SQL 2012 :: Data Not Filtering Properly

I have to filter my some of the data using below sql

select * from dbo.tmp_date
where issue_dt <'042015' but its not filtering out because of NVARCHAR an if suppose i used datatype to int its removing 0 (zero) from the begning

My data is in formate MMYYYY formate

CREATE TABLE dbo.tmp_date (issue_dt NVARCHAR(10));
INSERT INTO dbo.tmp_date (issue_dt)
SELECT '062012'
UNION
SELECT '062079'
UNION
SELECT '062015'
UNION
SELECT '062014'
GO
select * from dbo.tmp_date
where issue_dt <'042015'
go