JPS6253011B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a foamed film having heat shrinkability with excellent cushioning effect. Conventionally, foamed films made of polystyrene are known, and foamed films made of polystyrene that also have heat shrinkability are also known. It is well known that the latter film is generally used for the exterior of containers such as bottles, and is useful for preventing bottle breakage and as a buffer member. However, the aforementioned heat-shrinkable foamed film made of polystyrene is susceptible to impact and is so-called brittle due to the characteristics of its raw material.Therefore, even if it is packaged in a bottle, etc., it may break from the edge of the film during transportation or handling. Therefore, it cannot be said that the buffer member has a sufficient function as a buffer member, and this also causes a decrease in the bottle-breaking effect. In addition, the film requires a relatively high temperature to be heat-shrinked, and the temperature range in which it can be shrunk is narrow, so it is easy to make mistakes in heat-shrinking, so careful attention must be paid to temperature control during the shrinking process to prevent this. This also became a problem.
Furthermore, when polystyrene foam is stretched, it is difficult to weft-stretch it using a tenter, etc., perhaps due to its brittleness.
Because longitudinally stretched films are the mainstream, when using films produced in this way as exterior packaging for bottles, for example, their application to automatic packaging machines is limited, and the conventional automatic packaging machines for weft-stretched films cannot be used. It was not possible to adapt the method, and there were problems in this kind of usage. The present invention has been made in order to improve each of the above-mentioned problems, and the first invention as a heat-shrinkable foamed film is made by forming and stretching a composition consisting of an ionomer resin containing sodium ions and a foaming agent. The second invention is characterized in that a laminate layer made of a thermoplastic film is provided on at least one side of a film formed by forming and stretching a composition made of an ionomer resin containing sodium ions and a foaming agent. It is characterized by the following points. The present invention will be explained in detail below. The ionomer resin used in the present invention includes metal ions and carboxylic acid groups obtained by reacting a base copolymer obtained from α-olefin and αβ-ethylenically unsaturated carboxylic acid with an ionic metal compound that can be dissolved in water. An example is an ionic copolymer in which At this time, as the base copolymer, ethylene-acrylic acid copolymer,
Examples include ethylene-methacrylic acid copolymer, ethylene-maleic acid copolymer, ethylene-acrylic acid-methyl methacrylate copolymer, and there are no particular limitations. In the present invention, it is particularly essential that the ionomer resin contains sodium ions, and other elements other than sodium ions, such as those of the periodic table of elements,...
-A and group monovalent to trivalent metal ions (...Mg ⁺⁺ , Zn ⁺⁺ , Al ^+++, etc.) lack stretchability and a good foamed film cannot be obtained. Next, the blowing agent used in the present invention can be exemplified by azodicarbonamide as an organic type, and one consisting of a carbonate such as sodium bicarbonate and an organic acid such as citric acid as an inorganic type. Also, any known material can be used and there are no particular limitations. The amount of this blowing agent used is 0.2 to 5 parts by weight, preferably 0.5 to 3 parts by weight, per 100 parts by weight of the ionomer resin. The foaming agent may be used by adding master pellets containing the foam or by kneading an appropriate amount of a blowing agent into the raw resin in advance. In addition to the composition according to the present invention, a lubricant, an antistatic agent, and other appropriate additives may be added. For film formation of the composition created as described above, for example, extrusion film formation can be performed, and conditions are set so that the composition does not foam in a die, so that the composition foams at the same time as it is discharged from the die. Any other known method may be used. The film formed in this way is stretched at a temperature ranging from the softening point to the melting point of the resin, preferably from 80 to 90°C. On the other hand, the magnification is 1.5 to 5 times, preferably 2 to 4 times in both the vertical axis and the latitude axis. Further, when biaxially stretching, the longitudinal and latitudinal stretching may be carried out within the above ranges. At this time, it is more preferable to carry out the stretching in one weft axis from the viewpoint of adaptability to conventional automatic packaging machines, automatic sealing machines, etc. In the present invention, for example, when carrying out weft stretching with a tenter, it can be carried out smoothly without requiring special consideration. can. Although it is more preferable that the film be made in a flat shape, it may be made in other known shapes. In the present invention, in order to reinforce the film produced as described above and improve printability, etc., a suitable thermoplastic film is further coated with a laminate layer on at least one side of the film with or without an adhesive layer. In this case, it is preferable to use a film made of an ionomer resin containing the same kind of sodium ions as the original foamed film and as thin as possible as the laminate layer. For this lamination method, coextrusion, melt extrusion lamination, or other known methods may be adopted as appropriate. However, when using a pre-formed film of the same type as the original foamed film, immediately after the extrusion foaming of the original foamed film, When laminated with Nipprol, the heat generated during extrusion of the original foamed film allows lamination to be carried out without the need for particular heating, which is convenient. The above heat-shrinkable foam film according to the present invention is
The thickness becomes quite thick after foaming, and it may not be appropriate to call it a film, but since the present invention involves a film formation process, the term "film" is used uniformly regardless of the thickness. . The present invention has been described above, and when this film is used for the exterior of bottles, for example, it exhibits exceptional effects such as excellent bottle breakage prevention effects and cushioning effects. Furthermore, it has excellent physical properties such as strength, is strong without the drawback of brittleness like previous products, and can be heat-shrinked at low temperatures.The temperature range in which heat-shrinkage is possible is also wide, so temperature control is relatively easy. This has the advantage of being extremely easy to handle without causing shrinkage errors during the shrinkage process. Moreover, since the weft uniaxial stretching can be carried out extremely easily using a tenter, the film produced by the mid-latitude uniaxial stretching in the example is highly adaptable to various automatic machines that have been used in the past, and its effects are immeasurable. There is. Although it is most frequently used as an exterior label for bottles and the like, it can also be used as a heat-shrinkable member for packaging general containers and various articles, and is not particularly limited. Next, examples of the present invention and comparative examples will be given. <Example (1)> To 100 parts by weight of ionomer resin containing Na ⁺ , 5 parts by weight of master pellet Dive-Blow PEM20NK (manufactured by Dainichiseika Kaisha, Ltd.; trade name) containing a highly concentrated blowing agent was added. A foamed original fabric having a thickness of 600 μm was obtained by extrusion using a T die. 85℃
A heat-shrinkable foamed film with a thickness of 200 μm was obtained by passing it through a tenter at a temperature of 3 times the width in the weft direction. <Example (2)> Immediately after extrusion foaming of the foamed fabric formed by extrusion in Example (1), a separately prepared 90μ thick film made from an ionomer resin containing Na ⁺ was laminated through a Nitpro roll directly. As a result, a foamed laminated original fabric with excellent adhesive strength was obtained. This original fabric was passed through the tenter in the same manner as in Example (1), and
A heat-shrinkable foamed film with a laminate layer was obtained by stretching the film twice as much. <Comparative example (1)> Add the same amount of the same blowing agent as in Example (1) to polystyrene, extrude it into a film using a T-die, roll stretch it three times at a temperature of 110°C, and heat shrink it in the longitudinal direction. A heat-shrinkable foamed film with a thickness of 200μ was obtained. Just to be sure, I tried to stretch it in the weft direction using a tenter, but cracks appeared and I couldn't stretch it. Table 1 shows the physical properties of the foamed films obtained in the above Examples and Comparative Examples. As is clear from this table, it can be seen that the film of the present invention has excellent low-temperature shrinkability, has a wide range of shrinkable temperatures, and is a strong heat-shrinkable foamed film. On the other hand, it is clear that the films of the comparative examples are inferior to the films of the present invention. 【table】

Claims (1)

[Scope of Claims] 1. A heat-shrinkable foamed film produced by forming and stretching a composition comprising an ionomer resin containing sodium ions and a foaming agent. 2. The heat-shrinkable foamed film according to claim 1, wherein the stretching is uniaxial in the weft direction. 3. A heat-shrinkable foamed film, characterized in that a laminate layer made of a thermoplastic film is provided on at least one side of a film formed by forming and stretching a composition made of an ionomer resin containing sodium ions and a foaming agent. 4. The heat-shrinkable foamed film according to claim 3, wherein the stretching is uniaxial in the weft direction. 5. The heat-shrinkable foamed film according to claim 3, wherein the thermoplastic film is mainly composed of an ionomer resin containing sodium ions.