JPH0533896B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a heat-shrinkable film useful as a packaging film, particularly a shrinkable packaging film, and which has excellent elastic modulus, low-temperature shrinkability, sealing properties, optical properties, impact resistance, etc. It concerns its manufacturing method. [Prior art and its problems] Heat-shrinkable packaging films made by stretching thermoplastic resin films can tightly package contents by shrinking them by applying heat such as hot air. It is used for many purposes, for example, for packaging various products such as miscellaneous goods, foods, toys, fruits and vegetables, and textile fabrics. The characteristics required for a heat-shrinkable film for packaging include the ability to generate a high shrinkage rate or strong shrinkage stress;
Having good transparency so that the contents of the package can be easily confirmed and good gloss that can increase the product value;
It must have good sealing properties during packaging, packaging creation and sealing, and it must have high elastic modulus (strength and surface hardness) necessary to improve workability during high-speed automatic packaging. Examples include having sufficient impact resistance and tear strength during the distribution stage. Films currently used for shrink wrapping include films made of resins such as polyvinyl chloride, polyethylene, polypropylene, and nylon. However, each of these films has drawbacks. Polyvinyl chloride shrink film is hard, has good gloss and transparency, has relatively good sealing properties, has a relatively low shrinkage temperature, and has a wide temperature range, so it is used in many applications. However, the seal strength is somewhat weak and care must be taken when sealing, the resin decomposes during fusing sealing and generates harmful gases that corrode packaging machinery, and decomposition slag may adhere to the seals. It lowers the strength and impact strength, and the decrease is especially large at low temperatures (below -10℃), and most of them contain a large amount of plasticizer, so the dimensions and physical properties are affected. It may change over time or contaminate the contents due to migration of plasticizer,
It has the disadvantage that gloss is reduced due to excessive bleeding onto the surface. Polyethylene heat-shrinkable film has high impact strength and strong sealing strength, but on the other hand, its gloss and transparency are inferior to that of polyvinyl chloride, and its low-temperature shrinkability is also poor, shrinkage stress easily escapes, and the appropriate shrinkage temperature is low. It has the disadvantage of being 20 to 50 degrees Celsius higher than polyvinyl chloride. Even with polyethylene films, films whose molecules are highly cross-linked using electron beams or the like and sufficiently stretched at high temperatures have a higher maximum shrinkage rate and maximum shrinkage stress, and have optical properties such as transparency compared to ordinary polyethylene films. Although it has excellent properties and heat resistance, etc., its transparency after shrinkage and strength after shrinkage tend to deteriorate due to the high shrinkage temperature, and due to cross-linking, it is difficult to heat seal, has no elongation, and has low tear strength. There are drawbacks. Although polypropylene heat-shrinkable film has advantages such as being relatively transparent, has good gloss, is relatively stiff, and has strong shrinkage stress, it has a low maximum shrinkage rate.
Moreover, it has drawbacks such as a high appropriate shrinkage temperature, which tends to melt at its upper limit, and a narrow appropriate temperature range. Nylon heat shrink film has relatively good transparency, firmness, high shrinkage stress, and excellent impact resistance, but compared to polyvinyl chloride film, it has a lower shrinkage rate and a lower shrinkage temperature. It had drawbacks such as high heat resistance and poor sealing performance. As mentioned above, as a heat shrink film for packaging,
Until now, there has been no film that simultaneously satisfies excellent properties such as modulus of elasticity (firmness), shrinkage (especially low-temperature shrinkage and maximum shrinkage), sealability, optical properties (transparency and gloss), and impact resistance. However, its development was desired. [Means for Solving the Problems] In view of the above, the present inventors have developed a packaging that has a large elastic modulus (stiffness), shrinkability (especially low-temperature shrinkability), sealability, optical properties, and impact resistance. In order to provide a heat-shrinkable film for use and a method for producing the same, as a result of intensive studies, the present invention has been completed. That is, the present invention is a multilayer film consisting of at least three layers including at least one inner layer,
The total thickness is 5 to 100 microns, the ratio of the outer layer thickness to the total thickness is 6 to 60%, and both outer layers have a crystallinity of less than 30% and a Vikato softening point.
At 40~150℃, tensile modulus is at least 75Kg/ ^mm2
The inner layer is made of a polymer mainly composed of at least one hard thermoplastic resin selected from copolymerized polyester resins, polycarbonate resins, and copolymerized polystyrene resins, and the inner layer is made of polypropylene polymers and ethylene polymers. Polymer, ethylene-vinyl acetate copolymer, ethylene-
Aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, soft polymer consisting of ethylene-α-olefin copolymer, ionic crosslinkable copolymer, vinyl aromatic hydrocarbon and The multilayer film is made of at least one polymer selected from block copolymers with conjugated diene derivatives and derivatives thereof, and the multilayer film has a tensile modulus of 60 to 60.
150Kg/mm ² , a heat shrinkage rate of at least 20% at 80°C, and a heat shrinkage stress value of 50 to 500g/mm ² ,
The present invention relates to a heat-shrinkable film that is characterized by not causing delamination in practical terms. Furthermore, the present invention melts the polymers of each layer of the multilayer film using respective extruders, and then coextrudes them using a multilayer die so that the ratio of the thickness of the outer layer to the total thickness is 6 to 60%. The film is cooled and solidified to obtain a multilayer film original fabric, and then this original fabric is heated and stretched at least uniaxially at an area stretching ratio of 5 to 50 times at a stretching temperature (T°C) according to the following formula. The present invention relates to a method for producing a heat-shrinkable film. V-20≦T≦V+35 However, V represents the Vikato softening point (°C) of the outer layer. The present invention will be explained in detail below. The heat-shrinkable multilayer film of the present invention has a
It has a tensile modulus of Kg/mm ² , preferably 70 to 140 Kg/mm ² , more preferably 80 to 130 Kg/mm ² . If the tensile modulus is less than 60 kg/mm ² , the film tends to lack stiffness and hardness, leading to problems in handling, wrinkles, etc. when the film is used. In addition, when used as a heat-shrinkable film for overlapping, which is one of its uses, in high-speed automatic packaging, it causes poor finishing of the packaged product, especially wrinkles and folded parts. On the other hand, if the tensile modulus exceeds 150Kg/ ^mm2 , the film becomes too hard, easily tears, and is inconvenient to handle.As a heat-shrinkable film for overlapping, it may cause poor finishing of the package, especially at the folded part. Problems such as difficulty in folding the film arise. The heat-shrinkable multilayer film of the present invention has a
g/mm ² , preferably 75 to 400 g/mm ² , more preferably 100 to 300 g/mm ² . In the present invention, if the heat shrinkage stress value of a part of the shrinkage stress curve measured at each temperature at which heat shrinkage occurs is within the above range, it is considered to be within the scope of the present invention. The preferred measurement temperature for developing heat shrinkage and obtaining a heat shrinkage stress curve is in the range of 60 to 160°C, more preferably 60°C.
-140°C, more preferably 60-120°C. If the heat shrinkage stress value is less than 50 g/mm ² , the film after shrinkage will have insufficient fitting properties, causing wrinkles and sagging after packaging. Also, 500
If it exceeds g/mm ² , the contents of the package may be deformed, impairing the appearance after packaging, and the seal portion tends to be damaged. In addition, if the temperature range at which heat shrinkage occurs is below 60°C, the dimensional stability of the film will decrease during the distribution stage, while if it exceeds 120°C, it may cause deterioration of the film or adversely affect the contents to be packaged. I'll wake you up. The heat-shrinkable multilayer film of the present invention has at least 20%
Preferably, it has a heat shrinkage value in the range of 30-90%, more preferably 40-80%. Values in these ranges are 60-160℃, more preferably 60/140
℃, more preferably a value expressed in the range of 60 to 120℃. If the heat shrinkage rate is less than 20%, the fit after shrinkage will be insufficient, leading to wrinkles and sagging after packaging. On the other hand, if the thermal shrinkage rate exceeds 90%, depending on the contents, the contents may become deformed or break at the sealed portion after shrinkage. Furthermore, if the shrinkage onset temperature is less than 60° C., it may cause a decrease in dimensional stability of the film during distribution or storage. On the other hand, if the shrinkage onset temperature exceeds 120°C, the film will deteriorate and the contents to be packaged will be adversely affected. The heat-shrinkable multilayer film of the present invention has an outer layer thickness of 6 to 60% of the total thickness of the multilayer film,
It is preferably 6 to 45%, more preferably 6 to 30%. If it is less than 6%, the elasticity of the film (waist), shrinkage stress, etc. will decrease, resulting in insufficient ability to fit the contents after shrinkage, resulting in wrinkles, sagging, and insufficient sealing strength. From a processing point of view, the co-stretchability becomes poor, and in particular, there is a problem in the thickness accuracy of the outer layer. on the other hand,
If it exceeds 60%, the elastic recovery rate will be poor, the product will break easily, deformation may occur depending on the contents after shrinkage, tearing may occur at the sealing part, and there may be problems with economy and coextrusion. It comes to have. The heat-shrinkable multilayer film of the present invention has a total thickness of 5 to 100 microns, preferably 6 to 80 microns.
microns, more preferably 7 to 60 microns. If it is less than 5 microns, there will be problems with workability during handling, especially during packaging. Also, if it exceeds 100 microns, the waist of the film will become too high.
The fit becomes poor. In addition, the responsiveness of shrinkage may deteriorate and the finish may be impaired. In addition, in the present invention, the fact that the layers do not peel in practical terms means that the outer layer and the inner layer do not peel off during distribution, storage, or actual use, that is, after shrinkage and sealing, and no practical problems occur. The interlayer adhesive strength must be at least 75 g/10 mm width. Measurements were made in accordance with JIS-Z-0237 8,
It is expressed as the peeling force between the outer layer and the inner layer per 10 mm width of the film. If the interlayer adhesive strength is lower than the above value, the layers may peel off during shrinkage and wrinkles may occur. Furthermore, during sealing, the layers may peel off, resulting in insufficient sealing strength and tearing after shrinkage. The heat-shrinkable multilayer film of the present invention has an outer layer having a crystallinity of 30% or less and Vicat.
Softening point 40~150℃, tensile modulus at least 75
50% by weight or less, preferably 30% by weight, within the range that maintains the above properties, although it is composed of a polymer mainly composed of a hard thermoplastic resin that provides a film of Kg/mm ²
Other polymers may be mixed and used within the following ranges. The tensile modulus referred to in the present invention is a value measured on a rapidly cooled extruded resin sheet (0.1 mm thick). The polymer that forms the main body of the outer layer has a weight of 75 Kg/mm ² or more, preferably 100 Kg/mm ² or more, and more preferably
The polymer must give a sheet with a tensile modulus of 150 Kg/mm2 or ^higher . If it is less than 75 Kg/mm ² , when made into a multilayer film, it tends to lack stiffness and surface hardness, leading to problems in handling, wrinkles, etc. when using the film. In addition, when used as a heat-shrinkable film for overlapping and high-speed automatic packaging as one of the preferred uses, it causes poor finishing of the packaged product, especially wrinkles and folded parts. The polymer forming the main body of the outer layer needs to have a degree of crystallinity (according to the DSC method) of 30% or less, preferably 20% or less, and more preferably 10% or less.
If it exceeds 30%, when stretching a multilayer film, the stretching temperature will be high, stress will be large, shrinkage rate will be low, high temperature shrinkability will occur, and the degree of crystallinity will be reduced due to post-processing, etc. Go to altitude,
In addition, if the heat resistance has been significantly improved, it will be difficult to provide the film shrinkage performance described below.
This is because the low-temperature shrinkability disappears. The polymer forming the main body of the outer layer must have a Vikato softening point of 40 to 150°C, preferably 50 to 140°C, and more preferably 60 to 130°C. In the case of amorphous resins, the Vikatto softening point indicates a resin-specific value that is not related to the measurement method, but in the case of crystalline resins, it indicates the value after controlling the degree of crystallinity by processing methods, post-treatment, etc. The value must be within the above range. If the bit softening point is less than 40℃, the distribution of the multilayer film,
Problems arise with respect to dimensional stability during storage and stability of shrinkage characteristics over time. On the other hand, if the temperature exceeds 150℃, the temperature when stretching the multilayer film becomes high, making it difficult to provide the film shrinkability described below, resulting in poor low-temperature shrinkability and difficulty in processability. It comes to have. The hard thermoplastic resin that is the main component of the outer layer and has the above characteristics includes copolymerized polyester resin,
More preferred are copolyesters with low crystallinity and low crystal melting point, and even more preferred are substantially amorphous copolyesters. Specifically, when the above polyester resin is used as a copolymerization component, for example, ethylene glycol is generally used, but other copolymerization components such as propylene glycol, 1,4-
butanediol, 1,5-pentanediol,
At least one diol selected from 1,6-hexanediol, neopentyl glycol, polyethylene glycol, polytetramethylene glycol, cyclohexanedimethanol, or other known diols, and ethylene glycol and one of these diols may be used. Alternatively, it may be a combination of the following, or one that does not contain ethylene glycol but is based on one of the above diols and contains one of the other diols. Next, as the acid component for copolymerization, terephthalic acid is generally used, but in addition, isophthalic acid, phthalic acid, and other aromatic acids, or substituents on the aromatic ring that do not contribute to the esterification reaction. There are dicarboxylic acids and the like that have Further, it may contain at least one dicarboxylic acid selected from succinic acid, adipic acid, other aliphatic dicarboxylic acids, or other known dicarboxylic acids. Either one of the alcohol component and the acid component may be used, or both may be used at the appropriate time. Examples of preferable combinations include copolymerization of ethylene glycol as the main alcohol component, 40 mol% or less of 1,4-cyclohexanedimethanol, and terephthalic acid as the acid component. In that case, a more preferable copolymerization ratio is 20 to 40 mol% of 1,4-cyclohexanedimethanol, still more preferably 25 to 40 mol%.
It is about 36 mol%. Among these, those having a crystallinity of 30% or less as raw materials are preferable. Next, polycarbonate resins can be used as the main polymer for the outer layer, but preferred are those that use monomers that lower the softening point, or those that are copolymerized with such monomers. A mixture of 5 to 40% by weight of other types of polymers that can be mixed to form a film may also be used. Next, a copolymerized polystyrene resin can be mentioned as a polymer that mainly forms the outer layer. Examples of copolymerizable components with styrene include acrylic esters and dienes. Preferred are acrylic esters (alcohol components having 3 or more carbon atoms). Among the hard thermoplastic resins forming the main component of the outer layer, the above-mentioned substantially amorphous copolyester is particularly preferred. In addition, the outer layer film may be a mixture of the above-mentioned main polymer with other types of polymers, additives such as antistatic agents and antifogging agents, plasticizers, auxiliary agents, pigments, or light-absorbing substances. A mixture may be used as long as it satisfies the above-mentioned characteristics, and a surface modification or coating treatment such as corona treatment or plasma treatment may be applied. The polymers forming the main inner layer of the heat-shrinkable multilayer film of the present invention include polypropylene polymers, polyethylene polymers, ethylene-vinyl acetate copolymers, ethylene-aliphatic unsaturated carboxylic acid copolymers, and ethylene-vinyl acetate copolymers. Aliphatic unsaturated carboxylic acid ester copolymers, soft polymers made of ethylene-α-olefin copolymers, ionic crosslinkable copolymers, block copolymers of vinyl aromatic hydrocarbons and conjugated diene derivatives, and derivatives thereof. selected from. Among these, the most preferred are polyethylene polymers, ethylene-vinyl acetate copolymers,
This is a composition in which 5 to 50% by weight of a soft polymer made of ethylene-α-olefin copolymer is added.The next preferred example is linear low-density polyethylene, ultra-low-density polyethylene, A polymer (with a vinyl acetate group content of 5 to 25% by weight and a main index of 0.2 to 10), an ethylene-α-olefin soft copolymer other than the above,
In addition, a composition in which 5 to 30 weight percent of a soft elastomer made of an ethylene-α-olefin copolymer is further added to these, or a composition in which 5 to 30 weight percent of crystalline polypropylene is mixed with 100 parts by weight of both groups. compositions etc. These not only have good stretchability by themselves, but also have the effect of greatly improving the stretchability of the outer layer. It also has the effect of preventing the occurrence of netting stretching of the outer layer during stretching. In addition, since there is an interlayer adhesion strength between the outer layer and the layer that does not cause delamination in practical terms, there is no stretching strain due to differences in the resins that make up each layer (strain that occurs due to different stretching conditions for each single layer). On the contrary, the width of the optimal stretching conditions is expanded as a whole, and a synergistic effect is exerted that makes the whole more stable. As a result, not only the stretching properties of all layers are improved, but the stretching effect of the outer layer in particular is significantly improved. For example, under conditions where the outer layer alone can be stretched only up to 6 times in area stretching ratio, for example, in a low temperature region, adding the inner layer makes it possible to stretch up to 10 times. Further, even when the stretched multilayer film is heat-treated, the strength of the inner layer is less reduced. Furthermore, an adhesive layer may be provided between the outer layer and the inner layer to further increase the interlayer adhesive strength. As the adhesive layer resin, among the above resins, an ethylene-vinyl acetate copolymer having a higher copolymerization ratio of components other than ethylene, or an ethylene-aliphatic unsaturated carboxylic acid copolymer may be used. Preferred examples include ethylene-vinyl acetate copolymers with a vinyl acetate content of 40 to 50% by weight;
It is an ethylene-aliphatic unsaturated carboxylic acid copolymer with an acrylic acid content of 10 to 20% by weight. Also, next preferred, known acid-modified polyolefins (according to the purpose) may be used as the glue layer. Moreover, the above-mentioned acid-modified polyolefin can also be blended into the above-mentioned inner layer. A preferred example of the polypropylene polymer, which is another example of the polymer constituting the inner layer of the heat-shrinkable multilayer film of the present invention, is a copolymer of propylene and another α-olefin. In addition, as the inner layer polymer, ethylene-aliphatic unsaturated carboxylic acid copolymer and ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer , ethylene-acrylic acid ester (methyl, ethyl, butyl, etc.) copolymer, ethylene-methacrylic acid ester (methyl, ethyl, butyl, etc.) copolymer, and the like. A soft polymer made of ethylene-α-olefin copolymer is a copolymer consisting of ethylene and α-olefin copolymer having 3 to 12 carbon atoms.
One or more α- selected from olefins
Refers to a soft copolymer with olefin, α
-Olefins include propylene and butene-
1, hexene-1, heptene-1, 4-methyl-
These include 1-pentene, 1-octene, and others, preferably propylene and 1-butene, and a small amount of nonconjugated diene derivatives may be copolymerized as a third component. The ethylene content of the copolymer is 10~
95 mol%, preferably in the range of 40 to 93 mol%.
These have a crystallinity of 30% or less and are soft thermoplastic polymers or soft elastomers. Next, what is the ionic crosslinkable polymer of the resin for the inner layer?
This is an ionomer resin in which at least a portion of an ethylene-methacrylic acid ester copolymer or an ethylene-acrylic acid ester copolymer is saponified and a further portion is ionically bonded. Next, the block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene derivative of the resin for the inner layer and the derivative thereof are a block copolymer of a vinyl aromatic hydrocarbon such as styrene and a block of a conjugated diene such as butadiene or isoprene. Examples include block copolymers consisting of these copolymers, products obtained by hydrogenating the conjugated double bonds of these copolymers, and products obtained by acid-modifying these copolymers. Next, a method for manufacturing the multilayer film of the present invention will be described. The polymers corresponding to each layer of the multilayer film are melted using an extruder, and coextruded using a multilayer die so that the thickness of the outer layer is 6 to 60% of the total thickness. The film is cooled and solidified to a predetermined temperature using other materials to obtain a multilayer film material. The extrusion method is not particularly limited, and the multilayer T
A die method, a multilayer circular method, etc. can be used. The latter method is preferred. Next, the obtained multilayer film original fabric was heated to the following stretching temperature (T
℃) in at least one axis at an area stretching ratio of 5 to 50 times to produce a rigid heat-shrinkable film. V-20≦T≦V+35 V is the Vikato softening point (°C) of the outer layer. More specifically, the simultaneous biaxial stretching method is more preferable, and the more preferable stretching temperature (T°C) is V-20≦T≦V+35.
15≦T≦V+20. Further, a preferable area stretching ratio is 10 to 36 times. Such stretching conditions are necessary to obtain the above-mentioned preferable properties of the multilayer film.
It is also a necessary condition to maintain the stability of the stretching process and to keep uneven thickness of the film in good condition. The film of the present invention may be cross-linked with energy beams such as electron beams. In this case, the heat-sealing properties are not inhibited at all, and the film is effective in expanding the packaging range, especially the upper temperature limit, and has improved tear strength and other properties. It is effective for improving packaging sagging due to stress relief and stress release. [Effects of the Invention] The heat-shrinkable multilayer film of the present invention has at least three layers including an outer layer mainly made of a specific hard resin and at least one inner layer mainly made of a specific soft resin. As a result of improving the stretchability of all layers, expanding the stretching range, and imparting high orientation to all layers, the elastic modulus (firmness, surface hardness, etc.), It is a hard heat-shrinkable film that has excellent low-temperature shrinkability, sealing properties, optical properties, impact resistance, etc., and has a highly balanced physical property.It is an extremely useful film that can cover a wide range of shrinkage temperatures from low to high temperatures. It is a heat-shrinkable film. [Example] Examples are shown below. Evaluation of various physical properties in the Examples was carried out by the following method. Tensile modulus It was performed according to ASTM-D-882-67, and the stress at 2% elongation was expressed as a value converted to 100%. Heat Shrinkage Rate A 100mm square film sample is placed in a constant temperature bath set at a specified temperature, and after being treated for 30 minutes to allow it to shrink freely, the amount of shrinkage of the film is determined and expressed as a percentage of the value divided by the original dimensions. did. In the case of uniaxial stretching, it is the stretching direction, and in the case of preferred biaxial stretching, it is the average of the longitudinal and lateral directions. Heat Shrinkage Stress A film was sampled in the form of a strip with a width of 10 mm, and it was set in a chuck with a strain gauge with a distance of 50 mm between the chucks without loosening, and then immersed in silicone oil heated to each temperature to remove the stress generated. Obtained by detection.
Silicone oil 80℃ and below, immersion 20
If the temperature exceeds 80°C after 10 seconds, the value after 10 seconds is used and expressed in the same manner as the shrinkage rate above. Falling weight impact strength Measured according to ASTM-D-1709-67. Haze Measured according to ASTM-D-1003-52. Gloss Measured according to ASTM-D-2454-65T. Fused seal strength Measured by sealing with a fusing type heat sealer. Anti-fogging property Cover a plastic container containing 200ml of water at 20°C with a film, leave it in a refrigerator at 5°C for 30 minutes, then take it out and visually evaluate it according to the criteria below. Rank 1: Small white mist on the entire surface.Rank 2: Transparent water droplets of 2 to 5 mmφ are deposited on almost the entire surface, and the inside can be seen. 3rd rank Large water droplets occupy almost the entire surface. Rank 4: There are breaks in the water film, and large droplet-like water films can be seen in some areas. 5 rank: Completely wet and completely homogeneous. It looks like a glass window so you can clearly see inside. Vicat Softening Point Measured according to ASTM-D-1525. Example 1 An acid component mainly composed of terephthalic acid and 1,4-
Substantially amorphous copolyester (Vikat softening point: 82°C, density: 1.27 g/cm ³ , intrinsic viscosity: 0.75) consisting of an alcohol component mainly consisting of 30 mol% of cyclohexanedimethanol and 70 mol% of ethylene glycol. Ethylene-vinyl acetate copolymer (vinyl acetate group content 10% by weight, melt index 1.0, Vikat softening point
81℃, melting point 95℃) 70% by weight, a soft elastomer (density
0.88g/cm ³ , melt index 0.44, amorphous,
A composition consisting of 15% by weight of crystalline polypropylene (density 0.90g/cm ³ , melt flow rate 7, melting point 43°C, 4% by weight random copolymerization of ethylene) Used as a polymer for the inner layer, each polymer was melted in its own extruder, coextruded from an annular multilayer (3 layer) die so that the thickness ratio of the outer layer was 20% of the total thickness, and rapidly solidified by cooling with a refrigerant. It was folded with a pair of pinch rolls to form a tube-like film material with a thickness of 250 microns. At this time, the annular die and 1
A surfactant was injected into the tube between the pair of pinch rolls from a pipe provided at the center of the annular die mandrel to form a thin film of surfactant on the inner surface of the tube. Next, this tube-shaped original film was immersed in the above-mentioned surfactant to form a similar thin film on the outer surface of the tube. This tube-shaped raw fabric is passed between two pairs of differential nip rolls, heated to 100°C in a heating zone, and stretched in a stretching zone (under a multistage hood) under the same atmosphere at a stretching ratio of
It was simultaneously biaxially stretched 5.0 times vertically and 5.0 times horizontally, cooled with 20°C air in a cooling zone, and bubble stretched. The edges (both ends) of the obtained film having a thickness of 10 microns were slit, and two films were wound into a roll using a winder. Next, the thickness ratio to the total thickness of the outer layer is 6,
Stretching was carried out in the same manner as above except that the ratios were changed to 10, 30, and 45%, and in all cases, the stretching was good and the stretching could be carried out stably. Almost no breakage due to punctures occurred, and no delamination occurred between the outer layer and the inner layer. or,
Similarly, films were stretched with an outer layer thickness ratio of 20% and final stretched film thicknesses of 20, 40, and 60 microns, but the stretchability was good in these cases as well.
No delamination occurred between the outer layer and the inner layer. Table 1 shows the evaluation results of the physical properties of the obtained film.

【table】

[Table] The results in Table 1 show that the film of the present invention has a high elastic modulus, low-temperature shrinkability, sealability, and excellent optical properties. Here, in Ratio-1 and Ratio-2 as comparative examples, the thickness ratio of the outer layer to the whole is outside the range of the present invention, and the commercially available film -1 is made of polyethylene cross-linked by electron beam. Yes, commercially available-
Film No. 2 is made of polyvinyl chloride (containing 30% by weight of plasticizer), and commercially available No. 3 is made of polypropylene. Also, ratio -1,
For Ratio-2, an attempt was made to stretch the film in the same way as Nos. 1 to 8 in Example 1, but the stretchability was poor and punctures occurred frequently, so the stretching ratio was lowered to 2.0 times in length and 2.0 times in width. Obtained. Dimensional stability for Nos. 1 to 8 is 60℃.
With the above, the shrinkage practically started and there was no problem, and it was commercially available.
1 and Commercially available-3 are similarly 120°C and 100°C, respectively. Commercially available -2 shrinks gently from 50℃, but the maximum shrinkage rate is at most 45% (vertical/
horizontal average). These films are processed by overlapping link packaging machine (margin rate 20 before shrinkage).
%) and a pillow shrink packaging machine (margin before shrinkage 40%), and the results of comparing the finished state are shown in Table 2. The margin ratio referred to herein is expressed as a percentage of the value obtained by subtracting the circumferential length of the packaged object from the length of the film before shrinking, divided by the circumferential length. The ranking of the packaging evaluation was as follows: ◎ Occurrence of wrinkles, sagging, and tears was 1/100 or less ○ Same as above 2 to 5/100 pieces △ Same as above 6 to 10/100 pieces × Same as above 21/100 pieces or more. As for the packaging conditions, No.-8, ratio-1, ratio-2
The shrinkage temperature was 120°C, and commercially available -1 did not shrink at this temperature, but the shrinkage temperature was increased to 200°C. Commercially available-2 similarly increased the shrinkage temperature to 160°C.
Commercially available product-3 similarly increased the shrinkage temperature by 200°C.
As can be seen from the results in Table 2, the film of the present invention has the ability to change from the overlapping push link to the pillow link.

[Table] It can be seen that a wide range of shrink wrapping can be performed with good finishing conditions, and that it has excellent low-temperature shrinkability compared to commercially available shrink films. Furthermore, compared to the films Nos. 1 to 8 of Example 1, the film of Ratio -1 tended to have an inner layer that was easily transferred during packaging, and the surface gloss tended to deteriorate. In this respect, the No. 1 film of the present invention had no problem. Further, when cold stretching was carried out at a stretching temperature of 50° C. with a layer structure having a ratio of -1, the film could only be stretched up to 3.2 times in length and 3.2 times in width, and the film had a tendency to whiten. Shrink wrapping with a large margin (70%) could not be done with this film. In addition, the margin ratio during packaging was increased to 70% compared to that shown in Table 2, and shrink packaging was performed using an L-type packaging machine. As a result, Nos. 1 to 8 were successfully packaged. The rank was ○ or higher. However, commercially available products 2 and 3 not only meet the shrinkage temperature conditions of the present invention but also meet the high temperature conditions (180 No.
Even at 200°C, the shrinkage was insufficient and only loose products were produced. Commercially available product 1 could only be loosely packaged under the shrinkage temperature conditions of the present invention, but it was only possible to tightly package the product by setting the shrinkage temperature to 180-200°C. However, transparency was declining. Comparative Example 1 The copolymerized polyester used for the outer layer in Example 1 was extruded alone and an attempt was made to stretch it in the same manner as in Example 1, but the film formation stability was poor and punctures occurred frequently, so the stretching ratio was changed to 2.0 times in the vertical direction, Thickness reduced to 2.0 times the width
A 20 micron film was finally obtained (ratio -3). A film thinner than this would break and could not be stretched at a stretching ratio greater than this. Describing the heat shrinkage characteristics of this film, the heat shrinkage rate at 80°C is 12%, the heat shrinkage stress at 80°C is 20g/ ^mm2 ,
The tensile modulus was 200Kg/ ^mm2 . Packaging using the overlapping link packaging machine resulted in many wrinkles, swells, and tears due to insufficient shrinkage, and the evaluation rank was ×. When the film thickness was increased to 30 microns, a film with a stretching ratio of 3 times in the vertical direction and 3 times in the horizontal direction was finally created, although it was unstable. This product was easily torn during packaging and had poor tear strength. Moreover, the packaging finish was not good, and shrinkage spots were likely to occur between the contact and non-contact parts of the packaged part. Furthermore, the elastic recovery of the packaged object was poor, and the deformation could not be recovered when pressed with a finger. Separately, a two-layer film made of copolyester and polyethylene terephthalate (thickness ratio: copolyester/polyethylene terephthalate = 4/9 (microns)) used as the outer layer in Example 1 was stretched in the same manner as in Example 1. Overall thickness 13
A micron film was obtained. The obtained film had the same tendency as the above-mentioned single-piece film, and had problems in being put to practical use as a shrinkable film, and its shrinkability was even worse than the above-mentioned single-piece film. Comparative Example 2 The resin composition used for the inner layer in Example 1 and the ethylene-vinyl acetate copolymer (vinyl acetate group content 10
60% by weight of linear low density polyethylene (melt index 2.1, melting point 122°C, Vikatsu softening point 109°C) 40% by weight When each was extruded individually and stretched in the same manner as in Example 1, the former had fair film formation stability and stretchability, and a film with a thickness of 10 microns was obtained, but the latter had poor film formation stability. In addition, uniform stretching was difficult. Regarding the heat shrinkage characteristics of the obtained film, the heat shrinkage rate at 80℃ is 40%, the heat shrinkage stress at 80℃ is 50g/ ^mm2 , and the tensile modulus is 20%.
It was Kg/ ^mm2 . When packaging with an overlapping push link packaging machine, the film had no stiffness, was difficult to handle, had many wrinkles, and was given an evaluation rank of ×. Example 2 Of the multilayer raw fabric in Example 1, the outer layer thickness ratio was
20%, hot air heating type batch type 2
Using an axial stretching device, the stretching temperature and stretching ratio (the same ratio in the longitudinal and lateral directions) were freely set within the scope of the present invention, and films each having a thickness of 20 microns were obtained. Table 3 shows the physical properties of the obtained film. To control physical properties, if you want to increase the shrinkage stress, stretch at a low temperature (65
℃), and when the stress was low and the shrinkage rate was high, a high stretching ratio was adopted on the high temperature side (108 ℃).

[Table] As a result, the physical properties of the material stretched within the scope of the present invention, including tensile modulus, heat shrinkage rate, and heat shrinkage stress, were all within the preferred range, and even if the stretching conditions were greatly changed, the elasticity It can be seen that it is possible to make a low-temperature shrinkable film with a high shrinkage rate. Comparative Example 3 The multilayer original fabric used in Example 2 was used in the batch type biaxial stretching apparatus used in Example 2, and the stretching ratio was lowered and the stretching temperature was raised compared to the stretching conditions of Example 2. As a result, films shown in Table 4 were obtained.

[Table] All of these films had physical properties outside the scope of the present invention, and had problems in being put to practical use as shrink films. Example 3 The same composition as in Example 1 was used for the inner layer, and the resin constituting the outer layer contained terephthalic acid as the main acid component, 60 mol% of ethylene glycol and 40 mol of 1,4-cyclohexanedimethanol as the alcohol components. % copolymer polyester (Vikat softening point 84°C), the acid component is the same, and the alcohol component is 80 mol% ethylene glycol and 20 mol% 1,4-cyclohexanedimethanol. copolymer polyester (Vikatto softening point 79°C), acid components 80 mol% terephthalic acid, 15 mol% isophthalic acid, 5 mol% adipic acid, alcohol components 70 mol% ethylene glycol, 15 mol% tetramethylene glycol. , a copolymer polyester mainly composed of 15 mol% of 1,4-cyclohexanedimethanol (Vikat softening point 75°C),
In the same manner as in Example 1, using each layer so that the thickness ratio of the entire outer layer was 20%,
A rapidly cooled amorphous multilayer original fabric was obtained. each in order
No.15, No.16, No.17. This was stretched 3×3 times at 95° C. using the batch-type biaxial stretching apparatus described above to obtain films each having a thickness of 10 microns. Regarding the heat shrinkage characteristics of the film, the heat shrinkage rates at 80°C were 35, 27, and 24%, and the heat shrinkage stresses at 80°C were 132, 137, and 144 g/mm ² , respectively.
Further, the tensile modulus was 87, 85, and 85 Kg/mm ² , respectively. In addition, all other film properties were within preferred ranges. As a result of packaging these films using an overlap link packaging machine, all evaluation ranks were ◎, and the finish was good even when the packaging was carried out at a margin rate (70%). Comparative Example 4 Nylon-6 resin (manufactured by Toray Industries, Inc., CM1021XF, melting point 220°C, Vikatsu softening point 217°C) was used as the resin constituting the outer layer, and the thickness ratio of the outer layer to the whole was
Using the same composition as in Example 1 for the inner layer, a multilayer raw fabric was obtained in the same manner as in Example 1, heated to 90°C and stretched 3x3 times to increase the thickness.
A 15 micron film was obtained. To describe the heat shrinkage characteristics of this film, the heat shrinkage rate at 80℃ is 10%, 80
The heat shrinkage stress at °C was 95 g/mm ² and the tensile modulus was 75 Kg/mm ² . As a result of packaging using this film, many wrinkles occurred and the evaluation rank was ×. Example 4 As an outer layer, polyethylene terephthalate (Tg: 69
°C, crystallinity when sufficiently annealed as a resin
A composition containing 25% by weight of 50%) was used so that the thickness ratio of the outer layer to the whole was 20%, the same composition as in Example 1 was used as the inner layer, and the same composition as in Example 3 was quickly stretched. A film with a crystallinity of 15% and a thickness of 15 microns was obtained (No. 19). Describing the heat shrinkage characteristics of the obtained film, the heat shrinkage rate at 80℃ is
The heat shrinkage stress at 35% and 80℃ is 100g/ ^mm2 ,
The tensile modulus was 85Kg/ ^mm2 . The packaging evaluation rank of this film was ○. Comparative Example 5 As the resin constituting the outer layer, the same polyethylene terephthalate as in Example 4 was used so that the thickness ratio of the outer layer to the whole was 20%, and as the inner layer, the same composition as in Example 1 was used. Stretched in the same manner, the resulting film was fixed and placed in an air oven at a temperature (100-140°C) and a time (1-140°C).
5 minutes) and heat-treated to obtain a film in which the outermost polyester layer was crystallized to a crystallinity of about 45%. The heat shrinkage properties of this film are 0% heat shrinkage and 0g/ ^mm2 heat shrinkage stress at 80°C.
Heat shrinkage rate 0% at 160℃, heat shrinkage stress 0g/mm ²
The heat shrinkage rate was 5% at 180°C, and the obtained film had problems in being put to practical use as a shrink film. Example 5 The copolymerized polyester of Example 1 was used as the outer layer so that the thickness ratio to the whole was 20%, and the inner layer was made of ethylene-vinyl acetate copolymer (vinyl acetate group content 10% by weight, melt index).
1.0, Vikatsu softening point 81℃, melting point 95℃) 25% by weight,
Soft polymer consisting of ethylene-α-olefin copolymer (density 0.88 g/cm ³ , melt index
0.44, amorphous, Vikatsu softening point below 40℃) 15% by weight, ultra-low density polyethylene (density 0.912g/cm ³ ,
Melt index 1.0, melting point 122℃) 40% by weight,
A composition consisting of 20% by weight of crystalline polypropylene (density 0.90g/cm ³ , melt flow rate 7, melting point 143°C, 4% by weight random copolymerization of ethylene) was stretched in the same manner as in Example 1. A film with a thickness of 10 microns was obtained (No. 20). The heat shrinkage property of this film is 55 at 80℃.
%, the heat shrinkage stress at 80° C. was 180 g/mm ² , and the tensile modulus was 105 Kg/mm ² . The packaging evaluation rank for this film was ◎. Example 6 The copolymerized polyester of Example 1 was used as the outer layer so that the thickness ratio to the whole was 20%,
As an inner layer, a soft polymer consisting of 50% by weight of the same ethylene-vinyl acetate copolymer as in Example 1 and the same ethylene-α-olefin copolymer as in Example 1.
15% by weight, 15% by weight of the same crystalline polypropylene as in Example 1, acid-modified polyolefin (Mitsui Petrochemical Co., Ltd.)
manufactured by Admer NE050, melt index 3.5,
A multilayer original fabric was obtained in the same manner as in Example 1 using a composition consisting of 20% by weight (melting point: 125°C, Vikat softening point: 98°C). The interlayer adhesive strength of this original fabric was measured and found to be 190 g/10 mm width. Subsequently, this multilayer original fabric was stretched in the same manner as in Example 1 to obtain a film with a thickness of 10 microns (No. 21). Describing the heat shrinkage characteristics of the obtained film, the heat shrinkage rate at 80℃ is 52
%, the heat shrinkage stress at 80° C. was 155 g/mm ² , and the tensile modulus was 95 Kg/mm ² . The packaging evaluation rank for this film was ◎. Example 7 The same copolymerized polyester as in Example 1 was used as the outer layer so that the thickness ratio to the whole was 20%, and one of the inner layers was the ultra-low density polyethylene used in Example 5. A layer having an adhesive inner layer of ethylene-acrylic acid copolymer (melt index 2.5, Vikat softening point 80°C, acrylic acid content 16% by weight) with a thickness ratio of 5% between the outer layer and the other inner layer. The composition is outer layer/adhesive inner layer/
A multilayer original fabric of inner layer/adhesive inner layer/outer layer was prepared in the same manner as in Example 1, and the interlayer adhesion strength between the outer layer and the adhesive inner layer, and between the adhesive inner layer and the inner layer was measured, and no peeling was found. . Subsequently, this multilayer original fabric was stretched in the same manner as in Example 1 to obtain a film with a thickness of 15 microns (No. 22). The heat shrinkage properties of the obtained film were as follows: heat shrinkage rate at 80°C: 55%, heat shrinkage stress at 80°C: 140g/mm ² , tensile modulus: 83Kg/mm ²
It was hot. The packaging evaluation rank for this film was ◎. Next, the 5 Mrad crosslinked multilayer original fabric was stretched in the same manner as above using an electron beam crosslinking device (500 KV energy) to obtain a film with a thickness of 10 microns. The heat shrinkage properties of the obtained film are as follows: heat shrinkage rate is 57% at 80°C, heat shrinkage stress is 250
g/mm ² , and the tensile modulus was 83 Kg/mm ² .
When this film was packaged using both overlap and pillow link packaging machines, the packaging evaluation rank was ◎. Surprisingly, even at a shrinkage temperature of 200℃, it can be packaged well.
It covered everything from low to high temperatures. Even if the margin ratio was increased further (70%), packaging without sagging was possible and a high elastic recovery rate was maintained.

Claims (1)

[Scope of Claims] 1. A multilayer film consisting of at least three layers including at least one inner layer, the total thickness of which is 5 to 100 microns, and the ratio of the thickness of the outer layer to the total thickness is 6 to 60%. , both outer layers have a crystallinity of less than 30% and a Vikatsu softening point of 40~150℃,
The inner layer is made of a polymer mainly composed of at least one hard thermoplastic resin selected from copolymerized polyester resins, polycarbonate resins, and copolymerized polystyrene resins, giving a film with a tensile modulus of at least 75 Kg/ ^mm2 . is polypropylene polymer, ethylene polymer, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ethylene-α-olefin The multilayer film is made of at least one kind of polymer selected from a soft polymer consisting of a copolymer, an ionically crosslinkable copolymer, a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene derivative, and a derivative thereof. , tensile modulus 60~150Kg/mm ² , heat shrinkage rate at 80℃ is at least 20% or more, heat shrinkage stress value 50
A heat-shrinkable film having a weight of 500 g/mm ² and not causing delamination in practical terms. 2 A multilayer film consisting of at least three layers including at least one inner layer, with a total thickness of 5 to 100 microns, a ratio of the thickness of both outer layers to the total thickness of 6 to 60%, and the outer layer is a crystalline film. The degree of softening is 30% or less, the softening point is 40 to 150℃,
The inner layer is made of a polymer mainly composed of at least one hard thermoplastic resin selected from copolymerized polyester resins, polycarbonate resins, and copolymerized polystyrene resins, giving a film with a tensile modulus of at least 75 Kg/ ^mm2 . is polypropylene polymer, ethylene polymer, ethylene-vinyl acetate copolymer, ethylene-aliphatic unsaturated carboxylic acid copolymer, ethylene-aliphatic unsaturated carboxylic acid ester copolymer, ethylene-α-olefin The multilayer film is made of at least one kind of polymer selected from a soft polymer consisting of a copolymer, an ionically crosslinkable copolymer, a block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene derivative, and a derivative thereof. , tensile modulus 60~150Kg/mm ² , heat shrinkage rate at 80℃ is at least 20% or more, heat shrinkage stress value 50
~500g/ ^mm2 , practically no delamination,
In producing a rigid heat-shrinkable film characterized by this, the polymers of each layer of the multilayer film are melted in respective extruders, and then the ratio of the thickness of the outer layer to the total thickness is 6 to 60%. So that
Co-extrusion with a multilayer die, cooling and solidification to obtain a multilayer film raw film, then heating this raw film to an area stretching ratio of 5 to 50 times in at least one axis at a stretching temperature (T°C) according to the following formula. A method for producing a heat-shrinkable film, which comprises stretching. V-20≦T≦V+35 However, V represents the Vikato softening point (°C) of the outer layer.