Masking adhesive suitable for three-proofing coating of connector and preparation method and application method thereofTechnical Field
The invention relates to the field of masking rubber materials for three-proofing coating of precise connectors and components and parts, which can be applied to electronic circuit boards, in particular to masking rubber for three-proofing coating of connectors, and a preparation method and an application method thereof.
Background
The use environment of the electronic circuit board is changeable, so that in order to avoid the influence of external high humidity, vibration, high dust, salt mist, chemical substances (corrosive gas, liquid) and the like when the electronic circuit board is used, the printed board assembly is bad or invalid due to electrochemical migration, electric leakage, short circuit and the like, the surface of the electronic circuit board is required to be sprayed with the three-proofing paint with the functions of moisture resistance, salt mist resistance and mildew resistance, and the three-proofing paint has excellent insulating property, so that the area on the PCB which does not need to be coated with the three-proofing paint is required to be covered before the three-proofing paint is sprayed, and particularly the metal connector and the component with the conductive function are required to be provided.
The existing three-proofing paint shielding is mainly carried out in the following modes:
covering and shielding device:
the method is mainly characterized in that shielding components with the same shape are prepared according to the areas needing to be shielded on the electronic circuit board, for example, an authorized bulletin number is CN102123564B, the patent name is an invention patent of a three-proofing lacquer coating shielding method for a circuit board, and shielding rubber sleeves with different shapes are prepared according to circuit boards with different types; the invention patent with the application publication number of CN114650664A and the patent name of printed board three-proofing coating shielding method and shielding device is used for preparing a shielding cover plate with a positioning structure; the shielding device has the advantages that the shielding device can be reused for circuit boards of the same type, and glue is not easy to leave; but its drawbacks are also more evident: 1. different dies or cover plate devices are required to be prepared for different electronic circuit boards, so that the application range is small, and the preparation cost is high; 2. the method is only suitable for products with large shielding area and simple shielding structure, and is not suitable for products with high precision, high integration level and scattered shielding area; 3. for shielding of some precision devices, such as connectors, precision components and the like, when the shielding device is covered or removed, the position of the shielding device is difficult to determine, and the components are easy to damage; 4. the coating stability and the sealing performance are poor, and the problems of displacement, poor edge sealing performance and the like are easy to occur after the coating.
Winding shielding adhesive tape
The shielding tape is wound at the position to be shielded, and the shielding is completed by tearing off the tape after the three-proofing paint is sprayed, so that the shielding technology is simple, the cost is low, the winding and tearing process of the tape is completed manually, the operation efficiency is low, and the sealing performance is difficult to ensure for special-shaped devices or connectors with higher precision, therefore, the shielding tape is mainly applicable to regular smooth shielding surfaces.
And (5) coating shielding glue.
Preparing a curable and peelable masking tape, spreading the masking tape on an electronic circuit board in a spot coating or large-area coating mode aiming at the shape of an area to be masked, curing the masking tape, wherein the common curing mode is photo-curing or thermosetting, and removing the cured masking tape after three-proofing paint is sprayed.
The method can conduct targeted and accurate shielding on the shielding area on the electronic circuit board, so that the method can meet the shielding requirements of high integration level and high precision; however, the method has higher requirements on the flowability, the curing efficiency, the curing mode, the glue remaining condition, the stripping strength and the like of the shielding glue; for example, the patent name of patent publication number CN114196299B, namely an invention patent of masking glue and application thereof, provides masking glue with low viscosity for masking large-area 3D curved surfaces; however, since the masking adhesive has low adhesiveness and good fluidity, the masking adhesive is used only for curved surfaces or flat surfaces with large areas; however, for some precision devices, especially high integration, precision connectors and components with high fall and small gaps, because of the high fluidity, accurate boundary positioning cannot be performed on the glue-coated area, especially for some three-dimensional shadow surfaces, the masking glue is easy to flow to the non-masking area, and because the components are shielded, partial shadow areas cannot be fully photo-cured, so that the masking effect is poor, and meanwhile, the glue is easy to leave after stripping.
For some masking glues with higher viscosity, a thermosetting or photo-curing mode is generally adopted, the heating temperature needs to be strictly controlled in a thermosetting mode, damage to components is avoided, and the photo-curing mode needs to consider the problem that the shadow surface cannot be fully photo-cured.
In addition, because the integration level of the plug connector is high and the surface is sharp, the problems of glue retention or damage to connectors and components and the like caused by overlarge stripping force of the shielding glue are extremely easy to occur when the shielding glue is stripped, when the shielding glue is coated thinner, the whole piece of the shielding glue is difficult to tear off, the shielding glue is easy to remain, and the efficiency is low; when the masking adhesive is coated thicker, on one hand, the curing difficulty is increased, and on the other hand, the requirements on the flexibility and the strippability of the adhesive are higher, so that the masking adhesive is easy to break when stripped due to insufficient flexibility or damage a precise device due to large stripping force, and in addition, the adhesive force of the masking adhesive is required to be better, otherwise, the masking effect is easy to be influenced by stripping in the use process; in the electronic circuit board with high integration, the connectors and components in the shielding area are made of different materials, so that the shielding glue needs to have better adhesive force and peelability for different connector or component materials.
Disclosure of Invention
Therefore, in order to solve the problems, the invention provides the shielding glue for three-proofing coating, and the preparation method and the application method thereof, which are suitable for connectors.
The invention is realized by the following technical scheme:
the masking adhesive for three-proofing coating suitable for the connector comprises the following components in parts by mass:
30-60 parts of polyurethane acrylic resin;
30-45 parts of monofunctional acrylate monomer;
0.5-5 parts of photoinitiator;
2-5 parts of rheological auxiliary agent.
The polyurethane acrylic resin is isocyanate modified polyurethane acrylic ester, the mass content of NCO in the polyurethane acrylic resin is 0% -15%, the number average molecular weight is 3000-10000, the viscosity is 10000cps-30000cps, the glass transition temperature of the monofunctional acrylic ester monomer is-60 ℃ to-20 ℃, and the viscosity of the shielding glue for three-proofing coating suitable for connectors is 15000cps +/-1000 cps.
Preferably, the carbon number of the monofunctional acrylate monomer is more than or equal to 10.
Preferably, the monofunctional acrylate monomer is an oxygen-containing monofunctional acrylate monomer.
Preferably, the monofunctional acrylate monomer is a mixture of ethoxyethoxyethyl acrylate and cyclotrimethylolpropane formal acrylate.
Preferably, the ratio of the ethoxyethoxy ethyl acrylate to the cyclotrimethylolpropane formal acrylate is 1 (1-3).
Preferably, the adhesive further comprises 1-2 parts by mass of wetting dispersant, wherein the wetting dispersant is polyether siloxane copolymer.
Preferably, the photoinitiator includes, but is not limited to, one or more of benzoin dimethyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexyl phenyl ketone, and the like.
Preferably, the rheology aid is fumed silica.
The preparation method of the masking tape for the three-proofing coating of the connector comprises the following steps:
step S1: the preparation method of the monofunctional acrylate monomer comprises the following steps of: the ethoxy ethyl acrylic acid vinegar and the cyclo-trimethylol propane formal acrylic acid ester of the (1-3) are added with 1-2 parts of wetting dispersant and mixed by a double-planetary stirring kettle at the environment temperature of <20 ℃, the stirring speed is more than 100rpm, the mixing time is more than 30min, and the monofunctional acrylic acid ester monomer with the surface tension of <25dynes/cm is prepared;
step S2: the components of the masking adhesive for three-proofing coating suitable for the connectors are uniformly dispersed in a double-planetary stirring kettle at the temperature below 20 ℃ for more than 30min, the dispersion speed is more than 1000rpm, the components are further dispersed by grinding by a three-roller grinding machine, the roller spacing is 20um, the grinding is more than two times, and the grinding speed is less than 100rpm, wherein the mixing environment is as follows: vacuum environment < -0.1MPa, and the prepared masking adhesive with the viscosity of 15000cps +/-1000 cps is suitable for three-proofing coating of connectors.
The application method of the masking tape for the three-proofing coating of the connector comprises the following steps:
step one: coating the masking adhesive for three-proofing coating suitable for the connector assembly, which is described in any one of claims 1-8, on a product in a dispensing or large-area coating mode, wherein the thickness of the adhesive coating is 1-20 mm;
step two: under the condition that the ambient humidity is more than or equal to 50 percent, the radiation energy is more than 1000mJ/cm2 Curing by UV light;
step three: and (5) continuously standing for 1-3 min under the condition that the ambient humidity is more than or equal to 50%, and completing curing.
The technical scheme of the invention has the beneficial effects that:
1. the masking adhesive for three-proofing coating of precise connectors and components and parts which can be applied to electronic circuit boards is prepared by strictly controlling the proportion of polyurethane acrylic resin and single-functional acrylate monomers and adding a certain amount of flow aid to obtain masking adhesive with proper viscosity and molecular weight, so that the flow property of the masking adhesive is controlled, the masking adhesive is ensured to be coated on a three-dimensional surface, and particularly, the masking positioning can be better carried out when the masking adhesive is coated on a small-area and narrow-sized side surface of precise devices such as connectors and components, the boundary is accurately masked, and the masking adhesive is prevented from flowing to a three-proofing adhesive coating area.
2. On one hand, the epoxy acrylate monomer with better flexibility is added into the polyurethane acrylate resin, and the polyurethane acrylate resin is crosslinked by the low-molecular-weight mono-functional acrylate monomer, so that the viscosity of the polyurethane acrylate resin is diluted, the structural rigidity of the cured polyurethane acrylate resin is weakened, and the peeling strength and other characteristics of the shielding glue are unfavorable; on the other hand, the polyurethane acrylic resin and the monofunctional acrylate monomer have good flexibility, so that the whole piece of shielding glue can be conveniently stripped, and the working efficiency is improved.
3. The polyurethane acrylate resin modified by isocyanate is simultaneously suitable for moisture curing and UV curing, so that when a UV lamp cannot irradiate a shadow position of a shielded light ray in a shielding area, the moisture curing and the UV curing are ensured to be simultaneously carried out in a humidifying environment, the complete curing of shielding glue is realized, and the glue remaining problem caused by incomplete curing is avoided; in addition, by controlling the proportion of the polyurethane acrylic resin and the monofunctional acrylic monomer and the content of isocyanate groups (NCO) in the polyurethane acrylic resin, the curing work is ensured to be mainly carried out through photo-curing, so that the curing time is shortened, after photo-curing, the surface curing of the shielding glue is finished, the inside of the shielding glue is basically cured, and the inside of the subsequent shielding glue is continuously cured through moisture curing to realize complete curing.
4. The single-functional acrylate monomer adopts ethoxy ethyl acrylate and cyclo-trimethylolpropane formal acrylate with lower glass transition temperature and better flexibility, and simultaneously, the glass transition temperature of the shielding glue is further reduced and the flexibility is improved by limiting the proportion between the ethoxy ethyl acrylate and the cyclo-trimethylolpropane formal acrylate, so that the low-temperature flexibility and cold resistance of the shielding glue are improved along with the reduction of the glass transition temperature of the shielding glue, the stability is improved, the shielding glue still keeps better plasticity and flexibility even in a lower temperature environment, the problems of hardness increase or cracking and the like do not occur, and the whole piece of the subsequent shielding glue is conveniently stripped; in addition, the curing speed of the cyclotrimethylolpropane formal acrylic ester is high, and the cyclotrimethylolpropane formal acrylic ester has better adhesive force on plastics and metals, so that the working efficiency and the suitability among shielding glue, connectors and components can be further improved.
5. The polyether siloxane copolymer is added into the monofunctional acrylate monomer as a wetting dispersant, the polyether siloxane copolymer is formed by graft copolymerization of polyether and polydimethylsiloxane, a polyether chain segment has good hydrophilicity and foamability, and good compatibility with the acrylate monomer, and a polysiloxane chain segment has hydrophobicity and penetrability, so that the surface tension of the monofunctional acrylate monomer is reduced, the wettability and the dispersion performance are improved, the overall stability and uniformity of the shielding adhesive are improved by increasing the dispersion performance of the monofunctional acrylate monomer in the shielding adhesive, local defects are avoided, and the whole stripping of the shielding adhesive is ensured.
6. The product performance of the shielding glue can be selected according to the setting of the shielding area, the spot coating and the large-area coating can be simultaneously applied to the shielding areas such as a plane, a curved surface, a high-precision three-dimensional surface, a narrow and sharp connector and the like, the shielding glue has good adhesive force, curing effect and stripping performance on various shielding areas, no glue is left, and meanwhile, the shielding glue has good sealing performance and shielding effect before stripping; when the shielding glue is peeled off, the shielding glue has better flexibility and peelability, so that the connector and the components are not damaged.
Detailed Description
So that the manner in which the objects, advantages and features of the invention are attained and can be more clearly understood, a more particular description of the preferred embodiments will be rendered by the following non-limiting description thereof. The embodiment is only a typical example of the technical scheme of the invention, and all technical schemes formed by adopting equivalent substitution or equivalent transformation fall within the scope of the invention.
Furthermore, the terms "first," "second," and the like in this description are used for descriptive purposes only and are not to be construed as indicating or implying a ranking of importance, or as implicitly indicating the number of technical features shown. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the present invention, the meaning of "plurality" means two or more, unless specifically defined otherwise.
The invention discloses a shielding adhesive for three-proofing coating of a connector, which comprises the following components in parts by mass:
30-60 parts of polyurethane acrylic resin;
30-45 parts of monofunctional acrylate monomer;
0.5-5 parts of photoinitiator;
2-5 parts of rheological auxiliary agent.
The polyurethane acrylic resin is isocyanate modified polyurethane acrylic ester, the mass content of NCO in the polyurethane acrylic resin is 0% -15%, the number average molecular weight is 3000-10000, the viscosity is 10000cps-30000cps, the glass transition temperature of the monofunctional acrylic ester monomer is-60 ℃ to-20 ℃, the viscosity of the shielding glue for three-proofing coating suitable for connectors is 15000cps +/-1000 cps, the adhesive force can be better within the viscosity range, meanwhile, the fluidity of the shielding glue can be better controlled, and the shielding boundary can be conveniently and accurately controlled; the single-functional acrylate monomer with low molecular weight, low viscosity and good flexibility is mixed, so that the viscosity and average molecular weight of the shielding glue are reduced, and after the single-functional acrylate monomer and the polyurethane acrylic resin are crosslinked and cured, the overall hardness of the shielding glue can be reduced, and the flexibility and the strippable performance of the shielding glue are improved.
In a preferred embodiment, the isocyanate modified urethane acrylate is an isocyanate urethane acrylate with the product of allnex corporation under the trade name EBECRYL 4250, and in other embodiments, the isocyanate modified urethane acrylate may be another urethane acrylate material modified by isocyanate, which is not described herein.
In some embodiments, the monofunctional acrylate monomer has a carbon number of 10 or more, specifically, the monofunctional acrylate monomer has a carbon number of between 10 and 16.
In some embodiments, the monofunctional acrylate monomer is an oxygen-containing monofunctional acrylate monomer, and the monofunctional acrylate monomer is a mixture of ethoxyethoxyethyl acrylate (EOEOEA) and cyclotrimethylolpropane formal acrylate (CTFA), and in a preferred embodiment, the ratio of ethoxyethoxyethyl acrylate to cyclotrimethylolpropane formal acrylate is 1 (1-3); the epoxy ethoxy ethyl acrylate has strong adhesive force on plastic substrates, the epoxy trimethylolpropane formal acrylate has good adhesive force on plastic substrates and metal substrates, and the glass transition temperature of the epoxy ethoxy ethyl acrylate and the metal substrates is low, and the flexibility of the epoxy ethoxy ethyl acrylate and the metal substrates is good, so that the masking adhesive prepared by mixing the monofunctional acrylate monomers mixed in the proportion with polyurethane acrylic resin can dilute viscosity, improve flexibility, reduce stripping strength and can be well adhered to the surfaces of masking areas made of various materials such as resins, metals and the like.
The water-based polyurethane foam adhesive also comprises 1-2 parts by mass of wetting dispersant, wherein the wetting dispersant is a polyether siloxane copolymer, and a common organosilicon polymer, such as polysiloxane, has a larger difference between the structure and the polarity of a monofunctional acrylate monomer, has a larger difference between the free energy of the surface and the free energy of the surface, and is easy to migrate to the surface, so that the compatibility is poor.
In some embodiments, the photoinitiator is primarily a free radical photoinitiator including, but not limited to, one or more of benzoin dimethyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexyl phenyl ketone, and the like.
In some embodiments, the rheology aid is fumed silica, so that sag resistance of the masking gel is improved, positioning performance of the masking gel on a three-dimensional surface can be improved when the masking gel is coated, and masking flow out of a masking region is avoided.
The invention also discloses a preparation method of the shielding glue for the three-proofing coating, which is suitable for the connector, and comprises the following steps:
step S1: the preparation method of the monofunctional acrylate monomer comprises the following steps of: the ethoxy ethyl acrylate and the cyclo-trimethylol propane formal acrylate of (1-3) are added with 1-2 parts of wetting dispersant and mixed by a double-planetary stirring kettle at the environment temperature of <20 ℃, the stirring speed is more than 100rpm, and the mixing time is more than 30min, so that the monofunctional acrylate monomer with the surface tension of <25dynes/cm is prepared.
Step S2: the components of the masking adhesive for three-proofing coating suitable for the connectors are uniformly dispersed in a double-planetary stirring kettle at the temperature below 20 ℃ for more than 30min, the dispersion speed is more than 1000rpm, the components are further dispersed by grinding by a three-roller grinding machine, the roller spacing is 20um, the grinding is more than two times, and the grinding speed is less than 100rpm, wherein the mixing environment is as follows: vacuum environment < -0.1MPa, and the prepared masking adhesive with the viscosity of 15000cps +/-1000 cps is suitable for three-proofing coating of connectors.
Specifically, when the polyurethane acrylic resin and other materials are mixed, the stability of the polyurethane acrylic resin is ensured by strictly controlling the material preparation environment (the temperature is less than 20 ℃ and the vacuum environment is < -0.1 MPa), so that the pre-curing is avoided.
Examples 1-5 were provided according to the above-described ratios of the components in the masking tape for three-proofing coating of connectors, while comparative examples 1-3 were provided, and the specific material ratios of the examples and comparative examples are shown in the following table:
in each of the above examples and comparative examples, the urethane acrylate was isocyanate urethane acrylate having the product of the company allnex, which is a product of the company allnex, under the trade name EBECRYL 4250; masking tape samples were obtained from the above tables for each of the components of examples 1 to 5 and comparative example 1 according to the above-described preparation method of masking tape for three-proofing coating applicable to connectors; the comparative example 2 and the comparative example 3 are uniformly dispersed in a double-planetary stirring kettle under the environment of below 20 ℃ at a dispersion speed of >1000rpm for more than 30min, and are further dispersed by grinding by a three-roller grinder, wherein the roller spacing is 20um, the grinding is more than twice and the grinding speed is less than 100rpm, and the mixing environment is that: vacuum environment < -0.1MPa, and preparing the masking gel sample.
Masking gel performance test:
a planar substrate made of three materials commonly used for the shielding region was prepared: the first substrate is a PCB, the second substrate is a tin plate, and the third substrate is a copper plate; a PCB board with a metal connector arranged on the surface is prepared as a substrate IV, wherein the average height of the surface connectors of the substrate IV is 3cm, and the average interval distance between the connectors is 5mm.
The masking tape samples prepared in examples 1 to 5 and comparative examples 1 to 3 were coated on the surfaces of the first to fourth substrates at a thickness of 1mm, respectively, and were irradiated with radiant energy under conditions of an ambient humidity of 50% or moreThe amount is more than 1000mJ/cm2 Curing by UV light;
after the masking gel samples are cured, testing the adhesive force of each masking gel sample on one surface of the substrate;
peeling each cured masking adhesive sample from the first surface to the fourth surface of the base material by adopting a peeling angle of 180 degrees, observing the adhesive remaining condition by naked eyes, and observing whether the adhesive remains on the surface of the base material or the connector; meanwhile, whether the masking tape sample can be peeled off on the four surfaces of the substrate or not is observed independently.
The test results are shown in the following table:
compared with the examples 1-5, the proportion of the monofunctional acrylate monomer is higher, and the proportion of the rheological additive is insufficient, on one hand, the viscosity of the masking rubber is reduced due to the increase of the proportion of the monofunctional acrylate monomer, and on the other hand, the sagging resistance of the masking rubber on a three-dimensional surface is reduced due to the insufficient proportion of the rheological additive, so that the masking rubber is left on the first substrate, the third substrate and the fourth substrate of the comparative sample, particularly on the fourth substrate with uneven surface, and the situation of the remaining rubber is more obvious.
In comparative example 2, a trifunctional acrylate monomer is used, and in comparative example 3, a tetrafunctional acrylate monomer is used, and compared with a monofunctional acrylate monomer having a lower molecular weight and viscosity and better flexibility, as the number of functional groups of the acrylate monomer increases, the flexibility decreases, the hardness increases, the elongation decreases after curing, and after crosslinking reaction with urethane acrylic resin, the hardness further increases, which results in difficulty in stripping, and even in the curing process, cracks are easily generated, or the connector is damaged in the stripping process.
The invention also discloses an application method of the shielding glue for the three-proofing coating of the connector, which comprises the following steps:
step one: coating the masking adhesive for three-proofing coating, which is suitable for the connector, on a product in a dispensing or large-area coating mode, wherein the adhesive coating thickness is 1-20 mm;
step two: under the condition that the ambient humidity is more than or equal to 50 percent, the radiation energy is more than 1000mJ/cm2 Curing by UV light;
step three: and (5) continuously standing for 1-3 min under the condition that the ambient humidity is more than or equal to 50%, and completing curing.
Specifically, in step two, the method is carried out by using the radiation energy of more than 1000mJ/cm2 The Ultraviolet (UV) light is used for curing, when the ultraviolet light is used for curing for 30 seconds, the surface curing of the shielding glue is finished, the inside of the shielding glue is basically cured, and after the step three, the inside of the shielding glue is further accelerated to be cured by moisture; in practical application, after the third step is completed, before the masking gel is stripped (during the process of spraying the three-proofing paint and during the process of conveying products), moisture curing can be continuously performed in the masking gel by contacting with water vapor in the environment until the masking gel is completely cured.
The invention has various embodiments, and all technical schemes formed by equivalent transformation or equivalent transformation fall within the protection scope of the invention.