無事以下のように追加して表示できるようになりました。
ありがとうございました。

foreach ($arrRet as $key => $value) {
$col = 's_i.*, tax_rate, tax_rule, c1.name AS class_name1, c2.name AS class_name2';
$from = 'dtb_shipment_item AS s_i JOIN dtb_order_detail AS o_d
ON s_i.order_id = o_d.order_id AND s_i.product_class_id = o_d.product_class_id
JOIN dtb_products_class AS p_c ON s_i.product_class_id = p_c.product_class_id
LEFT JOIN dtb_classcategory AS c_c1 ON p_c.classcategory_id1 = c_c1.classcategory_id
LEFT JOIN dtb_class AS c1 ON c_c1.class_id = c1.class_id
LEFT JOIN dtb_classcategory AS c_c2 ON p_c.classcategory_id2 = c_c2.classcategory_id
LEFT JOIN dtb_class AS c2 ON c_c2.class_id = c2.class_id';
$where = 'o_d.order_id = ? AND shipping_id = ?';
$arrWhereVal = array($order_id, $arrRet[$key]['shipping_id']);
$objQuery->setOrder('order_detail_id');
$arrItems = $objQuery->select($col, $from, $where, $arrWhereVal);
$arrRet[$key]['shipment_item'] = $arrItems;
}



tolに以下追加
<!--{$item.class_name1}-->
<!--{$item.class_name2}-->