JPS6351092B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has gas barrier properties, water vapor barrier properties,
The present invention also relates to a method for producing a multilayer film with excellent transparency. (Technical Background) Conventionally, multilayer films or sheets (hereinafter simply referred to as multilayer films) composed of an olefin resin and a gas barrier resin such as a saponified vinyl acetate copolymer resin have Especially as a film that has excellent water vapor permeability and high gas barrier properties possessed by saponified vinyl acetate copolymers, especially saponified vinyl acetate copolymers with low ethylene content. Widely used for food packaging, etc. Multilayer films with such combinations can be obtained by methods such as coextrusion or dry lamination, but these non-oriented multilayer films lack transparency and cannot be expected to have high performance in terms of gas barrier properties. . For this reason, attempts have been made to further improve transparency and gas barrier properties by further orienting the above multilayer film. Methods such as rolling have been proposed and are being researched. However, in the orientation method by stretching, that is, by pulling, the gas barrier layer, which is intended to have a thin wall structure, cannot follow the orientation by stretching due to economical problems, etc., and problems such as pinholes and breakage occur. Further, the improvement in transparency is not so noticeable in the case of uniaxial stretching, and in particular when low density polyethylene is used as the olefin resin, the transparency may even be reduced compared to non-oriented. In addition, the cold constant velocity roll rolling method (Japanese Patent Application Laid-Open No. 51-52475), which has been practiced in recent years, imparts uniaxial orientation by compressive force, and the disadvantages of the tensile stretching method described above are temporarily eliminated. Although it can be resolved, it has other disadvantages. In other words, in this method, firstly, a huge reduction force (compression force) must be applied to improve transparency or to achieve orientation to a magnification sufficient to further improve barrier properties against gases, etc., and it is difficult to achieve economical speed for industrialization. Therefore, the scale of the equipment would have to be enormous. Secondly, although this method uses a low temperature range of 50° C. or lower as a suitable rolling condition, it has been found that it is difficult to significantly improve transparency at such temperatures. (Object of the invention) The present inventors have discovered that the transparency of an unstretched multilayer film,
The present invention was achieved as a result of intensive research aimed at solving the deficiencies of the above-mentioned cold constant velocity roll rolling method and developing an effective roll rolling method that can be put to practical use in order to improve the barrier properties against gases, water vapor, etc. This is what I did. (Method of the Present Invention) The method of the present invention is characterized in that a multilayer film composed of at least one layer of olefinic resin and a gas barrier resin is heated to the lowest melting point or softening point of the resin group constituting the multilayer film. (Hereinafter simply referred to as melting point) The resin is heated to a temperature range that does not exceed the melting point of the resin and is not lower than 30°C than the melting point, and is rolled using at least a pair of non-uniform speed rolls. This is a method of imparting orientation to the multilayer film. The non-uniform rolling rolls used in the present invention have a circumferential speed ratio between the non-uniform rolling rolls ranging from 1.1 or more to less than the rolling ratio (the thickness of the film after rolling relative to the thickness of the film before rolling). It is essential that the rolling agent be used, and thereby the rolling force of the rolls required for rolling can be dramatically reduced, and at the same time, the rolling efficiency can be increased. It should be noted that if the circumferential speed ratio is made higher than the rolling magnification, there is a risk that the multilayer film may be cut or the rolls may cause abnormal vibrations, which may impede the operation. Further, in the present invention, the rolling magnification of the multilayer film is preferably 1.5 to 8 times, preferably 2 to 6 times, so that each characteristic of the multilayer film can be significantly improved. This rolling magnification is difficult to achieve with the conventional constant speed roll rolling method.
Even if it were obtained, the film would be extremely narrow compared to the effective width of the roll, and in this case, the rolling roll could only be operated at a low speed. In order to roll the multilayer film in the above temperature range, the rolls may be heated in a conventional manner, and the multilayer film may be preheated by an appropriate method if necessary. At this time, if the rolling temperature is 30°C or more lower than the melting point of the resin that has the lowest melting point among the resin groups constituting the multilayer film, rolling efficiency, transparency, etc. will decrease, and the rolling force of the rolls will be higher than necessary. Not only will it become more expensive, but the economic speed will also slow down. Further, the peripheral speed on the high speed side of the non-uniform speed roll is equal to the speed of the oriented film sent out from the rolling roll. (Multilayer film) When the multilayer film to be compared with the present invention is conveniently expressed as layer A for the olefin resin layer and layer B for the gas barrier resin layer, its structure is A.
-B or ABA configuration. Moreover, it is also possible to mainly add one or more resin layers of other types to such a structure. Although there is no particular restriction on the thickness, the method of the present invention becomes even more effective when the layer B is made thinner. The multilayer film used in the present invention is a coextruded multilayer film formed by coextrusion molding, or a multilayer film formed in advance by dry lamination, etc., and the polyolefin film and gas barrier resin film are each rolled. Sometimes, they may be introduced simultaneously and used in a multilayered manner. In the present invention, typical resins constituting the layer A include high-density polyethylene, low/medium density polyethylene, polypropylene, polybutene-1, poly-4-methylpentene-1, and the like. Furthermore, a copolymer or a mixture containing each of the above resins as a main component may also be used. Note that, among these olefin resins, the water vapor permeability and the like of the resulting multilayer film vary depending on the type of resin selected. Therefore, the selection must be made appropriately depending on the purpose of use. In particular, when low-density or medium-density polyethylene is selected, an excellent film can be obtained that has a high degree of transparency at a relatively low rolling ratio and is less prone to longitudinal tearing, which is a characteristic of uniaxially oriented materials. It can also be demonstrated with the effect of By the way, when a multilayer film with this structure is oriented by a stretching method using tensile force,
Due to surface roughness, transparency tends to be lower than before orientation. The gas barrier resin of layer B used in the present invention includes gas barrier resins such as saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol resin, acrylonitrile resin, polyamide resin, and polyvinylidene chloride resin. Examples include resins with an ethylene content of 20 to 50 mol%.
The saponified product of ethylene-vinyl acetate copolymer with a high degree of saponification of 90% or more in the range of is a material suitable for obtaining multilayer films with excellent gas barrier properties, as well as excellent water vapor permeability and transparency. It is. In addition, as an adhesive layer between these A layer and B layer, if necessary, an ionomer, an ethylene-unsaturated carboxylic acid (or derivative thereof) copolymer, a modified polyolefin with maleic acid, etc., an ethylene-vinyl acetate copolymer, etc. It is possible to insert a polyolefin polymer having a polar group, or a resin having adhesive properties to both layers A and B. (Effects of the present invention) As detailed above, according to the method of the present invention, not only can a multilayer film with a width almost matching the roll effective width and a high rolling ratio be obtained at an economical speed, but also The rolling force is dramatically reduced, the delamination strength after rolling is greater than that of the conventional constant speed rolling method and stretching method, and the gas barrier layer is thinner.
A multilayer film with improved transparency can be produced at low cost. In addition, the surface of the rolling roll is processed such as hard chrome plating, and the surface roughness (JIS
It is also possible to further improve transparency by keeping the B0601) below the IS, preferably below 0.85S. EXAMPLES Below, the present invention will be explained in more detail by describing examples of the present invention. Example Regarding the production of a multilayer film, the same film raw material is used to produce it by the warm non-uniform roll rolling method of the present invention, and by the conventional cold constant velocity roll rolling method or the near-field rolling method. Tables 1 and 2 show the results of comparative tests on the quality of product multilayer films produced by the roll drawing method. The conditions for the comparative test are as follows. Raw materials used: Low density polyethylene MI 2.0g/10 minutes Density 0.924g/cm ³ Softening point 98℃ Saponified ethylene-vinyl acetate copolymer Ethylene content 32 mol% Saponification degree 99% Intrinsic viscosity 0.14/g (Solvent: Water) (phenol-based) Film production: Inflation coextrusion multilayer film,
After cutting, the film is slit to a width of 400 mm and is used as the original film. Die diameter 150mmφ 3 types 3 layer circular die Innermost layer: Low density polyethylene Intermediate adhesive layer: Surlyn (ionomer) MI 1.5g/10min Outermost layer: Saponified ethylene-vinyl acetate copolymer roll Rolling: Rolling heating roll (vs. )；Surface length 500mm,
Length/diameter (L/D) 1.9 Surface roughness 0.2S Preheating device: Film contact length approx. 2m A load cell is attached to the rolling roll (lower) bearing to detect rolling force.Roll the film through it as shown in Figure 1. . Proximity roll stretching: Stretching heating roll (pair) surface length 500
mm, diameter 250mmφ Roll gap 1mm Preheating device Film contact length approximately 2m Stretching is performed as shown in Figure 2 by the difference in circumferential speed of a pair of stretching and heating rolls.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of roll rolling in the warm non-uniform roll rolling method of the present invention or the conventional cold constant velocity roll rolling method, and FIG. 2 is a schematic explanatory diagram of the conventional close roll stretching method. . Code, 1... original film, 2... preheating device,
3...lower roll, 3'...upper roll, 4,
4'... Proximity roll, α... Roll gap.

Claims (1)

[Claims] 1 A multilayer film or sheet consisting of at least one layer of olefin resin and a gas barrier resin layer has the lowest melting point (or softening point) of the resin group constituting the multilayer film or sheet. The multilayer film is formed by warm non-uniform roll rolling at a temperature that does not exceed the melting point (or softening point) of the resin and is not lower than 30°C or more than the melting point (or softening point). 1. A method for producing a multilayer film, which comprises rolling a pair of rolling rolls at different speeds with a circumferential speed ratio of at least 1.1 and less than a rolling magnification. 2. The method for producing a multilayer film according to claim 1, wherein the rolling ratio (the film thickness after rolling relative to the film thickness before rolling) in the roll rolling is 1.5 times or more and 8 times or less. 3. The method for producing a multilayer film according to claim 1 or 2, wherein the gas barrier resin is a saponified ethylene-vinyl acetate copolymer. 4. The method for producing a multilayer film according to any one of claims 1 to 3, wherein the olefin resin is low-density or medium-density polyethylene with a density of 0.91 to 0.94.