If the printer is dedicated to this VM, there's really no need to create a VLAN interface on the MX.
You can simply setup a new VLAN on the vSwitch, configure that VLAN on the trunk ports on the switches through the network to the switch where the printer is connected and configure the printer port as an access port in that VLAN.
Don't set any default gateway on either the printer or the computer and you're good to go. Those devices will not be able to communicate with anything outside of that VLAN.
The only 'risk' of this is VLAN bleeding if someone misconfigures the network in the future. To minimize that, you can add switch ACL's to allow on the specific communication (IP's and ports) on that VLAN and deny all other communication from those hosts.