Method of forming composite seal structure of peel seal and tear seal

Abstract

A method of forming a composite seal structure having great resistance to rupture, rare generation of pinholes is provided which comprises using a heat sealer having two blocks which presses sheets to be heat-sealed and at least one of which is a heating block provided with a seat which renders its surface at a temperature forming peel seal, on a part of its surface pressing the sheets, heating the heating block at a temperature forming tear seat, and pressing the sheets to form a heat seal having the composite seal structure of peel seal and tear seal.

Description

FIELD OF THE INVENTION[0001]This invention relates to a method of forming a composite seal structure of peel seal and tear seal.BACKGROUND OF THE INVENTION[0002]Generally, heat sealing is applied to the production and sealing of bags and containers using plastic films or sheets.[0003]In conventional heat sealing, heating is carried out at a high temperature region where thermal adhesive layer is melted, and bonded area becomes tear seal uniformly.[0004]As a type of heat seal, peel seal is also known as well as tear seal. The inventor has investigated as to peel seal, patent applications were carried out (Japanese Patent Nos. 381145 and 3876990 corresponding to U.S. Pat. No. 6,952,959 B2).[0005]However, heating temperature range for forming peel seal is narrow and delicate compared with tear seal. Heretofore, there is no case of combining peel seal with tear seal, and moreover, it is not known any necessity for combining them.SUMMARY OF THE INVENTION[0006]The inventor continues inves...

AI Technical Summary

Benefits of technology

[0009]The bonded area formed by conventional heat sealing heated in tear seal region is bonded through cohesive adhesion of which tensile strength by JIS Z 0238 is great. However, since there is no cushioning action against breaking force, breaking stress is concentrated on minor portions to induce bag rupture or generation of pinholes. Thus, thickness of the adhesive layer is increased, or strong materials are employed, without utilizing average resistance to bag rupture of packaging materials to increase cost.

[0011]It is an object of the invention to provide a method of forming a heat seal structure which is resistant to bag rupture and generation of pinholes by dispersing bag rupture stress, without formation of polymer bead, and which can be formed by using cheap packaging materials with high reliability.

[0024]When peel progresses to reach near to outer periphery of the heat seal, bag rupture caused by the peel is avoided by stopping to peel by the tear seal zone having strong adhesive force. Energy consumed in the meantime is several times as much as the load bearing ability of the tear seal. In the method of forming a composite seal structure of the invention, the peel seal is followed by the tear seal. Since the formation can be conducted at an optimum temperature for the material to be heat-sealed, formation of polymer bead can be avoided.

[0025]According to the method of the invention, since heating can be conducted surely in a boundary region of peel seal and tear seal, optimum adhesion conditions for the material to be heat-sealed can be obtained in heat seal region. Since a bag rupture stress greater than the load bearing ability loaded to the heat seal line can be buffered by the consumption of the bag rupture energy by the peel energy, bag rupture and generation of pinholes can be avoided. Since temperature gradient is formed on heat seal area to form peel seal and tear seal continuously from the inside of bag or container, formation of polymer bead can be controlled. Since bag rupture stress can be dispersed in bonding area, generation of troubles can be prevented even by using cheap materials without increasing thickness or choosing strong materials. Since heat sealing can be controlled by reasonable method, reliability of heat seal can be ensured and improved.

Problems solved by technology

However, they are not radical measures to solve the problems of bag rupture and pinholes because of increasing material cost, lengthening heating period or elevating heating temperature.

However, since there is no cushioning action against breaking force, breaking stress is concentrated on minor portions to induce bag rupture or generation of pinholes.

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