United States Patent Office
Patented Dec. 26, 1967
PROCESS AND SYSTEM FOR PRODUCING HEAT SEALED LAMINATES Albert L. James, Anoka, Minn., assignor of forty percent to Win. C. Heller, Jr., Milwaukee, Wis. Filed June 29,1964, Ser. No. 378,491 6 Claims. (CI. 156—229)
ABSTRACT OF THE DISCLOSURE
A process and apparatus for producing a heat seal lamination from a film of polyolefin material, such as polyethylene, and a substrate web formed from a material dissimilar from the polyolefin film. Exposing one surface of the polyolefin film to an electrical corona discharge or an oxidizing gas flame to render the exposed surface polar, so that the surface is capable of chemical bonding with a dissimilar material through heat sealing. Heating the substrate web to a temperature at least approximating the heat sealing temperature of the treated surface of the polyolefin film and then bringing the polyolefin film into firm contact with the heated substrate web by providing means for compressing the web and film together, so that the web and substrate adhere to each other. The heat seal laminated structure which is formed by this process and through the use of this apparatus.
This invention relates to a method and system for producing a novel heat sealed lamination from a thermoplastic web and substrate webs.
Because of the many desirable physical and chemical properties of the thermoplastics such is polyolefins and the like, these thermoplastic materials are extremely valuable in the coating of other materials to produce a laminate which is impervious to water, water vapor, heat and is generally inert to most chemicals. Laminations of thermoplastics with other materials including paper, paperboard, foils and other plastics is of increasing interest and value in the packaging industry and specifically in the food packaging field. For example, for packaged articles such as milk, frozen food and butter, cartons are now coated or laminated with thermoplastic materials since these thermoplastic materials generally do not produce any deleterious chemical or physical effect with respect to the food stuff with which they come in contact.
Welding or uniting thermoplastic materials with other similar or dissimilar materials is usually accomplished by cementing the materials together through the use of an intermediate bonding agent and in some instances thereafter applying pressure and in some instances heat sufficient to activate the adhesive but not high enough to melt and heat seal the materials joined together. However, certain types of thermoplastic materials are nonadherent to adhesives as well as other substrate materials thereby preventing bonding of such materials together.
Apparatus and processes have been evolved for coating or laminating thermoplastic materials with other materials even though the thermoplastic materials would not ordinarily adhere to the substrate materials. One such process comprises an extrusion coating method wherein a
from an economic standpoint. For example, the larger extrusion coaters require a substantial time to heat up to operational temperatures as well as an extended period of corresponding length to allow them to cool down. Thus during the heating up and cooling down stage of these extrusion coaters, a substantial quantity of the polyolefin is actually lost, as well as labor and machine time. Another undesirable feature in the extrusion coating process is that the lamination or coated product produced must have the longitudinal edges thereof trimmed since a bead is formed along these edges during the coating operation. In trimming, it is also necessary to trim a small amount of the substrate with the bead and this trim cannot be reclaimed either as substrate or polyolefin since these materials are adhered to each other. Further, another cause of waste with respect to the extrusion coating process is the waste experienced while "getting gauge" during the initial operational phases of this process. It has been found that even after the extruders have been heated up to operational temperatures, considerable time is involved before the operator is able to "get gauge." It will be appreciated that every width change, every screw speed change, every change of type of polyolefin requires the . operator to "get gauge" before the apparatus is capable of 25 a production run.
An additional disadvantage of the extrusion coating process is the waste experienced during the operation of the extruder and generally described as running waste. Thus any malfunctioning or any condition which requires the extrusion coating apparatus to be slowed down, results in unmarketable material since the product produced during the slow down period and the subsequent speed up period to and from operational speeds results in a product which cannot be used.
Even though certain plastics, as pointed out above, may be bonded to others through the use of an intermediate bonding agent, other plastics including some of the thermoplastic materials are relatively non-adherent to adhesives and other materials so that lamination merely through a cementing operation cannot be accomplished. It is pointed out though that methods and means for treating non-adherent surfaces to render them more adherent have been developed. Such processes involve pre-activation of polyethylene by either surface oxidation or electrical discharge. Thereafter, inks and adhesives may be employed which are then compatible with the treated polyethylene surfaces.
However, the use of adhesives in laminating operations also requires these adhesive materials to be subjected to fairly high temperatures to drive off the volatile substances, which operation quite often results in blistering or bubbles forming and the ultimate undesirable production or non-uniform laminates. Thus the high degree of quality control is ordinarily not possible in the laminating operations wherein an intermediate bonding agent is utilized. Further, the use of chemical adhesives involves not only expensive equipment but rather time consuming procedures.
A general object of this invention is to provide a novel method and system for producing a heat sealed laminate from a thermoplastic web and a substrate web.
Another object of this invention is to provide a continuous process and system for producing a heat sealed
thermoplastic material such as polyolefin is extruded at
an extremely high temperature upon a substrate such as 6g multi-ply lamination from an unsupported plastic film
paper and the like. During this extrusion operation the extremely hot molten polyolefin is exposed to the air which together with the extremely high temperature apparently oxidizes the surface of the molten polyolefin and permits the polyolefin to bond to the substrate material.
While producing an effective laminated product, this extrusion process has certain disadvantages especially
and substrate webs formed of materials dissimilar from the thermoplastic film.
A more specific object of this invention is to provide a continuous, highly efficient, economical system and proc70 ess for producing a heat sealed lamination from an unsupported thermoplastic film and a substrate web in which the substrate web is heated to a temperature at least