test

The flexible circuit board 1 obtained in example 1 was subjected to a tape peeling test. The flexible circuit board 1 was attached using a standard polyimide tape, and then the tape was slowly torn off, and the procedure was repeated 3 times to complete the peeling test. The sheet resistance of the flexible circuit board 1 after the tape peeling test was measured as 5.96 Ω/sq according to the method described above, and was hardly changed from that before the tape peeling.

2) Ultrasonic treatment test

The flexible circuit board 1 obtained in example 1 was subjected to ultrasonic treatment. The flexible circuit board 1 is soaked in deionized water, put into a 300W ultrasonic cleaner for ultrasonic treatment for 30 minutes, taken out and dried, and ultrasonic treatment is completed. The sheet resistance of the flexible circuit board 1 after ultrasonic treatment was 5.90 Ω/sq as measured by the method described above, and was almost unchanged from that before ultrasonic treatment.

The results of the tape peeling test and the ultrasonic treatment test show that the conductive layer of the flexible circuit board of the present invention is excellent in peeling resistance.

Industrial applicability

The polyurethane elastomer of the invention can be widely used for flexible circuit substrates, such as wearable equipment, flexible display devices, flexible sensors, brain-computer interfaces, soft robots and the like.

Claims

1. A surface-patterned crosslinked polyurethane elastomer, characterized by comprising a polyurethane having a dynamic crosslinked structure, and in a partial region of its surface, the polyurethane having a dynamic crosslinked structure further having a permanent chemical crosslinked structure, the polyurethane having a dynamic crosslinked structure being obtained by polymerization of a raw material composition comprising a benzophenone compound, an isocyanate compound and a polyol, the benzophenone compound being one or more selected from the group consisting of 4,4 '-dihydroxybenzophenone, 2, 4-dihydroxybenzophenone, 4' -diaminobenzophenone and 2, 4-diaminobenzophenone, the isocyanate compound comprising a compound having 3 or more isocyanate groups.

2. The surface-patterned crosslinked polyurethane elastomer of claim 1, wherein, in the raw material composition, on a molar basis, the benzophenone compound: isocyanate compound: polyol = 1: (0.8-3): (0.3-3).

3. The surface-patterned crosslinked polyurethane elastomer of claim 2, wherein, in the raw material composition, on a molar basis, the benzophenone compound: isocyanate compound: polyol = 1: (1-2.5): (0.5-2).

4. The surface-patterned crosslinked polyurethane elastomer according to claim 1 or 2, wherein the isocyanate-based compound further comprises a compound having 2 isocyanate groups.

5. The surface-patterned crosslinked polyurethane elastomer of claim 4, wherein the compound having 2 isocyanate groups has the structure:

wherein R' is a hydrocarbon group having 2 to 30 carbon atoms, and n is 2.

6. The surface-patterned crosslinked polyurethane elastomer according to claim 4, wherein the compound having 2 isocyanate groups is one or more selected from aliphatic diisocyanates.

7. The surface-patterned crosslinked polyurethane elastomer according to claim 4, wherein the compound having 2 isocyanate groups is one or more selected from hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, xylylene diisocyanate, cyclohexyldimethylene diisocyanate, tetramethylm-xylylene diisocyanate, 2, 4-trimethylhexamethylene diisocyanate, methylcyclohexyl diisocyanate; the compound having 3 or more isocyanate groups is a polymer of diisocyanate.

8. The surface-patterned crosslinked polyurethane elastomer of claim 7, wherein the compound having 3 or more isocyanate groups is a trimer of diisocyanate.

9. The surface-patterned crosslinked polyurethane elastomer according to claim 8, wherein the compound having 3 or more isocyanate groups comprises one or more selected from hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, dicyclohexylmethane diisocyanate trimer.

10. The surface patterned crosslinked polyurethane elastomer of claim 1 or 2, wherein the polyol is a polymer polyol.

11. The surface patterned crosslinked polyurethane elastomer of claim 10, wherein the polymer polyol has the following structure:

wherein R' is a polyester or polyether chain segment, and m is an integer of 2 or more.

12. The surface patterned crosslinked polyurethane elastomer of claim 10, wherein the polyol is one or more selected from the group consisting of polycaprolactone polyol and polybutylene adipate polyol.

13. The surface patterned crosslinked polyurethane elastomer of claim 1 or 2, wherein the feedstock composition further comprises a catalyst; in the raw material composition, the molar ratio of the diphenyl ketone compound to the catalyst is 1: (0.0001-0.01).

14. The surface patterned crosslinked polyurethane elastomer of claim 13, wherein the catalyst is an organic base.

15. The surface patterned crosslinked polyurethane elastomer of claim 13, wherein the catalyst is one or more selected from the group consisting of triethylenediamine and bis (dimethylaminoethyl) ether.

16. The surface patterned crosslinked polyurethane elastomer of claim 14 or 15, wherein the molar ratio of benzophenone compound to catalyst in the starting composition is 1: (0.0005 to 0.01).

17. The method for producing a surface-patterned crosslinked polyurethane elastomer according to any one of claims 1 to 16, comprising the steps of:

18. The method according to claim 17, wherein the polymerization reaction temperature is 40 to 120 ℃ and the reaction time is 6 to 48 hours; the wavelength of ultraviolet light is 300-500 nm; the irradiation time of ultraviolet light is 5-60 minutes.

19. The method of claim 18, wherein the ultraviolet light has a wavelength of 365nm.

20. A circuit substrate comprising the surface patterned crosslinked polyurethane elastomer of any one of claims 1-16.

21. A flexible circuit board comprising the circuit substrate of claim 20, and a conductive layer laminated on the circuit substrate.

22. The flexible circuit board of claim 21, wherein the conductive layer comprises one or more conductive fillers selected from the group consisting of metal nanowires, carbon nanotubes, graphene, liquid metal, and metal particles.

23. The method of manufacturing a flexible circuit board according to claim 21 or 22, comprising the steps of:

preparing a surface patterned crosslinked polyurethane elastomer by the preparation method of claim 17 or 18;

24. The method of manufacturing according to claim 23, wherein the conductive layers are laminated by spraying or transferring.

25. The method according to claim 23, wherein a filter film deposited with a conductive filler is coated on the surface of the obtained surface-patterned crosslinked polyurethane elastomer, and the obtained laminate is heated and then cooled, and the filter film is removed, whereby the conductive layer is laminated.