Sealing system for forming thermal seals and method of operation thereof

A sealing system which forms spaced apart thermal seals along at least one moving web by contact of the moving at least one web with heated portions of sealing elements mounted on a sealing wheel during rotation comprising:

• seal forming elements which peripherally contact the at least one web to form the thermal seals by heat transfer to the at least one web;
• each seal forming element has an outer section on which is located at least one electrical heater, an inner section which contains the sealing wheel and an intermediate section which includes thermal insulation which insulates the outer section from the inner section;
• each electrical heater comprises a film electrical resistance;
• and
• a pair of film electrical resistances are disposed on opposed surfaces of each outer section and a seal forming surface touches the moving at least one web, is opposed to the thermal insulation and intersects the opposed surfaces of the outer section.

A sealing system which forms spaced apart thermal seals along at least one moving web by contact of the moving at least one web with heated portions of sealing elements mounted on a sealing wheel during rotation comprising:

• seal forming elements which peripherally contact the at least one web to form the thermal seals by heat transfer to the at least one web;
• each seal forming element has an outer section on which is located at least one electrical heater, an inner section which contains the sealing wheel and an intermediate section which includes thermal insulation which insulates the outer section from the inner section;
• each sealing forming element is radially adjustable to vary the spacing between the spaced apart thermal seals;
• each electrical heater comprises a film electrical resistance;
• and
• a pair of film electrical resistances are disposed on opposed surfaces of each outer section and a seal forming surface touches the moving at least one web, is opposed to the thermal insulation and intersects the opposed surfaces of the outer section.

A thermal sealing element comprising:

• a support;
• a film heating element having a resistance to which electric current for the generating heat to thermally seal film contacting the heating element;
• insulation separating the film heating element from the support;
• and
• the insulation comprises a section having a slot providing an air gap between the film heating element and the support with the section having a pair of projections which separate the support from the film heating element and which define ends of the air gap.

A thermal sealing element comprising:

• a support;
• a film heating element having a resistance to which electric current for the generating heat to thermally seal film contacting the heating element;
• insulation separating the film heating element from the support;
• the film resistance is a thick film resistance;
• the thick film resistance has a substrate which is a metallic member which is joined to the insulation, and
• the insulation comprises a section having a slot providing an air gap between the substrate and the support with the section having a pair of projections which separate the support from the substrate and which define ends of the air gap.

In a process for sealing one film ply to another by contacting one of said plies with one of a plurality of an outer heated sealing sections, the process including the steps of:

• running said plies longitudinally onto a moving outer sealing section;
• energizing an electrical heater wholly disposed on said outer sealing section and raising the temperature of said outer sealing section to heat and seal together two film plies lying across said outer sealing section;
• substantially thermally isolating said outer sealing section;
• stopping said movement of said plies while on said outer sealing section and thereby producing a uniform seal having parallel sides without destruction of said seal.

Apparatus for sealing one film ply to another film ply to form a moving chain of two sided pouches, said apparatus comprising:

• a sealing element having a sealing land and an inner section;
• a sealing land of one thermal mass, said thermal mass being lower than that of said inner section;
• a heater means disposed on said land for heating said land to seal two plies when introduced onto said land;
• said heater means comprising a thick film heater wholly disposed on said sealing land;
• and
• said land being at least partially thermally isolated from said inner section such that the thermal mass heated by said heater means is sufficient to uniformly seal said plies when temporarily disposed on said land, but is insufficient to burn through said plies or produce uneven seals when said plies are disposed on said land longer than temporarily.

In a process of producing transverse seals of at least one film layer to another film layer, the steps of:

• introducing said film layers onto a sealing element with a heater means of said element contacting at least one of said film layers;
• energizing said heater means to produce a seal in said two film layers;
• and
• isolating heat produced by said heater means from other components of said sealing element,
• wherein the film layers are continuously introduced to at least one sealing element and including the further step of stopping relative motion of said film layers with respect to said sealing element, de-energizing said heater means and producing a usable seal therein without burn through or significant seal growth.