Laravel で CSV ダウンロード機能を実装する一例。

文字コードを SJIS で出力する場合の例。

use Symfony\Component\HttpFoundation\StreamedResponse;

class CsvController extends Controller
{
    public function download()
    {
        $users = Users::get();

        $response = new StreamedResponse(function () use ($users) {
            $stream = fopen('php://output', 'w');

            stream_filter_prepend($stream, 'convert.iconv.utf-8/cp932//TRANSLIT');

            fputcsv($stream, [
                'ID', '名前', 'メールアドレス'
            ]);

            foreach ($user as $key => $user) {
                fputcsv($stream, [
                    $user->id,
                    $user->name,
                    $user->email,
                ]);
            }

            fclose($stream);
        });

        $file_name = 'ファイル名.csv';

        $response->headers->set('Content-Type', 'application/octet-stream');
        $response->headers->set('content-disposition', 'attachment; filename=' . $file_name);

        return $response;
    }
}

class CsvController extends Controller
{
    public function download()
    {
        $csv_headers = ['No.', 'Name', 'Date'];
        $csv_body = [];

        // DB からデータを読み込むなどし csv_body に格納

        return response()->streamDownload(
            function () use ($csv_headers, $csv_body) {
                $stream = fopen('php://output', 'w');

                mb_convert_variables('SJIS-win', 'UTF-8', $csv_headers);
                fputcsv($stream, $csv_headers);

                foreach ($csv_body as $line) {
                    mb_convert_variables('SJIS-win', 'UTF-8', $line);
                    fputcsv($stream, $line);
                }

                fclose($stream);
            }, 'file_name.csv',
            ['Content-Type' => 'application/octet-stream']
        );
    }
}