JPH0351750B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a two-component solvent-free polyurethane curable composition used for protective coating of printed wiring boards after mounting. BACKGROUND OF THE INVENTION Protective coatings for printed wiring boards were first used in the United States for military applications. However, in recent years, the scope of use of printed wiring boards has expanded rapidly, and the conditions under which they are used have become more diverse, and the requirements for maintaining the performance of printed wiring boards have become more stringent. It is becoming common to apply a protective coating to printed wiring boards such as electronic components for automobiles and machine tools after mounting. Resins used for the protective coating of printed wiring boards after mounting include solvent-based acrylic resins, solvent-based urethane resins, two-component urethane resins, solvent-based epoxy resins, and silicone resins, but there are differences in price, work environment, and performance. Taking all aspects into account, it can be said that a two-component solvent-free urethane system is advantageous. Conventionally, a method using polybutadiene polyol as a polyol component has been proposed as a urethane system for this purpose. By reacting polybutadiene polyol with polyisocyanate, polybutadiene polyol exhibits flexibility even at low temperatures and has excellent electrical properties. A method using castor oil as a polyol component has also been proposed. By reacting castor oil with polyisocyanates, protective coatings with good electrical properties are obtained. Furthermore, attempts have also been made to use the above-mentioned polybutadiene polyol and castor oil in combination as polyol components. Furthermore, JP-A-60-53522 discloses a polyol composition consisting of a high viscosity hydrocarbon polyol and partially dehydrated or acylated castor oil. The hydroxyl value is 150 to 20, more preferably
It is said to be between 140 and 35. Problems to be Solved by the Invention However, since polybutadiene polyol has an extremely high viscosity, it has a serious drawback of extremely poor workability when handling it, and there is a limit to its widespread use when the resin is used alone. Therefore, in order to overcome this drawback, considerable amounts of solvents are blended into polybutadiene polyol, and mineral oil and plasticizers (such as dioctyl phthalate) are blended into the polybutadiene polyol. However, the use of solvents worsens the working environment,
It is unsuitable because it poses a fire hazard, and the use of mineral oil and ordinary plasticizers deteriorates the physical properties of the cured product, and if the cured product is exposed to high temperatures, the mineral oil and plasticizer will volatilize, resulting in the hardening of the cured product. As the weight decreases and shrinks, the hardness increases, causing problems such as damage to the wiring. In addition, when castor oil is used, the hardness of the cured product is too high and it lacks elasticity, especially at low temperatures.
After all, it is unsatisfactory as a protective coating for printed wiring boards. Furthermore, even in systems using polybutadiene polyol and castor oil in combination, the above-mentioned drawbacks of each component cannot be overcome. In the end, in addition to the generally required properties such as electrical properties and mechanical strength, the protective coating for printed wiring boards after mounting must have low viscosity, be easy to handle, and resist weight loss and increase in hardness at high temperatures. urethane systems that meet all of these properties have not been found. As mentioned above, JP-A-60-53522 discloses a polyol composition consisting of a high viscosity hydrocarbon polyol and partially dehydrated or acylated castor oil. Since acylated castor oil is only used as a part of the polyol component, it is not intended to be used as a completely or nearly completely acylated product.In addition, this publication also contains no information regarding the protective coating of printed wiring boards after mounting. It is not specified, and even if it is used for this purpose, it will not give satisfactory results. In view of the above-mentioned circumstances, the present invention has been developed to provide a cured product that has low viscosity before curing, electrical insulation and elasticity after curing, and does not cause weight loss or increase in curing even under high temperature conditions. Moreover, it is an object of the present invention to provide a urethane system for a protective coating of a printed wiring board that maintains flexibility even in a low-temperature environment. Means for Solving the Problems The present invention provides a two-component solvent-free system consisting of a polyol component (A), a polyisocyanate component (B), and a plasticizer component (C), ) is a two-component solvent-free polyurethane-based curable composition for protective coating of printed wiring boards, characterized in that the composition is made of highly acylated castor oil with a hydroxyl value of 18 mgKOH/g or less. By discovering the use of a specific plasticizer component in this way, the above object has been achieved. The present invention will be explained in detail below. As the polyol component (A) in the present invention, a wide range of polyols can be used as long as they are ordinary polyols for producing polyurethane, but from the viewpoint of electrical properties and mechanical strength, high viscosity hydrocarbon polyols, castor oil Alternatively, it is particularly desirable to use castor oil derivatives. Here, the high viscosity hydrocarbon polyols include hydrocarbon polyols with a large hydroxyl equivalent;
In particular, hydrocarbon polyols having a hydroxyl value of 70 mgKOH/g or less are used, and specific examples thereof include polybutadiene polyols, hydrogenated products thereof, polyolefin polyols, and the like. These hydrocarbon polyols may be copolymers with vinyl monomers. Commercially available products include, for example, "PB R-45HT" manufactured by Idemitsu Petrochemical Co., Ltd., which is a polybutadiene polyol, "G-1000" manufactured by Nippon Soda Co., Ltd., and "Polytail" manufactured by Mitsubishi Chemical Corporation, which is a polyolefin polyol. H.A.”
and so on. Castor oil, as is well known, is a triglyceride whose main component is ricinoleic acid. As a castor oil derivative, the hydroxyl value is 20 mg.
Partially acylated castor oil having a KOH/g value or more, partially dehydrated castor oil having a hydroxyl value of 20 mg KOH/g or more, a castor oil-hydroxyl group-free natural oil or fat transesterification reaction product, etc. are used. Among the partially acylated castor oils, partially acetylated castor oil is important. Partially dehydrated castor oil is obtained by heating castor oil in the presence of an acidic catalyst such as sulfuric acid, phosphoric acid, or p-toluenesulfonic acid. Castor oil - hydroxyl group-free natural fat/oil transesterification product refers to a transesterification product of castor oil and hydroxyl group-free natural oil/fat in an appropriate ratio, for example, a weight ratio of 90-30:10-70. . During the esterification reaction, a small amount of low molecular weight polyol may be present. Examples of natural oils and fats that do not contain hydroxyl groups include linseed oil, tung oil, rapeseed oil, soybean oil, coconut oil, palm oil, palm kernel oil, horsetail oil, sunflower oil, safflower oil, lard, and various other vegetable oils. Animal oils are used. Next, as the polyisocyanate component (B), tolylene diisocyanate, diphenylmethane diisocyanate or carbodiimide-modified diphenylmethane diisocyanate, naphthalene diisocyanate, xylylene diisocyanate, diphenylsulfone diisocyanate, triphenylmethane diisocyanate, hexamethylene diisocyanate, 3- Methyl isocyanate-3,5,5
-trimethylcyclohexyl isocyanate, 3
-Ethyl isocyanate-3,5,5-trimethylcyclohexyl isocyanate, ethyl 3-isocyanate-3,5,5-trimethylcyclohexyl isocyanate, diphenylpropane diisocyanate, phenylene diisocyanate, cyclohexylylene diisocyanate, 3,3-diisocyanate dipropyl ether , triphenylmethane triisocyanate, diphenyl ether-4,4-diisocyanate, isophorone diisocyanate, and the like. Prepolymers having terminal isocyanate groups derived from these polyisocyanates and various polyols can also be used. Incidentally, an inert process oil, fatty acid ester, etc. may be added to the polyisocyanate component (B) in order to adjust the viscosity and improve storage stability. And the plasticizer component (C) which is the characteristic component of the present invention
Highly acylated castor oil with a hydroxyl value of 18 mgKOH/g or less, that is, castor oil that has been completely or nearly completely acylated, is used. Acylation of castor oil is carried out by conventional acylation means, and among the acylations, acetylation is the most important, and the industrial limit is actually limited to this acetylation, but in some cases, propionylation is partially carried out. It may be the same. As the acetylation method, a method of reacting with ketene and a method of reacting with glacial acetic acid are also employed, but acetylation with acetic anhydride is industrially most advantageous. Acylation is allowed to proceed as described above until the hydroxyl value becomes 18 mgKOH/g or less. The blending ratio of the above-mentioned polyol component (A), polyisocyanate component (B) and plasticizer component (C) is selected from the following range. First, the blending ratio of polyol component (A) and polyisocyanate component (B) is
It is preferable that the amount of isocyanate groups in (B) be 0.8 to 1.4 equivalents based on the total amount of hydroxyl groups in polyol component (A) because sufficient curing can be achieved. Next, highly acylated castor oil, which is a plasticizer component (C), is a polyol component (A) and a polyisocyanate component.
1 to 60% by weight, preferably 2% by weight based on the total amount with (B)
It is desirable to use ~50% by weight. If the amount is too small, the desired plasticizing effect cannot be obtained, while if the amount is too large, the cured product will lack mechanical strength. Highly acylated castor oil, which is a plasticizer component (C), reduces the viscosity of the polyol component (A), so it is usually blended into this polyol component (A). ) may be added to the polyol component (A) and polyisocyanate component.
It may be combined with (B) or both components.
(A) and (B) may be mixed at the same time. Furthermore, when the polyisocyanate component (B) is a prepolymer, the plasticizer component (C) may be added as a diluent during the production of the prepolymer. By blending the plasticizer component (C), the viscosity of the system is reduced, and the work from mixing to coating the mounted printed wiring board etc. becomes significantly easier and the work time is shortened. The above composition may contain fillers, pigments, flame retardants, other plasticizers, curing accelerators, crosslinking agents,
Various additives such as reinforcing materials, antioxidants, ultraviolet absorbers, and moisture adsorbents can be added. However, substantially no solvent is used. The composition of the present invention can be used in vending machines, electric washing machines,
Used as a protective coating for printed wiring boards after mounting in heated toilet seats, air conditioners, automotive electrical components, industrial machinery, etc. For the protective coating, methods such as coating, casting, dipping, potting, and caseless potting can be adopted. Effect In the present invention, the highly acylated castor oil constituting the plasticizer component (C) is determined by the viscosity of the polyol component (A) or the viscosity of the polyol component (A) and the polyisocyanate component.
It plays a role in significantly reducing the viscosity of the system after mixing (B). Since it has a sufficient plasticizing effect, it maintains the flexibility of the cured product and effectively prevents the hardness of the cured product from increasing even under low temperature conditions. In addition, it has low water absorption and excellent electrical insulation properties, so it does not deteriorate the electrical properties of the cured product. Furthermore, highly acylated castor oil has a molecular weight of 900
Since it has low volatility, there is little loss due to volatilization even if the cured product is kept under high temperature conditions for a long period of time, and there is no risk of hardness increasing. Examples Next, the curable composition of the present invention will be further explained with reference to Examples. Synthesis example of highly acylated castor oil 1 Castor oil (hydroxyl value: 160mgKOH/g, viscosity:
700cps/25℃) 3000g and acetic anhydride 915g with a thermometer,
A flask equipped with a stirrer and a reflux condenser was charged, and the reaction was continued at 120-150°C for about 2.5 hours. Then, the reflux condenser was replaced with a distillation condenser, and the temperature was gradually raised to recover by-product acetic acid and unreacted acetic anhydride by distillation. During this time, the degree of decompression was gradually increased using an aspirator. The temperature of the system reached 200°C after 1 hour, so it was kept at this temperature for 15 minutes and then cooled. As a result, highly acetylated castor oil having a hydroxyl value of O mgKOH/g and a viscosity of 230 cps/25°C was obtained. Synthesis example 2 3000g castor oil and 750g acetic anhydride at 120-150℃
The reaction was continued for about 2.5 hours, and highly acetylated castor oil was obtained in the same manner as in Synthesis Example 1.
Hydroxyl value is 18mgKOH/g, viscosity is 240cps/25℃
It was hot. Preparation of polyurethane composition Polyol component (A), polyisocyanate component (B)
And as a plasticizer component (C), the following were prepared. Polyol component (A) (A1) Polybutadiene polyol (PB R-45HT manufactured by Idemitsu Petrochemical Co., Ltd., number average molecular weight: 2800, number of functional groups: 2.2 to 2.4, iodine value:
398, hydroxyl value: 46mgKOH/g, viscosity:
6800cps/25℃) (A2) Castor oil (hydroxyl value: 160mgKOH/g,
Viscosity: 700cps/25℃) (A3) Partially acetylated castor oil (manufactured according to Synthesis Example 1 above, hydroxyl value: 140mgKOH/g,
Viscosity: 550 cps/25℃) (A4) Partially dehydrated castor oil (manufactured by heating and reacting castor oil at 190 to 250℃ under reduced pressure in the presence of acidic sodium sulfate, hydroxyl value: 137mgKOH/g, viscosity: 490cps/ (25℃) (A5) Castor oil - hydroxyl group-free natural fat and oil transesterification product (100 g of castor oil and 100 g of rapeseed oil)
Polyisocyanate component (B) B1) Carbodiimide-modified 4,4'-diphenylmethane diisocyanate (Millionate MTL manufactured by Nippon Polyurethane Co., Ltd.) (B2) Carbodiimide-modified 4 of (B1) above,
Prepolymer of 4′-diphenylmethane diisocyanate and castor oil (B3) Tolylene diisocyanate and polybutadiene polyol (manufactured by Idemitsu Petrochemical Co., Ltd.)
HTP-9) and highly acylated castor oil (C) (C1) Highly acetylated castor oil (synthesis example 1 above)
What was obtained, hydroxyl value: O mgKOH/g,
Viscosity: 230cps/25℃ (C2) Highly acetylated castor oil (synthesis example 2 above)
What was obtained, hydroxyl value: 18mgKOH/g,
Viscosity: 240 cps/25°C) Examples 1 to 6 Among the above components, first mix component (A) and component (C) and check their viscosity, then mix this with component (B) and check its viscosity. At the same time, it was cast onto a glass plate to a thickness of 3 mm, left at 60℃ for 16 hours, and the cured product was peeled off from the glass plate to determine hardness (at room temperature and low temperature), tensile strength, volume resistivity, and water absorption. was used for measurement.
Among the measurement items, hardness and tensile strength were measured based on JIS K6301, and volume resistivity and water absorption were measured based on JIS K6911. Further, the cured product was kept at a temperature of 100° C. for 120 hours, and the loss on heating was measured. Table 1 shows the types and blending ratios of each component, and the results. Note that Table 1 also shows comparative examples that do not use component (C).

【table】

[Table] As is clear from Table 1, in the composition of the present invention using highly acylated castor oil as the plasticizer component (C), the viscosity of the system is low and the cured product has high elongation. It can be seen that the material maintains its flexibility under both high and low temperature conditions, and there is no increase in hardness due to volatilization or dissipation even under high temperature conditions. On the other hand, in Comparative Example 1 in which polybutadiene polyol was used as the polyol component (A) and no plasticizer component (C) was blended, the viscosity was extremely high. In addition, in Comparative Example 2 in which castor oil was used as the polyol component (A) and no plasticizer component (C) was blended, the hardness of the cured product, especially at low temperatures, was high, making it suitable for use as a protective coating for printed wiring boards. Not yet. Furthermore, polybutadiene polyol and castor oil are used together as the polyol component (A), and the plasticizer component
Comparative Example 3, which does not contain (C), has a high viscosity and high hardness at low temperatures. On the other hand, process oil is contained in the polyol component (A).
In Comparative Example 4, in which dibutyl phthalate was blended into the polyisocyanate component (B), the hardness at low temperatures was relatively high, and the weight loss under high temperature conditions was not negligible. Similarly, in Comparative Example 5 in which process oil was blended into both the polyol component (A) and the polyisocyanate component (B), the weight loss was remarkable under high temperature conditions. As mentioned above, all of the comparative examples are inferior in viscosity, hardness at low temperatures, and change at high temperatures, and are therefore unsatisfactory as protective coatings for printed wiring boards. Effects of the Invention Since the composition of the present invention has a low viscosity, it is easy to work with, and the working time can be significantly shortened. In addition, the obtained cured product has flexibility, and even if it is kept under low temperature conditions, the increase in hardness is suppressed, and even under high temperature conditions, the volatilization of the plasticizer component,
It does not damage the objects coated with this cured product, since there is no escape and therefore it remains flexible when used under any temperature conditions. Furthermore, the cured product has low water absorption and excellent electrical insulation properties at high temperatures and high humidity. Therefore, if the composition of the present invention having such an excellent balance of properties is coated on a printed wiring board after mounting, the board will be safely protected for a long period of time, and troubles such as disconnection of wiring will not occur. .

Claims (1)

[Claims] 1. Polyol component (A), polyisocyanate component
A two-component solvent-free system consisting of (B) and a plasticizer component (C), wherein the plasticizer component (C) has a hydroxyl value of 18 mg.
A two-component solvent-free polyurethane-based curable composition for protective coating of printed wiring boards, characterized by comprising highly acylated castor oil of KOH/g or less. 2 The polyol component (A) is a high viscosity hydrocarbon polyol, castor oil, or a hydroxyl value of 20mg
A patent claim that is a castor oil derivative selected from the group consisting of partially acylated castor oil having a KOH/g or more, partially dehydrated castor oil having a hydroxyl value of 20 mgKOH/g or more, and a castor oil-hydroxyl group-free natural oil or fat transesterification product. The composition according to item 1.