DataTables pagination prevents $_POST from getting all checkbox values

I have a table that has a checkbox on it. I'm trying to POST all the checked checkboxes but whenever I submit my button the only values it gets are from the current page of checked row.

form

<form method="post" action="post_chk.php">
    <td>
        <input type="checkbox" name="chkbx[]" value="$key[data]">
    </td>
</form>

post_chk.php

<?php
   $data = $_POST['chkbx'];
   var_dump($data); exit;
?>

how can I get all data from the datatables pagination..