【Rails】seedデータ作成後に、新規作成(newアクション)をするとエラー

ActiveRecord::RecordNotUnique at /products/1/product_documents
PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "product_documents_pkey"
DETAIL:  Key (id)=(5) already exists.

2.times do |n|
  ProductDocument.create!(id: n,
                          user_id: 8,
                          product_id: n + 1,
                          name: 'name',
                          content: 'content',

end

3.times do |n|
  ProductDocument.create!(id: n + 2,
                          user_id: 9,
                          product_id: n + 3,
                          name: 'name',
                          content: 'content',
end