The transaction certificates don't actually address privacy matters. rather, they authenticate that the transaction comes from a valid node.
These certificates invoke transaction in the chaincode.
I suggest you to start using the v1.0 of the Hyperledger Fabric coz v0.6 can't scale very well and can't support true private transactions and confidential contracts.
The v1.0 allows you to isolate Blockchain inside your network. That's possible through the channels, that when defined,let you define who are the members of it, so, only those peers could send transactions through that channel. Therefore, only members of the channel could see your transactions.
So, for your use case, you should create four channels, each one for each supplier, and the manufacturing company should be a member of all channels.