KR20050059107A - Polypropylene wrap film - Google Patents

Abstract

A multi-layer wrap film which little suffers from changes of properties with time, constituted of surface layers (A) made of a material comprising 100 parts by weight of a composition consisting of 50 to 80 % by mass of a crystalline polypropylene resin and 20 to 50 % by mass of at least one softener selected from among amorphous and lowly crystalline propylene/alpha- olefin copolymers and butene-1 polymers, 5 to 15 parts by mass of a hydrogenated terpene resin, and 10 to 20 parts by mass of an aliphatic hydrocarbon liquid at ordinary temperatures and a core layer (B) made of a material comprising 80 to 98 % by mass of a crystalline polypropylene resin and 2 to 20 % by mass of an aliphatic hydrocarbon liquid at ordinary temperatures.

Description

Polypropylene Wrap Film {Polypropylene Wrap Film}

The present invention relates to a film used for packaging an article, such as a food packaging film. In particular, the present invention relates to a polypropylene wrap film capable of maintaining a quality that does not change adhesion and drawability even after a certain time.

When preserving food or heating in a microwave in restaurants, food stores or homes, a thin thermoplastic film was used. Among them, the wrap film made of vinylidene chloride copolymer resin is often used as a wrap film for food packaging because it has excellent properties including moisture resistance, oxygen gas barrier properties, heat resistance, adhesion to containers, and transparency. .

In recent years, various food packaging wrap films having polyolefin resins as main components have been proposed. Examples of such films include polyethylene-based resins, polypropylene-based resins, and poly-4-methylpentene-1 resins. Since these films have little adhesiveness to the film surface, it is a fatal disadvantage that they are not sufficiently adhered to the container, for example, when used as a film for food packaging. In order to satisfy these desired performances, many films have been proposed in which a polyolefin-based film and various additives or other resins are mixed or other resins are laminated. However, these have not only the adhesiveness to a container but also the adhesiveness of films, and the drawability from a storage box worsens, and therefore, practicality is bad.

In order to solve the various problems mentioned above, various proposals regarding the adhesiveness of the wrap film have been made. Japanese Patent Laid-Open No. JP-A-10-202806 proposes a self-adhesive wrap film in which a core layer is a polypropylene resin and a surfactant is contained in the surface layer as an adhesive. However, in this technique, it is difficult to express high adhesiveness. In addition, when the food material having a high moisture content is packaged in a wrap film and heated in a microwave oven, there is a problem that the surfactant bubbles on the wrap film surface by the action of water.

In order to increase the adhesion, the output power must be increased. On the contrary, if the output power is low, the adhesion decreases. Increasing the elastic modulus, which is an index of the feeling of elasticity, deteriorates the stretchability. As such, the properties required for the wrap film tend to be opposite to each other. A good balance between these characteristics is a difficult problem.

For example, Japanese Unexamined Patent Publication No. JP-A-2002-46238 proposes a multilayer film having a surface layer of a resin layer containing a core layer containing a resin having barrier properties and an additive having adhesion. However, the additive for expressing adhesion has a low molecular weight or a low glass transition point, and exhibits a phenomenon called bleed in and moves in the film. Therefore, even after forming a film, even if the balance between adhesiveness and drawability is good, adhesiveness and drawability may fall as an additive moves inward from a surface layer with time.

In view of excellent heat resistance, wrap films using poly (4-methylpentene-1) resins are frequently proposed, for example, in JP-A-2001-121660. However, since poly (4-methylpentene-1) resin is a material having high elasticity, a large amount of plasticizer must be added to satisfy the degree of flexibility required for the wrap film. However, this damages the heat resistance or low tensile elongation at break inherent in the resin.

An object of the present invention is to provide a wrap film that contains a polypropylene resin and is excellent in adhesiveness, small in output from the storage box, and small in variation of these properties with time or storage temperature.

Summary of the Invention

MEANS TO SOLVE THE PROBLEM The present inventors came to complete this invention, as a result of earnestly researching in order to solve the said objective. That is, the present invention is mainly as follows.

(A) 50 to 80% by weight of (S1) crystalline polypropylene resin, (S2) 20 to 50% by weight of one or more softeners selected from amorphous or low crystalline propylene-α-olefin copolymers and butene-1 polymers A surface layer containing 5 to 15 parts by weight of (S3) hydrogenated terpene resin and (S4) 10 to 20 parts by weight of aliphatic hydrocarbon, which is liquid at room temperature, with respect to the first composition comprising% and 100 parts by weight of the first composition; And

(B) Polypropylene-based multilayer wrap containing 80 to 98% by weight of (C1) crystalline polypropylene resin and (C2) 2 to 20% by weight of aliphatic hydrocarbon which is liquid at room temperature, and comprising a core layer adjacent to the surface layer. film;

The cling energy when the wrap film wound around the paper tube is left for 3 weeks at 40 ° C. and 20% relative humidity changes within -20 to + 50% relative to the value before standing, and the output is left unattended. The polypropylene-based multilayer wrap film that varies within -50 to + 20% relative to the previous value; And

When the film surface is observed as a 40,000-times-phase image of an atomic force microscope, it has a structure consisting of a fibril network and a matrix existing therebetween, where the average width of the fibrils is 1 nm or more, 100 A polypropylene-based multilayer wrap film having a nm or less and an average pore size of 3 nm or more and 1 m or less.

By specifying the wrap film of this invention as mentioned above, this invention expresses the following effects. Specifically, by using a specific softener, a hydrogenated terpene resin and a resin composition containing a predetermined amount of aliphatic hydrocarbon which is liquid at room temperature in the surface layer of the wrap film, the resin is appropriately plasticized to achieve both adhesion and drawability. can do.

By adding the aliphatic hydrocarbon which is a liquid at normal temperature to the core layer (B) adjacent to the surface layer (A), the fall by time of both adhesiveness and drawability can be suppressed.

1 is a photograph of the wrap film of the present invention observed as a 40,000-fold phase image of an atomic force microscope.

Hereinafter, the present invention will be described in detail.

The polypropylene resin used in the present invention may be a homopolymer having only propylene units in the polymer molecular chain or may be a binary or ternary copolymer further having ethylene or butene-1. Among the copolymers, those obtained by random copolymerization in terms of transparency are preferable. Regarding stereoregularity, either one of the same arrangement or a regular arrangement structure, or a mixture thereof can be used. In addition, although it does not restrict | limit especially, In consideration of using for the film for food packaging, it is preferable to pass the specification standard about food packaging from a viewpoint of safety. The melt flow rate is preferably in the range of 1 to 20 g per 10 minutes with a load of 2.16 kg at 230 ° C. by a method according to ASTM D1238.

The component used as the 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. In terms of safety, it is desirable to pass the standard of food packaging.

As used herein, "amorphous or low crystalline propylene-α-olefin copolymer" means a copolymer of propylene with an α-olefin having 4 or more carbon atoms, such as butene-1 or pentene-1. It is preferable that the ratio of propylene is 65 to 85 weight%. The melt flow rate is preferably in the range of 1 to 10 g per 10 minutes with a load of 2.16 kg at 230 ° C. by a method in accordance with ASTM D1238. The density according to ASTM D1505 is preferably 0.85 to 0.89 g / cm 3. This is, in itself, rich in flexibility, and when incorporated into the crystalline polypropylene resin, it can bring about a softening effect without losing transparency. Examples of amorphous or low crystalline polypropylene-α-olefin copolymers include "TAFMER XR" (trade name; manufactured by Mitsui Chemicals, Inc.).

"Butene-1 polymer" means a homopolymer obtained by catalytic polymerization of a liquid butene-1 monomer. The melt flow rate is preferably in the range of 0.1 to 5 g per 10 minutes with a load of 2.16 kg at 190 ° C. by a method in accordance with ASTM D1238. The density according to ASTM D1505 is preferably in the range of 0.904 to 0.920 g / cm 3.

The softening agent has good compatibility with the crystalline polypropylene resin, and by adding an appropriate amount, the softening agent can reduce the tensile modulus and the flexural modulus without significantly impairing the transparency, moisture resistance, and heat resistance of the crystalline polypropylene resin. There is an effect, that is, the effect of giving flexibility.

Assuming that the total amount of the crystalline polypropylene resin and the softening agent is 100% by weight, the addition amount of the softening agent is 20% by weight or more in terms of flexibility, feel, and shape followability to the article to be packaged, and stable film formability, It is 50 weight% or less from a viewpoint of workability, an external appearance and quality of a film, a feeling of elasticity, and the ease of use of a packaging film. The amount is more preferably 20 to 40% by weight, still more preferably 20 to 30% by weight.

(A) Hydrogenated terpene resin which functions as another component to a surface layer is used as an adhesive agent.

The hydrogenated terpene-based resin is a hydrogenated product of a homopolymer using α-pinene, β-pinene, limonene or dipentene, or a copolymer thereof, obtained from pine bark or orange fruit bark as a raw material. As for the softening point of hydrogenated terpene resin, 120 degreeC or more is preferable at the adhesive surface of the film obtained, and 135 degreeC or less is preferable at the softness | flexibility and adhesiveness of the surface layer part (A) containing this. When the amount of the resin composition including the crystalline polypropylene resin and the softening agent is assumed to be 100 parts by weight, the addition amount of the hydrogenated terpene resin is 5 parts by weight or more in terms of adhesion performance, reducing blocking between films, and reducing the output power. It is 15 weight part or less from the point of making it. The amount is preferably 5 to 10 parts by weight, more preferably 5 to 8 parts by weight.

(A) Aliphatic hydrocarbons that are liquid at room temperature contained in the surface layer are used as adhesion aids. Saturated hydrocarbons obtained by refining crude oil such as liquid paraffin, mineral oil and white mineral oil, polyisobutylene obtained by homopolymerization of isobutene, and polybutene obtained by copolymerizing isobutene and n-butene are added as adhesion aids. do. Among these, the most preferable is mineral oil. Assuming that the amount of the composition including the crystalline polypropylene resin and the softening agent is 100 parts by weight, the addition amount of the adhesion assistant is 10 parts by weight or more and 20 parts by weight or less in terms of texture and stable adhesion. 15 weight part or more is more preferable.

By using together the hydrogenated terpene resin which functions as an adhesive agent, and the aliphatic hydrocarbon which is liquid at normal temperature which functions as an adhesion | attachment adjuvant, the wrap film of this invention is high in adhesiveness and excellent in drawability. In the case of a wrap film containing an excess of hydrogenated terpene resin as in the prior art, the film may have adhesiveness by strongly pressing the films together, but in the case of pressing at a low load, the adhesiveness and the drawability are poor. On the contrary, in the case of a film containing an aliphatic hydrocarbon that is liquid at room temperature, the film surface is excessively plasticized, so that the desired high adhesiveness cannot be achieved.

When the addition amount of the hydrogenated terpene resin as the component of the surface layer (A) is d parts by weight and the amount of the aliphatic hydrocarbon which is a liquid at room temperature, respectively, when (A) satisfies the following formula 1, better adhesion and drawability are obtained. Can be achieved.

d ≥ 0.75 × c + 3.8

That is, by mixing (S3) hydrogenated terpene resin and (S4) aliphatic hydrocarbons that are liquid at room temperature in a specific ratio, the resulting film can be appropriately plasticized, and can exhibit better adhesion and drawability.

A well-known additive, such as antioxidant, can be added to the surface layer (A) containing a polypropylene resin composition in the quantity which does not deviate from the objective of this invention. However, the additive preferably does not contain aliphatic esters of aliphatic polyhydric alcohols, such as glycerin fatty acid esters. The additive is used for the purpose of antifogging, plasticization, processability improvement and antistatic. As described above, when the wet food material is packaged with a film containing the aliphatic ester and heated in a microwave oven, bubbles may appear on the wrap surface to cause discomfort to the user.

The film of this invention has the (B) core layer adjacent to said (A) surface layer. This structure prevents the density gradient from being generated when the aliphatic hydrocarbon, which is liquid at room temperature (A) at the surface layer, migrates to the core layer (B) by the bleeding phenomenon, so that only an appropriate amount of aliphatic hydrocarbon can be retained in the surface layer. The crystalline polypropylene resin forming the core layer (B) may be similar to that used in the surface layer (A). It is desirable to pass the specifications for food packaging.

Aliphatic hydrocarbons that are liquid at room temperature (C2) used in the core layer (B) of the present invention are saturated hydrocarbons such as liquid paraffin, mineral oil and white mineral oil. Although these physical properties are not specifically limited, Usually, it is preferable that kinematic viscosity in 40 degreeC is 10-80 cSt, and it is more preferable that it is 10-40 cSt.

Assuming that the total amount of the (C1) crystalline polypropylene resin and (C2) the aliphatic hydrocarbon that is liquid at room temperature is 100% by weight, the addition amount of the (C2) aliphatic hydrocarbon suppresses the bleed-in phenomenon and adheres even after time passes. In order to maintain drawability, it is 20 weight% or less from a viewpoint of 2 weight% or more and a feeling of elasticity and stable film formability. The addition amount is preferably 2 to 15% by weight, more preferably 2 to 12% by weight.

(A) Aliphatic hydrocarbons that are liquid at room temperature of the surface layer migrate from the surface layer (A) to the core layer (B) due to the bleed-in phenomenon, and the ratio of the aliphatic hydrocarbon to the hydrogenated terpene resin in the surface layer (A) decreases. Therefore, the adhesiveness and drawability obtained at the initial stage change. As a countermeasure against the bleed-in phenomenon, it is easy to consider increasing the composition ratio of (A) surface layer, but in order to express high adhesiveness, (A) surface layer has a flexible composition. Therefore, such a countermeasure lowers the elasticity modulus of the whole film and remarkably reduces the elasticity. Therefore, in the present invention, by adding a specific amount of a low-viscosity aliphatic hydrocarbon to the core layer adjacent to the (A) surface layer, the bleed-in phenomenon is suppressed, and the adhesion and drawability are not reduced significantly. I can keep it.

In the following manner, the bleed-in phenomenon of the aliphatic hydrocarbon in the surface layer (A) can be smoothly controlled. (A) The amount of aliphatic hydrocarbon that is liquid at room temperature of surface layer is d weight part, (B) The amount of aliphatic hydrocarbon that is liquid at room temperature of core layer is e weight%, (B) Surface layer with respect to (B) core layer Assuming that the volume ratio of (the total when the surface layer is provided on both surfaces of the core layer (B)) is f, when the amount satisfies the following expression (2), the adhesiveness and the drawability are maintained in a good state, The elasticity of the film can be satisfied.

0.13 × d / (3√f) ≤ e ≤ 0.66 × d

It is preferable that (B) core layer does not contain resin whose highest melting | fusing point is 200 degreeC or more. By adding resin with the highest melting | fusing point like poly (4-methylpentene-1) resin, although high heat resistance of 170 degreeC or more is expressed, the elasticity modulus of the film obtained simultaneously becomes large. As a result, not only the desired adhesiveness may not be achieved, but also the ease of use including elasticity may worsen.

In order to maintain moldability or formability, well-known additives, such as antioxidant, can be added to the composition of (B) core layer within the range which does not deviate from the objective of this invention.

As layer composition ratio, when a volume ratio of (A) surface layer with respect to (B) core layer is assumed to be f, it is preferable that f is the range of 0.2-2.7. (A) When the volume ratio of a surface layer is less than 0.2, adhesiveness cannot be exhibited over the whole film. On the other hand, when it exceeds 2.7, since a film becomes soft and a elasticity falls, the usability of a film worsens.

When (A) surface layer exists on both surfaces of a core layer, the ratio of (A) surface layer is not restrict | limited in particular, Since it is not necessary to distinguish which side, it is preferable that it is almost the same ratio.

The multilayer film may have other layers besides (A) surface layer and (B) core layer, for example, a rework layer including a trim end formed during manufacture, within a range that does not impair the object of the present invention. have. Considering the balance between adhesion and drawability, the other layer is preferably 5% by weight or less of the total layer and at the same time 5% or less of the total volume ratio. However, another layer must be laminated so that (A) surface layer and (B) core layer do not lose adjacent state.

The term "adhesion energy" is used as an index on the adhesion of the wrap film of the present invention. "Adhesive energy" is an index that evaluates the adhesion of a film-to-film or film-to-container when a wrap film is placed on a container or food. This adhesiveness is an important characteristic along with the drawability in the wrap film as described above. The adhesion energy is measured by the energy required to separate the films in close contact with each other. Detailed measurement methods will be described later. This adhesion energy is preferably 1.0 to 3.0 mJ, more preferably 1.5 to 2.5 mJ in terms of appropriate adhesion.

The "printing power" of the wrap film used in the present invention is a property that is as important as adhesiveness, and evaluates the ease in taking the film out of the wound film enclosed in the storage box. In-output is measured by the method mentioned later. This pull-out power is preferably 200 to 1000 mN, more preferably 200 to 800 mN, still more preferably 200 to 600 mN in terms of good drawability.

The wrap film may be stored under high temperature and high humidity conditions, for example, in a general home kitchen or a work cooker. It is desirable that the adhesion energy and the phosphorus output do not change significantly during storage. As an indicator of such a change, the rate of change of adhesion energy or withdrawal power before and after leaving the wrap film wound on a paper tube for 3 weeks at 40 ° C. and 20% relative humidity is used. The change rate of the adhesion energy is preferably -20 to + 50%, and the change rate of the pulling output is preferably -50 to + 20%. Within this range, there will be no case where the balance between adhesion and drawability is broken during the period until the wrap film is distributed and consumed as a product.

When imaging phase information resulting from stimulation of an atomic force microscope (AFM) cantilever, the film surface of the present invention preferably has a predetermined structure. When the phase information attributable to the stimulus of the cantilever is observed at a magnification of 40,000 times, the portion with low delay, that is, the hard portion, appears as a bright phase image, and the portion with high delay, that is, the soft portion, appears as a dark phase image. When the desired film surface of the wrap film of this invention is observed by the said method, there exists a fibrous network structure and the matrix which exists between them. This observed image is shown in FIG. 1. "Network structure" refers to the parts of the image that are continuously bright, and "matrix" refers to the discontinuous and dark parts that are surrounded by this network. This continuously visible fibrous bright part is referred to as a "fibrillary network structure", and the discontinuous dark part is referred to as a "matrix". Randomly select 50 images of 2 microns by 2 microns in an area of 10 mm by 10 mm. From these images, the part where the fibrill is the most uniform in width, and the distance between each fibrill is also uniform. The fibril width and the distance between the fibrils are selected from the extracted images by 100, and the top and bottom of these are excluded from each other, and their average values are calculated, and the widths of the fibrils and the matrix are described below.

As for the average width of this fibril, 1 nm or more and 100 nm or less are preferable. If it is in this range, the smoothness of the film surface is maintained and adhesiveness can be improved more. The average width is more preferably 10 nm or more and 50 nm or less.

The size of the matrix (ie, the average distance of fibrils-to-fibrils) is preferably at least 3 nm and at most 1 μm. If it is in this range, the adhesive component which comprises a matrix is maintained in a network structure on the film surface, and can maintain the balance between adhesiveness and drawability without being exposed to a surface more than necessary. The size of the matrix is more preferably in 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, and the amorphous portion of the polypropylene resin, a softening agent, a hydrogenated terpene resin, and an aliphatic hydrocarbon which is liquid at room temperature mainly form a matrix. . As mentioned above, the fibrils take a network of a certain size, so that the softened component of the matrix portion that greatly affects the adhesion is retained by the fibrils, and only the minimum amount necessary for the development of the adhesion is present on the surface, so that Both adhesiveness and drawability can be expressed.

When the softened component is present locally on the film surface having no network structure, or when the softened portion is present as a sea-island structure in a form larger than the size of the hole of the network structure specified in the present invention, The component providing the adhesion is not uniformly present on the surface, and the balance between the adhesion and the drawability is lowered.

It is preferable that the film of the present invention has specific flexibility. More specifically, the tensile modulus is preferably 200 to 1000 MPa. Tensile modulus is the longitudinal (MD direction) and transverse (MD direction) of the film using a tensile force tester (a universal tensile compression tester manufactured by Shinko Tsushin Kogyosha) according to the method described in ASTM-D-882. It is obtained by measuring the average value of the tensile modulus of elasticity at the time of 2% distortion of the TD direction perpendicular | vertical with respect to). The tensile modulus is preferably 200 MPa or more in terms of flexibility, elasticity and ease of use of the film, and preferably 1000 MPa or less in view of flexibility, adhesion and ease of use. 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 in view of strength, elasticity, and ease of use in packaging, and adhesion to the article to be packaged, ease of use of the film, its weight and roll in the case of household wrap film 25 micrometers or less are preferable from a viewpoint of the diameter and the ease of handling at the time of use. In particular, it is preferable that the thickness is 6-15 micrometers as a household food packaging wrap film for which adhesiveness, drawability, ease of use, etc. are calculated | required.

As a manufacturing method of this film, a well-known film formation method can be used. (A) The surface layer polypropylene resin composition is manufactured by melting and kneading in an extruder. The softener and hydrogenated terpene resin, which are solid at room temperature, are filled in a blender with a predetermined amount together with commercially available polypropylene resin pellets. After mixing sufficiently uniformly, the mixture thus obtained is filled into an extruder for the surface layer. Since the aliphatic hydrocarbon of (A) surface layer and (B) core layer is a liquid at normal temperature, a liquid injection facility is installed in the middle of each screw of the extruder for surface layer and a core layer, and is added to melt plasticized resin. The composition is uniformed by kneading under appropriate extrusion conditions and extruded into a multilayer film having a surface layer, a core layer, and a rework layer, if necessary, with a multilayer die or the like. Furthermore, each composition for (A) surface layer and (B) core layer is melt-kneaded sufficiently in well-known apparatuses, such as a twin screw extruder which can add intermediate | middle, and the obtained material is pelletized, and each in the extruder for surface layers and a core layer, respectively You can call

A film having a multilayer structure, for example, a three layer structure, can be produced as follows. The surface extruder and the core layer extruder are arranged in parallel, and these are filled with predetermined resins, respectively, and then melt kneaded sufficiently. On their downstream side, the resins from these extruders are joined to have three layers and then extruded into sheet form using a T die with a circular die or a slit discharge port. The extruded resin is allowed to cool and solidify in a known manner such as passing through a cooling water tank or contacting a cold air or a cooling roll. The cooling temperature of the extruded sheet surface is preferably 10 ° C. or more in terms of smoothness and appearance of the surface, and (A) 50 ° C. or less in view of preventing bleeding on the surface or adhesion due to the adhesive agent incorporated into the surface layer.

In the longitudinal direction and in consideration of the strength as a film and the cutting property of the film used as a wrap film for food packaging by a conventionally well-known method, such as uniaxial stretching by the roll method or the tenter method, biaxial stretching by the tubular method, etc. (Or) It is preferable to extend | stretch 2 times or more in a horizontal direction. The stretching ratios in the longitudinal and transverse directions need not be the same. It is more preferable to extend | stretch at two or more draw ratios in a longitudinal direction and a lateral direction by multiaxial stretching by a tubular method. After finishing the stretching, the film is formed into the intended shape by trimming the end of the film, cutting to the desired size, or winding around the paper tube.

The film obtained by the multiaxial stretching by the tubular method can be heat-set by a known method in order to adjust its thermal contraction rate. Examples of methods usable for this purpose include a method of indirect heating by infrared heating or contact heating from a roll while constraining the motion of the film in the MD direction; Heating by hot air or radiant heat while constraining the movement of the film in the transverse direction with a tenter; And a method of heating by hot air or radiant heat while forming bubbles again.

The film according to the present invention is not only a balance between the adhesion and drawability required as the performance of the wrap film, but also excellent in transparency, heat resistance, adequate flexibility, good feel, cutting property and safety, and is therefore preferably used as a wrap film for food packaging for home use. Used.

Hereinafter, embodiments for carrying out the present invention will be described. These are each embodiments according to the present invention, and the present invention is not limited by these examples. The performance evaluation method of the film obtained by this invention and a comparative example is as follows.

(Adherence energy)

The adhesiveness of the film-to-film was evaluated when the wrap film was put on a container or food such as a tableware, and measured as follows.

Two columns with a bottom area of 25 cm 2 and a weight of 400 g were prepared. The same area of filter paper was previously bonded to each lower surface. The wrap film was firmly fixed to each lower surface to which the filter paper was adhered so as not to be wrinkled. The film surface was closely aligned inside and both columns were pressed for 1 minute at a load of 500 g under conditions of 23 ° C. and RH 50%. Subsequently, the superimposed film was separated in the direction perpendicular to the surface at a speed of 5 mm per minute in a tensile force tester (a universal tensile compression tester manufactured by Shinkotsu Shin Kogyo Co., Ltd.), and the energy (mJ) generated at this time was used as the adhesion energy. .

(Change of adhesion energy)

The stability of the adhesion energy over time was evaluated. The adhesion energy of the wrap film after 24 hours at 23 ° C. and RH 50% after formation, and the adhesion energy after storing the wrap film under an atmosphere of 40 ° C. and RH 20% for 21 days were measured by the above method.

The adhesion energy before storage was evaluated according to the following criteria.

◎: 1.5 mJ or more, less than 2.5 mJ

○: 0.5 mJ or more, less than 1.5 mJ, or 2.5 mJ or more, less than 3.5 mJ

△: 3.5 mJ or more, less than 4.0 mJ

×: less than 0.5 mJ or 4.0 mJ or more

The change of the adhesive energy of the wrap film before and after storing for 21 days in the temperature of 40 degreeC and RH20% atmosphere was evaluated based on the following reference | standard.

◎: -20% ≤ (change) <+ 50%

○: -50% ≤ (change) <-20%, or + 50% ≤ (change) <+ 75%

Δ: (change) <-50%, or + 75% ≤ (change)

×: film cannot be taken out and cannot be measured

(Output)

The drawability of the wrap film from the wound film was evaluated in the following manner.

A film slit of 300 mm in width was wound around a paper tube of 41 mm in outer diameter, 38 mm in inner diameter and 308 mm in width at a tension of 20 N and a speed of 100 m per minute to prepare a wound film of 20 m in length.

Both ends of the paper tube of the winding film are fixed by being fitted into a dedicated jig having a rotating part rotating with a small load, and the jig is fixed to a lower part of a tensile tester (a universal tensile compression tester manufactured by Shinkotsu Shin Kogyo Co., Ltd.). It was. The distal end of the film was adhered to and fixed by an upper fixing tool having a width of 330 mm, and the force obtained while unwinding the film at a speed of 1000 mm per minute was measured. The maximum load at this time was taken as the output.

In order to determine the change over time of this withdrawal, the withdrawal of the sample after 24 hours after formation and the withdrawal of the sample stored for 21 days in an atmosphere of 40 ° C. and RH 20% were measured.

The printout before storage was evaluated according to the following criteria.

◎: 50 mN or more, less than 600 mN

○: 600 mN or more, less than 1200 mN

△: 1200 mN or more, less than 1500 mN

X: less than 50 mN or 1500 mN or more

The in-output of the samples stored for 21 days in an atmosphere of temperature 40 ° C. and RH 20% was evaluated according to the following criteria in comparison with the in-output before storage.

◎: -50% ≤ (change) <+ 20%

○: -80% ≤ (change) <-50%, or + 20% ≤ (change) <+ 50%

Δ: (change) <-80%, or + 50% ≤ (change)

×: film cannot be taken out and cannot be measured

(Transparency)

According to the method described in ASTM-D-103, "NDH-300A" (manufactured by Nippon Denshoku Industries, Ltd.) was used to measure the cloudiness of the film, according to the following criteria. Transparency was evaluated.

◎: less than 1.0

○: 1.0 or more, less than 2.0

(Triangle | delta): 2.0 or more and less than 3.0

×: 3.0 or more

(Heat resistance)

In order to evaluate heat resistance, heat resistance temperature was measured based on the Article 11 of the Tokyo Metropolitan Government. The thing of (circle), 130 degreeC, or 135 degreeC of the film whose heat resistance temperature is 140 degreeC or more was made into (triangle | delta) about the thing of (circle) and 125 degrees C or less.

(flexibility)

In order to evaluate the flexibility, the tensile strength tester (a universal tensile compression tester manufactured by Shinko Tsshin Kogyo Co., Ltd.) was used in accordance with the method described in ASTM D882 to obtain tensile strength at 2% distortion in the longitudinal (MD) and transverse (TD) directions of the film. Elastic modulus was measured. This was evaluated based on the following criteria.

In the average value of the tensile modulus of the film in the transverse direction and the longitudinal direction,

◎: 400 MPa or more, less than 700 MPa

○: 200 MPa or more, less than 400 MPa, or 700 MPa or more, less than 1000 MPa

△: 100 MPa or more, less than 200 MPa

×: less than 100 MPa or 1000 MPa or more

(touch)

In order to evaluate the touch, 50 randomly selected housewives were asked to evaluate the texture of the film in a sensory receptive manner, and the following criteria were evaluated.

(Double-circle): 45 people or more evaluated that the texture was good

(Circle): 40 or more and less than 45 people evaluated that texture was good

(Triangle | delta): More than 30 people and less than 40 people evaluated that texture was good

X: Less than 30 people evaluated that texture was good

(Cleavability)

The obtained film was wound around a paper tube at a width of 300 mm and a winding length of 20 m, and placed in a storage box called "Saran Wrap" (trade name; manufactured by Asahi Kasei Corporation). The film was cut into blades attached to the box. From the cut state at that time, the cutability of the film was evaluated by the following criteria.

◎: light cutting force

○: some force is required, but can be cut clean

△: cutable but not easy

×: Unable to cut smoothly, often the film is elongated without being cut, or is torn at an angle, or the storage box is broken due to excessive force when cutting the film

(Observing the surface of the film)

The film surface was observed as a phase image of an atomic force microscope. The film was adhesively fixed to the glass, and the surface was observed with a phase image in a Tapimg mode of "Nano Scope IIIa" (trade name; manufactured by Digital Instrument). The cantilever (spring constant: 0.07-0.58 N / m) of Si single crystal was used, and it measured on the conditions with a scanning ratio of 0.5-1 Hz, a scanning size of 2 micrometers, a Z limit of 440 V, and a sampling score of 512512. According to the film, when the contact pressure of the cantilever was controlled, when the target amplitude was 2V, the set point was 0.8 to 1.4V, and when the target amplitude was 4V, the set point was in the range of 2.0 to 3.5V. 50 images of 2 μm × 2 μm were randomly selected from a sample of an area of 10 mm × 10 mm. Among these images, the width of the fibrils was the most uniform, and the portions with the most uniform distances between the respective fibrils were extracted. From the 80 mm x 80 mm image which enlarged the 2 micrometer x 2 micrometer field of view which extracted this by 40,000 times, the width | variety of fibril and the distance between fibrils were selected, respectively. The average value of 80 widths and 80 distances was used except 10 up and down. The surface structure was evaluated by the following criteria by the average width.

◎: 1 nm or more, less than 50 nm

○: 50 nm or more, less than 100 nm

×: 100 nm or more

The average distance between fibrils was evaluated by the following criteria.

◎: 10 nm or more, less than 50 nm

○: 3 nm or more, less than 10 nm, or 50 nm or more, less than 1000 nm

X: less than 3 nm or 1000 nm or more

The results were summarized to comprehensively evaluate the film. In all evaluation items, the case where the film judged as (circle) was the most excellent and only the evaluation of (circle) or (circle) was evaluated is considered as practically possible, and it was judged that there existed a problem in practical use about the item judged as (triangle | delta) or x.

<Example 1>

Crystalline polypropylene-based resin ("Grand Polypro F327", trade name; manufactured by Grand Polymer Co., Ltd., terpolymer of propylene, ethylene, butene-1), and softening agent As a low-crystalline propylene-α-olefin copolymer resin ("Tafmer XR110T" (trade name; Mitsui Chemicals, Inc.)) was mixed in a weight ratio of 75:25. To 100 parts by weight of the resulting mixture, 5 parts by weight of a hydrogenated terpene resin ("Clearon P125" (trade name; manufactured by Yasuhara Chemical Co., Ltd.)) was charged to the blender and then 5 minutes. During mixing at room temperature. The resulting mixture was kneaded in a molten state in a co-rotating twin screw extruder ("TEM-35BS" (trade name; manufactured by Toshiba Machine)) having a screw diameter of 37 mm and L / D 42 to prepare pellets. Mineral oil (“MORESCO white P70” (trade name; manufactured by Matsumura Oil Research) // (kinetic viscosity 9.6 cSt at 40 ° C.)) as aliphatic hydrocarbon that is liquid at room temperature Add via infusion pump. The addition amount was 15 weight part with respect to 100 weight part of total amounts of crystalline polypropylene resin and a softening agent. The obtained mixture was used as resin for surface layers.

In addition, the same crystalline polypropylene resin as mentioned above was melted in a coaxial rotary twin screw extruder ("TEM-35BS" (trade name; manufactured by Toshiba Machine Co., Ltd.)) having a screw diameter of 37 mm and L / D 30, and 20 parts by weight of mineral oil ("Moresco White P70" (trade name; manufactured by Matsumura Oil Research)) was added via an infusion pump. The addition amount was adjusted so that the weight ratio of crystalline polypropylene resin to mineral oil might be 90:10. The obtained composition was uniformly mixed and the pellet thus obtained was prepared as a resin for the core layer. The volume ratio of each layer is shown in Table 1 below.

The resin thus obtained was used to form a multilayer stretched film. First, a resin mixture was filled in each of three types of extrusion apparatuses for surface layers and an extrusion apparatus for core layers of a multilayer extruder in which two layers were extruded in a symmetric resin layer configuration. After sufficiently melting in each extrusion apparatus, the raw film was extruded through a multilayer circular die at 220 ° C., and then cooled with water.

The obtained raw film was extended | stretched 5 times in the longitudinal direction and 4 times in the horizontal direction by the tubular aligning machine at 120 degreeC. Then, the terminal part of the cylindrical film was trimmed and wound up one by one. The tenter which set the width | variety of the clip which restrains a film transversely to a predetermined | prescribed width was heat-set for 20 second residence time in hot air temperature 130 degreeC. As a result, a nearly uniform film having a thickness of 10 μm was obtained having a surface layer having a thickness of 0.25 μm, a core layer having a thickness of 0.5 μm, and another surface layer having a thickness of 0.25 μm. As a result of measuring the physical property of this film, as shown in Table 2, the favorable performance was shown. The film thus obtained was observed at a magnification of 40,000 times as a phase image of an atomic force microscope, and as a result, a structure formed of the reticular fibrils and the matrix existing therebetween was observed.

<Example 2>

As the surface resin, a mixture of a crystalline polypropylene resin and a low crystalline propylene-α-olefin copolymer resin in a weight ratio of 65:35 was used, and the addition amount of the mineral oil in the core layer was 7% by weight, and the surface layer and the core were A film having a thickness of 10 μm was formed in the same manner as in Example 1, except that the thickness ratio of the layer and the other surface layer was changed to 0.20: 0.60: 0.20. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

<Example 3>

As the resin composition of the surface layer, a mixture of crystalline polypropylene resin and low crystalline propylene-α-olefin copolymer resin in a weight ratio of 55:45 was used, and the thickness ratio of the surface layer, the core layer and the other surface layer was 0.15: 0.70: Except having changed to 0.15, the film of 10 micrometers in thickness was obtained in the same manner as Example 1. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

<Example 4>

A resin obtained by adding hydrogenated terpene resin and mineral oil in an amount of 15 parts by weight and 10 parts by weight with respect to 100 parts by weight of the resin composition of the surface layer formed of a crystalline polypropylene resin and a low crystalline propylene-α-olefin copolymer resin, respectively. A film having a thickness of 10 μm was obtained in the same manner as in Example 1, except that was used as the surface layer resin. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

Example 5

The crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin are mixed in a weight ratio of 55:45; Hydrogenated terpene resin and mineral oil are added in amounts of 10 parts by weight and 20 parts by weight, respectively, relative to 100 parts by weight of the total amount of the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin; The composition ratio of the core layer polypropylene resin and the mineral oil was changed to 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 the surface layer, the core layer, and the other surface layer was changed to 0.15: 0.70: 0.15. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

<Example 6>

The mineral oil in the resin composition of the surface layer was made into an amount of 15 parts by weight of "MORECO WHITE P70" (trade name; Matsumura Oil Research Co., Ltd., kinematic viscosity at 40 ° C: 4.4 cSt), and the mineral induction of the resin composition of the core layer "MORECO A film having a thickness of 10 μm was obtained in the same manner as in Example 1, except that White P70 ″ (trade name; manufactured by Matsumura Oil Research, Inc.) was obtained. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

<Example 7>

Polybutene ("Nissan Polybutene 06SH" (kinetic viscosity 95 cSt at 40 ° C), trade name; manufactured by NOF CORPORATION as aliphatic hydrocarbon that is liquid at room temperature, instead of mineral oil for surface resin composition) A film having a thickness of 10 µm was obtained in the same manner as in Example 1, except that 15 parts by weight) was added. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

<Example 8>

A film having a thickness of 10 µm was obtained in the same manner as in Example 1, except that 30 wt% of butene-1 polymer ("Tafmer BL4000", manufactured by Mitsui Chemicals) was used as the softening agent for the resin composition of the surface layer. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

Example 9

Thickness in the same manner as in Example 1, except that 70% by weight of ethylene propylene random copolymer ("PC630A", trade name; manufactured by Sun Allomer) was used as the crystalline polypropylene resin for the resin composition of the surface layer. A 10 μm film was obtained. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

<Example 10>

Thickness 10 in the same manner as in Example 1, except that 75 wt% of an ethylene propylene block copolymer ("Grand Polypro J705", trade name; manufactured by Grand Polymer Co., Ltd.) was used as the crystalline polypropylene resin for the resin composition of the surface layer. A μm film was obtained. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

<Example 11>

A film having a thickness of 10 μm was obtained in the same manner as in Example 1, except that the raw film obtained by extrusion was stretched at a draw ratio of 2.5 in the longitudinal direction and 2.5 in the transverse direction. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

<Example 12>

A film having a thickness of 10 μm was obtained in the same manner as in Example 1, except that the raw film was stretched at a draw ratio of 4 in the longitudinal direction and 3 in the transverse direction at 60 ° C., and the heat setting treatment after stretching was not performed. As a result of measuring the physical properties of the obtained film, good performance was shown as shown in Table 2 below.

Comparative Example 1

As the surface resin, a resin composition obtained by mixing a crystalline polypropylene resin and a low crystalline propylene-α-olefin copolymer resin in a weight ratio of 40:60 was used, and the thickness ratio of the surface layer, the core layer and the other surface layer was 0.15: 0.70. A film having a thickness of 10 μm was obtained in the same manner as in Example 1, except that it was changed to: 0.15. It shows in Table 3 about the volume ratio etc. between each layer. As a result of measuring the physical property of this film, initial stage adhesiveness and pull-out power became excess as shown in following Table 4.

Comparative Example 2

A film having a thickness of 10 μm was produced in the same manner as in Example 1, except that the resin composition obtained by mixing the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin in a weight ratio of 85:15 was used for the surface layer. Got it. As a result of measuring the physical properties of the obtained film, as shown in Table 4 below, the adhesion was low at the initial stage.

Comparative Example 3

Except for using the resin composition obtained by adding the hydrogenated terpene resin at 20 weight part with respect to 100 weight part of total amounts of crystalline polypropylene resin and the low crystalline propylene-alpha-olefin copolymer resin, it carried out similarly to Example 1 A film having a thickness of 10 μm was obtained in a manner. As a result of measuring the physical properties of the obtained film, the adhesion was low at the initial stage as shown in Table 4 below.

<Comparative Example 4>

Except for using the resin composition obtained by adding the hydrogenated terpene resin at 2 weight part with respect to 100 weight part of total amounts of crystalline polypropylene resin and low crystalline propylene-alpha-olefin copolymer resin, it carried out similarly to Example 1 A film having a thickness of 10 μm was obtained in a manner. As a result of measuring the physical property of the obtained film, as shown in following Table 4, the initial stage adhesive force was low at the initial stage.

Comparative Example 5

Except having used the resin composition obtained by adding 10 weight part of hydrogenated terpene resins and 5 weight part of mineral oil with respect to 100 weight part of total amounts of crystalline polypropylene resin and the low crystalline propylene-alpha-olefin copolymer resin, it used for the surface layer. In the same manner as in Example 1, a film having a thickness of 10 μm was obtained. As a result of measuring the physical property of the obtained film, as shown in following Table 4, adhesive force was low and the pullout output was high.

Comparative Example 6

Except having used the resin composition obtained by adding 10 weight part of hydrogenated terpene resins and 25 weight part of mineral oil with respect to 100 weight part of total amounts of crystalline polypropylene resin and the low crystalline propylene-alpha-olefin copolymer resin, it used for the surface layer. In the same manner as in Example 1, a film having a thickness of 10 μm was obtained. As a result of measuring the physical properties of the obtained film, as shown in Table 4 below, due to excessive flexibility, poor elasticity, poor touch and the like exhibited poor performance.

Comparative Example 7

A film having a thickness of 10 μm was obtained in the same manner as in Example 1, except that the weight ratio of the crystalline polypropylene resin and the mineral oil constituting the core layer was changed to 99: 1. As a result of measuring the physical properties of the obtained film, as shown in Table 4 below, the adhesion and the pullout were good at the initial stage, but after leaving it at 40 ° C. for 21 days, the adhesion and the pullout were increased.

<Comparative Example 8>

Except for changing the weight ratio of the mineral oil ("Moresco White P70" (trade name; manufactured by Matsumura Oil Research Co., Ltd.)) as a crystalline polypropylene resin and an aliphatic hydrocarbon that is liquid at room temperature, the same as in Example 1 Tried film formation in a manner. However, film formation was poor and a film was not formed.

Comparative Example 9

Change the resin composition (weight ratio) of the crystalline polypropylene resin and the low crystalline propylene-α-olefin copolymer resin ("Tafmer XR110T" (trade name; manufactured by Mitsui Chemicals)) of the core layer to 75:25 A film having a thickness of 10 µm was obtained in the same manner as in Example 1 except for the one. As a result of measuring the physical properties of the obtained film, as shown in Table 4 below, the flexibility, the adhesion at the initial stage and the pullout power were about the same as in Example 1, but after leaving at 40 ° C. for 21 days, the adhesion and the pullout power were decreased. Increased.

Comparative Example 10

A film having a thickness of 10 μm was obtained in the same manner as in Example 1, except that the film was changed to a single layer film having the composition of the surface layer of Example 1. As a result of measuring the physical property of the obtained film, as shown in following Table 4, although adhesiveness and drawability were stable, the elasticity fell because of excessive flexibility.

In addition, the meaning of an abbreviation in a table | surface is as follows.

F327: Crystalline polypropylene resin ("Grand Polypro F327", trade name; Grand Polymer, MFR = 7.0 g / 10 minutes)

PC630: single polypropylene resin ("PC630A", trade name; manufactured by Sun Alomer, MFR = 7.5 g / 10 min)

J705: Crystalline block polypropylene resin ("Grand Polypro J705", trade name; Grand Polymer, MFR = 10 g / 10 min)

110T: Low crystalline propylene-α-olefin copolymer resin ("Tafmer XR110T", trade name; manufactured by Mitsui Chemicals, MFI = 6.0 g / 10 min (230 ° C), density: 0.890 g / cc)

BL4000: Butene-1 copolymer ("Tafmer BL4000", trade name; manufactured by Mitsui Chemicals, MFR = 1.8 g / 10 min, density: 0.915 g / cc)

P125: hydrogenated terpene resin ("Clearon P125", brand name; manufactured by Yashara Chemical Co., Ltd.)

P70: mineral oil ("Smoil P70", trade name; manufactured by Matsumura Oil Research, Kinematic Viscosity: 12.35 (40 ° C, cSt))

P40: Mineral oil ("Moresco White P-40", brand name; manufactured by Matsumura Oil Research, Kinematic Viscosity: 4.3 (40 ° C, cSt))

06SH: Aliphatic hydrocarbon that is liquid at room temperature ("Nissan Polybutene 06SH", trade name; manufactured by ENF, Kinematic Viscosity: 95 (40 ° C, cSt))

Although this invention was demonstrated in detail with reference to the specific embodiment thereof, it is clear for those skilled in the art that various changes or correction can be added without deviating from the mind and range of this invention.

This application is based on the JP Patent application 2002-250192 of an application on August 29, 2002, The content is taken in here as a reference.

According to the present invention, it is possible to provide a polypropylene-based multilayer film having excellent balance between adhesion and drawability, little change in performance over time, and excellent transparency, heat resistance, flexibility, touch and cutability. This film can be preferably used as a wrap film for food packaging.

Claims (6)

(A) 50 to 80% by weight of (S1) crystalline polypropylene resin, (S2) 20 to 50% by weight of one or more softeners selected from amorphous or low crystalline propylene-α-olefin copolymers and butene-1 polymers A surface layer containing 5 to 15 parts by weight of (S3) hydrogenated terpene resin and (S4) 10 to 20 parts by weight of aliphatic hydrocarbon, which is liquid at room temperature, with respect to the first composition comprising% and 100 parts by weight of the first composition; And (B) A core layer containing 80 to 98% by weight of (C1) crystalline polypropylene resin and (C2) 2 to 20% by weight of aliphatic hydrocarbon which is liquid at room temperature, and adjacent to the surface layer. Polypropylene-based multilayer wrap film comprising a. The polypropylene-based multilayer wrap film of claim 1, wherein the cling energy at 23 ° C. and 50% relative humidity is 1.0 to 3.0 mJ and the phosphorus output is 200 to 1000 mN. The adhesive energy when the wrap film wound around the paper tube is left for 3 weeks at 40 ° C. and 20% relative humidity is within -20 to + 50% of the value before standing. The polypropylene-based multilayer wrap film that changes and the output changes within -50 to + 20% of the value before standing. The film surface of claim 3, wherein the film surface is viewed as a 40,000-fold phase image of an atomic force microscope, has a structure composed of a fibril network and a matrix present therebetween, wherein the average width of the fibrils Silver is 1 nm or more and 100 nm or less, The average distance between fibrils is 3 nm or more and 1 micrometer or less, The polypropylene type multilayer wrap film. The polypropylene-based multilayer wrap film of claim 1 or 2, which is stretched at a draw ratio of two or more in the longitudinal direction and / or the transverse direction. The polypropylene-based multilayer wrap film of Claim 1 or 2 whose thickness of the whole film is 3-25 micrometers.