JPH0259056B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Background of the Invention Tubes and other containers made of laminate webs made from metal foil and layers of synthetic resin are widely used for packaging various products such as toothpaste and others. For example, American Greenwich, Connecticut, USA.
Can Company sells such tube-like containers under the GLAMINATE trademark. By properly designing and constructing laminates, they can provide the oxygen and moisture barrier properties necessary for packaging many products. Similarly, desirable in tubular packages is also the ability to heat seal and have the ability to permanently crease. Generally, the laminate web product side consists of an olefin polymer, such as low density polyethylene, ethylene acrylic acid copolymer (EAA) or Surlyn ionomer, adhered to the inner surface of a metal layer, usually aluminum foil. Although containers constructed in this manner are quite adequate in most environments, the ingredients contained in some products have a tendency to degrade or attack the material of the container. , resulting in destruction of the container. As is well known, certain toothpaste products are difficult to package in such laminated web containers, especially those containing fluoride as a caries preventive.
This is true for products containing tin or sodium fluoride. In the presence of acidic environments and/or essential oils and detergents, toothpaste ingredients have a strong tendency to migrate through the inner layer to the interface, thus promoting delamination and packaging in the web structure. This will result in product deterioration. Of course, it goes without saying that the longer the storage period, the greater the deterioration that occurs in the laminate web. Moreover, this deterioration is particularly significant when the packaged product is stored at relatively high temperatures. Conventionally, various treatments have been used not only to increase the initial adhesion level between the plastic film and the foil, but also to improve the delamination resistance during long-term storage, i.e. to extend the shelf life.
It is being taken. These efforts include flame treatment of the foil, use of interlayers of various adhesive materials, and chemical priming of the metal to increase bond strength at the interface.
An important example of the latter method is the use of chromium polyacrylate complex products as foil primers to enhance adhesion to polyethylene. Laminated structures produced in this way are used for packaging alcohol-soaked swabs. Although the use of such primers appears to significantly increase the strength of the bond, it is still not entirely sufficient for long-term storage, and the use of polyethylene as a product-side surface layer
undesirable in some cases. This is because this material is prone to environmental stress cracking in the presence of certain products such as toothpaste. Therefore, the main object of the present invention is to provide long-term protection for products consisting of an aluminum foil and a layer of ethylene copolymer, an acrylic acid or acrylic ester monomer between said foil and said layer, and which also has deteriorating properties. An object of the present invention is to provide a new laminate web suitable for packaging and storage over time. Another object of the invention is to provide a new method for manufacturing such webs. (2) Summary Some of the above-mentioned and related objects of the present invention are to provide an aluminum foil, a film of a copolymer of ethylene having carboxylic acid or carboxylic acid ester groups as side chains in the molecule, and a combination of the foil and the film. It has been found that this can be easily achieved by providing a laminate web consisting of a layer of chromium polyacrylate complex primer between. In a preferred embodiment of the web, the copolymer film comprises poly(ethylene/acrylic acid),
It can be selected from the group consisting of poly(ethylene/methacrylic acid), poly(ethylene/methyl acrylate), poly(ethylene/methyl methacrylate), poly(ethylene/vinyl acetate), and ionomeric resins. The primer coating must be at least a monolayer thick and the web usually includes at least one additional layer. That is, the web generally includes at least one synthetic resin polymer layer disposed on the foil surface opposite the side to which the primer is applied. Other objects of the invention are achieved by carrying out a method for manufacturing a laminate web. In this method, at least a monolayer of a chromium polyacrylate complex primer, formulated as an aqueous alcohol solution, is deposited and coated on at least one surface of an aluminum foil substrate. The coated foil is then heated to substantially dry the primer, after which an ethylene copolymer film (as described above) is extrusion coated onto the primer coated surface, thus forming The laminate is then cooled to finish the web. Preferably, in the extrusion coating process, the melt temperature of the copolymer is about 288 to 316 °C (about 550 to 600 °C).
〓), most preferably about 302 to 310℃ (about
575 to 590〓). (3) DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As mentioned above, foil/ethylene copolymer laminate webs have traditionally been used in container manufacturing. With the method provided by the invention, the adhesion between the foil and the copolymer layer on the product side is greatly increased and the susceptibility to components with degrading properties that can migrate to the interface is considerably reduced. The chromium complex used to prime the aluminum foil surface was MICA A-291 from Mica Corporation of Stanford, Conn.
It is sold under the product name. This is a 7% aqueous solution of chromium polyacrylate complex. It is also acidic and has a viscosity of about 10 centipoise. The instructions for MICA A-291 describe the bonding of polyethylene to aluminum foil for packaging and industrial applications that require high adhesion and resistance to various difficult-to-pack substances such as fluorides and essential oils. Usage is explained. However, hitherto, the use of such primers has prevented the results achieved in the method of the invention, namely the formation of a very durable bond between the aluminum foil and the extruded coating of a copolymer containing a carboxylic acid or carboxylic acid ester of ethylene. The result is that this bond persists despite close contact with products that are thought to have a significant degrading property.
It is likely that it was not recognized. The chromium complexes mentioned above appear to be the most effective primers for use here, but other similar materials can be substituted if desired. For example, the length of the polyacrylic acid chains can be varied to vary the proportion of acrylic acid moieties within the copolymer and the ratio of metal to organic portion of the complex. It is also indeed possible to replace the chromium ion with other transition metals such as cobalt, copper, nickel, etc. As mentioned above, primers are generally applied as dilute water/alcohol solutions. This is to maximize the leveling and wetting of the support and thereby the adhesion of the polymer layer to the support. For adjusting the liquid used, commercially available MICA A
-291 can be suitably mixed with additional water and isopropyl alcohol in a volume ratio of 30:60:10, respectively. The solution thus obtained, when dry, weighs about 0.014 to 0.036 Kg (about 0.03 to ^{0.08 lb), preferably 0.016 Kg (about 0.035 lb) per ream (i.e., 3000 ft 2 surface} area). Use only a sufficient amount to form a complex solid. In all cases, the primer must be at least a single molecule thick, and will generally be at least somewhat thicker. Generally, after drying the foil primer through an oven maintained at a suitable temperature (i.e., approximately 250 to 400 degrees), the web is sent directly to a copolymer extrusion station where it is The temperature of the web is generally about 38 to 66°C (about 100 to 150°C). The techniques used to extrusion coat ethylene copolymers onto aluminum foil are well known to those skilled in the art and need not be described in detail. However, considering that the copolymer must not only strongly adhere to the foil but also retain tack (i.e., heat sealability) and adhesion to other parts of the final product container, It will be appreciated that temperature is critical to achieving optimal adhesion. In particular, as mentioned above, the laminate web of the present invention finds widest application in the manufacture of tubular containers. In that case, the web must have side seams and must be able to be securely attached to the molded headpiece.
High melt temperatures are preferred for adhesion to foils, but this also promotes oxidation, which prevents the formation of good bonds with other polymeric surfaces (eg, headpieces). Therefore (and depending on the size of the extrusion die lip gap width), the EAA is
Generally, in the practice of this invention, temperatures between 288 and 316
℃ (550-600〓), and the optimal balance of adhesion is usually at a melt temperature of 302-310℃
(575 to 590〓). EAA or ionomers usually constitute the product side layer of the laminate web, but other ethylene copolymers with carboxylic acid or carboxylic acid ester groups as side chains, such as acrylic or methacrylic acid, methyl acrylate, methyl methacrylate, and vinyl acetate, Copolymers can also be used. For economic reasons and practical advantages,
The technique commonly used in the manufacture of foil/copolymer composites is extrusion coating, although other techniques may be appropriate in some circumstances and may be used if necessary. In general, the product side polymer thickness should be approximately 25.4 to 102μ (approximately 1.0 to
4.0 mil), more commonly 38.1 to 76.2μ
(1.5 to 3.0 mils). As far as foil components are concerned, as a practical matter thin (approximately 0.285 to 3.0 mil) aluminum is typically used, although foils of other metals may be substituted for certain applications. can.
Laminated web is used for various purposes.
It usually includes another polymer layer and usually includes a paper layer to allow for convenient printing or decoration of the item. A typical laminate cross section consists of (from the outside) polyethylene, paper, polyethylene, EAA, foil, primer, and EAA;
(apart from the lower-level combinations of) and are conventionally used, and are not essential aspects of the present invention. The following examples are intended to illustrate the effects of the present invention. EXAMPLE A web was produced using a subassembly consisting of a layer of polymer and paper adhered to 18μ (0.7 mil) aluminum foil. The total thickness of this subassembly is approximately 259μ (approximately 10.2 mils). Use a gravure cylinder to cover the exposed surface of the foil.
The chromium polyacrylate complex was primed in a somewhat thicker layer than a monolayer. At this time,
MICA A-291: Water: Isopropyl alcohol
A 30:60:10 solution was used. Then about 121
It was dried by forced air in an oven at ℃ (approximately 250㎓). The first laminate was made by extrusion coating the primed foil side with 19.7 Kg (43.5 lbs) per ream of low density polyethylene. The temperature of the extrudate is about 316
℃ (approximately 600〓). This laminate is shown below as A
It is called. The second laminate B coated the primed foil side with the same thickness of EAA containing 3.5% acrylic acid monomer.
Manufactured by extrusion coating with a copolymer. In this case as well, the melt temperature is approximately 316℃ (approximately 600℃).
〓). A third laminate C was made in a similar manner using an EAA copolymer containing 8.0% acrylic acid content instead of the 3.5% resin. The laminate mentioned above is 2.54 x 14.3 cm (1 x 5
5/8 inch) into small pillows and use commercially available toothpaste (Procter & Gamble).
CREST toothpaste) was filled and then sealed. Several pillows made with each of the three laminates were held at controlled temperatures for periods ranging from two weeks to six months, after which time the condition of the web was examined. Specifically, five pillows of each specimen were heated to 24°C.
A temperature of 41°C (75〓 and 105〓) was maintained, and the three pillows of each specimen were held at a temperature of 49°C (120〓).
These were evaluated after 2, 4, 8, 12 and 26 weeks. The results are shown in Table 1.

[Table] The symbols E, G, F, and P used in this table indicate that the web condition was judged to be excellent, good, fair, and poor, respectively. A dash indicates that the test was not conducted under the conditions indicated. To be rated as excellent, the adhesion force must be such that the polymer layer stretches against the force that tends to separate it from the foil.
In the case of good adhesion, separation occurs, but the bond is barely bonded. Adhesion is considered acceptable if the laminate exhibits a fairly strong resistance to separation, and poor adhesion if delamination occurs easily. As can be seen from Table 1, the adhesive strength is much higher when the EAA film is laminated to the primed foil (laminates B and C) compared to the adhesive strength when the laminating polymer is polyethylene (laminate A). can get. To be more specific, 49℃ (120〓)
After 4 weeks storage at and 41℃ (105〓)
After 8 or 12 weeks of storage, both laminates containing EAA exhibit good to excellent adhesion, while laminates containing polyethylene exhibit only fair adhesion. This is the most significant difference that can be seen from Table 1, but it can also be seen that in all examples the laminates containing EAA are exceptionally superior to the laminates containing low density polyethylene. In addition to the delamination tests described above, the environmental stress cracking of three laminate webs was evaluated by hand squeezing appropriately selected pillows. 41
Pillows made from webs containing polyethylene were found to be significantly susceptible to cracking when squeezed by hand after a storage period of 6 weeks at 105 °C. In contrast, webs containing EAA exhibited satisfactory durability to such handling under the same conditions. As explained above, the present invention consists of an aluminum foil and a layer of a copolymer of ethylene with acrylic acid or acrylic acid ester monomers, and is suitable for use in the packaging of products with degrading properties over long periods of time. This provides a new laminated web. The present invention also provides a new method for manufacturing such webs.

Claims (1)

[Scope of Claims] 1. An aluminum foil, a film of an ethylene copolymer having carboxylic acid or carboxylic acid ester groups as side chains in the molecule, and at least a monomolecular layer of polyacrylic acid between the foil and the film. A laminate web suitable for use in the production of containers for products having properties that degrade container materials, characterized in that it consists of a chromium complex primer. 2 The copolymer is poly(ethylene/acrylic acid), poly(ethylene/methacrylic acid), poly(ethylene/methyl acrylate), poly(ethylene/methyl methacrylate), poly(ethylene/
2. The laminate web of claim 1, wherein the laminate web is selected from the group consisting of vinyl acetate), and ionomers. 3 consisting of an aluminum foil, a film of an ethylene copolymer having carboxylic acid or carboxylic acid ester groups as side chains in the molecule, and at least a monomolecular layer of a chromium polyacrylate complex primer between the foil and the film; A laminate suitable for use in the manufacture of containers for products having properties that degrade the container material, characterized in that it has a synthetic resin polymer film on the foil surface opposite to the side to which the primer layer is applied. web. 4. On at least one side of an aluminum foil substrate, at least a monomolecular layer of a chromium polyacrylate complex primer is deposited as an aqueous alcohol solution to coat the foil, and the coated substrate is heated to substantially remove the primer. drying; extruding and coating a film of ethylene copolymer having carboxylic acid or carboxylic acid ester groups as side chains in the molecule onto at least one side of the foil coated with the primer; thus formed; 1. A method for producing a laminate web suitable for use in manufacturing containers for products having properties that degrade container materials, the method comprising cooling a laminate to obtain a laminate web. 5. The method of claim 4, wherein the copolymer is selected from poly(ethylene/acrylic acid) and ionomeric resins. 6 the copolymer is poly(ethylene/acrylic acid), and the copolymer is heated at about 288 to 316°C.
6. The method of claim 5, wherein the method is extruded through an extrusion die at a melt temperature of about 550 to 600 degrees Celsius. 7. The method of claim 6, wherein the melt temperature is about 302 to 310C (about 575 to 590C).