CS247273B1 - Polyimide binder and method of its production - Google Patents

Abstract

The solution relates to a polyimide binder and a method for preparing such a binder for electrical engineering purposes. Binders are used as impregnant layered masses usable at temperatures of 160 to 250 ° C. The essence of the solution is that polyimide bismaleimide-type prepolymer prepared from a mixed solvent environment is reacted with a ketone in the next step. Polyimide binder according to this solution it has high temperature resistance and in application in the laminates they increase their mechanical strength strength and improves dielectric1 vlastosti.

Description

The invention provides a polyimide binder and a process for preparing a polyimide binder for layered materials, in particular of the electrotechnical type with reinforcement from inorganic or organic fabrics, fibers or mats.

The purpose of the invention is to prepare a suitable binder for both technically and economically advantageous types of layered insulators usable at temperatures of 180 to 250 ° C.

The application of polyimide thermosetting resins to composite materials is increasingly widespread in the world due to their excellent mechanical and electrical insulating properties under long-term increased thermal stress. Products based on polyimide resins, e.g. fiberglass laminates, including materials clad with metal foil, mats, synthetic paper, stamping and potting materials, are found in the electrical and electronics industries, as well as in the engineering and aerospace industries.

The thermosetting polyimide prepolymers, which are used either pure or modified with other additives, form the bituminous base of the layered insulators with higher temperature resistance. The solvent for these polymers is usually an amide solvent such as N-methyl-2-pyrrolidone or Ν, Ν-dimethylformamide. For preparing the impregnating solution of the polyimide prepolymer, 1-methoxyethanol (methylcellosolve) or 2-ethoxyethanol (ethylcellosolve), respectively, may be used as solvent. other glycol ether.

A disadvantage of these solvents is that the polyimide prepolymer solution is unstable and has a short shelf life. When N-methyl-2-pyrrolidone or Ν, Ν-dimethylformamide is used as solvent, the high volatile content of the impregnated prepreg remains due to the strong polarity of the solvent, when using glycol ethers, especially methoxyethanol, there is a risk of explosion due to low autoignition temperature.

The patents of General Electric BP 1374126 and BP 1 374 127 disclose a one-step preparation of polyimide prepolymers in ketone solvents (without separation of bismaleinimide as an intermediate) in the presence of nickel acetate catalyst and acetic anhydride. If acidic components remain in the product, they prevent the preparation of laminates, in particular clad with metal foils.

The invention solves the drawbacks of the prior art. SUMMARY OF THE INVENTION The present invention provides a polyimide binder for electrotechnical type bismaleinimide based laminates suitable for preparing high temperature resistant laminates obtainable by reacting bismaleimide and diamine in a molar ratio of 2: 1 to 50: 1 in the presence of 1 to 30 weight percent wherein R is an aromatic or aliphatic hydrocarbon radical having 1 to 6 carbon atoms in the chain, R1 is an alkyl radical having 1 to 3 carbon atoms, optionally also in the presence of 2 to 50 percent by weight of epoxy or 2 to 6 carbon atoms; 40 weight percent of the phenolic resin or a mixture thereof in an arbitrary ratio so as to have a total amount of 2 to 50 weight percent of the dry weight of the polyimide prepolymer. The present invention also provides a process for the preparation of a polyimide binder, characterized in that bismaleimide is reacted with diamine in a molar ratio of 2: 1 to 50: 1 in an amide and non-polar mixed solvent, preferably N-methyl-2-pyrrolidone, Ν, Ν-dimethylformamide, dimethylacetamide and benzene, toluene, xylene, or theta solvents or mixtures thereof in a ratio of 3: 0.5 to 3: 2 and in the next step the resulting solution is reacted with 1 to 30% by weight to dryness of the prepolymer, ketone of the above formula at a temperature of 15 to 60 ° C, for a period of 3 to 24 hours, also in the presence of the aforementioned epoxy or phenolic resins.

According to the present invention, ketones are not mere inert solvents, but react with the polyimide prepolymer and cooperate in its crosslinking in such a way that the imide content of the polymer is increased by about 10% compared to polyimides without ketones. The laminate prepared from the polyimide prepolymer of the present invention exhibits increased temperature resistance after curing.

The polyimide prepolymer in combination with phenolic resins, respectively. with epoxy resins when applied in composite materials increases their resistance to fire propagation.

The prepolymers are prepared by known procedures by reaction of bisimides with diamines in solvents or in the melt (in a molar ratio of 2-2.5: 1), respectively. diamines with dianhydrides of aromatic tetracarbonic acids, preferably pyromellitic acid in combination with bisimides in solvents and in the presence of a catalyst (cf. AO 174 567) .The formation of curable compositions is accelerated by the addition of peroxides such as benzoyl peroxide, dicumyl peroxide and the like. up to 5% on the dry weight of the prepolymer.

If the prepolymers thus prepared precipitate in non-solvents, e.g. in water, the product dried at 30 to 50 ° C is suitable as a base for polyimide molding and encapsulating materials. A prepolymer prepared in a mixed solvent of amide and nonpolar liquid in a ratio of 3: 0.5 to 3: 2 is used to impregnate the reinforcement of the layered material. This ratio ensures that no two-phase system or formation is formed. precipitating a prepolymer whose content in the solvent is 20 to 60 wt. % dry matter. The amide component of the mixed solvent is e.g. Ν, Ν-dimethylformamide, N-methyl-2-pyrrolidone, dimethylacetamide; the non-polar component is e.g. benzene, toluene or xylene, reisp. thetrar solvents, e.g. dioxane, 1,2-dimethoxyethane, dimethylsulfoxide or mixtures thereof. Combination of N-methyl-2-pyrrolidone and toluene in a ratio of 3: 2 is preferred.

The polyimide prepolymer solution containing from 20 to 60% by weight of the dry weight of the polyimide is then reacted with the ketone hydrocarbon R-CO-RI in an amount of 1 to 30% by weight. %, Preferably with acetone in an amount of up to 24 wt. %, at 15 to 60 ° C, for 3 to 24 hours with stirring. Under these conditions, the imide content of the polyimide prepolymer is increased by about 10%, the gelation time of the polyimide is reduced, and the curing of the laminates is accelerated, while increasing their temperature resistance, especially during long-term thermal stress. The following table shows the flexural strength values during thermal aging of polyimide fiberglass:

Table: Flexural strength (MPa) after thermal aging

sample Supplied condition 25 ° C (MPa) 2,500 h at 200 ° C 5000 h at 200 ° C 2,500 h at 220 ° C 625 h at 240 ° C 1 626 389 150 192 408 2 627 551 350 350 500 3 608 450 320 270 517

where:

sample 1:

fiberglass prepared from polyimide prepolymer in N-methyl-2-pyrrolidone solution, sample 2:

fiberglass prepared from epoxide-modified polyimide in N-methyl-2-pyrrolidone-1-methylethylketone solution, sample 3:

fiberglass prepared from an epoxide-modified polyimide prepolymer in a solution of N-methyl-2-pyrrolidone-1-acetone.

The impregnating base solution may be modified after reacting with the ketones by some thermosetting plastics, e.g.

a) with epoxy dianum resins, gram equivalent / 100 g 0.17-0.50 in an amount of 2 to 50% by weight on dry matter,

(b) with epoxy novolac resins, gram equivalent / 100 g 0,25-0,60 in an amount of 2 to 50% w / w of dry matter,

c) with diano-type bromo-epoxy resins, gram equivalent (100 g 0.17-0.50 with a bromine content of 15-25 ° / o in an amount of 2-50 parts by weight per dry weight of the polyimide prepolymer,

(d) the combinations referred to in points a, b, c may be further crosslinked by the addition of aromatic amine hardeners for epoxides, e.g. 4,4‘-diaminodiphenylmethane, 4,4‘-diaminodiphenylsulfone in an amount of 1 to 10 parts by weight per dry mass of epoxy resin used,

(e) with phenolic resin molecules of a mass of 600 to 2 500 in an amount of 2 to 40% per dry weight of polyimide resin;

(f) a mixture of the phenolic and epoxy resins referred to in (a), (b), (c) and (e) in any ratio such that their amount is 2 to 50% by weight per dry weight of the polyimide prepolymer.

The solution of the polyimide composition is adjusted to the required impregnation viscosity, depending on the resin used, the impregnation device and the impregnation conditions, by adding a suitable solvent, e.g. N-methyl-2-pyrrolidone and toluene.

The solution according to the invention makes it possible in an efficient manner to produce an impregnating resin for the preparation of high-quality laminates with increased temperature resistance and good electrical and insulating properties.

Examples of preparation of bituminous binders and their applications for laminated materials and prepregs are given in the following examples.

Example 1

To 100 g of a 40% solution of polyimide prepolymer, prepared by synthesis of 2.5 moles of 4,4'-diaminodiphenylmethane-bismaleinimide with 1 mole of 4,4'-diaminodiphenylmethane at 105 ° C for 4 hours in a solution of N-methyl-2- of pyrrolidone and toluene (3: 2 by weight) is admixed with 15 g of acetone and after standing for 3 hours at 25-30 ° C, a 48% solution of the polyimide composition is impregnated with a glass fabric to a dry binder content of 38-40%; after evaporation of the solvents in the drying tunnel of the impregnation machine at 155-160 ° C, a preperg is obtained. Compressing the superimposed prepreg at 170 ° C and 7 MPa for 2 hours followed by curing for 48 hours at 200 ° C without pressure affords a fiberglass having high mechanical properties at operating temperatures of 180 ° C and 200 ° C.

Example 2

Mix 100 g of a 45% polyimide resin solution prepared by synthesizing 12.5 moles of 4,4'-diaminodiphenylmethane-bis-maleimide with 1 mole of 4,4'-diaminodiphenylmethane at 105 ° C for 4 hours in a solution of N -methyl-2-pyrrolidone-y-toluene 3: 2, with 37 g of a 60% acetone solution of diane epoxy resin gram equivalent / 100 grams 0.18-0.24 and after stirring for 3 hours at 20-25 ° C a solution having a solids content of about 57% and a gelation time of 160 ° C for 6 minutes is obtained. This was used to impregnate the aminosilane-treated glass fabric to a 33% dry bituminous binder content. Dry for 5-10 minutes at 150-180 ^° C.

From the cut sheets, the laminate is pressed at 160 ° C at a pressure of 7 MPa for 5 hours and cured at 24 h / 190 ° C and 48 h / 200 ° C. After 2,500 hours of aging at 220 ° C, the laminate has a flexural strength of 300 MPa. The laminate prepared without the addition of epoxide and acetone exhibits a flexural strength of only 190-200 MPa after such aging.

Example 3

Mix 100 g of a 50% resin solution formed by condensing 2.5 mol of 4,4'-diammodiphenylmethane-bis-maleimide and 1 mol of 4,4'-diaminodiphenylmethane in a 2: 2 mixture of N-methyl-2-pyrrolidone and toluene: 1 with 31 g of brominated epoxy resin as an 80% solution in methyl ethyl ketone. After 24 hours, it is used to impregnate the glass fabric as in Example 2 and the impregnated fabric is pressed and cured. The laminate obtained after 2,500 hours of aging at 220 ° C achieves a flexural strength of 350 MPa. The laminate prepared without the addition of epoxide and methyl ethyl ketone achieves a bending strength of only 200 MPa under the same conditions.

Example 4

100 g of a 45 '% polyimide prepolymer solution prepared according to Example 2 are mixed with 15 g of a dianepoxide resin with an epoxy equivalent of 0.17-0.25 / 100 g, 10 g of acetone and 0.9 g of 4,4'-diaminodienylmethane, and homogenization for 2-3 hours at room temperature gives a solution with a solids content of about 56% and a gelation time of 160 ° C for about 3 minutes, impregnating a specially treated glass fabric (aminosilanes, epoxysilanes) to the binder content after adding 1.2 g of dicumylperoxide in impregnated material 40-45% and after removal of solvents in the drying tunnel of the vertical machine at 150-180 ° C for 5-10 minutes, a prepreg is obtained, suitable for preparing copper-clad laminate by pressing for 4-6 hours at 165-170 ° C and at a pressure of 4-6 MPa. The material has optimum properties after re-curing without pressure for 48 hours at 180-190 ° C. The planned material thus prepared is characterized by a dimensional stability of at least (0.0004 mm < 0.02-0.04%), a high temperature resistance on a solder bath for 3 minutes at 270-288 ° C and is suitable for the production of printed circuit boards.

Example 5

Rotzoc for impregnation is prepared by mixing 100 g of the polyimide prepolymer prepared as in Example 2 with 19 g of epoxy-equivalent bromo-epoxy resin / 100 g of 0.18-0.24, as an 80% solution in methyl ethyl ketone and 0.6 g of dicumylperoxide. The solution is diluted to a viscosity with N-methyl-2-pyrrolidone + toluene 3: 2 to give a bituminous binder deposit of 150% on the glass cloth when impregnated without the use of squeezing rollers. j. 60% binder content. After evaporation of the solvents in the vertical furnace of the impregnating machine at 140 to 160 ° C, a prepreg suitable as an adhesive sheet for self-extinguishing multilayer printed circuit boards into thermally stressed devices is obtained.

Example 6

A solution for impregnating glass cloth or carbon fibers is prepared by mixing 80 g of a 50% prepolymer solution prepared as in Example 1 with 20 g of cresolaniline formaldehyde resol (50% solution in ethanol or methanol) and after homogenization at room temperature. The dry prepreg is pressed together with the copper foil at a pressure of 4-7 MPa, at a temperature of 160-170 ° C, for 3 hours after being chopped and laminated in the number of presses required for the desired depth. the laminate after curing for 48 hours at 200 ° C is characterized by a high value of flexural strength measured at 200 ° C (about 70% of the value measured in the delivered state) and high values of electrical properties In the flammability test according to IEC 707/1981 (9) by the FV method, the material corresponds to class Vl.

Example 7

To 100 g of a 50% solution of the polyimide prepolymer prepared by the synthesis described in Example 3, 12 g of cresolaniline formaldehyde resin are added and the mixture is heated at 80 ° C for 10 minutes with stirring. Finally, 10 g of methyl ethyl ketone is added and the glass fabric is impregnated with this solution to a dried binder content of 40-45% and after evaporation of the solvents with the drying tunnel of the impregnation machine at t = 150-160 ° C, a prepreg is obtained. Compressing 28 layers of prepreg at 165 ° C and 5 MPa for 3 hours gives a fiberglass thickness of about 3 mm with a permanent temperature resistance of 180 ° C and excellent mechanical properties suitable for slot wedges in high-speed rotating machines.

Claims (2)

Polyimide binders for electrotechnical type bismaleinimide based laminates, suitable for the production of high temperature resistant laminates, obtainable by reacting bismaleinimide and diamine in a molar ratio of 2: 1 to 50: 1 in the presence of 1 to 30% by weight, to dry solid polyimide prepolymer of ketone of formula R - CO - R 1, wherein R is an aromatic or aliphatic hydrocarbon radical having 1 to 6 C atoms in the chain, R 1 is an alkyl radical having 1 to 3 C atoms, optionally also in the presence of 2 to 50 percent by weight epoxy or 2 to 40 weight percent of a phenolic resin, respectively. mixtures thereof in any ratio so as to have a total amount of 2 to 50 weight percent of the polyimide prepolymer solids. 2. A process for the preparation of a polyimide binder according to claim 1, characterized in that bismaleimide is reacted with diamine in a molar ratio of 2: 1 to 50: 1 in an amide and non-polar mixed solvent, preferably N-methyl-2-pyrrolidone, Ν, Ν. -dimethylformamide, dimethylacetamide and benzene, toluene, xylene or theta solvents or mixtures thereof in a ratio of 3: 0.5 to 3: 2 and in the next step the solution is reacted with 1 to 30 percent by weight, based on the dry weight of the polyimide prepolymer, ketone wherein R and R 1 are as defined in item 1, at a temperature of 15 to 60 ° C for 3 to 24 hours, optionally also in the presence of 2 to 50 percent by weight epoxy or 2 to 40 percent by weight phenolic resin , respectively. mixtures thereof in any ratio such that their total amount is 2 to 50% by weight per dry weight of the polyimide prepolymer.