JPH0380418B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-shrinkable composite foamed resin film, and more particularly to a heat-shrinkable composite foamed resin film comprising a laminated structure of a foamed resin layer and a non-foamed resin layer suitable for protective packaging of containers, etc. Regarding the film. Conventionally, as a heat-shrinkable resin film for protective packaging of glass bottles, etc., for example, Japanese Patent Publication No. 58-15382 discloses a closed-cell polymer layer mainly composed of a C ₂ -C ₄ olefin polymer and a C _{2 -C 4} olefin polymer layer. Disclosed is a heat-shrinkable sleeve formed by coextrusion comprising a non-cellular polymer layer based on a _C4 olefin polymer and having a heat-shrinkability of at least 50% in the machine direction and not more than 20% in the transverse direction. Also, JP-A-58-
Japanese Patent No. 134718 discloses a heat-shrinkable film having a foam layer formed by applying a foam material to a thermoplastic film and foaming the film during a stretching process. However, the former heat-shrinkable sleeve is made of a resin composition mainly composed of olefin homopolymer.
Since the film is formed by blown bubble extrusion, it has the drawback that it is not possible to obtain a film with a high expansion ratio and large heat shrinkability. On the other hand, the heat shrinkability of the latter heat-shrinkable film is dominated by the heat-shrinkability of the thermoplastic film, so in order to obtain a film with high heat-shrinkability, the thickness of the thermoplastic film must be increased. Not only is it uneconomical, but the resulting film has disadvantages in that its flexibility is impaired and its cushioning properties are poor. Therefore, the object of the present invention is to provide a heat shrinkable material which does not have the above-mentioned drawbacks, has excellent tensile strength, cushioning properties, heat insulation properties, printability, formability, stretching processability, etc., and which can reduce the heat shrinkage temperature. It is to provide sex films. According to the invention, the above objects are achieved by: (a) 1.5-3.5% by weight of ethylene, 91-95% of propylene;
The melt flow rate (MFR) obtained by mutually polymerizing 3.5-5.5% by weight of _C4 - _C8 α-olefins is 7-10% by weight.
g/10 min ethylene/propylene/C ₄ ~
C ₈ α-olefin ternary random copolymer 40~
80% by weight and vinyl acetate content from 5 to 15% by weight
(b) a foamed resin layer consisting essentially of a mixture with 60 to 20% by weight of an ethylene/vinyl acetate copolymer having a melt index (MI) of 0.5 to 2.5; A heat-shrinkable composite resin film comprising a non-foamed resin layer containing a crystalline thermoplastic polymer laminated on one side, the film being stretched at least three times in one axis direction. Achieved by foamed resin film. Hereinafter, the heat-shrinkable composite foamed resin film of the present invention (hereinafter referred to as "composite film") will be explained in more detail. The foamed resin layer constituting the composite film of the present invention has a specific ethylene/propylene/C ₄ -C ₈ α-
Olefin ternary random copolymer (hereinafter referred to as “EPT”)
It can be formed by foaming a resin mixture consisting essentially of a specific ethylene/vinyl acetate copolymer (hereinafter referred to as an "EVA polymer"). Used to form the foamed resin layer above
EPT polymers include ethylene, propylene and _C4 ~
It is obtained by mutually polymerizing three types of monomers of C ₈ α-olefin, and the polymerization ratio of these monomers is ethylene 1.5 to 3.5% by weight, preferably 2 to 3% by weight; propylene 91 -95% by weight, preferably 92-94% by weight; and 3.5-5.5% by weight, preferably 4-5% by weight of _C4 - _C8 α-olefins (wherein weight% is the proportion of the above three types). (based on the total weight of monomers). Examples of the _C4 to _C8 α-olefin used in the above polymerization include butene-1, pentene-1, hexene-1, heptene-1, and octene-1.
Among them, butene-1 is particularly preferred because of its ease of availability. The above monomer can be polymerized by a method known per se. For example, according to the method described in JP-A-56-143207, a small amount of C ₂ to C ₁₂ α-olefin and trialkylaluminum are added. The objective is achieved by copolymerizing ethylene, propylene and C ₄ -C ₈ α-olefin in the above proportions in the presence of a titanium trichloride composition preactivated with an aromatic ester and a catalyst consisting of an organoaluminum halide. EPT polymers can be produced. The EPT polymer used in the present invention should have a melt flow rate (measured according to ASTM-D-1238, hereinafter abbreviated as "MFR") in the range of 7 to 10 g/10 min, particularly 7 to 9 g/10 min. /10 minutes is desirable. Further, the EPT polymer generally has a melting point within the range of 135 to 150°C, preferably 140 to 145°C, as measured by a differential scanning calorimeter.
℃ range is suitable, and furthermore, those with a specific gravity of about 0.91±0.02 are advantageously used. On the other hand, the EVA polymer to be mixed with the above EPT polymer can be selected from those known per se, and in the present invention, the vinyl acetate content is within the range of 5 to 15% by weight, preferably 7 to 13% by weight. and melt index (measured according to ASTM-D-1238,
(hereinafter abbreviated as “MI”) is 0.5 to 2.5, preferably
Use a value within the range of 1.0 to 2.0. Also,
The EVA polymer used in the present invention is generally 0.93±0.01
It is desirable that the specific gravity be approximately the same. One major feature of the present invention lies in the use of a mixture of the EPT polymer and EVA polymer.
This makes it easier to adjust the extrusion viscosity when foaming and extruding a mixture of EPT polymer and EVA polymer as described below, making it easier to adjust the extrusion molding conditions and creating a dense foam with fine bubbles. It has been found that various excellent advantages can be obtained, such as a marked reduction in breakage during stretching, improved stretching processability, and the ability to perform heat-shrinking operations at relatively low temperatures. A mixture with such excellent properties is EPT
40-80% by weight of polymer and 60-20% by weight of EVA polymer
It can be produced by mixing. When the mixing ratio of EPT polymer is less than 40% by weight, the resulting composite film has a low heat shrinkage rate;
There are problems such as being too flexible and lacking in binding force after heat shrinking, making it unsuitable for shrink packaging.On the other hand, if the mixing ratio of EPT polymer exceeds 80% by weight, the above-mentioned problem due to EVA polymer combination There is a possibility that the effects such as these may not be fully exhibited. Therefore, a suitable mixing ratio of EPT polymer and EVA polymer is 50 to 70% by weight of EPT polymer.
EVA polymer is 50-30% by weight. The EPT polymer and the EVA polymer can be mixed by a method known per se, for example, using a ribbon blender, tumbler, Henschel mixer, or the like. The mixture thus obtained generally contains 4 to 6
g/10 min, preferably within the range of 4.5 to 5.5 g/10 min. Furthermore, the mixture may contain suitable auxiliary agents, such as ultraviolet absorbers (e.g., benzophenones, benzotriazoles, salicylic acid esters, etc.), antioxidants (e.g., 2,6-
Di-t-butyl-p-cresol, 4,4'-thiobis(3-methyl-6-t-butylphenol),
2,2-di-(4-hydroxyphenyl)propane, 2,2'-methylenebis(4-methyl-6-t
-butylphenol), phosphite antioxidants such as trinonyl phenyl phosphite, tetrakis [3-
(4-hydroxy-3,5-di-t-butylphenyl)propionyloxymethyl]methane, etc.),
Flame retardants (e.g., halogenated hydrocarbons, phosphate esters, antimony oxide, etc.), antistatic agents (e.g., ethylene oxide adducts of alkylamines, fatty acid esters of glycerin, polyoxyethylene alkyl phenyl ethers, etc.), lubricants (e.g. , higher fatty acid amides, higher fatty acid esters, wax, metal soap, etc.), antiblocking agents (e.g., silica, calcium carbonate, magnesium silicate, calcium phosphate, etc.), antifogging agents (e.g., sorbitan monostearate, sorbitan monopalmium, etc.) sorbitan surfactants such as tate, sorbitan monobehenate, glycerin surfactants such as glycerin monolaurate, diglycerin monopalmitate, glycerin monostearate, polyethylene glycol monostearate, polyethylene glycol monopalmitate, etc. polyethylene glycol surfactants, alkylene oxide adducts of alkylphenols, esters of sorbitan/glycerin condensates and organic acids), foaming nucleating agents (e.g. talc,
silica, etc.), foaming aids (e.g., urea, metal salts of carboxylic acids, etc.), coloring agents (e.g., titanium oxide, carbon black, phthalocyanine blue, etc.), etc. may be added to the extent that they do not impair the purpose of the present invention. good. The amount of these auxiliaries varies depending on the intended use of the final product, etc., but in general, they can be used in the following amounts per 100 parts by weight of the mixture: Ultraviolet rays Absorbent 0.1 to 1 part by weight, antioxidant 0.1 to 1 part by weight, flame retardant 0.5 to 10 parts by weight, antistatic agent 0.01 to 1 part by weight.
parts by weight, 0.1 to 1 part by weight of lubricant, 0.1 to 1 part by weight of antiblocking agent, 0.1 to 5 parts by weight of antifogging agent, 0.1 to 0.5 parts by weight of foam nucleating agent, 0.1 to 1 part by weight of foaming aid, 0.1 to 1 part by weight of colorant. 5 parts by weight. Furthermore, fillers such as talc, clay, silica, alumina, barium sulfate, calcium carbonate, metal powder, glass beads, short glass fibers, etc. may be added to the mixture as long as they do not impede the purpose of the present invention. well, the amount is generally the same as that of the mixture.
A range of 0.1 to 5 parts by weight per 100 parts by weight is suitable. In order to form the resin foam layer of the composite film of the present invention from the polymer mixture described above, a method known per se can be used. For example, a blowing agent is blended into the polymer mixture and This can be carried out by melt-kneading under conditions where foaming is suppressed and then extruding into a film from a die. The blowing agent that can be used is either a thermally decomposable type or a low-boiling liquid or liquefied gas type, but the former thermally decomposable type is generally easier to handle. It is suitable because it is easy to obtain a closed-cell foam.
Examples of thermally decomposable blowing agents include inorganic blowing agents such as ammonium carbonate, sodium bicarbonate, a mixture of sodium nitrate and ammonium chloride; dinitrosopentamethylenetetramine, N,N'-dimethyl-N,N'-dinitros Nitroso blowing agents such as terephthalamide; benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, p,
Sulfohydrazide blowing agents such as p′-oxybis(benzenesulfonylhydrazide); azo blowing agents such as azobisisobutyronitrile, azodicarbonamide, barium azodicarboxylate, and diethyl azodicarboxylate can be used. . On the other hand, examples of low-boiling liquid or liquefied gas blowing agents include pentane, hexane,
Alkanes such as heptane; halogenated alkanes such as methyl chloride, methylene chloride, trichloroethane, dichloroethane, dichlorotetrafluoroethane, trichlorofluoromethane, trichlorotrifluoroethane, and dichlorodifluoromethane. The amount of these foaming agents used varies depending on the degree of foaming desired for the foamed resin layer, but generally
Suitably, the amount used is within the range of 0.1 to 3 parts by weight, preferably 0.3 to 1.0 parts by weight, per 100 parts by weight of the total amount of EPT polymer and EVA polymer. Also, in terms of the foaming ratio of the foamed resin layer, it is about 1.1 to about 2.5.
It is desirable to use an amount of blowing agent such that a blowing ratio is obtained, preferably within the range of about 1.3 times to about 2.0 times. Here, "expansion ratio" refers to the density of a non-foamed resin film (film molded without using a foaming agent) as _d0 , and the density of a foamed film of the same resin (film molded using a foaming agent) as d0. When set to ₁ , the value is expressed by the following formula. Expansion ratio = d ₀ / d ₁ A method for forming a foamed resin film as a foamed resin layer from the above-mentioned polymer mixture, foaming agent, and auxiliary agents blended as necessary is as follows:
Any method known per se can be used,
For example, when using a non-vent type single or twin screw extruder, the maximum cylinder temperature is 170
A foamed resin film can be extrusion-molded by extruding a film of an appropriate width from a T-shaped die under temperature conditions of -200°C and a die temperature of 160-190°C. The foamed resin film thus formed mainly contains closed cells with an average cell diameter of 1 to 10 microns and has an expansion ratio of usually 1.1 to 2.5 times, preferably 1.3.
The film is within the range of ~2.0 times, and the thickness is generally 0.5 to 1.2 mm in an unstretched state, preferably 0.7 to 1.2 mm.
It can be about 1.0mm. According to the present invention, a non-foamed resin layer containing a crystalline thermoplastic polymer is laminated on at least one surface of the foamed resin film constituting the foamed resin layer described above. The resin constituting this non-foamed resin layer may be of the same kind of material as the resin constituting the aforementioned foamed resin film, or may be a different type of resin containing a crystalline thermoplastic polymer. Generally, it is more advantageous to use the same type of material. Therefore, as the resin constituting the non-foamed resin layer, a mixture of the above-mentioned EPT polymer and EVA polymer is preferably used.
The mixing ratio of EPT polymer and EVA polymer is not necessarily
It is not necessary to match the mixing ratio in the mixture used for the foamed resin film, and the EPT polymer and
The mixing ratio of EVA polymer is EPT polymer/EVA polymer weight ratio of 40/60 to 80/20, preferably 50/50.
It can be changed freely within the range of ~70/30.
However, it is undesirable for there to be a large difference in physical properties, especially stretchability and heat shrinkability, between the foamed resin layer and the non-foamed resin layer. It is desirable that the constituent resins are substantially the same. The resin constituting the non-foamed resin layer is laminated in a film form onto the foamed resin film constituting the foamed resin layer. The thickness of the non-foamed resin layer is not particularly limited and can vary widely depending on the intended use of the resulting composite film, but it is generally 0.05 to 0.8 mm, preferably 0.1 to 0.6 mm in an unstretched state.
It is appropriate to set it within the range of . In addition, the ratio of the thickness of the foamed resin layer to the non-foamed resin layer is not strictly limited, but it is generally determined by the ratio of the foamed resin layer/non-foamed resin layer in an unstretched state.
A suitable range is 10/1 to 10/10, preferably 10/1 to 10/5. The lamination between the foamed resin layer and the non-foamed resin layer is
There is no particular restriction on the method as long as both layers are tightly joined and integrated to form a composite (laminated) film, and any method known per se can be used.
For example, dry or wet lamination using an adhesive; extrusion lamination, such as extrusion lamination, tandem lamination and coextrusion lamination; thermal lamination; or a combination thereof, can be used. The specific operations of these laminating methods can be carried out in accordance with known operating methods, for example, "Lamination Processing Handbook" edited by the Processing Technology Research Group (Processing Technology Research Group, published September 15, 1978). This can be done as described in . The composite film laminated as described above is stretched in at least one axis. Stretching may be carried out by subjecting the formed composite film to a stretching machine,
Further, when lamination is carried out by a coextrusion lamination method, the coextruded laminated film may be stretched as it is, for example, using a tenter. Although stretching can be carried out only in one direction,
In general, it is preferable to carry out the process in two axes, vertical and horizontal. When biaxial stretching is carried out, it may be carried out by either a sequential stretching method in which stretching is carried out in the longitudinal and transverse directions sequentially, or a simultaneous stretching method in which stretching is carried out simultaneously in the longitudinal and transverse directions. The stretching ratio should be 3 times or more in terms of area ratio.
If the stretching ratio is less than 3 times, not only will the film not have a large heat shrinkage rate, but even if it is heat-shrinked, the binding force after shrinkage will be extremely weak, and the film will not function as a heat-shrinkable film. cannot be granted. Therefore, a suitable stretching ratio is 5 to 15 times in terms of area ratio, more preferably 6 to 15 times.
10x range. In addition, the temperature during stretching is the highest of the glass transition points (Tg) of the resins that make up the composite film.
It is desirable that the temperature be within the range above and lower than the melting point of the resin constituting the composite film, specifically within the range of about 80 to about 120°C. The composite film of the present invention produced as described above has excellent tensile strength, cushioning properties, heat insulation properties, etc., and also has a high ability to prevent glass from scattering when a bottle is broken, and prints on the surface of the non-foamed resin layer. It is also suitable for use as shrink wrapping labels for protecting glass containers and/or indicating contents, shrink wrapping materials for insulating glass containers and plastic containers, and decorative materials for daily necessities. Can be widely used. For these applications, the composite film of the present invention can generally have a thickness on the order of 0.08-0.4 mm, preferably 0.1-0.2 mm. Next, the present invention will be further explained with reference to Examples. Example 1 Ethylene/propylene/butene-1 ternary random copolymer [XF-7500 manufactured by Chitsuso Corporation; 2.5% by weight of ethylene, 93% by weight of propylene, and 4.5% by weight of butene-1; MFR = 8.5 g/10 Minutes; Melting point=
143°C; specific gravity = 0.91] 60 parts by weight, ethylene/vinyl acetate copolymer [DQDJ- manufactured by Nippon Unica Co., Ltd.
1830 vinyl acetate content 10% by weight; MI = 1.3; specific gravity = 0.93] 40 parts by weight and a master pellet containing a blowing agent [Cellmic MB-3013 manufactured by Sankyo Kasei Co., Ltd.;
Foaming agent = azodicarbonamide] 3 parts by weight were uniformly mixed in a tumbler to prepare an extrusion material for a foamed resin layer. This material was charged into a 90 mm single screw extruder (manufactured by Ikegai Iron Works Co., Ltd., L/D = 22, CR = 3.0), melted and kneaded under the temperature conditions of a cylinder temperature of 185 °C and a die temperature of 175 °C. A foamed sheet with a thickness of 0.8 mm was obtained by extrusion. This foam sheet has a foaming ratio of 2.0 times and contains fine air bubbles densely.
It was a uniformly foamed white sheet. Next, 60 parts by weight of the same ethylene/propylene/butene-1 ternary random copolymer as above and 40 parts by weight of the same ethylene/vinyl acetate copolymer as above were mixed, and the mixture was charged into the same 90 mm extruder as above and the cylinder temperature was 200°C. , melt-kneaded at a die temperature of 195°C, extruded through a T-shaped die into a film with a thickness of 0.15 mm, and while melting, overlapped with the foamed sheet of 0.8 mm obtained above and placed on the first cooling roll. , and the two were crimped together. In this way, a composite foamed resin sheet having a thickness of 0.95 mm and having a non-foamed resin layer (skin layer) on one side was obtained. This composite foam resin sheet was stretched 5.8 times in the uniaxial width direction using a stretching machine at an ambient temperature of 100 to 110°C to a thickness of 0.18 mm and specific gravity.
A heat-shrinkable composite foamed resin film (hereinafter referred to as composite film) having a diameter of 0.48 was obtained. The heating shrinkage rate of the composite film thus obtained is
When immersed in ethylene glycol baths at temperatures of 100℃, 110℃, 120℃, 130℃, and 140℃ for 5 seconds,
22%, 40%, 60%, 70%, 78 in the stretching direction, respectively
% shrinkage. When shrink packaging labels for glass bottles were made from this composite film and shrink-wrapped on glass bottles, the label adhered tightly to the glass bottles, demonstrating its strong shrinkage binding force. In addition, glass bottles equipped with packaging labels made of this composite film,
Two glass bottles attached in the same way were stacked and allowed to fall naturally from a height of 60 cm.
There was a 95% chance that all three films would not be damaged, demonstrating that this composite film has excellent cushioning performance. Furthermore, when a glass bottle equipped in the same manner was allowed to fall naturally onto a concrete floor from a height of 70 cm, the glass bottle broke, but no glass fragments were observed to be scattered. Example 2 40 parts by weight of ethylene/propylene/butene-1 ternary random copolymer [XF-7500 manufactured by Chitsuso Corporation], 40 parts by weight of ethylene/vinyl acetate copolymer [NVC-3750 manufactured by Nippon Unica Corporation; containing vinyl acetate Rate 15% by weight;
MI = 1.5, specific gravity = 0.94] 60 parts by weight, foaming agent azodicarbonamide [Vinihole AC manufactured by Eiwa Kasei Kogyo]
1 part by weight, 0.1 part by weight of aluminum stearate,
0.1 part by weight of calcium carbonate and 0.2 part by weight of wetting agent DOP were uniformly mixed in a tumbler to prepare an extruded material for a foamed resin layer. This material was extrusion molded under the same conditions as in Example 1 to obtain a white sheet with a thickness of 0.8 mm and a foaming ratio of 2 times. Next, 80 parts by weight of the same ethylene/propylene/butene-1 ternary random copolymer as above and 20 parts by weight of the same ethylene/vinyl acetate copolymer as above
Parts by weight were mixed and laminated under the same conditions as in Example 1 to obtain a composite foamed resin sheet with a thickness of 0.95 mm. Furthermore, the stretching process was performed in the same manner as in Example 1 to obtain a thickness of 0.18 mm.
A composite film with a specific gravity of 0.50 was obtained. The heat shrinkage rate, buffering performance, and glass shatter prevention performance of the thus obtained composite film were tested in the same manner as in Example 1, and the results are shown in the table below together with the results of comparative examples. Comparative Example 1 In place of the ethylene/propylene/butene-1 ternary random copolymer used in the composition of the extruded material for the foamed resin layer and the extruded material for the non-foamed resin layer in Example 1, an ethylene/propylene block was used. Copolymer [F-8277 manufactured by Chitsuso Co., Ltd., MFR
= 7 g/10 min; specific gravity 0.90] was molded in the same manner as in Example 1, and the performance was confirmed. Comparative Example 2 Ethylene/propylene/butene-1 ternary random copolymer and ethylene/vinyl acetate copolymer used in the composition of the extruded material for the foamed resin layer and the extruded material for the non-foamed resin layer in Example 1 [Nippon Unica DQDJ-1830] and ethylene/propylene block copolymer [Chitsuso Co., Ltd.]
F-8277] and ethylene/vinyl acetate copolymer [Nippon Unica NVC3460; vinyl acetate content 20% by weight; MI = 20; specific gravity = 0.94], and molded in the same manner as in Example 1 to confirm performance. I went. 【table】

Claims (1)

[Claims] 1 (a) 1.5 to 3.5% by weight of ethylene, 91% of propylene
~95% by weight and _C4 ~ _C8 α-olefin 3.5~5.5
The melt flow rate (MFR) obtained by mutually polymerizing the weight% is 7-10 g/
Ethylene/Propylene/ _C4 ~ _C8α in 10 minutes
- 40-80% by weight of an olefin ternary random copolymer and 60-20% by weight of an ethylene/vinyl acetate copolymer with a vinyl acetate content of 5-15% and a melt index (MI) of 0.5-2.5; (b) a non-foamed resin layer containing a crystalline thermoplastic polymer and laminated on at least one side of the foamed resin layer; 1. A heat-shrinkable composite foamed resin film, the film being stretched at least three times in one axial direction.