Checkbox group array always empty

I have a really irritating problem with a form I'm working on. There are two inputs:

• a text input field to enter email address (no problem)
• a checkbox group generated by a foreach'es with info from the database (leaves empty input)

The whole form looks like this:

<form role="form" id="contactForm" class="contact-form" data-toggle="validator" class="shake">`

$post_type = 'education';
$taxonomies = get_object_taxonomies( array( 'post_type' => $post_type ) );

foreach( $taxonomies as $taxonomy ) :
$terms = get_terms( $taxonomy );

foreach( $terms as $term ) : ?>

        <h2><?php echo $term->name; ?></h2>

    <?php
    $args = array(
            'post_type' => $post_type,
            'posts_per_page' => -1,  //show all posts
            'tax_query' => array(
                array(
                    'taxonomy' => $taxonomy,
                    'field' => 'slug',
                    'terms' => $term->slug,
                )
            )

        );
    $posts = new WP_Query($args);


    if( $posts->have_posts() ): while( $posts->have_posts() ) : $posts->the_post(); ?>
                <h4><?php the_title();?></h4>
     <div class="form-group">
            <div class="controls">
            <?php $fil = get_field('fil');
            if( !empty($fil) ): ?>
              <input type="checkbox" value="test" name="download_file[]" class="form-control">
              <?php endif; ?>
              <div class="help-block with-errors"></div>
            </div>
        </div>

    <?php endwhile; endif; ?>
    <div class="clear"></div>
    <br />
    <hr>
    <br />

<?php endforeach;

endforeach;  ?>
          <div class="form-group">
            <div class="controls">
              <input type="email" class="email form-control" name="email" placeholder="Email" id="email" required data-error="Please enter your email">
              <div class="help-block with-errors"></div>
            </div>
          </div>

          <button type="submit" id="submit" class="btn btn-success"></i> Send Message</button>
          <div id="msgSubmit" class="h3 text-center hidden"></div> 
          <div class="clearfix"></div>   

        </form>  

As soon as the button gets clicked, the content from the form gets sent as an email. The email address from the form is visible, but the download_file part is always empty, no matter how many checkboxes I check.

I use the following code to see the output from the form:

<table>
<?php 


foreach ($_POST as $key => $value) {
    echo "<tr>";
    echo "<td>";
    echo $key;
    echo "</td>";
    echo "<td>";
    echo $value;
    echo "</td>";
    echo "</tr>";
}


?>
</table>

and this outputs [object Object] for each checkbox that is checked.

Does anyone know why this happens? Can it be something with the foreach'es that ends before the form ends?

Many thanks in advance!