Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1983-11-18
1986-12-16
Weston, Caleb
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156 85, 156 87, 156200, 156229, 15624411, 15624424, 156494, 156500, 2642896, 2642902, 2641761, B32B 3114
Patent
active
046295259
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of preparing a high strength sheet material comprising forming a laminate comprising at least two layers of a thermoplastic polymer material, each layer having a fibrillar grain structure providing a predominant direction of splitability in said layer, the layers being bonded to one another with the said predominant directions of splittability transverse to each other, and biaxially orienting the molecules of said layers by stretching the layers in substantially uniaxial steps, the transverse stretching being effected by applying pressure to the surface of the laminate along lines extending substantially in the longitudinal direction of the laminate to impart thereto a waved configuration.
British patent specification No. 1.526.722 describes the manufacture of a laminate by a method comprising extruding at least two layers, each consisting of a blend of polymers which are incompatible to such a degree that the blend on solidification forms a dispersion of particles of one polymer in a polymeric matrix melt, attenuating each layer to obtain a fibrillar grain structure having a predominant direction of splittability after solidification into a film, bonding the two layers to one another with the predominant directions of splittability transverse to one another and biaxially stretching the solidified laminate in substantially uniaxial steps, the stretching being conducted at a temperature sufficiently low to maintain the predominant direction of splittability in each layer.
The specification of British Pat. No. 1.526.724 describes the manufacture of a laminate comprising at least two films of a polymeric material by a method which comprises pressing the film together along lines extending substantially in the longitudinal direction of the films and simultaneously stretching the films in the transverse direction, thereby forming a laminate having a waved or sinuous configuration in its transverse direction.
The latter method may advantageously by utilized to bond the two layers together and to effect the transverse stretching of the laminate in the method described in the British patent specification No. 1.526.722. However, the laminates thus produced ordinarily exhibit longitudinal striations which impart to the laminate thickness variations in the transverse direction and consequently an unsatisfactory rigidity, low temperature tear strength and sealability.
The object of the invention is to provide a laminate having an improved rigidity, an improved low temperature tear strength and improved sealability.
Another object of the invention is to provide a laminate which is suitable for use in the manufacture of heavy duty sacks or bags, e.g. sacks for Portland cement.
A further object of the invention is to provide a laminate having an increased yield point and improved anti-creep properties.
These objects and other objects which will become clear from the following description are obtained by the invention.
According to a first aspect of the invention there is provided a method of the above mentioned type which method comprises the additional step of subjecting the biaxially oriented laminate to a heat treatment while allowing at least 7% shrinkage of the laminate to take place in at least its transverse direction.
This aspect of the invention is based on the discovery that the relatively thin zones of the transversely stretched laminates are overstretched and that the material in these zones exhibit a pronounced tendency to contract when heated to an elevated temperature. Consequently, variations in the thickness of the laminate tend to be reduced or almost eliminated during such a heat treatment.
It is preferred to effect a shrinkage of at least 12% in the transverse direction.
The heat treatment may be effected in an oven but in practice it is preferably effected by contacting the laminate with the surface of a heated body because the transverse contraction of the laminate will then occur under more controlled conditions. The heated body is preferably a heated roller.
In o
REFERENCES:
patent: 3484916 (1969-12-01), Johnstone
patent: 3539439 (1970-11-01), Calderwood et al.
patent: 4039364 (1977-08-01), Rasmussen
patent: 4116892 (1978-09-01), Schwarz
patent: 4415523 (1983-11-01), Barham et al.
patent: 4426343 (1984-01-01), Vittone et al.
patent: 4496413 (1985-01-01), Sharps
Daniel William J.
Weston Caleb
LandOfFree
Method and apparatus for preparing a high strength sheet materia does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for preparing a high strength sheet materia, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for preparing a high strength sheet materia will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-244025