What does Conv1d do in a sentiment analysis?
Just think of it as another feature transformation that grasp a set of sequential data group into a convoluted, compressed data. The text is a sequence of words(tokens), and each focus word would have different relationship to another words back and front of it. Conv1D help us to get nice and neat set of features that represent such relationship. 

https://realpython.com/python-keras-text-classification/