JP3966782B2 - Heat-shrinkable film and method for producing the same - Google Patents

Description

【００３９】
【発明の効果】
本発明によれば、シュリンク包装材料として適当な熱水収縮率を有すると共に、包装材料として適当な表面易滑性を有する熱収縮性ポリアミドフィルムを提供することが可能である。したがって本発明のシュリンクフィルムは、水物食品、食肉加工品をはじめとする収縮包装用途において、その利用価値は極めて高い。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat-shrinkable film (hereinafter also referred to as a shrink film) and a method for producing the same. More particularly, the present invention relates to a shrink film and a shrink film excellent in shrinkability and slipperiness suitable for shrinkage packaging of processed meat products such as marine foods, ham and sausage, and a method for producing the same.
[0002]
[Prior art]
A so-called heat-shrinkable (hereinafter also referred to as shrink) film that causes a large dimensional change by heating is used as a packaging material taking advantage of its characteristics. Conventionally, polyvinyl chloride, polyvinylidene chloride, polyolefin, polyamide, and their copolymers are known as constituent materials for heat-shrinkable films. Among them, polyamide resin inherently has excellent mechanical, chemical and optical properties, so a shrink film with appropriate heat shrinkability satisfies many performance requirements for shrink packaging materials. Therefore, it is widely used as liquid and heavy packaging materials including processed meat products such as marine foods, hams and sausages.
[0003]
In the manufacturing process of a biaxially stretched film, generally, a so-called heat setting process is performed in which heat treatment is performed near the melting point of the main constituent resin after the stretching process to promote crystallization and fix the orientation. In the manufacturing process of the shrink film, this heat setting condition is relaxed. That is, the film after stretching is heat-treated at a relatively low temperature. Therefore, since a certain structural strain remains in the shrink film, the film is given shrinkage characteristics. Similarly, shrinkage characteristics are imparted to polyamide-based shrink films.
[0004]
On the other hand, in order to use a plastic film as a packaging material, it is necessary that the slipperiness of the surface is good. In general, a technique of adding inorganic particles or a low molecular weight organic compound as a so-called lubricant to a film to impart easy slipping to the film surface is known and widely practiced. In particular, organic lubricants are effective in reducing dynamic friction and are effective in improving the filling of the contents into the package.
[0005]
In order for the organic lubricant to fully exert its effect, the component must be quickly and reliably transferred to the film surface. Surface migration called so-called bleed-out of the organic lubricant proceeds by subjecting the lubricant component to a kneaded sheet with a raw material resin in advance and biaxially stretching, followed by heat treatment exclusively at a high temperature in the heat setting step described above.
[0006]
In other words, the conventional shrink film needs to be set at a low heat treatment temperature in order to provide the heat shrinkability that is an essential characteristic. Therefore, the surface migration of the organic lubricant is inevitably promoted, and the slipperiness is generally sufficient. Not expressed in In particular, when the film is used as a package and printing / laminating or filling food, it often causes a process failure.
[0007]
By adding a large amount of fine particles composed of inorganic components such as silicate, a certain level of slipperiness can be obtained even under low heat treatment conditions, but this method has a poor film appearance such as a significant increase in haze and loss of surface gloss. This will significantly impair the commercial value of the food packaging material. In addition, excessive addition of inorganic particles is a problem that cannot be overlooked in the manufacturing process, such as wear of screws and barrels in the extruder in the melt extrusion process of the raw resin, and shortening of the service life due to clogging of the filter for removing foreign matter. In general, it is difficult to say that it is a preferable method.
[0008]
As described above, when using a polyamide-based shrink film as a food packaging material, it is difficult to simultaneously provide heat shrinkability and slipperiness that are indispensable as properties, and it is difficult to make it parallel to the current food packaging materials. In view of strict quality standards, the demand is often not met.
[0009]
[Problems to be solved by the invention]
The present invention aims to provide a shrink film that maintains heat shrinkability, which is an indispensable characteristic for shrink wrapping materials, and is excellent in slipperiness.
[0010]
[Means for Solving the Problems]
The present inventor pays attention to the behavior of the polyamide-based elastomer resin as a component in the production process of the film comprising the polyamide resin composition, and appropriately sets the compounding concentration in the polyamide resin and the heat treatment temperature after the biaxial stretching is completed. By setting, it has been found that a polyamide film having excellent slipperiness can be produced without impairing heat shrinkability, and the present invention has been achieved.
[0011]
That is, the gist of the present invention is as follows.
A film comprising a polyamide-based resin (a) and a polyamide-based elastomer resin (b), wherein the content of (a) is 80 to 97% by mass, the content of (b) is 3 to 20% by mass, It is a heat-shrinkable film excellent in slipperiness, having a dynamic friction coefficient of 0.8 or less and a shrinkage rate of 15 to 40% when treated in hot water at 80 ° C. for 30 minutes.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The heat-shrinkable film of the present invention is composed of a polyamide resin (a) and a polyamide elastomer resin (b). Examples of the polyamide-based resin (a) include poly-ε-capramide (nylon 6), polyhexamethylene adipamide (nylon 66), polyhexamethylene sebacamide (nylon 610), polyundecamide (nylon 11), polylauramide (nylon) 12), polytetramethylene adipamide (nylon 46), polymetaxylylene adipamide (MXD6), polymetaxylylene sacacamide, polymetaxylylene speramide, polyparaxylylene adipamide and mixtures thereof, A polymer etc. can be illustrated. When the above polyamide-based resin is applied to the film of the present invention, excellent effects can be obtained, and a film having properties suitable as a packaging material such as mechanical properties, heat resistance, and transparency can be obtained.
[0013]
The polyamide-based elastomer resin is a block copolymer obtained by block copolymerizing a polyamide component as a hard segment and a polyether or polyester component or both components as a soft segment.
[0014]
As a polyamide component, the component similar to the polyamide resin mentioned above can be illustrated arbitrarily. Examples of the polyether which is a soft segment component include so-called polyether glycols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol, and copolymers thereof. Polyesters include terephthalic acid, phthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid, adipic acid, sebacic acid, succinic acid, dodecanedioic acid and other polycarboxylic acid components, ethylene glycol, propylene glycol, 1 , 4-butanediol, 1,6-hexanediol, neopentylglycol, cyclohexanedimethanol, bisphenol and other polycondensates and reactants are included, and modified products such as acrylic resins and epoxy resins are also included. .
[0015]
In the heat-shrinkable film of the present invention, the content of the polyamide-based resin (a) in the film is 80 to 97% by mass, and the content of the polyamide-based elastomer resin (b) is 3 to 20% by mass. is necessary. If the content of (b) is lower than 3% by mass, a predetermined slip property cannot be obtained. On the other hand, if it is set higher than 20% by mass, the slipping property becomes excessive, and the product form may be broken due to so-called winding deviation that occurs during film winding in the film slitting process. It will damage the product value such as problems. On the other hand, it is not economically preferable from the standpoint of operation, such as film formation failure due to die swell and sheet thickness failure in the width direction become remarkable.
[0016]
The film of the present invention needs to have a dynamic friction coefficient of 0.8 or less. The dynamic friction behavior of the film is an indispensable characteristic because the packaging material applied to the filling device smoothly flows through the device and is used for the filling process when continuously filling the contents including food. In particular, it is an extremely important characteristic in recent high-speed filling. If the dynamic friction coefficient is 0.8 or less, problems such as wrinkling in the filling device and catching on device parts are unlikely to occur.
[0017]
The film of the present invention needs to have a shrinkage ratio in the range of 15 to 40% when treated in hot water at 80 ° C. for 30 minutes. When the shrinkage rate is less than 15%, it is impossible to ensure appropriate shrinkage as a shrink wrapping material, and the adhesion with the package contents is poor and the characteristics of shrink wrapping cannot be exhibited. When it exceeds 40%, the packaging form collapses due to the excessive film shrinkage, the contents are damaged and the packaging material is broken, and the function as a food packaging material and the appearance of the product are remarkably impaired.
[0018]
Any known method can be adopted as a method for producing the heat-shrinkable film of the present invention. For example, after the mixed raw materials are heated and melted by an extruder, an unstretched sheet is extruded from a die such as a T die or an I die, and this is rotated by a known casting method such as an air knife casting method or an electrostatic application casting method. The film is rapidly cooled by being brought into close contact with the cooling drum.
[0019]
Next, the obtained unstretched sheet is stretched by 2.5 times or more in the traveling direction (hereinafter referred to as MD direction) and the width direction (hereinafter referred to as TD direction) of the film, and then heat-treated to cause oriented crystallization. As a method for stretching the film, it is possible to apply methods such as a flat sequential biaxial stretching method and a flat simultaneous biaxial stretching method. When the draw ratio is 2.5 or less, oriented crystallization is insufficient and mechanical strength such as impact resistance cannot be obtained.
[0020]
In the present invention, the heat treatment step after the end of biaxial stretching is preferably performed at a heat treatment temperature of not less than the melting point of the polyamide-based elastomer resin (b) and not more than 170 ° C. If the heat treatment temperature is lower than the melting point of the resin (b), the slipperiness of the film may not be obtained, the shrinkage will be excessive, the packaging form will collapse and the contents will be damaged, etc. It may disappear. On the other hand, when the heat treatment temperature exceeds 170 ° C., the orientation crystallization is excessively promoted, conversely, the heat shrinkability is lowered and the characteristics as a shrink wrapping material are lost, and the product value is significantly impaired. become.
[0021]
Various additives such as an antistatic agent, an anti-coloring agent and an inorganic filler are added to the polyamide resin constituting the film of the present invention or the film provided by the present invention, as long as the effects of the present invention are not lost. It is also possible to mix.
[0022]
The polyamide film provided by the present invention adds various performances by performing surface activation treatment such as corona treatment on the surface, printing, various functional coatings, laminating, etc., and further improving its utility value. It is also possible to make it.
[0023]
The shrink film thus obtained has appropriate heat shrinkage and excellent slipperiness and is suitable as a shrink film for packaging.
[0024]
【Example】
EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited only to these Examples. The measurement methods and evaluation methods used in the examples and comparative examples are as follows.
[0025]
(1) A film piece having a hot water shrinkage ratio of 10 mm and a length of 100 mm was immersed in hot water at 80 ° C. for 30 minutes, and the dimensional change before and after the treatment was measured to obtain the percentage of the original length.
[0026]
(2) Coefficient of dynamic friction The coefficient of dynamic friction was measured according to the procedure described in JISK7125. The measurement ambient temperature was 20 ° C. and the relative humidity was 65%. The measurement surface is a film piece to be measured for both the test piece and the sliding piece.
[0027]
Example 1
93% by mass of poly-ε-capramide (nylon 6, relative viscosity 3.0 (25 ° C., 95% by mass in sulfuric acid)) and polyamide-based elastomer resin <A> (Pebux 2533, manufactured by Atofina, melting point 134 ° C.) 7 After being mixed and melted at 240 ° C. and extruded into a sheet using a T-die, it was brought into close contact with a rotating drum at 25 ° C. by an air knife cast method and rapidly cooled to obtain an unstretched sheet having a thickness of 150 μm. .
Subsequently, this unstretched film was stretched 3.0 times in the longitudinal direction on a metal roll heated to 50 to 70 ° C. to obtain a uniaxially stretched film, and further 3 ° C. at 90 ° C. in the width direction. The film was stretched 3 times to obtain a biaxially stretched film.
Next, the biaxially stretched film was heat-treated at a heat treatment temperature of 150 ° C. for 10 seconds, wound after cooling, and a heat-shrinkable film having a thickness of 15 μm was obtained. The evaluation results of the obtained film are shown in Table 1.
[0028]
Example 2
Heat shrinkability in the same procedure as in Example 1 except that the unstretched sheet is stretched simultaneously at 90 ° C. by 3.0 times in the longitudinal direction and 3.3 times in the transverse direction at 90 ° C. A film was obtained. The evaluation results of the obtained film are shown in Table 1.
[0029]
Examples 3-4
A heat-shrinkable film was obtained in the same procedure as in Example 1, except that the content of the polyamide-based elastomer resin <A> used in Example 1 was changed to the amount shown in Table 1. The evaluation results of the obtained film are shown in Table 1.
[0030]
Example 5
A heat-shrinkable film was obtained in the same procedure as in Example 1 except that the polyamide-based elastomer resin <A> was changed to another elastomer resin <B> (Pebux MX1205 manufactured by Atofina, melting point 147 ° C.). The evaluation results of the obtained film are shown in Table 1.
[0031]
Example 6
A heat-shrinkable film was obtained in the same procedure as in Example 1 except that the polyamide-based elastomer resin <A> was changed to another elastomer resin <C> (Daicel E40 manufactured by Daicel Industries, Ltd., melting point 146 ° C.). The evaluation results of the obtained film are shown in Table 1.
[0032]
Example 7
A heat-shrinkable film was obtained in the same procedure as in Example 1 except that the heat treatment temperature was changed to 165 ° C. The evaluation results of the obtained film are shown in Table 1.
[0033]
Comparative Example 1
A heat-shrinkable film was obtained in the same procedure as in Example 1 except that the polyamide-based elastomer resin <A> was not added. The evaluation results of the obtained film are shown in Table 1.
[0034]
Comparative Examples 2-3
A heat-shrinkable film was obtained in the same procedure as in Example 1, except that the content of the polyamide-based elastomer resin <A> used in Example 1 was changed to the amount shown in Table 1. The evaluation results of the obtained film are shown in Table 1.
[0035]
Comparative Example 4
A heat-shrinkable film was obtained in the same procedure as in Example 1 except that the heat treatment temperature was changed to 120 ° C. The evaluation results of the obtained film are shown in Table 1.
[0036]
Comparative Example 5
A heat-shrinkable film was obtained in the same procedure as in Example 1 except that the heat treatment temperature was changed to 200 ° C. The evaluation results of the obtained film are shown in Table 1.
[0037]
Comparative Example 6
A heat-shrinkable film was obtained in the same procedure as in Example 1 except that the polyamide-based elastomer resin <A> was changed to another elastomer resin <D> (Pebux 7033 manufactured by Atofina, melting point 172 ° C.). The evaluation results of the obtained film are shown in Table 1.
[0038]
[Table 1]

[0039]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the heat-shrinkable polyamide film which has a suitable hot-water shrinkage rate as a shrink packaging material, and has a suitable surface slipperiness as a packaging material. Therefore, the shrink film of the present invention has extremely high utility value in shrink wrapping applications including marine foods and processed meat products.

Claims (2)

A film comprising a polyamide-based resin (a) and a polyamide-based elastomer resin (b), wherein the content of (a) is 80 to 97% by mass, the content of (b) is 3 to 20% by mass, A heat-shrinkable film excellent in slipperiness, having a dynamic friction coefficient of 0.8 or less and a shrinkage rate of 15 to 40% when treated in hot water at 80 ° C. for 30 minutes. The method for producing a heat-shrinkable film according to claim 1, wherein the film after biaxial stretching is heat-treated at a temperature not lower than the melting point of the polyamide-based elastomer resin (b) and not higher than 170 ° C.