What is the role of "but" in this context?

For the electronics industry, the television is an important but increasingly difficult product to sell.

I've already searched over the internet about all the meanings the conjunction but can have in a sentence, but I don't understand its meaning in this very context. I have read a text saying that the conjunction "but" can be used to add informations to a first sentence. Can you guys give me a hand and help me understand?

The purpose of but is a conjunction, meaning "on the contrary; in contrast" (New Oxford American Dictionary). It is the same as and, but emphasizes contrast. You can replace it with "however" or "yet".

In a comment, John Lawler wrote:

It's just a conjunction. But means "and". Try substituting and to see: television is an important and increasingly difficult product to sell. The only difference between but and and is that but implies some surprise on the part of the speaker -- something is not going as expected. What that might be is determined by context.