JPH0153184B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a composite foam material having excellent cushioning effect, printability, etc. and having heat shrinkability in the longitudinal direction. Conventionally, heat-shrinkable foam materials such as foam sheets and films have mainly been made from polystyrene, which has been particularly effective in preventing bottles from breaking when used for the exterior of containers such as bottles. It is well known as a useful packaging material because it exhibits a cushioning effect. However, heat-shrinkable foam sheets or films made of polystyrene are weak and fragile due to the characteristics of their raw materials, and are not used for labels that have the effect of preventing bottles from breaking or having a cushioning effect. However, the disadvantage is that the foamed material is damaged during the cleaning process, filling process, and even transportation, and even if the surface of the material is printed, it cannot be clearly printed, and the foamed material is layered. Phenomena such as curling and partial peeling were observed, which was a problem. This invention was made in order to solve the above-mentioned problems, and as a composite foam material having heat shrinkability in the longitudinal direction, an ethylene-propylene copolymer having an ethylene content of 1 to 10 mol%, A composition containing an elasticity-modifying polymer and a foaming agent is formed into a film, and then stretched in the longitudinal direction to form a foam material having heat-shrinkability in the longitudinal direction. The gist of the invention is that thermoplastic films are laminated, and the invention will be described in detail below. The ethylene-propylene copolymer used in the present invention usually has an ethylene content of 1 to 10 mol%, preferably 2 to 6 mol%; if the ethylene content exceeds 10 mol%, the produced foam material becomes sticky. If it is less than 1 mol %, its properties are too close to those of polypropylene, and therefore the shrinkage rate is small even when stretched, making it unsatisfactory as a heat-shrinkable member and causing the foam cells to tear. The phenomenon of fluffing becomes more likely. Preferably, the copolymer contains ethylene randomly. At this time, the amount of the copolymer to be used may be an appropriate amount that exhibits the effect, but it is preferably about 50 to 95% by weight based on the total amount of the polymer. Next, the elasticity-modifying polymer used in the present invention is added to give elasticity to the foam cells of the foam material, and if this polymer is not added, it will not be able to withstand the internal pressure during foaming. First, the foam cells tend to expand, making it impossible to obtain a fine foam structure. This polymer preferably has the property of imparting elasticity to cells during foaming; examples include low, medium,
Contains polar groups such as high-density polyethylene, polybutene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate, ethylene-1-butene copolymer, propylene-1-butene copolymer, unsaturated carboxylic acid and its derivatives, etc. Typical examples include modified polyolefin, 1:2 type polybutadiene, and linear low density polyethylene (LL DPE). In this case, a more preferable elasticity-modifying polymer is ethylene-vinyl acetate containing 3 to 40% by weight.
Examples include vinyl acetate copolymers and ethylene-1-butene random copolymers having an ethylene content of 85 to 95 mol% (density 0.86 to 0.91, crystallinity 3 to 20%). The amount of the elasticity-modifying polymer to be used may be at least an amount that exhibits its effect, and preferably about 5 to 50% by weight based on the total amount of the polymer. The blowing agent used in the present invention may be any known blowing agent. Examples of suitable blowing agents include pentane and butane as volatile ones, and hydrazine as organic ones. There are nitroso-based, nitroso-based, azo-based, etc., and inorganic ones such as sodium bicarbonate and ammonia carbonate. In this case, more preferable examples include azo blowing agents such as azodicarbonamide and azobisisobutyronitrile, and inorganic blowing agents including carbonates such as sodium bicarbonate and ammonium carbonate, and citric acid.
Examples include those consisting of an organic acid such as acetic acid. The amount of this blowing agent to be used should be at least the amount that exhibits its effect, but the total amount of the ethylene-propylene copolymer with an ethylene content of 1 to 10 mol% and the elasticity-modifying polymer ( The total amount of polymer may be 0.2 to 5 parts by weight, more preferably 0.5 to 2 parts by weight, based on 100 parts by weight. The above blowing agent may be directly blended with the ethylene-propylene copolymer according to the present invention, or may be blended with the addition of master pellets containing a high concentration of blowing agent.
An appropriate amount of a blowing agent may be kneaded into the copolymer in advance, and there are no particular restrictions on its usage. In addition, in the present invention, appropriate additives, fillers, etc. may be added in addition to the above three components, and for example, lubricants, antistatic agents, etc. may be added as necessary to improve physical properties. If necessary, desired coloring can be achieved by adding a pigment. Next, in the present invention, in order to improve the printability of the foamed material and improve its surface condition, a laminate layer is formed on the foamed material. Examples of the plastic film include films made of various commonly used thermoplastic polymers, and are not particularly limited. Examples of polyolefin resins include low, medium, and high density polyethylene, polypropylene and its copolymers, polyamide resins, polyester resins, polyvinyl resins, ethylene-vinyl acetate copolymers, and ethylene. -1-butene copolymer, etc. Among these, particularly preferred examples are those made of the same kind of polymer as the foamed material of the present invention, such as an ethylene-propylene copolymer with an ethylene content of 1 to 10 mol% or, for example, a vinyl acetate content of 3 to 40% by weight. For elastic modification of ethylene-vinyl acetate copolymers, ethylene-1-butene random copolymers with an ethylene content of 85 to 95 mol%, a density of 0.86 to 0.91 g/cm ³ , and a crystallinity of 3 to 20%. When a polymer is used alone or as a blend thereof, an anchor coat layer is not required and it is possible to directly laminate with the foam material by thermocompression bonding, which is extremely convenient. On the other hand, if a different type of thermoplastic film is used, it may be difficult to collect and reuse the scraps, but of course it can be used. Note that the thermoplastic film forming the laminate layer may also contain appropriate additives and fillers, such as lubricants,
If necessary, an antistatic agent or the like may be added to improve the physical properties, and if necessary, a pigment can be added to provide the desired coloration. The composite foamed material according to the present invention can be exemplified by laminating a thermoplastic film on a foamed material such as a film or sheet-like material, and the shape is not particularly limited, but a film or sheet-like material may be stretched. This is a suitable example because it is easy to operate. In the present invention, a composition for foamed materials or thermoplastic films containing the above-mentioned components is formed into a film, and then stretched in the longitudinal direction. The purpose of stretching in the longitudinal direction is to impart heat shrinkability in the longitudinal direction, and this is achieved by stretching in the direction in which the foamed material is produced, that is, in the longitudinal direction. Further, in the present invention, the most preferable results can be obtained if the flat foam material is longitudinally stretched by so-called roll stretching, in which the flat foam material is passed between rolls having different speeds. At this time, as a specific example of roll stretching, a method is exemplified in which the rolls are preheated to a temperature that allows stretching through several uniform speed preheating rolls, and then stretched to a desired magnification by stretching rolls set at a predetermined stretching ratio. can. The preheating roll temperature may be set as appropriate, but preferably
It is recommended to set the temperature between 90 and 130℃. If the temperature is too high, the low-temperature shrinkability will be impaired, requiring high temperatures during shrinkage, resulting in energy loss and the problem of partial melting of the sheet, while if it is too low, large stresses will occur during stretching. However, it is possible to implement this method, although it is not preferable since the mechanical load may increase or tearing may occur. The above-mentioned stretching rolls may be used as appropriate, but they are generally set at a temperature lower than that of the preheating rolls, for example, 60°C or less, and the sheet stretched here is gradually lowered by several cooling rolls so that natural shrinkage does not occur at room temperature. One way is to make it less likely to happen. The above explanation has been made using a flat film as an example, but a tubular film is difficult to combine, but it is possible to implement it. At this time, if longitudinal stretching is carried out using a normal inflation method, it is conceivable that some orientation may occur in the transverse direction, but these are all within the scope of the present invention, and the same applies to flat-shaped materials. Other longitudinal stretching means are not limited to those described above. Next, as an example of creating the composite foam material of the present invention, the method of forming a film or sheet using an extruder, then melt extrusion laminating a thermoplastic film, forming a laminate layer, and then longitudinally stretching is described below. state First, the conditions of the extruder were set to such an extent that a composition containing an ethylene-propylene copolymer with an ethylene content of 1 to 10 mol%, an elasticity-modifying polymer, and a foaming agent would not foam in the die. It can be extruded from a die into a flat sheet. At this time, it is preferable to foam at the same time. On the other hand, 1 to 10 ethylene of the same type as the raw material composition of the foamed material
At the same time, extruding a thermoplastic resin compound consisting of mol% of ethylene-propylene copolymer and an elasticity modifying polymer, melt extrusion and lamination onto the foamed material (foamed sheet), and laminated with a thermoplastic film. form a layer. At this time, the thermoplastic film is easily laminated and integrated with the foam sheet using a simple nip roll due to the heat generated during extrusion. Next, the foamed sheet and the thermoplastic film are stretched in the longitudinal direction by roll stretching, and as a result of this stretching, the foamed sheet and the thermoplastic film are bonded more strongly, and the two become as if they were a single layer, making it extremely difficult to separate them. Next, the stretching temperature (including preheating temperature)
However, this can be selected as appropriate, but for example 90~
130°C is preferred. In addition, the stretching ratio should be selected as necessary, but it should be at least 2 times, or 3 times if necessary.
It is only necessary to stretch the material by a factor of about 8 to 8. If the stretching is carried out under the above-mentioned numerical conditions, a composite foam material having preferable heat shrinkability in the longitudinal direction can be obtained, but the present invention is of course not limited to this. In this way, a composite foam material is created. At this time, the thickness of the foam material and thermoplastic film can be selected appropriately depending on the application, and in order to improve printability, the surface of the thermoplastic film can be It is also free to apply surface treatment such as corona discharge treatment. The above is a method of laminating the same type of thermoplastic film on a foam material (foamed sheet) by melt extrusion.
Simultaneously with foaming, the film may be laminated by pressing it onto a foamed sheet using a nip roll or the like. At this time, since the heat from extrusion remains on the foam sheet side, the two can be laminated and integrated extremely easily. Further, it is preferable that the foaming be carried out at the same time as the film formation, but it goes without saying that the foaming may be carried out before the film formation, after the film formation, or even simultaneously with the stretching. The above is just a description of the preferred method for manufacturing the composite foam material according to the present invention, and the present invention can also employ other appropriate methods. The composite foam material according to the present invention is most often used as a printed exterior heat-shrinkable foam label for bottles, etc., and is used in a cylindrical shape so that the stretching direction coincides with the circumferential direction of the bottle, etc. It is also widely used as a packaging material for various containers and articles, and its range of applications is wide and there are no particular limitations. Considering these uses, it is most preferable to use the composite foam material in the form of a sheet or film. The present invention is as described above, and when the composite foam material according to the present invention is used, for example, as an exterior label for a bottle or the like, it is particularly excellent in bottle breakage prevention effect and cushioning effect. It also has excellent physical properties such as strength and is not brittle like conventional products, so it can be folded into a cylindrical body, for example, and the creases that occur when folding are removed during heat shrinkage. Not only does it have the property of disappearing, but it also has remarkable effects such as being strong and strong without the disadvantage that it easily peels off in layers from the edges of the material. Examples of the present invention will be listed below along with comparative examples. <Example 1> 70% by weight of an ethylene-propylene random copolymer with an ethylene content of 4.5 mol% and 30% by weight of an ethylene-vinyl acetate copolymer (elasticity modification polymer) with a vinyl acetate content of 15% by weight 1 part by weight of a blowing agent consisting of a mixture of sodium bicarbonate and citric acid was mixed with 100 parts by weight of the mixture, and the mixture was extruded and foamed into a flat sheet through a die of an extrusion molding machine to create a foam sheet with a thickness of 900μ. . On the other hand, ethylene with an ethylene content of 4.5 mol%
A 100μ thick thermoplastic film consisting of 70% by weight propylene random copolymer and 30% by weight ethylene-vinyl acetate copolymer with 15% vinyl acetate content was extruded and laminated directly onto the foam sheet by melt extrusion. As a result, it was found that the two were considerably bonded together due to residual heat from extrusion of the thermoplastic film.
After that, it was sufficiently preheated using three sets of uniform speed preheating rolls having a surface temperature of 100 to 110°C, and then the speed ratio was 1:
5 in the longitudinal direction through a stretching roll with a surface temperature of 45°C.
Stretched twice, then at the same speed as the stretching roll at a surface temperature of 30
Foam layer 180μ by passing through a cooling roll at ℃
A composite foamed film with a thickness of 200μ with a laminate layer of 20μ was obtained. The foamed layer and laminate layer of this film were strongly bonded during the stretching process, and the film was preferably thermally shrinkable in the longitudinal direction. <Example 2> Ethylene with an ethylene content of 92 mol%, a density of 0.90 g/cm ³ , and a crystallinity of 10% as an elasticity-modifying polymer
Using 1-butene random copolymer and ethylene content as a thermoplastic film of the laminate layer.
4.5 mol% ethylene-propylene random copolymer 70% by weight and ethylene content 92 mol% density 0.90
g/cm ³ , except using a formulation of 30% by weight of ethylene-1-butene random copolymer with 10% crystallinity.
A similar composite foam material (film) was obtained in the same manner as in Example 1. <Example 3> Except for using 5 parts by weight of master pellets whose main component is low-density polyethylene (the blowing agent component is 1 part by weight) using sodium bicarbonate and citric acid as blowing agents (amount used: 20% by weight) Using the same composition as in Example 1, a film was formed in the same manner as in Example 1 to obtain a flat foam sheet with a thickness of 900 μm. After that, a laminate layer was formed in the same manner as in Example 1, and then roll stretching was carried out in the same manner as in Example 1, and when it was stretched approximately 5 times in the longitudinal direction, the total thickness of the foam layer was 180 μm and the laminate layer was 20 μm.
A longitudinally heat-shrinkable composite foam film having a thickness of 200μ was obtained. <Comparative Example 1> A blended composition in which 1 part by weight of a blowing agent consisting of sodium bicarbonate and citric acid was added to 100 parts by weight of an ethylene-propylene random copolymer with an ethylene content of 4.5 mol% was prepared in the same manner as in Example 1. thickness 900μ
A foamed film was obtained, and a thermoplastic film having a thickness of 100 μm made of the single copolymer was laminated by melt extrusion lamination. When the composite foam material (film) was then longitudinally stretched using a tenter in the same manner as in Example 1, the cells on the surface of the foam layer were ruptured in places and the surface was fluffy. <Comparative Example 2> The same amount of the same foaming agent as in Comparative Example 1 was added to polystyrene, and a film was formed in the same manner to obtain a foamed sheet with a thickness of 510 μm. On the other hand, a 90μ thick film made only of polystyrene was extruded and laminated on the foam sheet by melt extrusion lamination method, and then,
Roll stretching was carried out three times at a temperature of 110°C to obtain a longitudinally heat-shrinkable composite film with a thickness of 200 μm. The physical properties of the composite foamed films obtained in Examples 1, 2, and 3 and Comparative Example 2 are listed in Table 1 below.

[Table] From Table 1 above, the composite foam materials of Examples 1, 2, and 3 of the present invention are tough, have excellent tear strength, excellent impact strength, and have moderate elongation, making them extremely practical. It has been proven that it is a heat-shrinkable material. On the other hand, the material of Comparative Example 1 was not a satisfactory material, and the material of Comparative Example 2 also had extremely poor impact strength and other physical properties, and the buffering effect was insufficient. Phenomena such as peeling during handling and washing were also observed, and phenomena such as both layers peeling off were also observed. This also shows that the present invention has particularly significant effects.

Claims (1)

[Claims] 1 Ethylene with an ethylene content of 1 to 10 mol%
A composition containing a propylene copolymer, an elasticity-modifying polymer, and a foaming agent is formed into a film, and then stretched in the longitudinal direction to form a foamed material having heat shrinkability in the longitudinal direction. A composite foam material that is heat-shrinkable in the longitudinal direction and is characterized by being laminated with a thermoplastic film that is heat-shrinkable in the longitudinal direction.