Varchar While Transferring Server Table To CSV File

I am currently woking on transfering the table contents in sql server in an csv file i have created a stored procedure which would do same but the prob i am facing is the data in the table is not clean it contains tab,newline etc so i had to clean the data i had applied the folowing procedure

declare @columns varchar(8000), @sql varchar(8000), @sql1 varchar(8000),@data_file varchar(100)

set @columns=''
--'@columns+''replace(replace(replace(''+column_name +'',Char(10),''''''''),Char(13),''''''''),Char(19) ,'''''''')'''
--print @sql
select
@columns=@columns+'replace(replace(replace('+colum n_name+',Char(10),''''),Char(13),''''),Char(19),'' '') as '+column_name+ ', '
from

[code]...

the table_name contains around 300 columns with the column_name of min 20 characters .When i run the above query i get only few columns instead of all the columns so i tried to find the length which gives me the result as 4000.I had declared @columns as Varchar(8000) i dont know why this issue is coming up?? is there any other way i can clean the data an the transfer it into the file