Under German labor law am I entitled to health insurance/social security by my employer while on unpaid leave?

Unpaid leave in this case is not parental or sick leave but voluntary unpaid leave to take time off work.
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Information about German labor law from the German embassy in Washington DC: http://www.germany.info/relaunch/busines… It says this: Labor relations between employers and employees are regulated in the Federal Republic of Germany by legislation, collective agreements and contracts of employment. The so-called "freedom of coalition" is guaranteed to employers and employees alike under the Basic Law (Germany's constitution). For the social partners, this ensures the freedom to negotiate collective agreements, i.e. autonomy in collective bargaining. Employees are entitled to wages/salaries during their leave. An additional payment (holiday bonus) is also made. There is, however, no legal right to this payment unless it is stipulated in a collective agreement or individual agreement. In Germany employees have a legal right to the continued payment of 80% of wages or salaries in the event of sickness. This right extends to a period of six weeks. So the main question would be: (1) is there a collective agreement or (2) individual agreement which would negate this?
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