JPH021669B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a stretch packaging film in which the film is stretched while being wrapped during packaging. More specifically, the present invention relates to a multilayer film suitable for pallet stretch packaging, in which the film is stretched and wrapped around palletized cargo. [Prior art] Shrink packaging has traditionally been used as a packaging method for palletized packages, but recently the pallet stretch packaging method, in which a film is stretched and wrapped around the palletized packages, has attracted attention. I've come to feel like I'm being treated like that. The reason for this is that stretch packaging has the following features compared to shrink packaging. (1) Energy saving as no heating source is required. (2) The amount of film used can be reduced. (3) It is also possible to package products that are sensitive to heat. (4) There is a high degree of freedom in the shape and dimensions of luggage. Pallet stretch packaging films are used while being stretched during packaging work, and are required to tightly bind the packaged items. , elongation, drop impact strength, heat seal strength, etc. are required. For example, MODERN MATERIALS HANDLING, Volume 34.
No. 10, pp. 92-99 (1979) Ji, Ila et al. (G.
EALOR ET AL) MODERN PLASTICS (USA) Volume 55 No. 8 52~
Pages 54 and 57 (1978) describe the required performance for pallet stretch packaging films, which can be summarized as follows. (1) Cohesive force is obtained by wrapping the stretched film around the packaged item, so this cohesive force must be maintained until the package is unpacked. Therefore, the film needs to have a high stress retention rate, that is, a high binding force retention rate, in other words, it must have rubber elasticity. (2) And this cohesion has a moderate range. If the binding force itself is too weak, it is not preferable because the packaged items may collapse during transportation. Furthermore, if the binding force is too strong, it is not preferable because it may cause deformation or damage to the packaged items. Therefore, the film is required to have an appropriate "initial cohesion". (3) In order to stably obtain this cohesive force, the following must be done during packaging work. The process of stretching the film and encircling the object to be packaged is carried out, but at this stage there are cases where the film is pierced by corners or protrusions of the object, the tear in the film is enlarged from the torn part, and the film is separated from the edge of the film. tearing is more likely to occur than when the film is not stretched. Therefore, it is necessary to have high resistance to these, that is, to have excellent "piercing strength" and "tearing strength." (4) If a part of the film is pierced or torn by a sharp corner or metal from the outside after packaging, the tear will not spread further due to the binding force and the package will not be unpacked. "Tear propagation resistance"
In particular, it is necessary that it be good in the direction perpendicular to the longitudinal direction of the film. (5) It is desirable that the film has so-called "self-adhesive" properties, which can be secured by simply cutting the film at the end of packaging and pressing the other end onto the film already wrapped around the packaged object. It is conceivable to heat-seal the edges of the film or fasten them with separately prepared adhesive tape, but this is time-consuming and requires secondary costs. If you do not fasten the ends, it is not preferable because it will gradually unpack or the binding force in some parts will be insufficient. (6) It must be transparent enough to allow the surface printing of the packaged item and the letters on the label to be seen through. (7) It is desirable to use a film that requires less amount of film, that is, a thin film that can be further strongly stretched during packaging work, both from the viewpoint of economy and from the viewpoint of suppressing the generation of industrial waste after unpacking. . Various films that use polyethylene resin as a raw material are commercially available as films that satisfy such performance, but although it is possible to satisfy some of the qualities, no film that satisfies all of the qualities has yet been found. . For example, the low-density polyethylene inflation-molded film currently on the market failed in all of the seven evaluations mentioned above, but especially in three points: "initial cohesion,""piercingstrength," and "tear propagation resistance." was significantly inferior. The "cohesive strength" required for the above packaging is, for example,
As described in Package Eng. (USA) 24(7)38-41(79), a film mainly composed of ethylene-vinyl acetate copolymer is prepared by adjusting the vinyl acetate content, MFR, etc. of the resin composition appropriately. You can improve it by selecting it and using it. However, the problems of low tear strength, low puncture strength, and poor tear propagation resistance cannot be resolved. In addition, the tear strength and puncture strength required for packaging are
As described in Mod.Plas.Int.Nov.1980, 26, resins whose main component is linear low-density polyethylene should be used after appropriately selecting the α-olefin content, MFR, etc. of the resin composition. You can get it if you want. However, according to the inventors' investigation,
Despite the strong tear strength, the above-mentioned "tear propagation resistance"
It is not possible to solve the problem of defects, and on top of that, a new problem arises that the initial cohesion is too strong. Furthermore, a new problem arises in that the stress retention rate necessary for packaging cannot be obtained especially with films formed by inflation. In addition, polyvinyl chloride, which is conventionally used for overlapping fruits, vegetables, fish, etc. placed on trays, or the polybutadiene film described in JP-A-51-91953, for example, has a problem in that the cohesive strength decreases over time and the load collapses. There is. [Problems to be Solved by the Invention] Therefore, the present inventors have made extensive efforts using ethylene-vinyl acetate copolymer and linear low-density polyethylene material in order to obtain a film having the characteristics (1) to (7) above. investigated. First, JP-A-53-31751 and JP-A-57-
An inflation-molded film made of a blend of ethylene-vinyl acetate copolymer and linear polyethylene was evaluated in accordance with Publication No. 182341. As a result, it was found that the tear propagation resistance, which was a problem with single-layer films, was significantly improved. Next, a two-layer blown film of ethylene-vinyl acetate copolymer and linear low-density polyethylene was also evaluated in accordance with JP-A-58-24450, and similar effects were confirmed. However, in any case, if the cohesive force is too large,
Problems such as low cohesive strength retention and weak puncture strength remained. Therefore, in order to reduce the cohesive force, a film with the same blend composition and a two-layer film as described above were cast-molded (the latter was published in 1983).
(According to Publication No. 74737). As a result, a blend-based film was found that had satisfactory initial cohesive strength, cohesive strength retention, and puncture strength. However, this blend film still had insufficient adhesive strength and tear strength. The laminated film had sufficient puncture strength and self-adhesive strength, but the retention of cohesive strength was insufficient. Therefore, we further investigated three-layer cast films made of linear low-density polyethylene, blends of linear low-density polyethylene and ethylene-vinyl acetate copolymer, and ethylene-vinyl acetate copolymer, and finally completed the present invention. . [Means for Solving the Problems] and [Operation] Accordingly, the present invention relates to a three-layer film suitable for pallet stretch packaging, in which one of the outer layers is mainly composed of linear low-density polyethylene. The other outer layer consists of a layer mainly composed of ethylene-vinyl acetate copolymer, and the middle layer mainly consists of a blend of linear low-density polyethylene and ethylene-vinyl acetate copolymer. This is a three-layer cast stretch packaging film consisting of the following layers. This film has a shrinkage rate of 30% or less in the longitudinal direction of the film, and a shrinkage rate of 5% or less in the direction orthogonal to the longitudinal direction. The linear low-density polyethylene used to form one of the outer layers in the present invention includes a catalyst containing a transition metal compound (so-called Kegler process), a chromium oxide catalyst supported on alumina or silica-alumina (Philips process), Copolymerizing ethylene with a _C4 to _C20 , preferably _C4 to _C16 α-olefin or a mixture thereof in the liquid or gas phase in the presence of a molybdenum oxide catalyst supported on alumina (standard method). Melt flow rate (abbreviated as MFR, unit: g/10min)
is 0.15-15, preferably 1-10, density is 0.940
g/cm ³ or less, preferably 0.935 g/cm ³ or less. C ₄ to C ₂₀ α-olefins include butene-1,
Examples include pentene-1, hexane-1, 4-methyl-pentene-1, and octene-1. If the density is 0.940 g/cm ³ or more, it is not preferable because there are problems in that the cohesive force retention rate decreases, the cohesive force is too large, and the tear strength decreases. Furthermore, if the MFR is less than 0.15, the film will have poor formability, resulting in a film with large forming distortion, resulting in a decrease in tear strength and tear propagation resistance, which is not preferable. On the other hand, if the MFR is 15 or more, the strength of the film will be weak and the film will be easily torn during packaging, which is not preferable. The above ethylene-vinyl acetate copolymer contains 3 to 28% by weight of vinyl acetate, preferably 10 to 20% by weight.
The main component is an ethylene-vinyl acetate copolymer having an MFR of 0.5 to 30, preferably 1 to 20. If the content of vinyl acetate is low, the retention of cohesion and adhesive strength will decrease rapidly. If the content of vinyl acetate exceeds 28% by weight, it is not preferable because the adhesive strength is too high and the retention of cohesive strength in a high-temperature atmosphere decreases. Furthermore, if the MFR is less than 0.5, molding distortion due to film molding will be large and moldability will be poor, which is not preferable. On the other hand, if the MFR exceeds 20, the strength of the film becomes weak, which is not preferable. The above-mentioned ethylene-vinyl acetate copolymer and the above-mentioned linear low-density polyethylene are used for the blend of ethylene-vinyl acetate copolymer and linear low-density polyethylene, and the ethylene-vinyl acetate copolymer and linear low-density polyethylene are used. The composition ratio of polyethylene is 8/2~
The ratio is preferably 2/8, preferably 75/25 to 30/70. If the composition ratio of the ethylene-vinyl acetate copolymer and linear low-density polyethylene is out of this range, the tear propagation resistance will deteriorate, which is not preferable. Ethylene used to form the intermediate layer
For a composition mainly composed of a blend of vinyl acetate copolymer and linear low density polyethylene, it is preferable to use the ethylene-vinyl acetate copolymer and linear low density polyethylene used in the outer layer. When it is necessary to adjust the slipperiness, anteblocking property, and self-adhesiveness of the film surface for a layer mainly composed of ethylene-vinyl acetate copolymer and a layer mainly composed of linear low-density polyethylene. 0.01 to 5 parts by weight of lubricants, inorganic fillers, surfactants, adhesives, etc. may be added to 100 parts by weight of the resin constituting these compositions. Examples of the lubricant include fatty acid amides such as oleic acid amide, stearic acid amide, and erucic acid amide. Examples of inorganic fillers include inorganic substances such as light and heavy calcium carbonate, talc, and silica. As surfactants, glycerin, sorbitan,
Polyhydric alcohol fatty acid esters such as esters of polyhydric alcohols such as pentaerythritol and linear saturated fatty acids with an alkyl group of 6 to 18 carbon atoms or linear unsaturated fatty acids with an alkyl group of 18 to 22 carbon atoms, polyoxyethylene Polyoxyethylene alkyl phenyl ethers such as nonyl phenyl ether and polyoxyethylene octylphenyl ether, polyoxyethylene polyhydric alcohol fatty acid esters obtained by adding 5 to 20 units of ethylene oxide to the aforementioned polyhydric alcohol fatty acid esters,
Ethylene oxide 3 to 10 units Polyoxyethylene fatty acid ester, which is an ester of polyoxyethylene and the aforementioned fatty acid, ethylene oxide 5
-10 units of polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene oleyl cetyl ether, and polyoxyethylene dodecyl ether. Adhesives include castor oil derivatives, low-molecular viscous substances such as polybutene rosin or its derivatives, terpene resins, terpene-phenol resins, aromatic, aliphatic, alicyclic or copolymer petroleum resins, and coumaron. -Indene resins, styrene resins and hydrogenated resins thereof. From the viewpoint of compatibility and heat resistance, alicyclic or copolymerized hydrogenated petroleum resins are preferred. The linear low-density polyethylene layer, the ethylene-vinyl acetate copolymer, or a blend layer thereof may contain the above-mentioned additives, and the above-mentioned additives may be included as a result of ear loss recovery and reuse. I don't care if you get rejected. A layer mainly composed of an ethylene-vinyl acetate copolymer to be laminated, a layer mainly composed of a blend composition of an ethylene-vinyl acetate copolymer and linear low-density polyethylene, and a layer mainly composed of a linear low-density polyethylene The thickness of each layer is usually 2 to 50 μm, preferably 4 to 30 μm for the layer mainly composed of ethylene-vinyl acetate copolymer and the layer mainly composed of linear low-density polyethylene. It is preferable that the layer mainly composed of a blend composition of vinyl copolymer and linear low density polyethylene has a thickness of 6 to 30 microns. If the number of layers mainly composed of linear low density polyethylene is less than this range, the tear strength will be low, which is not preferable. On the other hand, if the thickness of the same layer is larger than this range, the cohesive force will be too large, which is not preferable. If the layer containing the ethylene-vinyl acetate copolymer as a main component is smaller than this range, the self-adhesive strength will be low, which is not preferable. If the layer mainly composed of a blend of ethylene-vinyl acetate copolymer and linear low-density polyethylene is smaller than this range, the tear propagation resistance and stress retention rate will decrease, which is not preferable. Moreover, if it is larger than this range, the cohesive force becomes too large, which is not preferable. The thickness ratio of each layer is as follows, but the ratio does not necessarily have to be constant depending on the overall thickness. The thickness of the layer mainly composed of a blend composition of ethylene-vinyl acetate copolymer and linear low density polyethylene is 0.2 to 7.5, preferably 0.5 to 4. , the thickness of the layer mainly composed of linear low-density polyethylene is
0.13-7.5 preferably 0.5-2. The overall thickness of the laminated film is usually 20 to 80μ.
It is the rank. In addition, the packaging film of the present invention may be used with a layer mainly composed of linear low-density polyethylene as the outer layer and a layer mainly composed of ethylene-vinyl acetate copolymer on the side facing the packaged object. many. Lamination of a layer mainly composed of ethylene-vinyl acetate copolymer, a layer mainly composed of a blend of ethylene-vinyl acetate copolymer and linear low-density polyethylene, and a layer mainly composed of linear low-density polyethylene. is carried out by a coextrusion cast molding method. Co-extrusion cast molding methods are broadly classified into in-die lamination and outside-die lamination, but either method may be used. Further, the intra-die stacking method includes a black box method, a multi-manifold method, etc., but the method is not particularly limited. Further, the conditions of the stretching and solidifying process from the die are not limited as long as the shrinkage rate of the film is within a predetermined range. Generally, the higher the stretching speed and the lower the stretching temperature, the higher the shrinkage rate of the film, which is not preferable. Here, the shrinkage rate is an index of residual strain during film molding, and α is the amount of film shrinkage when the film is immersed in ethylene glycol at 110°C for 5 seconds, and β is the dimension of the film before immersion. The shrinkage rate γ is the amount shown below. γ＝αβ ^-1 ×100 [%] If the shrinkage rate exceeds 30% in the longitudinal direction of the film (processing and pulling direction), the cohesion retention rate will decrease,
Also, the initial binding force becomes too strong, which is not preferable. If the shrinkage in the direction perpendicular to the longitudinal direction of the film exceeds 5%, the tear propagation resistance will deteriorate, the initial binding force will become too strong, the stress retention rate will decrease, and the puncture strength will decrease. This is not desirable as it will cause problems. [Effects of the Invention] The three-layer film according to the present invention can stably obtain an appropriate cohesive force over time, and has high tear strength and
Excellent tear propagation resistance and self-adhesion. In general, the greater the stretching of a thermoplastic film, the greater the initial binding force, and the greater the rate of decline in the binding force over time. In addition, tear strength and tear propagation resistance also decrease. Therefore, the stretching ratio is selected in consideration of these performances. Since the three-layer film according to the present invention has improved performance compared to conventional films, it has become possible to increase the degree of stretching during packaging operations. In other words, the thickness of the film after packaging can be made thinner than before. Therefore, it was possible to reduce the amount of film consumed. This also contributes to reducing the weight of the package as a whole and suppressing the production of film after unpacking, that is, the production of industrial waste. [Example] Next, the present invention will be explained with reference to an example. Example 1 Single screw extruder A (screw diameter 40 mm
Linear low-density polyethylene (MFR=2, density=0.920) from φL/D=28) was processed by 50% by weight of the above linear low-density polyethylene from single-screw extruder B (screw diameter 40mmφ, L/D=28). Ethylene-vinyl acetate copolymer (MFR=3.5, density=
0.93, vinyl acetate content 14 (weight)%) and 50% by weight, and the above ethylene-vinyl acetate copolymerization was carried out using a single-screw extruder C (screw diameter 65 mmφ, L/D = 28). Resin 98.8% by weight, hydrogenated petroleum resin based alicyclic adhesive (ring and ball softening point 90)
℃）1.2% by weight was co-extruded into a multi-manifold die at 200℃, and processed into linear low-density polyethylene, linear low-density polyethylene and ethylene-acetic acid using a cast molding machine at a film winding speed of 50m/min. Films containing a vinyl copolymer resin blend and an ethylene-vinyl acetate copolymer resin as main components and having layer thicknesses of 7μ, 11μ, and 7μ, respectively, were obtained. Example 2 In Example 1, linear low density polyethylene with MFR = 2 and density = 0.915 was used as the linear low density polyethylene fed into extruder A, and as an ethylene-vinyl acetate copolymer resin fed into extruder C.
A three-layer film was obtained in the same manner as in Example 1 except that MFR = 15, density = 0.94, and vinyl acetate content was 19% (by weight). [Film evaluation method] The films obtained in Examples 1 and 2 were evaluated by JISK-
The tear strength of the film was measured according to JISK-6781-77 (pulling speed 200 mm/min), and each stress was measured immediately after stretching the film by 30% and after holding for 20 minutes using a method according to JISK-6301. The stress retention rate was determined. Stress retention rate = (stress after 20 minutes of holding) (stress immediately after) ^-1 × 100 [%] Correlation with the cohesion retention rate of packages using the pallet stretching machine described below was found. It was found that when the degree of elongation was set to 30%, the cohesion retention rate, which had the same value as the stress retention rate, was obtained 5 days after packaging. Next is the pallet stretch packaging machine made by Konan Denki.
Using Infra Pak SW-4000, a collection of cardboard boxes (vertical, horizontal, and height each 1290 mm) was used as an object to be packaged.
× 1550 × 1380 mm) and conducted a cartridge test. In addition, a spring scale (area 160 x 210
The sample was placed inside the cardboard in such a way that the surface on which the sample was placed (mm) protruded 10 cm from the cardboard surface. Immediately after wrapping the cardboard box collection with a film elongation of 30%, the scale of the spring scale was read to determine the initial cohesive strength. Next, a sharp pencil-like tool was used to pierce the inclined film surface between the surface on which the sample was placed on the spring scale and the cardboard plane, and the maximum stress at that time was similarly read from the spring scale. The puncture strength was calculated using the following formula. Puncture strength = Maximum stress shown by the spring scale at the time of puncture - Initial cohesion force Furthermore, a 100 mm cut was made with a knife in the direction perpendicular to the wrapping direction of the film on the film wrapped on another plane of the cardboard, and after 20 minutes. The degree of expansion of the cut end was measured using a ruler and was taken as the amount of tear propagation. Separately, the film was cut to a width of 100 x 20 mm, stacked 10 times, and then under a load of 100 g/cm ² .
After standing at 23°C for 2 days, the adhesive strength between the films was measured. The peeling speed was 200 mm/min. Further, the film was cut into a size of 5 x 65 mm and immersed in ethylene glycol at 110°C for 5 seconds, and the shrinkage rate of the film was measured. The above measurement results are summarized in Table 1. Comparative Example 1 In Example 1, a composition consisting of 98.8% by weight of linear low-density polyethylene and 1.2% by weight of hydrogenated petroleum resin was added to each extruder, and linear low-density polyethylene was produced in the same manner as in Example 1. A cast film with a thickness of 25μ was obtained, the main component of which was . This film was evaluated in the same manner as in the examples, and the results shown in Table 1 were obtained. Comparative Example 2 The results shown in Table 1 were obtained in the same manner as in Comparative Example 1 except that the ethylene-vinyl acetate copolymer resin used in Example 1 was used instead of the linear low-density polyethylene. Comparative Example 3 In Example 1, a blend layer of linear low density polyethylene and ethylene-vinyl acetate copolymer resin was formed without melt extrusion on the single screw A.
A two-layer film was prepared in the same manner as in Example 1 except that the layer containing ethylene-vinyl acetate copolymer resin as the main component was 15 μm in thickness and 10 μm in thickness, and the results shown in Table 1 were obtained in accordance with Example 3. Comparative Example 4 In Example 1, uniaxial screw C was not melt-extruded, and uniaxial screw B contained 49.4% by weight of linear low density polyethylene, 49.4% by weight of ethylene-vinyl acetate copolymer resin, and hydrogenated petroleum resin. adhesive
1.2% by weight was melt extruded and the thickness of the linear low-density polyethylene layer was 10μ, and the layer thickness of the blend of linear low-density polyethylene and ethylene-vinyl acetate copolymer resin was 15μ. A two-layer film was prepared using the same method, and the results shown in Table 1 were obtained according to the example. Comparative Example 5 In Comparative Example 1, linear low density polyethylene was used instead of linear low density polyethylene and alicyclic adhesive.
49.4% by weight, ethylene-vinyl acetate copolymer resin
A single layer film was prepared in accordance with Comparative Example 1 except that 49.4% by weight and 1.2% by weight of hydrogenated petroleum resin adhesive were used.
25μ was obtained, and the results shown in Table 1 were obtained. Comparative Example 6 The same procedure was followed as in Example 1 except that the resin was not passed through extruder B in Example 1, except that the main components were a 12.5μ linear low-density polyethylene layer and a 12.5μ ethylene-vinyl acetate copolymer resin. A two-layer film consisting of two layers was obtained. The film was evaluated according to the example and the results shown in Table 1 were obtained. Comparative Example 7 In Example 1, instead of the multi-manifold type T-die, a circular die with an in-die merging method was used, and the resin temperature was 190°C, the blow ratio was 2.0, and the take-up speed was 15.
A film was obtained in the same manner as in Example 1 except that inflation molding was performed at m/min. This film was evaluated according to the example and the results shown in Table 1 were obtained.

[Table] Example 6 Adhesive ^{12 5} 〓Cast comparison L〓 LDPE ⁷ 〓〓L〓 LDPE〓 96 100
65 7 1.6 5 1.9
35 33
Example 7 EVA ¹¹ 〓〓EVA ⁷ 〓Bron

Claims (1)

[Claims] 1. One of the outer layers consists of a layer mainly composed of linear low-density polyethylene, the other outer layer consists of a layer mainly composed of ethylene-vinyl acetate copolymer, and the middle layer is composed of a layer mainly composed of ethylene-vinyl acetate copolymer. A three-layer cast stretch packaging film consisting of layers mainly composed of a blend of linear low-density polyethylene and ethylene-vinyl acetate copolymer. 2. The three-layer cast stretch packaging film according to claim 1, wherein the shrinkage rate of the film is 30% or less in the longitudinal direction and 5% or less in the direction perpendicular to the longitudinal direction. 3 A blend in which the blend composition of the ethylene-vinyl acetate copolymer and linear low-density polyethylene is within the range of 8/2 to 2/8, where the thickness of the layer containing the ethylene-vinyl acetate copolymer as the main component is 1. 2. The three-layer cast stretch packaging film according to claim 2, wherein the layer mainly composed of polyethylene has a thickness of 0.2 to 7.5, and the layer mainly composed of linear low density polyethylene has a thickness of 0.1 to 7.5.