How can I download file in admin Wordpress

Question

I faced with problem. I have my self written plugin (my-plugin). It has admin page "users".

That page uses script /wp-content/plugins/my-plugin/my-plugin.php which inludes file /wp-content/plugins/my-plugin/users.php In admin area i use such url: /wp-admin/admin.php?page=my-plugin.php

I made there csv export link: /wp-admin/admin.php?page=my-plugin.php?export=1

code in users.php:

if (isset($_GET['export']))
{
    user_export($_GET['export']);
}

function user_export($type)//export exel
{
    global $wpdb;

    $filename = "users_".date("Y-m-d_H-i",time());

    $result = mysql_query("SHOW COLUMNS FROM `".$wpdb->prefix . "users`") or die(mysql_error());
    $i = 0;
    if (mysql_num_rows($result) > 0)
    {
        while ($row = mysql_fetch_assoc($result))
        {
            $csv_output .= $row['Field']."; ";
            $i++;
        }
    }
    $csv_output .= "\n";

    $values = mysql_query("SELECT * FROM `".$wpdb->prefix . "users`") or die(mysql_error());
    while ($rowr = mysql_fetch_row($values))
    {
        for ($j=0;$j<$i;$j++)
        {
            $csv_output .= $rowr[$j]."; ";
        }
        $csv_output .= "\n";
    }


    header("Content-type: application/vnd.ms-excel");
    header("Content-disposition: csv" . date("Y-m-d") . ".csv");
    header("Content-disposition: filename=".$filename.".csv");
    print $csv_output;
    exit;
}

I'm getting the file by clicking on the link, but that file contains all wordpress admin panel design.

I need get just get excel export file by clicking on link on admin page of my plugin.

May anybody help me?