I just found an error while trying to write several keywords (an array) with the binary function... please consider using the following: 

<?php
function binary() {
            $iptc_new = '';
            foreach (array_keys($this->meta) as $s) {
                $tag = str_replace("2#", "", $s);
                if(count($this->meta[$s])>1){
                    foreach ($this->meta[$s] as $row){
                        $iptc_new .= $this->iptc_maketag(2, $tag, $row);
                    }
                }else {
                    $iptc_new .= $this->iptc_maketag(2, $tag, $this->meta[$s][0]);
                }
            }
            return $iptc_new;
        }
?>