JP4480578B2 - Polypropylene wrap film - Google Patents

Description

  The present invention relates to a film used for packaging an article such as a food packaging wrap. In particular, the present invention relates to a polypropylene-based wrap film that can maintain a quality in which adhesion and drawability do not change even after a certain period of time.

A thin film made of a thermoplastic resin has been used for storing food or heating it in a microwave oven in restaurants, food stores, etc. and general households. Among them, the vinylidene chloride copolymer resin wrap film has excellent properties such as moisture resistance, oxygen gas barrier properties, heat resistance, adhesion to containers, transparency, etc. It is used a lot.
In recent years, various food packaging wrap films mainly composed of polyolefin resin have been proposed. For example, there are polyethylene resin, polypropylene resin, poly 4-methylpentene-1 resin and the like. However, since these films have almost no adhesion on the film surface, for example, the adhesion performance to a container essential as a wrapping film for food packaging is insufficient. In order to satisfy these desired performances, many films have been proposed in which various additives and other resins are mixed or laminated with other resins. However, these films are not only adhesive to the container but also have high adhesiveness between the films, have poor drawability from the storage box, and are practically unusable.
In order to solve the various problems described above, various proposals have been made regarding the adhesion of the wrap film. JP-A-10-202806 proposes a self-adhesive wrap film in which the core layer is a polypropylene resin and the surface layer contains a surfactant as an adhesive. However, it is difficult to express high adhesion with this technique. Furthermore, when a food containing a lot of moisture is packaged and heated in a microwave oven, there is a problem that the surfactant foams on the surface of the wrap film.
If the adhesion is increased, the pulling power is increased. Conversely, if the pulling power is decreased, the adhesion is lowered. In addition, there are many conflicting properties, such as the extensibility deteriorates when trying to increase the elastic modulus, which is an index of stiffness, and it is a very difficult problem to maintain a good balance between these properties. is there.
For example, Japanese Patent Application Laid-Open No. 2002-46238 proposes a multilayer film having a resin layer containing a core layer made of a resin having a barrier property and an additive having an adhesive property as a surface layer. However, the additive for expressing the adhesiveness has a low molecular weight or a low glass transition point, and moves in the film so as to be called bleed-in. For this reason, even if the balance between good adhesion and drawability is maintained immediately after film formation, the adhesiveness and drawability are reduced by the addition of additives present in the surface layer over time. There is.
Moreover, many proposals, such as Unexamined-Japanese-Patent No. 2001-121660, are proposed of the wrap using a poly (4-methylpentene-1) type-resin from the point which is excellent in heat resistance. However, poly (4-methylpentene-1) resin is originally a highly rigid material, and in order to express the flexibility required for wrapping, a large amount of plasticizer must be added. Penten-1) The heat resistance and low tensile elongation at break of the resin are impaired.
It is an object of the present invention to provide a wrap film having excellent adhesion, small pulling force from a storage box, and little change in these properties over time and storage temperature while using a polypropylene resin. .

As a result of intensive studies to solve the above problems, the present inventors have reached the present invention. That is, the present invention is mainly as follows.
Crystalline polypropylene resin (S1) 50 to 80% by mass, at least one softener (S2) 20 to 50% by mass selected from amorphous or low crystalline propylene-α-olefin copolymer and butene-1 polymer % Hydrogenated terpene resin (S3) and liquid aliphatic hydrocarbon (S4) at room temperature, 5 to 15 parts by mass, A surface layer (A) containing 20 parts by mass;
A core layer (B) containing 80 to 98% by mass of a crystalline polypropylene resin (C1) and 2 to 20% by mass of an aliphatic hydrocarbon (C2) that is liquid at room temperature;
A polypropylene-based multilayer wrap film having:
The adhesion work when the wrap film wound in a paper tube is left to stand for 3 weeks at 40 ° C. and 20% relative humidity is a change within −20 to + 50% with respect to the value before leaving, and The polypropylene-based multilayer wrap film as described above, wherein the pulling power is a change within −50 to + 20% with respect to the value before being left;
When the film surface is observed with a phase image of an atomic force microscope at a magnification of 40,000 times, it has a structure composed of mesh-like fibrils and a matrix existing therebetween, and the average width of the fibrils is 1 nm or more. The polypropylene-based multilayer wrap film having a structure of 100 nm or less and an average pore size of 3 nm to 1 μm.
By setting it as said structural requirement, this invention has the following effects. That is, by using a resin composition that combines a specific amount of a specific softening agent, hydrogenated terpene resin, and a specific amount of aliphatic hydrocarbons that are liquid at room temperature, the resin is appropriately plasticized, achieving both adhesion and drawability. it can.
Moreover, it becomes possible to suppress the fall by time of adhesiveness and drawability by adding a liquid aliphatic hydrocarbon at normal temperature to the core layer (B) adjacent to the surface layer (A).

  FIG. 1 is a photograph of the wrap film of the present invention observed at a magnification of 40,000 in a phase image of an atomic force microscope.

The present invention will be specifically described below.
The polypropylene resin used in the present invention has a propylene unit in a polymer molecular chain, and may be a homopolymer consisting only of a propylene unit, or a binary or ternary copolymer with ethylene or butene-1. There may be. Among the copolymers, random copolymerization is preferable from the viewpoint of transparency. As the stereoregularity, either an isotactic structure, a syndiotactic structure, or a mixture thereof may be used. Although there is no other restriction | limiting in particular, Considering using for the film for food packaging, for example, what passed the standard standard regarding food packaging from a viewpoint of safety is preferable. In addition, the melt flow rate is more preferably in the range of 1 to 20 g / 10 min with a load of 230 ° C. and 2.16 kg applied in accordance with ASTM D1238.
The component used as a softening agent contained in the surface layer (A) is selected from an amorphous or low crystalline propylene-α-olefin copolymer and a butene-1 polymer. From the viewpoint of safety, those that pass the standards for food packaging are preferred.
Here, the amorphous or low crystalline propylene-α-olefin copolymer is a copolymer of propylene and an α-olefin having 4 or more carbon atoms such as butene-1 or pentene-1. The propylene ratio is preferably 65% by mass to 85% by mass. In addition, the melt flow rate is preferably in the range of 1 to 10 g / 10 min with a load of 230 ° C. and 2.16 kg applied in accordance with ASTM D1238. The density in ASTM D1505 is preferably 0.85 to 0.89 g / cm ³ . It itself is rich in flexibility, and when mixed with a crystalline polypropylene resin, it has the performance of being mixed without impairing transparency and providing a softening effect. In addition, examples of the polypropylene-α olefin copolymer having amorphous or low crystallinity include, for example, Mitsui Chemicals' Toughmer XR.
The butene-1 polymer is a homopolymer obtained by catalytic polymerization of liquid butene-1 monomer. The melt flow rate is preferably in the range of 0.1 to 5 g / 10 min with a load of 190 ° C. and 2.16 kg applied in accordance with ASTM D1238. Further, the density in ASTM D1505 is preferably 0.904 to 0.920 g / cm ³ .
The softening agent has good compatibility with the crystalline polypropylene resin, and by blending an appropriate amount, the elastic modulus, moisture resistance and heat resistance of the crystalline polypropylene resin are not greatly impaired, There is an effect of reducing the flexural modulus, that is, an effect of imparting flexibility.
When the blending amount of these softeners is 100% by mass of the crystalline polypropylene resin and the softener, the softener is from the viewpoint of the flexibility of the film obtained, the feel of the hand, and the shape followability to the package. The amount is 20% by mass or more, and is 50% by mass or less from the viewpoint of stable film formability, workability, appearance and quality of the product, feeling of stiffness, and ease of use of the packaging film. More preferably, it is 20-40 mass%, More preferably, it is 20-30 mass%.
The hydrogenated terpene resin further contained in the surface layer (A) is used as an adhesive.
The hydrogenated terpene resin is a homopolymer made from α-pinene, β-pinene, limonene, dipentene or the like obtained from pine bark or citrus fruit skin, or a hydrogenated product of these copolymers. is there. The softening point of the hydrogenated terpene resin is preferably 120 ° C. or higher from the viewpoint of stickiness of the film, etc., and 135 ° C. or lower is preferable from the viewpoint of the flexibility and adhesion of the surface layer (A) portion in which the hydrogenated terpene resin is blended. When hydrogenated terpene resin is 100 parts by mass of the composition comprising the above crystalline polypropylene resin and softening agent, 5 parts by mass or more from the viewpoint of adhesion performance, the blocking between films is reduced, and the pulling force is reduced. Therefore, the amount is 15 parts by mass or less. Preferably it is 5-10 mass parts, More preferably, it is 5-8 mass parts.
Aliphatic hydrocarbons which are liquid at normal temperature contained in the surface layer (A) are used as adhesion assistants. The adhesion aid is at least one of saturated hydrocarbons refined from crude oil such as liquid paraffin, mineral oil, white mineral oil, polyisobutylene obtained by homopolymerizing isobutene or polybutene obtained by copolymerizing isobutene and normal butene. Add type. Most preferred is mineral oil. Further, the addition amount is 10 parts by mass or more and 20 parts by mass from the viewpoint of the feel of touch and stable adhesion when the composition comprising the crystalline polypropylene resin and the softening agent is 100 parts by mass. Or less. Moreover, Preferably it is 15 mass parts or more.
The combined use of the hydrogenated terpene resin as the adhesion agent and the aliphatic hydrocarbon that is liquid at normal temperature as the adhesion aid makes the wrap film of the present invention high in adhesion and excellent in drawability. On the other hand, as in the prior art, a composition having an excessive amount of hydrogenated terpene resin provides adhesion by strongly pressing the films together, but is inferior in adhesion and drawability when pressed with a low load. On the other hand, a composition having an excess of liquid aliphatic hydrocarbons at room temperature does not provide the required high adhesion because the film surface is excessively plasticized.
In the above composition range, when the addition amount of the hydrogenated terpene resin of the surface layer (A) is c parts by mass, and the addition amount of the aliphatic hydrocarbon that is liquid at room temperature of the surface layer (A) is d parts by mass,
d ≧ 0.75 × c + 3.8
If the addition amount satisfies the above formula, it is possible to achieve both better adhesion and drawability. That is, by mixing the hydrogenated terpene resin (S3) and the aliphatic hydrocarbon (S4) that is liquid at room temperature in a specific ratio, the surface is appropriately plasticized, and further exhibits good adhesion and drawability. be able to.
In addition, it is also possible to mix well-known additives, such as antioxidant, in the surface layer (A) which consists of a polypropylene resin composition in the range which does not deviate from the objective of this invention. However, it is preferable not to contain an aliphatic ester of an aliphatic polyhydric alcohol such as glycerin fatty acid ester. These are generally added for the purpose of anti-fogging, plasticization, processability improvement and antistatic, but when the food containing a lot of moisture is packaged and heated in a microwave oven as described above, Bubbles may be generated and may cause discomfort to the user.
In the film of the present invention, the core layer (B) is arranged so as to be adjacent to the surface layer (A). As a result, the aliphatic hydrocarbon which is liquid at room temperature in the surface layer (A) is prevented from causing a concentration gradient due to migration to the core layer (B) due to the bleeding phenomenon, and only an appropriate amount of aliphatic hydrocarbon is obtained. It can be held in the surface layer. The crystalline polypropylene resin forming the core layer (B) may be the same as that used in the core layer (A). Similar to the core layer (A), those that conform to standards or standards for food packaging are preferred.
The aliphatic hydrocarbon (C2) that is liquid at room temperature and used in the core layer (B) of the present invention is a saturated hydrocarbon such as liquid paraffin, mineral oil, white mineral oil and the like. Although these physical properties are not particularly limited, usually, the kinematic viscosity at 40 ° C. is preferably 10 to 80 cSt, more preferably 10 to 40 cSt.
When the crystalline polypropylene resin (C1) and the aliphatic hydrocarbon (C2) that is liquid at room temperature are combined to be 100% by mass, the amount of the aliphatic hydrocarbon (C2) is added to suppress the bleed-in phenomenon. In order to maintain the adhesion and the drawability due to the progress of the above, it is blended in the range of 2% by mass or more, 20% by mass or less from the viewpoint of stiffness and stable film formability. Preferably, it is 2-15 mass%, More preferably, it is 2-12 mass%.
The aliphatic hydrocarbon which is liquid at normal temperature in the surface layer (A) shifts from the surface layer (A) to the core layer (B) due to the decrease in bleed-in, and thus the aliphatic group for the hydrogenated terpene resin in the surface layer (A). The hydrocarbon ratio decreases. Accordingly, the adhesiveness and the drawability obtained in the initial stage change. As a countermeasure, it can be easily considered to increase the layer composition ratio of the surface layer (A) to prevent the bleed-in phenomenon, but the surface layer (A) composition is a flexible composition in order to exhibit high adhesion. For this reason, the elastic modulus of the entire film is lowered, and the stiffness is remarkably lowered. Therefore, in the present invention, by adding a specific amount of low-viscosity aliphatic hydrocarbons to the core layer (B) adjacent to the surface layer (A), the bleed-in phenomenon is suppressed and the elastic modulus of the entire film is greatly reduced. In addition, adhesion and drawability can be maintained.
Furthermore, in order to control the bleed-in of the aliphatic hydrocarbon of the surface layer (A) satisfactorily, the amount of the aliphatic hydrocarbon that is liquid at room temperature of the surface layer (A) is set to d parts by mass and the room temperature of the core layer (B). The addition amount of the liquid aliphatic hydrocarbon was set to e mass%, and the volume ratio of the surface layer (A) to the core layer (B) (or the total when provided on both surfaces of the core layer (B)) was set to f. Sometimes,
0.13 × d / (3√f) ≦ e ≦ 0.66 × d
By making the addition amount satisfying the above formula, it is possible to satisfy the firmness of the film while maintaining good adhesion and drawability.
The core layer (B) preferably does not contain a resin having a melting peak temperature of 200 ° C. or higher. By adding a resin having a high melting peak temperature such as poly (4-methylpentene-1) resin, a high heat resistance of 170 ° C. or higher is exhibited, but at the same time, the elastic modulus of the film is increased and the target adhesion is increased. Cannot be obtained, and the usability represented by the feeling of stiffness is inferior.
In addition, in the composition of these core layers (B), it is possible to mix known additives such as antioxidants within the range not departing from the object of the present invention in order to ensure molding processability. is there.
The overall layer composition ratio is preferably in the range of 0.2 to 2.7, where f is the volume ratio of the surface layer (A) to the core layer (B). If the volume ratio of the surface layer (A) is smaller than 0.2, adhesion may not be exhibited over the entire film surface. When the volume ratio of the surface layer (A) is larger than 2.7, the whole film becomes soft, the feeling of stiffness is lowered, and the usability is deteriorated.
Further, the ratio of the front and back surfaces of the surface layer (A) is not particularly limited, but considering the ratio that does not require the distinction between the front and back surfaces of the film, it is preferably approximately equal.
In addition to the surface layer (A) and the core layer (B), a rework layer composed of, for example, trim edges at the time of manufacture is arranged in addition to the surface layer (A) and the core layer (B). May be. From the balance between adhesion and drawability, the other layers are preferably 5% by mass or less of the total layer and 5% or less of the volume ratio of the total layer. However, it is necessary to laminate other layers so as not to lose the state in which the surface layer (A) and the core layer (B) are adjacent to each other.
For the wrap film of the present invention, the work of adhesion is used as an index for adhesion. The adhesion work is an index for evaluating adhesion between films and containers when a container or food is covered with a wrap film. As described above, this adhesion is an important characteristic in the wrap film together with the drawability. The adhesion work is determined by the work when the films that are brought into close contact with each other are peeled off. The detailed measurement method is based on the method described later. This adhesion work is preferably 1.0 to 3.0 mJ, more preferably 1.5 to 2.5 mJ from the viewpoint of moderate adhesion.
The pulling power of the wrap film referred to in the present invention is an important characteristic together with the adhesiveness, and evaluates ease of pulling out the film from the wound film stored in the storage box. The measurement method is performed by the method described later. The pulling power is preferably 200 to 1000 mN, more preferably 200 to 800 mN, and still more preferably 200 to 600 mN, from the viewpoint of good drawability.
In addition, the wrap film may be stored under high temperature and high humidity, for example, in an ordinary household kitchen or a commercial kitchen, and it is desirable that the work of adhesion and the pulling force do not change significantly during that time. As an index of this change, the work amount of contact and the change rate of the pulling force before and after the wrap film wound in a paper tube is left at 40 ° C. and 20% relative humidity for 3 weeks are used. The change rate of the work of adhesion is preferably in the range of -20 to + 50%, and the change rate of the pulling force is preferably in the range of -50 to + 20%. If it is within this range, it is considered that the balance of adhesion or drawability is not lost during the period until the product is distributed and consumed.
Next, when the observation of the film surface in the present invention is performed by imaging phase information with respect to stimulation of an atomic force microscope (hereinafter AFM) cantilever, it is preferable to have a specific structure. When observing the phase information for cantilever stimulation at 40,000 times in the image, a portion with a small delay, that is, a hard portion is displayed bright in the phase image, and a portion with a large phase delay, that is, a soft portion is displayed dark in the phase image. The When the preferable film surface among the wrap films of the present invention is observed by this method, it consists of a fibril-like network structure and a matrix existing therebetween. The image example observed in this way is the image of FIG. The network structure refers to a portion that appears continuously bright on the image, and the matrix refers to a portion that is formed by discontinuously dark portions surrounded by the network structure. The continuously observed fibrous bright portion is a fibril network structure, and the discontinuous black portion is a matrix. In this observation, 50 images of 2 microns x 2 microns were randomly observed from a range of 10 mm x 10 mm, and among these images, the fibril width was the most uniform, and the distance between each fibril was also the most uniform. The part which is is extracted. 100 points of the fibril width and the distance between the fibrils are selected for the extracted image, and an average value is obtained for the remaining 80 points excluding the upper and lower 20 points, and set as the fibril width and matrix size described later.
The average width of the fibril is preferably 1 nm or more and 100 nm or less. When the average fibril width is within this range, the smoothness of the film surface is maintained, and the adhesion is further improved. More preferably, it is 10 nm or more and 50 nm or less.
As for the size of the matrix (that is, the average value of the interval between fibrils), the average width is preferably 3 nm or more and 1 μm or less. When the average size of the matrix is within this range, the adhesion component constituting the matrix is held in the network structure of the film surface, and is not exposed to the surface more than necessary, and the balance between adhesion and drawability is maintained. More preferably, it is the range of 10 nm or more and 50 nm or less.
In the network structure of the present invention, the crystalline portion of the polypropylene resin mainly forms fibrils. The amorphous part of polypropylene, softener, hydrogenated terpene resin, and aliphatic hydrocarbon that is liquid at room temperature mainly form a matrix. By adopting a network structure of fibrils of a specific size as described above, flexible components that greatly affect the adhesion of the matrix part are held in the fibrils, and only the minimum amount necessary for the expression of adhesion is present on the surface, which is good It becomes possible to express a good adhesion and drawability.
When the softened component is partially present on the surface of the film that does not form a network structure, or the softened component is larger than the size of the pores of the network structure specified in the present invention as a sea-island structure. When it exists, the adhesion component does not exist uniformly on the surface, and the balance between adhesion and drawability decreases.
The film of the present invention preferably has specific flexibility, and specifically, the tensile elastic modulus is preferably 200 to 1000 MPa. The tensile elastic modulus is determined in accordance with the method described in ASTM-D-882 using a tensile tester (manufactured by Shinsei Tsushin Kogyo Co., Ltd., universal tensile / compression tester) in the machine direction (MD-take-up direction) and transverse direction (TD It is obtained by measuring the average value of the tensile modulus at 2% strain in the direction perpendicular to the take-off direction. This value is preferably 200 MPa or more from the viewpoint of film flexibility, stiffness, and usability, and is preferably 1000 MPa or less from the viewpoint of flexibility, adhesion, and usability. More preferably, it is 400 MPa or more and less than 700 MPa.
The thickness of the film of the present invention is preferably 3 μm or more from the viewpoint of strength as a packaging film, stiffness, and ease of use in packaging. Adhesion to articles during packaging, ease of use of film, and household food wrap In view of the mass of the product, the winding diameter, ease of handling at the time of use, etc., 25 μm or less is preferable. In particular, 6 μm to 15 μm is more preferable as a food packaging wrap for home use that requires usability of adhesion and drawability.
As a method for producing the film, a known film forming method can be used. The polypropylene resin composition for the surface layer (A) is prepared by melt kneading using an extruder or the like. Since the softening agent and hydrogenated terpene resin are solid at room temperature, a predetermined amount is put into a blender or the like together with commercially available polypropylene resin pellets and mixed sufficiently uniformly. This is put into a surface layer extruder. Since the aliphatic hydrocarbons in the surface layer (A) and the core layer (B) are liquid at room temperature, a liquid injection facility is installed in the middle of the extruder for the surface layer and the core layer, and added to the resin melt-plasticized in the middle of the screw. To do. A uniform composition is obtained by kneading under an appropriate extrusion condition, and extrusion is performed with a multilayer die or the like so as to form a multilayer film together with a surface layer, a core layer, and a rework layer as necessary. In addition, the composition of the surface layer (A) and the core layer (B) is sufficiently melt-kneaded using a known apparatus such as a twin screw extruder capable of adding liquid in the middle, and then pellets are formed, and then the surface layer and the core are formed. Each can also be fed into a layer extruder.
In order to make a multilayer film, for example, in the case of a three-layer structure, the above-described surface layer extruder and the core layer extruder are arranged in parallel, and a predetermined resin is introduced into each of these to sufficiently melt. And kneading, and the resin from these extruders is merged into three layers on the downstream side, and formed into a sheet using, for example, an annular die or a T-die having a slit-like discharge port, and extruded. To do. The extruded resin is cooled and solidified by a known method such as passing through a cold water tank or contacting with cold air or a cooling roll. The cooling temperature of the extruded sheet surface at this time is preferably 10 ° C. or more from the viewpoint of surface smoothness and appearance, and from the viewpoint of bleeding to the surface of the adhesive agent blended in the surface layer (A) and adhesion. C. or lower is preferable.
Preferably, film strength, food packaging wrap, in the longitudinal and / or transverse direction by a commonly known method such as uniaxial stretching or biaxial stretching by a roll method, a tenter method, or multiaxial stretching by a tubular method. When used as a film, the film is stretched twice or more from the viewpoint of the cut property of the film. In the case of the sequential biaxial stretching method, the stretching order in the longitudinal and lateral directions is not particularly specified. Further, the magnifications in the vertical and horizontal directions need not be the same. More preferably, it is desirable to stretch each of the longitudinal and transverse directions twice or more by multiaxial stretching by a tubular method. The film that has been stretched is made into a product through processes according to the form of the target product, such as trimming of the film end, cutting to a desired size, or winding around a paper tube.
Moreover, when carrying out multiaxial stretching with a tubular, you may heat-process the stretched film by a well-known method in order to adjust the heat shrinkage rate of a film. Constraining the MD direction with a roll, contact heating from the roll or indirect heating with infrared rays, etc., constraining the transverse direction with a tenter and heating with hot air or radiant heat, or hot air or radiant heat with bubbles formed again The heating method can be used.
The film has not only the balance between adhesion and drawability required for the performance of wrap film, but also transparency, heat resistance, moderate flexibility, good touch feeling, cutability, and safety, It can be suitably used as a food packaging wrap film.

Next, embodiments of the present invention will be illustrated. Each of them is a form of the present invention and is not limited to these examples. In addition, the performance evaluation method of the film obtained by this invention and a comparative example is as follows.
(Close contact work)
The adhesion between films when a wrap film was put on a container such as tableware or food was evaluated and measured as follows.
A filter paper having the same bottom area was attached in advance to the bottom surfaces of two cylinders having a bottom area of 25 cm ² and a mass of 400 g. The wrap film was tensioned and fixed so that no wrinkles would enter the bottom surfaces of the two cylinders to which the filter paper was attached. Then, the two cylinders were put together so that the film surfaces were exactly overlapped with each other, and pressed under a condition of 23 ° C. and a relative humidity of 50% under a load of 500 g for 1 minute. Next, the overlapped films are separated from each other in a direction perpendicular to the surface at a speed of 5 mm / min with a tensile tester (manufactured by Shinsei Tsushin Kogyo Co., Ltd., a universal tensile / compression tester), and the energy (mJ) generated at this time is adhered. The amount of work.
(Change in close contact work)
This is an evaluation of how stable the work of cohesion is over time. The above-mentioned measurement of the work of adhesion after film formation at 23 ° C. and 50% relative humidity for 24 hours or more, and the storage work after storing this wrap film in an atmosphere of 40 ° C. and 20% relative humidity for 21 days Measured by the method.
Evaluation of the adhesion work before storage was shown by the following criteria.
◎: 1.5 mJ or more and less than 2.5 mJ ○: 0.5 mJ or more and less than 1.5 mJ and 2.5 mJ or more and less than 3.5 mJ Δ: 3.5 mJ or more and less than 4.0 mJ ×: Less than 0.5 mJ and 4.0 mJ or more Moreover, the change with respect to the contact work before storage of the sample which was stored for 21 days in an atmosphere of a temperature of 40 ° C. and a relative humidity of 20% was evaluated according to the following criteria.
A: −20% ≦ (change) <+ 50%
○: −50% ≦ (change) <− 20%, or + 50% ≦ (change) <+ 75%
Δ: (Change) <− 50% or + 75% ≦ (Change)
×: Cannot be pulled out and cannot be measured (drawing output)
The pulling power is an evaluation of the pulling property when the film is pulled out from the wound film, and was measured as follows.
A film slit to a width of 300 mm was wound around a paper tube having an outer diameter of 41 mm, an inner diameter of 38 mm, and a width of 308 mm at a speed of 100 m / min.
Both ends of the paper tube of the wound film are fixed with a special gripping tool having a rotating part that rotates at a light load, and this gripping tool is fixed to a tensile testing machine (manufactured by Shinsei Tsushin Kogyo Co., Ltd., universal tensile compression testing machine). ) Fixed at the bottom. Next, the tip of the film was affixed and fixed to an upper fixture having a width of 330 mm, the force obtained while unwinding the film at a speed of 1000 mm / min was measured, and the maximum load obtained at this time was used as the drag output.
In order to see the change of the pulling power with the passage of time, the pulling power of a sample that had passed for 24 hours or more after film formation and the pulling power of a sample stored for 21 days in an atmosphere of 40 ° C. and 20% relative humidity were measured.
The pulling power before storage was evaluated according to the following criteria.
◎: 50 mN or more and less than 600 mN ○: 600 mN or more and less than 1200 mN Δ: 1200 mN or more and less than 1500 mN ×: Less than 50 mN and 1500 mN or more Before storage of the sample output stored for 21 days in an atmosphere at a temperature of 40 ° C. and a relative humidity of 20% The pulling power was evaluated according to the following criteria.
A: −50% ≦ (change) <+ 20%
○: −80% ≦ (change) <− 50%, or + 20% ≦ (change) <+ 50%
Δ: (change) <− 80% or + 50% ≦ (change)
×: Cannot be pulled out and cannot be measured (transparency)
Transparency measured the haze of the film obtained using NDH-300A (made by Nippon Denshoku) based on the method of ASTM-D-103, and evaluated it on the following reference | standard.
◎: Less than 1.0 ○: 1.0 or more and less than 2.0 Δ: 2.0 or more and less than 3.0 ×: 3.0 or more (heat resistance)
The heat resistance was measured based on Article 11 of the Tokyo Consumer Life Ordinance. A film having a heat resistant temperature of 140 ° C. or higher was rated as “◎”, 130 ° C. and 135 ° C. as “◯”, and 125 ° C. or lower as “X”.
(Flexibility)
Flexibility is based on the method described in ASTM D882, using a tensile tester (manufactured by Shinsei Tsushin Kogyo Co., Ltd., universal tensile / compression tester), tensile at 2% strain in the machine direction (MD) and transverse direction (TD) of the film. The elastic modulus was measured. Evaluation was made according to the following criteria.
A: The average value of both vertical and horizontal is 400 MPa or more and less than 700 MPa ○: 200 MPa or more and less than 400 MPa and 700 MPa or more and less than 1000 MPa Δ: 100 MPa or more and less than 200 MPa ×: Less than 100 MPa or 1000 MPa or more (hand feeling)
The hand touch was evaluated by sensually evaluating 50 good housewives with good and bad touches to a predetermined number of housewives selected at random. Evaluation was performed according to the following criteria.
◎: 45 or more people who feel good ○: 40 or more people less than 45 people who feel good △: 30 or more people less than 40 people who feel good ×: Number of people who feel good Is less than 30 (cutability)
The cut property of the film was obtained by winding the obtained film around a paper tube with a width of 300 mm and a winding length of 20 m, and then storing this in a cosmetic box for saran wrap manufactured by Asahi Kasei Co., Ltd. and cutting with an attached saw blade. From the state of cutting at that time, the following criteria were evaluated.
◎: Can be cut cleanly with light force ○: Can be cut cleanly even though some force is required △: Can be cut but difficult to cut ×: Cannot cut well, film stretches, tears diagonally, force is applied The dressing box was crushed too much.
(Film surface observation)
Observation of the film surface with a phase image of an atomic force microscope was performed by the following method. The film was affixed to glass and fixed, and the phase image was observed in the Tapping mode with NanoScope IIIa manufactured by Digital Instruments. For the measurement, a Si single crystal cantilever (spring constant = 0.07-0.58 N / m) was used. Scan rate was 0.5-1 Hz, Scan size was 2 μm, Z limit was 440 V, and sampling point was 51512. It carried out in. When the contact pressure of the cantilever was controlled by the film, when the target amplitude was 2V, the set point was 0.8-1.4V, and when the target amplitude was 4V, the set point was within the range of 2.0-3.5V. It was. Observe 50 images of 2 microns x 2 microns randomly from the 10mm x 10mm range of the sample. Of those images, the part with the most uniform fibril width and the most uniform distance between each fibril To extract. From the 80 mm × 80 mm image obtained by enlarging the extracted 2 μm × 2 μm field of view by 40,000 times, 100 points of fibril width and fibril distance are each extracted. The average value of 80 points excluding 10 points of the largest and 10 points of the smallest was adopted. The surface structure was evaluated according to the following criteria based on the average width.
A: The average width of fibrils is 1 nm or more and less than 50 nm. O: 50 nm or more and less than 100 nm. X: 100 nm or more The average distance between fibrils was evaluated according to the following criteria.
A: 10 nm or more and less than 50 nm B: 3 nm or more and less than 10 nm or 50 nm or more and less than 1000 nm X: less than 3 nm or 1000 nm or more The above evaluations were collectively performed for comprehensive evaluation. In any evaluation item, the item judged as ◎ is the best, and the case where only ◎ or ○ is evaluated is considered to be practically possible, and those having items judged as △ and × are practical. Judged that there was a problem.

As a crystalline polypropylene resin (Grand Polymer Co., Ltd., Grand Polypro F327, propylene-ethylene-butene-1 terpolymer) and a softening agent, a low crystalline propylene-α-olefin copolymer resin (Mitsui Chemicals ( Co., Ltd., Tuffmer XR110T) 75:25 was mixed at a mass ratio. To 100 parts by mass of this, 5 parts by mass of hydrogenated terpene resin (Yasuhara Chemical Co., Ltd. Clearon P125) was put into a blender and mixed well at room temperature for 5 minutes. Next, pellets were prepared by melt-kneading with a twin screw extruder (TEM-35BS manufactured by Toshiba Machine Co., Ltd.) having a screw diameter of 37 mm and L / D 42. Further, mineral oil (Matsumura Petroleum Institute Moresco White P70 / (Kinematic viscosity at 40 ° C. 9.6 cSt)) as an aliphatic hydrocarbon which is liquid at normal temperature was added from the middle of the barrel using an injection pump. The addition amount was 15 parts by mass with respect to 100 parts by mass of the mixed amount of the crystalline polypropylene resin and the softening agent. This was used as a resin for the surface layer.
In addition, the same crystalline polypropylene resin as described above was melted in a co-rotating twin screw extruder (TEM-35BS manufactured by Toshiba Machine Co., Ltd.) with a screw diameter of 37 mm and L / D 30 and further injected from the middle of the extruder. 20 parts by weight of mineral oil (Matsumura Oil Research Institute Moresco White P70) was added using a pump. The addition amount was such that the crystalline polypropylene resin and mineral oil were 90:10 in mass ratio. This composition was uniformly mixed, and the resulting pellet was prepared as a core layer resin. Table 1 shows the volume ratio relationship of each layer.
A multilayer stretched film was prepared using the above resin. First, the resin mixture obtained above was charged into each of a surface layer extruder and a core layer extruder of a multilayer extruder capable of extruding a symmetrical two-kind three-layer symmetrical resin layer configuration. After being sufficiently melted in each extruder, the original film was extruded at 220 ° C. with a multilayer annular die, and then cooled with water.
The obtained film original was stretched 5 times longitudinally and 4 times laterally at a stretching temperature of 120 ° C. by an inflation bubble stretching apparatus. Then, the edge part of the cylindrical film was trimmed and wound up one by one. Thereafter, heat setting was performed with a tenter having a fixed clip width in the lateral direction at a hot air temperature of 130 ° C. and a residence time of 20 seconds. As a result, a film having a substantially uniform thickness of 10 μm was obtained with each layer thickness ratio of 0.25, 0.50, 0.25 in the order of the surface layer, the core layer, and the surface layer. When the physical properties of this film were measured, it showed good performance as shown in Table 2. Moreover, when the film obtained here was observed 40,000 times in the phase image of the atomic force microscope, the structure which consists of the network-like fibril and the matrix which exists among them was able to be seen.

  A crystalline polypropylene resin and a low crystalline propylene-α olefin copolymer resin in a mass ratio of 65:35 are used as the surface layer resin, and the amount of mineral oil added to the core layer is 7% by mass. Further, a film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the thickness ratio of each layer was 0.20, 0.60, and 0.20 in the order of the surface layer, the core layer, and the surface layer. When the physical properties of this film were measured, good performance was shown as shown in Table 2.

  The resin composition of the surface layer is a ratio of 55:45 in terms of mass ratio of the crystalline polypropylene resin and the low crystalline propylene-α olefin copolymer resin, and the thickness ratio of each layer is 0 in the order of the surface layer, the core layer, and the surface layer. A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the thickness was 0.15, 0.70, and 0.15. When the physical properties of this film were measured, good performance was shown as shown in Table 2.

  The amount of hydrogenated terpene resin added is 15 parts by weight with respect to 100 parts by weight of the resin composition of the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin in the surface layer of Example 1, and mineral oil Except that a resin for which 10 parts by mass of the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin was added in an amount of 10 parts by mass was used as a surface layer resin. Thus, a film having a thickness of 10 μm was obtained. When the physical properties of this film were measured, good performance was shown as shown in Table 2.

  The crystalline polypropylene resin and the low crystalline propylene-α olefin copolymer resin are in a mass ratio of 55:45, and the hydrogenated terpene resin and mineral oil are mixed with the crystalline polypropylene resin and the low crystalline. 10 parts by weight and 20 parts by weight, respectively, with respect to 100 parts by weight of the total propylene-α-olefin copolymer resin, and the composition of the core layer polypropylene resin and the mineral oil resin is 97: 3. A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the thickness ratio of each layer was 0.15, 0.70, and 0.15 in the order of the surface layer, the core layer, and the surface layer. When the physical properties of this film were measured, good performance was shown as shown in Table 2.

  The mineral oil in the resin composition of the surface layer is 15 parts by mass of Moresco White P40 (Kinematic viscosity at 40 ° C) made by Matsumura Oil Research Institute, and the mineral oil in the resin composition of the core layer is the same as above. A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that Moresco White P40 was used. When the physical properties of this film were measured, it showed good performance as shown in Table 2.

  Instead of mineral oil in the resin composition of the surface layer, 15 parts by weight of polybutene (Nippon Yushi Co., Ltd. Nissan Polybutene 06SH (kinematic viscosity 95 cSt at 40 ° C.)) was added as a liquid aliphatic hydrocarbon at room temperature, A film having a thickness of 10 μm was obtained in the same manner as in Example 1. When the physical properties of this film were measured, good performance was shown as shown in Table 2.

  A film having a thickness of 10 μm was formed in the same manner as in Example 1, except that 30% by mass of butene-1 polymer (Mitsui Chemicals, Tuffmer BL4000) was used as the softening agent in the resin composition of the surface layer of Example 1. Obtained. When the physical properties of this film were measured, good performance was shown as shown in Table 2.

  A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that 70% by mass of an ethylene propylene random copolymer (manufactured by Sun Allomer Co., Ltd., PC630A) was used as the crystalline polypropylene resin for the surface layer. . When the physical properties of this film were measured, good performance was shown as shown in Table 2.

  The same method as in Example 1 except that 75% by mass of an ethylene propylene block copolymer (manufactured by Co., Ltd., manufactured by Grand Polymer Co., Ltd., Grand Polypro J705) was used as the crystalline polypropylene resin of the surface layer resin composition. A film having a thickness of 10 μm was obtained. When the physical properties of this film were measured, good performance was shown as shown in Table 2.

  In Example 1, a film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the extruded film original was stretched 2.5 times in length and 2.5 times in width. When the physical properties of this film were measured, good performance was shown as shown in Table 2.

なお、表中の略語は下記を意味する。
実：実施例、比：比較例
Ｆ３２７：（株）グランドポリマー製結晶性ポリプロピレン系樹脂
（グランドポリプロＦ３２７、ＭＦＲ＝７．０ｇ／１０ｍｉｎ）
ＰＣ６３０：サンアロマー（株）製結晶性ホモポリプロピレン樹脂
（ＰＣ６３０Ａ、ＭＦＲ＝７．５ｇ／１０ｍｉｎ）
Ｊ７０５：（株）グランドポリマー製結晶性ブロックポリプロピレン樹脂
（グランドポリプロＪ７０５、ＭＦＲ＝１０ｇ／１０ｍｉｎ）
１１０Ｔ：三井化学（株）製低結晶性プロピレン−αオレフィン共重合体樹脂
（タフマーＸＲ１１０Ｔ、ＭＦＩ＝６．０ｇ／１０ｍｉｎ（２３０℃）、密度０．８９０ｇ／ｃｃ）
ＢＬ４０００：ブテン−１共重合体
（三井化学（株）製 タフマーＢＬ４０００、ＭＦＲ＝１．８ｇ／１０ｍｉｎ、密度０．９１５ｇ／ｃｃ）
Ｐ１２５：水添テルペン樹脂
（ヤスハラケミカル（株）製 クリアロンＰ１２５）
Ｐ７０：松村石油研究所製ミネラルオイル
（スモイルＰ７０、動粘度１２．３５（４０℃ ｃＳｔ））
Ｐ４０：松村石油研究所製ミネラルオイル
（モレスコホワイトＰ−４０、動粘度４．３（４０℃ ｃＳｔ））
０６ＳＨ：日本油脂（株）製常温液体の脂肪族炭化水素
（ニッサンポリブテン０６ＳＨ、動粘度９５（４０℃ ｃＳｔ））
本発明を詳細にまた特定の実施態様を参照して説明したが、本発明の精神と範囲を逸脱することなく様々な変更や修正を加えることができることは当業者にとって明らかである。
本出願は、２００２年８月２９日出願の日本特許出願（特願２００２−２５０１９２）に基づくものであり、その内容はここに参照として取り込まれる。In Example 1, the same method as in Example 1 except that the film original fabric was stretched at a temperature of 60 ° C., the stretching ratio was 4 times in length and 3 times in width, and the heat setting after stretching was not performed. A film having a thickness of 10 μm was obtained. When the physical properties of this film were measured, good performance was shown as shown in Table 2.
[Comparative Example 1]
A resin composition in which a crystalline polypropylene resin and a low crystalline propylene-α-olefin copolymer resin are mixed at a mass ratio of 40:60 is used as a surface layer resin, and the thickness ratio of each layer is defined as the surface layer, the core layer, and the surface layer. A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the thickness was 0.15, 0.70, and 0.15 in this order. Table 3 shows the volume ratio between the layers. When the physical properties of this film were measured, as shown in Table 4, the initial adhesion and pulling force were excessive.
[Comparative Example 2]
The same method as in Example 1 except that the resin composition of the surface layer was a resin composition in which a crystalline polypropylene resin and a low crystalline propylene-α-olefin copolymer resin were in a mass ratio of 85:15. A film having a thickness of 10 μm was obtained. When the physical properties of this film were measured, the initial adhesion was insufficient as shown in Table 4.
[Comparative Example 3]
The resin composition of the surface layer was a resin composition in which the amount of hydrogenated terpene resin added was 20 parts by weight with respect to 100 parts by weight of the sum of the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin, A film having a thickness of 10 μm was obtained in the same manner as in Example 1. When the physical properties of the film were measured, the initial adhesion was low as shown in Table 4.
[Comparative Example 4]
The resin composition of the surface layer was the same as in Example 1 except that the amount of hydrogenated terpene resin added was 2 parts by weight with respect to 100 parts by weight of the sum of the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin. Thus, a film having a thickness of 10 μm was obtained. When the physical properties of this film were measured, as shown in Table 4, the initial adhesion was low.
[Comparative Example 5]
Resin composition in which 10 parts by weight of hydrogenated terpene resin and 5 parts by weight of mineral oil are added to 100 parts by weight of the sum of the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin. A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the product was used. When the physical properties of this film were measured, as shown in Table 4, the adhesion was low and the pulling power was high.
[Comparative Example 6]
The resin composition of the surface layer is 10 parts by weight of the hydrogenated terpene resin with respect to 100 parts by weight of the sum of the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin, and the amount of mineral oil added is 25 masses. A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the part was used. When the physical properties of this film were measured, as shown in Table 4, since it was excessively flexible, it showed inferior performance with inferior stiffness and inferior touch.
[Comparative Example 7]
A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that the mass ratio of the crystalline polypropylene resin and the mineral oil in the core layer was 99: 1. When the physical properties of this film were measured, as shown in Table 4, good adhesion strength / pulling force was expressed in the initial stage, but the adhesion strength / pulling force increased when left at 40 ° C. for 21 days.
[Comparative Example 8]
The same as in Example 1 except that the crystalline polypropylene resin of the core layer and the aliphatic hydrocarbon which is liquid at normal temperature and the mineral oil (Matsumura Petroleum Institute Moresco White P70) at a mass ratio of 60:40 Film formation was attempted by this method, but film formation was poor and no film was obtained.
[Comparative Example 9]
Other than the resin composition of the core layer, a crystalline polypropylene resin and a low crystalline propylene-α-olefin copolymer resin (Tafmer XR110T, manufactured by Mitsui Chemicals, Inc.) were used in a mass ratio of 75:25. Obtained a 10 μm thick film in the same manner as in Example 1. When the physical properties of this film were measured, as shown in Table 4, the flexibility and the initial adhesion strength / pulling force were the same as those in Example 1, but the adhesion strength / pulling force after standing at 40 ° C. for 21 days. Increased.
[Comparative Example 10]
A film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that a single layer film having the composition of the surface layer of Example 1 was used. When the physical properties of this film were measured, as shown in Table 4, the adhesion pulling out property was stable, but it was inferior in the feeling of firmness because it was excessively flexible.

In addition, the abbreviation in a table | surface means the following.
Fact: Example, ratio: Comparative example F327: Crystalline polypropylene resin made by Grand Polymer Co., Ltd.
(Grand Polypro F327, MFR = 7.0g / 10min)
PC630: Crystalline homopolypropylene resin manufactured by Sun Allomer Co., Ltd.
(PC630A, MFR = 7.5g / 10min)
J705: Crystalline block polypropylene resin made by Grand Polymer Co., Ltd.
(Grand Polypro J705, MFR = 10g / 10min)
110T: Low crystalline propylene-α-olefin copolymer resin manufactured by Mitsui Chemicals, Inc.
(Toughmer XR110T, MFI = 6.0 g / 10 min (230 ° C.), density 0.890 g / cc)
BL4000: Butene-1 copolymer
(Tafmer BL4000 manufactured by Mitsui Chemicals, MFR = 1.8 g / 10 min, density 0.915 g / cc)
P125: Hydrogenated terpene resin
(Clearon P125, manufactured by Yashara Chemical Co., Ltd.)
P70: Mineral oil made by Matsumura Oil Research Institute
(Smoyl P70, Kinematic viscosity 12.35 (40 ° C. cSt))
P40: Mineral oil made by Matsumura Oil Research Institute
(Molesco White P-40, Kinematic viscosity 4.3 (40 ° C cSt))
06SH: A normal temperature liquid aliphatic hydrocarbon manufactured by Nippon Oil & Fats Co., Ltd.
(Nissan polybutene 06SH, kinematic viscosity 95 (40 ° C. cSt))
Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on August 29, 2002 (Japanese Patent Application No. 2002-250192), the contents of which are incorporated herein by reference.

  According to the present invention, as described above, the balance between adhesion and drawability is excellent, and the performance is less changed with the passage of time, and the transparency, heat resistance, flexibility, touch, and cutability are improved. An excellent polypropylene multilayer film can be provided. The film can be suitably used for a food packaging wrap film.

Claims (6)

Crystalline polypropylene resin (S1) 50 to 80% by mass, at least one softener (S2) 20 to 50% by mass selected from amorphous or low crystalline propylene-α-olefin copolymer and butene-1 polymer % Hydrogenated terpene resin (S3) and liquid aliphatic hydrocarbon (S4) at room temperature, 5 to 15 parts by mass, A surface layer (A) containing 20 parts by mass;
Polypropylene system having 80 to 98% by mass of crystalline polypropylene resin (C1) and 2 to 20% by mass of aliphatic hydrocarbon (C2) that is liquid at room temperature and a core layer (B) adjacent to the surface layer. Multi-layer wrap film. 2. The polypropylene-based multilayer wrap film according to claim 1, wherein the work of adhesion at 23 ° C. and a relative humidity of 50% is 1.0 to 3.0 mJ and the pulling force is 200 to 1000 mN. The adhesion work when the wrap film wound in a paper tube is left to stand for 3 weeks at 40 ° C. and 20% relative humidity is a change within −20 to + 50% with respect to the value before leaving, and The polypropylene multilayer wrap film according to claim 1 or 2, wherein the pulling force is a change within -50 to + 20% with respect to a value before being left standing. When the film surface is observed with a phase image of an atomic force microscope at a magnification of 40,000, it has a structure composed of a network of fibrils and a matrix existing therebetween, and the average width of the fibrils is 1 nm or more and 100 nm or less. The polypropylene-based multilayer wrap film according to claim 3, which has a structure in which the average distance between fibrils is 3 nm or more and 1 µm or less. The polypropylene multilayer wrap film according to claim 1 or 2, which has been stretched twice or more in the machine direction and / or the transverse direction. The polypropylene multilayer wrap film according to claim 1 or 2, wherein the entire film has a thickness of 3 to 25 µm.

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