Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Patent
1999-09-16
2000-10-31
Acquah, Samuel A.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
528298, 2642101, 2642106, 2642107, 26421112, 264212, 428174, 428332, 428340, 200512, B32B 516, C08G 6302, H01H 110
Patent
active
061399523
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a film for a membrane switch and, more specifically, to a biaxially oriented polyester film for a membrane switch, which is made from a polyester comprising ethylene-2,6-naphthalene dicarboxylate as a main recurring unit and which has excellent deformation resistance during its use at high temperatures.
BACKGROUND ART
As disclosed at page 111 of the "'85 edition of Switch Latest Technology" published by Sogo Gijutsu Syuppansha on Sep. 28, 1984, a membrane switch comprises a spacer between two base films to define a space between the two base films and contact points (electrodes) arranged on the opposed surfaces of the two base films which face each other with the space in between. By depressing one of the base films, two contact points are brought into contact with each other to conduct electricity and by releasing the depressed base film, they are disconnected from each other, thus effecting a switching function.
In recent years, such a membrane switch has been frequently used as a key board switch for calculators and personal computers, a panel switch for the remote controller of TVs and VTRs, and the like.
Since this membrane switch effects a switching function by alternating being depressed and released, flexibility, that is, deformation resistance is required for the base film of the membrane switch. Heretofore, a polyethylene terephthalate (may be abbreviated as "PET" hereinafter) film has been generally and frequently used as the base film of this membrane switch due to its deformation resistance, adhesion to electrodes, adhesion to printing and the like.
However, owing to the recent use of touch panels for car audio systems and car air conditioning systems or remote control switches in a vehicle due to the popularization of car navigation systems, deformation resistance at high temperatures is required for the base film of the membrane switch.
When a PET film is used as the base film of the membrane switch as before, temperature inside a vehicle (about 80.degree. C.) may exceed the glass transition temperature of PET in summer and the membrane switch may malfunction due to the great deformation of a PET film.
To prevent this, JP-B 4-75610 proposes that a polyethylene naphthalene dicarboxylate (may be abbreviated as "PEN" hereinafter) film which has a higher glass transition temperature than a PET film be used as the base film in place of the PET film.
That is, JP-B 4-75610 discloses a membrane switch having contact points on the opposed surfaces of two base films, at least one of which is a biaxially oriented polyethylene naphthalene dicarboxylate film having an F-5 value (5% elongation stress) of 11 kg/mm.sup.2 or more, a density of 1.375 g/cm.sup.3 or less and a thermal shrinkage factor of 1.0% or less when heated at 120.degree. C. for 30 minutes.
JP-B 6-4276 discloses a polyester film for a membrane switch which is made from polyethylene naphthalate having a haze increase rate defined by the following expression of 20% or less when heated at 150.degree. C. for 2 hours: haze value after the heat treatment, and thermal shrinkage factors in both longitudinal and transverse directions of 0.5% or less.
However, standards for deformation resistance have been reviewed due to the influence of the recent enforcement of the PL Act and it has been pointed out that even a PEN film is unsatisfactory in terms of deformation resistance. When a membrane switch is used as a pressure sensor, especially when it is embedded in a seat of an automobile equipped with an air bag as a pressure sensor of a weight detection system for detecting pressure to alter the inflation speed of the air bag according to an adult or a child, a conventional PEN film has large residual deformation and cannot be used.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a biaxially oriented polyester film for a membrane switch, which is made from a polyester comprising ethylene-2,6-naphthalene dicarboxylate as a main recurring unit and which has excellent
REFERENCES:
patent: 4725479 (1988-02-01), Utsumi
patent: 5312893 (1994-05-01), Hamano et al.
patent: 5380577 (1995-01-01), Hamano et al.
patent: 5731071 (1998-03-01), Etchu et al.
Taiwan Office Action dated Nov. 24, 1999.
International Search Report.
Furuya Koji
Kawai Shinichi
Suzuki Kenji
Watanabe Shinya
Acquah Samuel A.
Teijin Limited
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