Acrylic resins with perfluoroalkyl groups in their side chains are typically used as coating components for our company's fluorine-based moisture-proof coating agent "Fluorosurf® FG-3000 Series." This resin forms a film with the lowest surface energy among fluororesins and has excellent water and oil repellency and electrical properties. In addition, it can be copolymerized in combination with other unsaturated monomers, and by selecting the copolymerizable monomer, it is possible to impart properties such as solubility in various solvents and film strength. It is possible to create resin compositions with tailored properties.

Additionally, Fluorosurf® FG-3000 series uses fluorine-based solvents as solvents. Fluorinated solvents differ from general organic solvents in that they are non-flammable (non-hazardous), have low toxicity, and have a mild odor. It is not subject to the hazardous materials regulations of the Safety and Health Act, the PRTR Act, and the Fire Service Act, and as it can be used safely and freely, it has great benefits in the field, but it is expensive as a raw material.

Furthermore, with the Fluorosurf® FG-3000 series, it is possible to set the concentration of the resin component and select the drying speed of the solvent component to match the film thickness required by the customer, allowing the user to select the product with the best specifications according to the user's usage process. You can choose.

Fluorosurf® FG-3000 series, which is specially designed for moisture-proof, waterproof, and acid-resistant applications such as printed wiring boards, has excellent moisture-proof and insulation properties, and has high performance as an insulating moisture-proof coating and acid-resistant and corrosion-resistant coating agent for electronic boards and components. shows. With conventional water and oil repellent treatments, the film did not have good mechanical properties and was prone to cracking due to thermal shock, so only products that can form a film thickness of at most 1 μm (2% resin concentration) are on the market. There wasn't. Table 1 shows moisture permeability data by coating type and film thickness. As seen in this table, the moisture-proofing performance is proportional to the film thickness, so if the film thickness was less than a few μm, even a fluororesin film with high moisture-proofing properties could not exhibit sufficient functionality. Fluorosurf® FG3000 series can easily form films in a wide range of thicknesses, from a few μm thin film to several 10 μm thick or more, and even at high film thicknesses, it can withstand cooling and heating cycles without cracking, making it a sufficient moisture-proof and waterproof film. be able to perform its functions.

Table 1: Comparison of moisture permeability by coating type and film thickness

When compared to moisture-proof coatings for electronic boards that have conventionally been commonly used urethane and acrylic resin film components, the moisture permeability is 1/6 to 1/6 at the same film thickness, as seen in the same table. It is quite low at around 1/5 and exhibits high moisture resistance. The moisture permeability is about 1/30 compared to silicone resin used for potting etc. In other words, if the same level of moisture resistance is desired, the film thickness may be thinner by the proportional multiplier. For mobile devices that seek weight reduction, the use of fluorine-based coating agents is extremely advantageous, as it can provide moisture resistance with a thinner film than other types of resin.

Another characteristic of fluororesin is that it is chemically stable and exhibits saltwater resistance and acid resistance. Figure 1 shows the results of salt spray. No change in the fluorine-coated sample surface was observed even after 480 hours of salt spray. Figure 2 shows a copper foil (t=0.1mm) immersed in a 10wt% nitric acid aqueous solution.In contrast to the uncoated sample, the copper foil dissolved and disappeared in 24 hours, while a thin film of about 5 microns remained. Even with fluorine coating, copper foil remains.

Figure 1: Usefulness of fluorine-based moisture-proof coating agent (resistance to salt water)

Figure 2: Immersion in nitric acid 10% solution, room temperature 25℃

Table 2 shows the dielectric breakdown properties of an insulated electrode with a 200μm slit exposed to 5wt% salt water, and how long the film of each coating agent maintains its insulating properties. This is the result. The urethane-based moisture-proof coating agent used as a comparative example has been used by major automobile manufacturers for many years, but it has dielectric breakdown resistance of only a few seconds, and its performance is only a comfort. In contrast, fluorine-based materials were shown to be overwhelmingly superior, being able to exhibit insulation for several minutes to three hours in proportion to the film thickness.

Table 2: Dielectric breakdown resistance

Based on these results, Table 3 summarizes the relationship between actual usage levels, film thickness, and resin concentration based on our own opinion .

Table 3: Usage level and recommended film thickness/recommended concentration

In terms of electrical properties, in addition to the above points, it has a low dielectric constant of around 2.5, making it less susceptible to noise and can be used for high-frequency boards, and it also has higher insulation properties than other resins.

Please refer to Table 4 for comparisons with other resins regarding various other performances .

Table 4: Characteristics of each coating agent

Generally, the moisture-proof coating film of a substrate is desired to be self-extinguishing in the event of a fire caused by a short circuit in an electric circuit, or to be nonflammable in order to prevent the spread of fire. Fluorine resin itself requires a large amount of oxygen when it burns, so the coating film has a nonflammability equivalent to V-0 of the UL94 standard even without the addition of flame retardants. With other resins other than urethane resins that have nitrogen atoms in their structure, it is necessary to use flame retardants such as phosphorus compounds and inorganic compounds in order to obtain nonflammability equivalent to V-0. Furthermore, some olefin-based coating agents are used without eliminating their flammability.

Furthermore, the Fluorosurf® FG-3000 series uses a non-flammable fluorinated solvent as a volatile solvent for the fluoropolymer. As a result, it is treated as a non-hazardous material under the Fire Service Act, and the coating and drying processes do not require management by a person with a hazardous materials handling qualification of Category B or higher, or certification of a hazardous materials handling facility. There is no need to manage quantities such as the amount brought into the warehouse or the amount stored in the hazardous materials warehouse. Furthermore, since there is no need for explosion-proof measures for electrical equipment such as coating equipment, ventilation, and lighting, the amount of investment in new equipment can be significantly reduced. Furthermore, since it does not fall under the category of organic solvents under the Industrial Safety and Health Act, there is no need for periodic environmental measurements or organic solvent examinations as stipulated by the same law, and infrastructure-related management items can be significantly reduced.

However, coating agents using older types of fluorinated solvents, such as fully fluorinated solvents such as PFPE (perfluoropolyether) and PFC (perfluorocarbon), have low global warming potential because these solvents are difficult to decompose. The disadvantage is that the (GWP) is high. In recent years, fluorinated solvents such as HFE (hydrofluoroether) and HFO (hydrofluoroolefin) have become mainstream as alternative low-GWP fluorinated solvents.

With coating agents that cure by chemical reactions such as UV-curable and thermosetting types, if reaction inhibition occurs during curing, the curing reaction may not be completed completely and unreacted substances (monomers, oligomers) may remain. be. To give an example of curing failure, UV curing/thermal curing types may have unstable curing conditions due to deterioration of the light source or the presence of oxygen. Since it is difficult to conduct a 100% in-line non-destructive inspection of the curing status, the only way to manage the curing status is to indirectly manage it using reaction conditions.

Unreacted substances that remain without being completely cured will have a negative effect on electrical properties, and since the film is in a swollen state, unreacted substances will bleed to the film interface after a long period of time, resulting in adhesive peeling of the coating. may occur.

In the Fluorosurf® FG-3000 series, the resin component forms a film when the fluorine-based solvent simply evaporates and dries. Since film formation does not involve any chemical reactions, the electrical properties that meet the designed values ​​are always stably obtained and are highly reliable, regardless of the coating and drying process conditions, except for properties that depend on film thickness.

We will discuss practical examples of Fluorosurf® FG-3000 series in electronic moisture-proof, waterproof, and acid-proof applications.

As mentioned in Section 2, the Fluorosurf® FG-3000 series has higher moisture resistance than conventional moisture-proof coating agents such as urethane-based, acrylic-based, and silicone-based coatings, and the film can be made thinner, contributing to weight reduction. . It is ideal for lightweight mobile devices such as smartphones, tablet PCs, game devices, and Bluetooth headphones, and has a proven track record in waterproof and moisture-proof applications.

The thin film is also effective in preventing leaks that occur in narrow pitch areas such as the lead wires of semiconductor packages, the joints of flexible cables, and the LED lead wires of LED display boards.

Lithium-ion batteries are often used in mobile devices because they are compact and have high output, but on the other hand, it is well known that they are highly dangerous, with many fire accidents. When a mobile device is dropped and damaged, the charging/discharging control circuit is damaged due to electrolyte leakage, and the loss of charging/discharging control can lead to thermal runaway, which can lead to fire. In the event of an electrolyte leak, fluorine-based coatings have the best electrolyte resistance and electrical properties and can protect the control circuit, but other resins such as urethane and acrylic cannot protect the circuit. This electrolyte resistance is correlated with the dielectric breakdown resistance shown in Table 2. It has been used in a variety of lithium battery control boards, including not only mobile devices such as tablet computers and smartphones, but also passenger aircraft, electrically assisted bicycles, and electric drivers.

Figure 3 Structure of LED

LED lighting is increasingly replacing incandescent and fluorescent lights due to its advantages such as low power consumption and long lifespan, but thin LEDs may gradually deteriorate in brightness. The structure of the LED is such that there is a silver-plated reflector on the back of the light emitting element, which efficiently projects light forward. ( Figure 3 ) The light emitting element is sealed with a silicone sealing resin, but trace amounts of hydrogen sulfide present in the atmosphere pass through the sealing resin and sulfurize the silver on the reflector, causing the silver surface to deteriorate. The cause of the brightness reduction is that silver sulfide turns black and reduces reflected light. This phenomenon is particularly likely to occur with surface-mounted low-profile LEDs because the encapsulant resin is thinner than with bullet-shaped LEDs.

Several coating resins have been tried as a way to avoid this phenomenon, but it has been found that fluorine-based coating agents are the most effective. 2) Figure 4 shows a silver plated plate for LED exposed to an atmosphere containing 15-20 ppm hydrogen sulfide. When uncoated, the surface changes to silver sulfide and becomes black in a short time, but when coated, no change is observed. For this reason, our products are effective as a measure to prevent sulfurization of LEDs and have a proven track record.

Figure 4: Sulfur resistance test

Fluorine-based compounds, including PTFE, have long been recognized as durable and safe compounds, but in recent years, due to their properties, they have been found to remain in nature for many years if released into the environment through illegal dumping or other means. This started to be seen as a problem. In particular, low-molecular-weight compounds containing both perfluoro groups and hydrophilic groups with 8-10 carbon atoms, which have been widely used as surfactants and emulsifiers, are easily diffused and released into the environment due to their water solubility. In addition, it was suggested that it is easily taken into the human body and may accumulate in the body. 3) These compounds are represented by PFOS (perfluorooctane sulfonic acid) and PFOA (perfluorooctanoic acid), and are collectively called PFAS (Per Fluoro Alkyl Substances).
These compounds have a half-life in the human body of 8.6 years for PFOS and 4.3 years for PFOA, so they do not fall under the category of highly bioaccumulative compounds, which are defined as having a half-life of 10 years or more in the human body. Because there are concerns that residual organic substances may cause problems in the future, regulations based on the POPs Convention (Stockholm Convention on Persistent Organic Pollution) have been instituted. Four)

Regarding fluorine-based moisture-proof coating agents and water- and oil-repellent treatment agents, polymer compounds with a perfluoroalkyl group of 8-10 carbon atoms in their structure have traditionally been used to provide various properties such as water and oil repellency, waterproofness, acid resistance, and insulation. It has been used as the main ingredient because it has the best properties. Since this compound is a stable polymer compound and poorly water-soluble, it is safe with no impact on the environment or possibility of being taken into the human body. However, there is a theory that if it is dispersed into the natural world, it may decompose through several chemical reactions in the environment and turn into PFOA. All compounds with a structure of 8 or more are legally regulated. Compounds with a perfluoro group having 6 or fewer carbon atoms have low bioaccumulation potential, so there are currently no legal regulations in place. Several years ago, our company completed the transition to fluorine compounds with completely different structures, such as compounds with a perfluoro group of 6 or less carbon atoms and perfluoropolyether, for water and oil repellents, moisture-proof coating agents, anti-fouling coating agents, etc. ing.