<?php $args = array(
'post_type' => 'product',
'post_status' => 'publish',
'meta_query' => array(
        array(
             'key' => '_visibility',
             'value' =>  'visible',
             'compare' => 'IN'
             )
),
'posts_per_page' => 20);

$loop = new WP_Query( $args );
while ( $loop->have_posts() ) : $loop->the_post();  ?>