Cross-laminate of films and method of manufacturing
OwnerOle-Bendt Rasmusseninventor
Life of this patent
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Abstract
A cross-laminate web is formed of two oriented films, the films being arranged so that the main direction of orientation of the first film (A) generally follows the longitudinal direction (D) of the web and the main direction of the second film (B) is perpendicular (F) to that direction. The coefficient of elasticity of the material of the first film, in an unoriented state, is at least 115% lower than that of the material of the second film, and the heat shrinkability of the first film is greater than that of the second film. Bags formed from the cross-laminate have heat seals with improved shock peel strength.
Claims22
A webformed cross-laminate consisting of two or more mutually bonded films or film assemblies, each of which is uniaxially oriented or unbalanced biaxially oriented, characterised in that said laminate comprises (A) on one side of the cross-laminate either a) a film in which the main direction of orientation generally follows the longitudinal direction of the web, or b) an assembly of films, the resultant main direction of which generally follows the said direction, and (B) on the other side of the cross-laminate either a) a film in which the main direction of orientation is generally perpendicular to the longitudinal direction of the web, or b) an assembly of films, the resultant main direction of which is generally perpendicular to the longitudinal direction of the web, in that the coefficient of elasticity (E) of the material A in unoriented state is at least 15% lower than the coefficient of elasticity of the material of B in unoriented state and in that upon heating the cross laminate A and B exhibit differential shrinkability along the said longitudinal direction, A being more shrinkable.
A webformed cross-laminate according to any preceding claim characterised in that the cross-section of the web has a waved shape with stabilized waves.
A cross-laminate according to claim 5, characterised in that the wavelength measured from wave-top to wave-top on one surface of the web is less than 5 mm.
A cross-laminate according to any of the preceding claims, characterised in that B in a generally symmetrical arrangement is composed of at least 2 films, each with a main direction of orientation forming an angle higher than 50° and lower than 90° to the longitudinal direction of the web.
A cross-laminate according to any of the preceding claims, in which A and/or B consists of at least 2 films mutually bonded together, characterised in that said mutual bondings are stronger than the bonding between A and B.
A cross-laminate according to any of the preceding claims, characterised in that each of the films in both groups A and B is a coextruded film with a major layer for strength in the middle and on each side of this minor layers, whereby the minor layers forming the surfaces of the laminate are selected for achieving desired surface properties and the other minor layers are selected to facilitate the bonding of the films to each other.
A cross-laminate according to any of the preceding claims characterised in that the main layer in the film or each of the films which constitute B, consists of high molecular weight high density polyethylene (HMWHDPE) or a blend of HMWHDPE and lineary low density polyethylene (LLDPE), and the main layer in the film or each of the films which constitute A, consists of LLDPE or a blend of LLDPE and HMWHDPE.
A method of manufacturing a cross-laminate in which there is formed a sandwich-web of different films, each exhibiting a main direction of orientation, and wherein these directions cross each other, and subsequently the sandwiched films are further oriented below their melting range by being stretched together in the longitudinal direction of the web, and before or after this longitudinal stretching, also in the transverse direction of the web, this transverse stretching being carried out between grooved rollers, and the films in the sandwich are bonded to form a laminate before, during or after said longitudinal and transverse stretching operations, characterised in that said sandwich-web consists of two films or assemblies of films (A′) and (B′) respectively, (A′) on one and (B′) on the other side of the sandwich-web, whereby (A′) is either a) a film in which the main direction of orientation generally follows the longitudinal direction of the sandwich-web, or b) an assembly of films, in which the resultant main direction of orientation generally follows the said direction, and said orientation or resultant orientation is stronger—as measured by shrink testing before (A′) and (B′) have been brought together to a sandwich—than the orientation or resultant orientation in (B′) in the same direction, and further (B′) is either a) a film in which the main direction of orientation is generally perpendicular to the longitudinal direction of the web, or b) an assembly of films, in which the resultant main direction of orientation is generally perpendicular to the longitudinal direction of the web, in which the coefficient of elasticity (E) of (A′) in unoriented state is at least 15% lower than the coefficient of elasticity of (B′) in unoriented state and said orientation or resultant orientation is stronger—referring to shrink testing before A′ and B′ have been brought together in a sandwich—than the orientation in (A′) in the said perpendicular direction.
Dependencies are inferred from the claim text.