Resin composition, method for producing resin composition, prepreg, film with resin, metal foil with resin, metal-clad laminate, and wiring board

A resin composition comprising:

• a thermosetting resin;
• a curing agent that reacts with the thermosetting resin;
• silica;
• and
• a flame retardant,
• wherein
• the thermosetting resin contains a modified polyphenylene ether compound which is terminal-modified with a substituent having a carbon-carbon unsaturated double bond,
• the curing agent contains at least one kind selected from the group consisting of a trialkenyl isocyanurate compound and a polyfunctional vinyl compound having two or more vinyl groups in a molecule,
• the flame retardant contains a compatible phosphorus compound that is compatible with a mixture of the thermosetting resin and the curing agent, and a non-compatible phosphorus compound that is not compatible with the mixture,
• the compatible phosphorus compound contains at least one kind selected from the group consisting of a phosphoric acid ester compound and a phosphazene compound,
• the non-compatible phosphorus compound contains at least one kind selected from the group consisting of a phosphinate compound and a diphenylphosphine oxide compound,
• a content of the compatible phosphorus compound is 1 to 3.5 parts by mass per 100 parts by mass of a total of the thermosetting resin and the curing agent,
• a content of the non-compatible phosphorus compound is 14 to 30 parts by mass per 100 parts by mass of the total of the thermosetting resin and the curing agent,
• a content ratio of the compatible phosphorus compound and the non-compatible phosphorus compound is 3:97 to 19:81 in mass ratio, and
• a content of the modified polyphenylene ether compound is 30 to 90 parts by mass per 100 parts by mass of the total of the modified polyphenylene ether compound and the curing agent.