WO2015186532A1

WO2015186532A1 - Porous film and storage bag

Info

Publication number: WO2015186532A1
Application number: PCT/JP2015/064663
Authority: WO
Inventors: 幸一長谷川
Original assignee: 三菱樹脂株式会社
Priority date: 2014-06-03
Filing date: 2015-05-21
Publication date: 2015-12-10
Also published as: CN106414571A; TW201546142A; JPWO2015186532A1; JP6597608B2; CN106414571B; TWI687475B

Abstract

The present invention is a porous film comprising a resin composition in which 50-200 parts by mass of an inorganic filler have been blended with respect to 100 parts by mass of a polyethylene resin composition in which at least 50 parts by mass of a linear low density polyethylene (LLDPE) have been blended with a total of less than 50 parts by mass of a high pressure-polymerized low density polyethylene (HP-LDPE) and a metallocene linear low density polyethylene (m-LLDPE). The porous film is characterized in that the heat-sealing temperature of the mechanical flow direction (MD) is at least 90°C and the maximum heat-seal strength is at least 4.0 N/50 mm.

Description

Porous film and storage bag

The present invention relates to a porous film and a storage bag comprising the porous film, and more specifically, a high-strength and thin-film porous film excellent in heat sealability, hot tackiness and air permeability, and the porous film. It is suitably used as a storage bag for storing heat-sealing materials such as disposable warmers and hot compresses by heat sealing.

Conventionally, a porous film based on a polyethylene resin is often used as a storage bag for a breathing exothermic substance such as this type of disposable body warmer. In the state covered with the film, the periphery of the opening is heat-sealed and sealed. JP-A-10-152570 (Patent Document 1) discloses a porous film having excellent heat sealability used as the storage bag, together with polyethylene resin, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer. A porous film produced by multilayer extrusion such as an extrusion lamination method by adding a resin such as a polymer (EEA) or an ethylene-methacrylic acid copolymer (EMA) is provided.

Japanese Patent Application Laid-Open No. 2011-104993 (Patent Document 2) contains a layer containing a low melting point metallocene polyethylene resin and a high melting point polyethylene resin as a porous film for a heat sealing bag constituting member. A laminated porous film in which layers are laminated is provided. The laminated porous film is improved in mechanical properties and heat sealability by providing the low melting point easy heat seal layer on the surface layer.

However, the porous film described in Patent Document 1, that is, an ethylene copolymer having a polar group such as EVA, EEA, and EMA, is excellent in adhesiveness with a base material, but has poor thermal stability. There are various problems such as generation of resin burns and yellowing of the porous film.
Moreover, since the laminated porous film containing polyethylene with different melting points described in Patent Document 2 has a laminated structure, it is difficult to reuse and recycle defective products from resin raw materials, and there is a problem of low economic efficiency.

Furthermore, depending on the type of the machine for filling the bag made of a porous film with the ventilation exothermic substance, the peripheral edges of the porous film in the machine flow direction (MD) and the transverse direction (TD) are heat sealed. The seal temperature control is a single control. However, since a general porous film is strongly oriented to MD by extrusion and stretching, MD and TD have different heat seal temperatures (thermal conductivity). Therefore, it is required to make the heat sealing temperature range wider and lower temperature to enable high-speed filling. Moreover, since a heating element such as iron powder is filled immediately after heat sealing, hot tack property that prevents the bag from being broken even at a high temperature is important.

In addition, if the air permeability of the porous film is large and uneven, the ventilation heating elements such as disposable warmers and hot compresses may generate abnormal heat, and the user may receive low-temperature burns. Is important.
In order to obtain the uniformity of the air permeability, it is important that the appearance of the porous film is good, that is, there is no stretching unevenness and thickness unevenness and it is uniform. Causes of unevenness in stretching and thickness are the instability of the original fabric that occurs when the film is transported at high speed and formed into a film (sway of the film due to vibration of the transport), draw resonance (unstable extrusion of molten resin) Pulsation of extruded resin, etc.), variation in cooling and solidification, and defective or unstable operation of equipment.

The present invention has been made in view of the above-mentioned problems and importance, and has a performance required for a porous film used for a storage bag for a ventilating and exothermic substance such as a disposable body warmer and a hot compress. It is.
That is, the present invention is a high-strength and thin film that does not use an ethylene copolymer having a polar group such as EVA, EEA, or EMA in addition to excellent heat sealability, hot tackiness, and quality stability. It is an object to provide a porous film having a layer structure and a storage bag made of the porous film.

In order to solve the above-mentioned problems, the present invention provides 50 parts by mass or more of linear low density polyethylene (LLDPE), high pressure polymerization low density polyethylene (HP-LDPE) and metallocene linear low density polyethylene (m-LLDPE). Is a porous film containing a resin composition containing 50 to 200 parts by weight of an inorganic filler with respect to 100 parts by weight of a polyethylene resin composition containing less than 50 parts by weight in total, and the machine flow direction (MD) The porous film is characterized by having a heat seal temperature of 90 ° C. or higher and a heat seal maximum strength of 4.0 N / 50 mm or higher.

In the polyethylene resin composition used in the present invention, the linear low density polyethylene (LLDPE) has a density of 0.910 to 0.940 g / cm ³ , a melting point of 110 to 130 ° C., a blending amount of 55 to 92 parts by mass, High-pressure polymerization low density polyethylene (HP-LDPE) has a density of 0.910 to 0.930 g / cm ³ , a melting point of 100 to 120 ° C., a blending amount of 3 to 15 parts by mass, and the metallocene linear low density polyethylene (m- LLDPE) preferably has a density of 0.880 to 0.930 g / cm ³ , a melting point of 85 to 130 ° C., and a blending amount of 5 to 30 parts by mass.
Further, the polyethylene resin composition used in the present invention preferably contains high density polyethylene (HDPE; density 0.940 to 0.970 g / cm ³ , melting point 125 to 145 ° C.).

The porous film of the present invention preferably has a basis weight of 10 to 100 g / m ² .
Furthermore, the porous film of the present invention has a difference TD (max) − which is the difference between the minimum fusion temperature MD (min) in the machine flow direction (MD) and the maximum fusion temperature TD (max) in the transverse direction (TD). The MD (min) is preferably 1 ° C. or higher.
In addition, the porous film of the present invention is preferably a film that is made porous at a stretch ratio of 2.5 to 5.0 times in at least a uniaxial direction.

Furthermore, the present invention provides a storage bag of a ventilation exothermic substance including at least one layer of the porous film and having an opening edge bonded by heat sealing, and is particularly preferably used as a storage bag for a disposable body warmer. It is done.

Since the porous film of the present invention is a porous film that does not use an ethylene copolymer such as EVA, EEA, or EMA that is expensive and has poor thermal stability, it is excellent in economy and productivity. Further, it has a high strength and a thin film, and has a suitable air permeability and a heat sealing property and a hot tack property suitable for high-speed filling processing of a heating element, and can be more suitably used as a storage bag for a ventilation heat generating material.

The top view of an example of the disposable warmer using the storage bag of the ventilation | gas_flowing exothermic substance of this invention is shown. Sectional drawing of an example of the disposable body warmer using the storage bag of the ventilation | gas_flowing exothermic substance of this invention is shown.

Hereinafter, the porous film of the present invention will be described in detail.
The porous film of this invention contains the resin composition which mix | blended the inorganic filler with the polyethylene resin composition. The polyethylene resin composition comprises 50 parts by mass or more of linear low density polyethylene (A) (LLDPE), high pressure polymerization low density polyethylene (B) (HP-LDPE) and metallocene linear low density polyethylene (C). (M-LLDPE) and a polyethylene resin composition containing less than 50 parts by mass in total. The porous film of the present invention is a porous film containing a resin composition in which 50 to 200 parts by mass of an inorganic filler is blended with 100 parts by mass of the polyethylene resin composition, and has a machine flow direction (MD). The heat seal temperature is 90 ° C. or higher, and the maximum heat seal strength is 4.0 N / 50 mm or higher.

In the polyethylene resin composition, the linear low density polyethylene (A) (LLDPE) serving as a base material preferably has a density of 0.910 to 0.940 g / cm ³ and a melting point of 110 to 130 ° C. Is preferably 55 to 92 parts by mass. The high-pressure polymerization low-density polyethylene (B) (HP-LDPE) to be blended with the substrate preferably has a density of 0.910 to 0.930 g / cm ³ and a melting point of 100 to 120 ° C. The amount is preferably 3 to 15 parts by mass. The metallocene linear low density polyethylene (C) (m-LLDPE) preferably has a density of 0.880 to 0.930 g / cm ³ and a melting point of 85 to 130 ° C. It is preferable that it is a mass part.
Thus, the polyethylene resin composition of the present invention does not contain any ethylene copolymer composed of EVA, EEA, and EMA.

The inorganic filler is preferably blended in an amount of 50 to 200 parts by weight, more preferably 60 to 150 parts by weight, with respect to 100 parts by weight of the polyethylene resin composition.
When the blending amount of the inorganic filler is less than 50 parts by mass, it is difficult to develop an appropriate air permeability, and when it exceeds 200 parts by mass, the strength and waterproofness of the film are lowered.

(Components of polyethylene resin composition)
Examples of the linear low density polyethylene (A) (LLDPE) used as the substrate include ethylene-propylene, ethylene- (1-butene), ethylene- (1-hexene), and ethylene- (4-methyl-1-pentene). ) And ethylene- (α-olefin) copolymers such as ethylene- (1-octene) can be used. Any linear low density polyethylene (excluding metallocene linear low density polyethylene (C)) polymerized by a conventional porous film polymerized by a multi-site catalyst such as Ziegler type or Philips type can be used. .
As described above, the linear low density polyethylene (A) is a DSC in which the density by the pycnometer method (JIS K7112B method) is set to 0.910 to 0.940 g / cm ³ and the scanning speed is set to 10 ° C./min. The melting point according to the melting peak temperature (JIS K7121) when measured in (110) is preferably 110 to 130 ° C. The MFR at 190 ° C. and a 2.16 kg load (JIS K7210 condition D) is preferably 0.5 to 10 g / 10 min.

The blending amount of the linear low-density polyethylene (A) is 50 parts by mass or more with respect to 100 parts by mass of the polyethylene resin composition. By being 50 mass parts or more, sufficient hot tack property can be ensured. On the other hand, the upper limit is not particularly limited, but since it is preferable to blend the component (B) and the component (C) described later in detail, the blending amount of the component (A) is preferably 55 to 92. Part by mass, more preferably 60 to 80 parts by mass.

The high pressure polymerization low density polyethylene (B) (HP-LDPE) preferably has a density of 0.910 to 0.930 g / cm ³ and a melting point of 100 to 120 ° C. The MFR is preferably 0.5 to 10 g / 10 min.
The component (B) is preferably blended in an amount of 3 to 15 parts by weight, more preferably 5 to 10 parts by weight, although the preferred blending amount varies depending on the molding method. Since the blending amount of the component (B) is in the range of 3 to 15 parts by mass, shaking of the original fabric, draw resonance, etc. that occur when the original fabric is conveyed at a high speed and formed into a film shape are suppressed. A porous film having a uniform thickness and air permeability can be obtained.
Moreover, the said (B) component does not have limitation in particular, such as a manufacturer and a grade, A commercial item can be used arbitrarily.

Metallocene-based linear low-density polyethylene (C) (m-LLDPE) was polymerized with highly active single-site catalysts such as zirconocene, titanocene, hafnocene (collectively metallocene) Kaminsky catalyst, post metallocene catalyst, etc. It refers to an ethylene- (α-olefin) copolymer. The metallocene linear low density polyethylene (C) is characterized by improved kneadability and uniform dispersibility of the inorganic filler, improved molding processability to a thin film, low modulus and low melting point. This contributes to the improvement of low-temperature heat sealability, in addition to the reduction of stretching and uneven stretching, and is different from the function of the linear low-density polyethylene (A).

As the metallocene linear low density polyethylene (C), those having a density of 0.880 to 0.930 g / cm ³ and a melting point of 85 to 130 ° C. are preferably used in view of the above characteristics and purposes. When the density and melting point are smaller than the upper limit of the range, heat sealability, hot tack, uniformity of air permeability and the like are good, and when larger than the lower limit of the range, there is no extreme deterioration in mechanical properties, Troubles such as film-to-film blocking and fusion during molding process do not occur.
Further, MFR is preferable from the viewpoints of uniform film formability by extrusion molding method, air permeability of the resulting porous film, uniformity of heat sealability, and prevention of breakage at the time of fusion due to a decrease in film mechanical strength. Is 0.5 to 10 g / 10 min, more preferably 0.5 to 5 g / 10 min. As described above, the blending amount is preferably 5 to 30 parts by mass, and more preferably 15 to 30 parts by mass.

Examples of the metallocene linear low density polyethylene (C) include “Kernel” and “Harmolex” manufactured by Nippon Polyethylene Co., Ltd., “Evolue” manufactured by Prime Polymer Co., Ltd., and Sumitomo Chemical Co., Ltd. "Sumikasen E", "Excellen FX", "ELITE" manufactured by Dow Chemical Company, "Enable", "Exceed" manufactured by Exxon Mobil Chemical Company, and the like.

If necessary, high-density polyethylene (D) (HDPE) may be added to the polyethylene resin composition of the present invention. The production method is not particularly limited, such as a low-pressure method (Ziegler method) and a medium-pressure method (Phillips method, standard method). The high density polyethylene (D) has a density of 0.940 to 0.970 g / cm ³ , an MFR of 0.5 to 10 g / 10 min, a melting point of 125 to 145 ° C., and a blending amount of 3 to 30% by mass in the polyethylene resin composition. It is preferable that it is the range of these.

Examples of the inorganic filler to be blended in the polyethylene resin composition include fine particles such as calcium carbonate, calcium sulfate, barium carbonate, barium sulfate, titanium oxide, talc, clay, kaolinite, and montmorillonite, and minerals. In the present invention, an inorganic filler composed of calcium carbonate and barium sulfate is suitably used because of the advantages of the porousness of the film to be produced, high versatility, low cost and variety of kinds. The average particle size of the inorganic filler is preferably 0.5 to 5 μm, more preferably 0.8 to 3 μm. By setting the thickness to 0.5 μm or more, there is no dispersion distribution failure and secondary aggregation, and uniform dispersion can be achieved. On the other hand, when the thickness is 5 μm or less, strength and water resistance can be sufficiently ensured without generating large voids when the film is thinned.
In addition, for the purpose of improving the dispersion and mixing properties with the polyethylene resin, it is preferable that the inorganic filler is coated with fine particles of fatty acid, fatty acid ester or the like in advance so that the surface of the fine particles can be easily blended with the polyethylene resin.

Other additives may be added as necessary. Specifically, higher fatty acid, higher fatty acid ester, higher fatty acid amide, metal soap, higher alcohol, petrolatum, paraffin wax, glycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, castor oil, hydrogenated castor oil Additives that favorably disperse plasticizers such as hardened castor oil, dehydrated castor oil, aromatic esters, aromatic amides and polyethers, low molecular weight polymers (oligomers) such as polyester, lubricants, and inorganic fillers.

In addition to the above additives, compatibilizers, processing aids, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, antiblocking agents, antifogging agents, matting agents, depending on the intended use An appropriate amount of antibacterial agent, deodorant, antistatic agent, flame retardant, colorant, pigment, and the like may be added to the resin composition.

(Method for producing porous film)
After mixing the above-mentioned polyethylene resin (linear low density polyethylene (A), high pressure polymerization method low density polyethylene (B), metallocene linear low density polyethylene (C)), inorganic filler, etc. with a mixer And melt kneading with a kneader. Specifically, after mixing for a required time with a mixer such as a tumbler mixer, mixing roll, Banbury mixer, ribbon blender, super mixer, etc., using a kneader such as a different direction twin screw extruder or the same direction twin screw extruder, Promotes uniform distribution of the kneaded product. Alternatively, polyethylene resin, inorganic filler and the like can be directly fed into an extruder and kneaded without being mixed and dispersed by a mixer. The kneaded resin composition is preferably pelletized once by a method such as strand cutting or die cutting, but it may be formed into a film-like raw material through a die as it is.

First, the kneaded resin composition is made into a film-shaped raw material by a method such as melt extrusion. The method for producing the film-shaped original fabric is not limited, and a film-shaped original fabric may be produced using a known method, but from the viewpoint of production efficiency, cost, etc., after melt extrusion of the resin composition, A method of forming into a film by a forming method such as inflation, tubular, or T-die is preferable, and inflation is more preferable.

As a method for making the film-shaped raw material obtained by the melt extrusion molding porous, a stretch opening method is common, but the method is not limited. For example, a known stretching method such as a biaxial stretching method such as a roll stretching method, a tenter method, a simultaneous method, or a sequential method can be applied.
In the present invention, it may be carried out at least once in a uniaxial direction, or twice or more in consideration of stretching unevenness and air permeability. The stretching temperature is preferably 0 to 90 ° C, more preferably 40 to 90 ° C. The stretching ratio is preferably 2.5 to 5.0 times in total, and more preferably 3.0 to 4.5 times in total. By setting the draw ratio to 2.5 times or more in total, a porous film that is drawn uniformly and has a sufficiently excellent appearance can be obtained.
Therefore, when the porous film is used as a storage bag for a ventilation exothermic composition, the porous film has sufficiently uniform air permeability, so that abnormal heat generation of a ventilation heating element such as a disposable body warmer can be suppressed. On the other hand, when the stretch ratio is 5.0 or less in total, a heat-sealing property can be sufficiently secured when heat-sealing the four sides of the storage bag, and a porous film having a balanced mechanical property can be obtained. can get.

As a measure against heat shrinkage in the stretching direction of the porous film, heat setting may be performed after stretching. Here, heat setting refers to suppressing the shrinkage of the product roll by heating the film in advance and causing the film to thermally shrink. In the case of the roll stretching method, there is a method in which the draw ratio (ratio of winding side roll speed / unwinding side roll speed) is set to a negative number while heating the stretched film with a heated roll (annealing roll). In the case of the tenter stretching method, the film is heated in the vicinity of the tenter exit, and the film is self-contracted by making the clip width at both ends narrower than the width after stretching.

If the heat setting temperature is too low, the film is not sufficiently heat fixed. On the other hand, if the temperature is too high, production troubles such as film winding around the roll or tearing may occur. Considering the above points, the heat setting temperature in the present invention is preferably 70 to 120 ° C. Further, the negative draw ratio is preferably −20 to −5% in total, and if it is within the specified range, heat fixation can be performed without any trouble in production, and sufficient thermal dimensional stability can be obtained.
Further, similarly to the stretching, the heat setting may be divided into a plurality of times. Even if the porous film which passed through this process is stored for a long time as a roll-shaped roll, there are few elastic recovery, shrinkage | contraction and squeezing by heat | fever, film sticking, and blocking, and it can process it in the next process without a problem.

(Storage bag for ventilation exothermic composition using porous film)
The storage bag of the present invention is a storage bag of a ventilation exothermic composition containing at least one layer of the porous film of the present invention and having an opening edge bonded by heat sealing.
More specifically, the storage bag of the present invention is a bag formed using the porous film of the present invention on the entire surface or one surface. The storage bag can be in the form of a conventional bag (such as a four-sided bag, a three-sided bag, or a pillow bag) such as a bag formed by joining the edges of a porous film.
An appropriate method can be adopted for joining the film edge, but in the present invention, a fusion method is preferably used from the viewpoint of the production efficiency of the storage bag, etc., and heat fusion, ultrasonic fusion, etc. A publicly known system can be adopted, and the storage bag of the present invention is bonded by heat sealing by heat sealing.

A storage bag 12 shown in FIGS. 1A and 1B is formed from the porous film 11 of the present invention, and uses the air permeability of the porous film 11 to store the ventilation heat-generating substance 13 of the disposable warmer 10. It is said. The storage bag 12 is a four-sided bag, the ventilation heat-generating substance 13 of the disposable warmer 10 is disposed between the porous films 11 on both sides, and the four-side periphery is joined by a heat seal part 14 to form the disposable warmer 10. Yes. In addition, a storage bag is not limited to a four-sided bag, It is good also as another above-mentioned bag form.
The air permeability of the porous film 11 used as a storage bag is 500 to 50,000 seconds / 100 ml so that the temperature is appropriate according to the site of the aeration exothermic substance 13 that generates heat based on the air permeability. Is preferred. Here, the air permeability refers to an air permeability measuring device (Asahi Seiko Co., Ltd., Oken type air permeability measuring device, EGO1-55 type) according to the method defined in JIS P8117 (Gurley tester method). ) Means the one specified by the measuring method.
In addition, you may form a storage bag with the porous film 11 of this invention, and other materials, such as a nonwoven fabric.

(Physical properties of porous film used as storage bag)
The basis weight of the porous film 1 is preferably 10 to 100 g / m ² , more preferably 30 to 100 g / m ² , and still more preferably 40 to 80 g / m ² . When the basis weight is 10 g / m ² or more, the tensile strength, tear strength, and rigidity of the porous film can be sufficiently secured as a storage bag for a breathable exothermic substance such as a disposable body warmer or a hot compress. Further, when the basis weight is 100 g / m ² or less, a sufficient lightweight feeling can be obtained.

The heat seal temperature in the machine flow direction (MD) of the porous film 1 of the present invention is 90 ° C. or higher, preferably 95 ° C. or higher. By setting the temperature to 90 ° C. or higher, it is possible to suppress production troubles in which the porous film adheres to the porous films that are bonded on both sides or to the heat setting roll at the time of stretching opening and heat setting.
In addition, the heat seal temperature in this invention says what is measured by the method as described in an Example.

The heat seal maximum strength of the porous film 1 of the present invention is 4.0 N / 50 mm or more, and preferably 6.0 N / 50 mm or more. When it is 4.0 N / 50 mm or more, problems such as breakage of the storage bag and exposure of the heating element can be sufficiently solved when used as a storage bag for a ventilating heat-generating substance such as a disposable body warmer or a warm compress. .
In addition, the heat seal maximum strength in this invention says what is measured by the method as described in an Example.

Further, the porous film of the present invention has a difference TD (max) that is a difference between the minimum fusion temperature MD (min) in the machine flow direction (MD) and the maximum fusion temperature TD (max) in the transverse direction (TD). -MD (min) is preferably 1 ° C or higher. When this temperature difference is 1 ° C. or more, when the porous film of the present invention is used, for example, as a storage bag for a breathing exothermic substance such as a disposable body warmer or a hot compress, the storage bag is broken when the heating element is filled. And there is no peeling and excellent productivity.
From the above viewpoint, TD (max) −MD (min) is preferably 6 ° C. or more, and more preferably 10 ° C. or more.

Hereinafter, although the Example and comparative example of this invention are described, this invention is not limited to these. The raw materials and compositions of Examples 1 to 3 and Comparative Examples 1 to 5 are shown in Table 1.

LLDPE (A-1): Linear low-density polyethylene (A-1) uses Novatec LL UF230 (density 0.920 g / cm ³ , MFR 1.0 g / 10 min, melting point 122 ° C.) manufactured by Nippon Polyethylene Co., Ltd. did.
LLDPE (A-2): linear low density polyethylene (A-2, ethylene- (1-octene) copolymer) is DOWLEX 2032 (density 0.926 g / cm ³ , MFR 2.0 g / manufactured by Dow Chemical Company) 10 min, melting point 124 ° C.).
HP-LDPE (B): High-pressure polymerization method Low-density polyethylene (B) was Novatec LD LF441 (density 0.923 g / cm ³ , MFR 2.3 g / 10 min, melting point 110 ° C.) manufactured by Nippon Polyethylene Co., Ltd.
m-LLDPE (C): Metallocene linear low density polyethylene (C) uses Harmolex NF324A (density 0.906 g / cm ³ , MFR 1.0 g / 10 min, melting point 120 ° C.) manufactured by Nippon Polyethylene Co., Ltd. did.
HDPE (D): As a high-density polyethylene (D), Novatec HD HF560 (density 0.962 g / cm ³ , MFR 6.0 g / 10 min, melting point 135 ° C.) manufactured by Nippon Polyethylene Co., Ltd. was used.
PP (polypropylene): Novatec PP SA03 (density 0.901 g / cm ³ , MFR 36 g / 10 min, melting point 160 ° C.) manufactured by Nippon Polypro Co., Ltd. was used.
Calcium carbonate (inorganic filler): Ryton BS-0 (average particle size 1.1 μm, fatty acid surface treatment) manufactured by Bihoku Flour Industry Co., Ltd. was used.
Plasticizer: Hardened castor oil HCO-P manufactured by KEF Trading Co., Ltd. was used.
Thermal stabilizer: IRGANOX B225 manufactured by BASF Japan Ltd. was used.

Examples 1 to 3
All the raw materials shown in Table 1 were put into a super mixer, mixed for a predetermined time, melt-kneaded at an extrusion temperature of 180 ° C. with a same-direction twin screw extruder, and compound pellets were obtained by a strand cut method. Thereafter, it was formed into a film by a single screw extruder and an inflation die. A porous film was obtained by performing uniaxial stretching in the MD direction at a stretching temperature of 76 ° C. and a stretching ratio of 3.50 times using a roll-type longitudinal stretching machine, and heat fixing at 90 ° C.

Comparative Example 1
As shown in Table 1, a porous film was obtained under the same production conditions as in Example 1 except that the metallocene linear low-density polyethylene (C) was not used.

Comparative Example 2
As shown in Table 1, a porous film was obtained under the same production conditions as in Example 1 except that a propylene homopolymer (PP) was used instead of the metallocene linear low-density polyethylene (C).

Comparative Example 3
As shown in Table 1, except that a linear low density polyethylene (A-2; ethylene- (1-octene) copolymer) was used instead of the metallocene linear low density polyethylene (C). A porous film was obtained under the same production conditions as in Example 1.

Comparative Example 4
As shown in Table 1, a porous film was obtained under the same production conditions as in Example 1 except that high-density polyethylene (D) was used instead of metallocene-based linear low-density polyethylene (C).

Comparative Example 5
As shown in Table 1, a porous film was obtained under the same production conditions as in Example 1 except that the high-pressure polymerization method low-density polyethylene (B) was not blended.

(Measurement method and evaluation)
Examples 1 to 3 and Comparative Examples 1 to 5 were evaluated on the following items. The evaluation results are shown in Table 2.

(1) Weight per unit area (g / m ² )
After collecting a test piece (MD: 250 mm, TD: 200 mm) from the obtained porous film, the weight (g) was measured with an electronic balance, and the numerical value was multiplied by 20 to obtain a basis weight.

(2) Appearance, presence / absence of stretching unevenness The porous film was visually judged in the following four stages.
A: No stretch unevenness, uniformly stretched whitening B: No stretch unevenness C: Some stretch unevenness D: Stretch unevenness, stretch whitening nonuniform

(3) Heat seal temperature (° C.), hot tack property Using a heat seal test device, the temperature of the seal heating part is increased by 1 ° C. under the conditions of time 2 seconds and pressure 0.5 MPa. The quality film is fused. The definition of fusion is that immediately after heat sealing, the porous film joint is not peeled even when a tensile load of 12 gf / 10 mm is applied, and when the film is melted and does not retain the original shape, it is not regarded as fusion. The minimum fusion temperature MD (min) of MD and the maximum fusion temperature TD (max) of TD are obtained. From Table 2, the higher the numerical value of TD (max) -MD (min), the higher the heat sealable temperature range. Indicates that it is suitable for high-speed filling with a continuous heat seal. The numerical value of TD (max) −MD (min) is preferably 1 ° C. or higher, more preferably 6 ° C. or higher, and 0 ° C. or a negative number is not suitable for the processing method.
In Table 2, negative numbers are indicated by “▲”.

(4) Maximum heat seal strength (N / 50mm)
Using the heat seal test device, after bonding at a temperature of 100 ° C. and 120 ° C. for 2 seconds and a pressure of 0.5 MPa, the strength of the bonded portion was measured with a tensile tester in accordance with JIS K7127 in an environment of 23 ° C. and 50% humidity. Was done. It implemented in MD direction and TD direction of a porous film, respectively. Since the heating element of the disposable body warmer is filled with about 40 to 100 g, the preferable maximum heat seal strength is 4.0 N / 50 mm or more, more preferably 6.0 N / 50 mm or more as described above. From this, it can be said that it has sufficient strength at the time of use from the time of manufacturing and filling processing.

From Table 2, Examples 1 to 3 have no stretching unevenness and are excellent in heat seal strength, hot tackiness, and appearance. Therefore, even when a heating element such as a disposable body warmer or a hot compress is filled, it can withstand practical production. In particular, in Examples 1 and 2, since the MD heat sealable temperature is 107 ° C. or higher and TD (max) −MD (min) = 11 ° C., the storage bag is not broken or peeled off when the heating element is filled. It is excellent for high-speed production. This is considered to be the result of the addition of the metallocene-based linear low-density polyethylene (C) to the functions of elasticity reduction, suppression of stretching unevenness, and low-temperature heat sealability. Further, the maximum heat seal strength is 4.0 N / 50 mm or more, and it has sufficient strength during use from the time of manufacturing and filling processing.
On the other hand, Comparative Examples 1 to 5 are poor in heat seal strength and appearance of MD, and TD (max) −MD (min) is a negative number. Therefore, heat seal processing is difficult, and the storage bag is broken and the heating element is exposed. There are fears. Furthermore, since Comparative Example 5 did not contain high-pressure polymerization low-density polyethylene, when forming into a film at a high speed with an inflation die, the raw fabric (bubbles) vibrated unstablely, and the appearance of uneven thickness and stretch unevenness A defect occurred. A bubble is a cylindrical sheet (film) formed by an inflation method.

The porous film of the present invention has high strength and a thin film and is excellent in heat sealability, hot tackiness, and appearance, and therefore can be suitably used as a storage bag for aeration exothermic compositions such as disposable warmers and hot compresses.

Claims

50 parts by mass or more of linear low density polyethylene (LLDPE), high pressure polymerization method low density polyethylene (HP-LDPE) and metallocene linear low density polyethylene (m-LLDPE) were blended in less than 50 parts by mass in total. A porous film comprising a resin composition containing 50 to 200 parts by mass of an inorganic filler with respect to 100 parts by mass of a polyethylene resin composition, wherein the heat seal temperature in the machine flow direction (MD) is 90 ° C. or higher, and A porous film having a maximum heat seal strength of 4.0 N / 50 mm or more.
The linear low density polyethylene (LLDPE) has a density of 0.910 to 0.940 g / cm 3 , a melting point of 110 to 130 ° C., a blending amount of 55 to 92 parts by mass, and the high pressure polymerization low density polyethylene (HP-LDPE) is The density is 0.910 to 0.930 g / cm 3 , the melting point is 100 to 120 ° C., the blending amount is 3 to 15 parts by mass, and the metallocene linear low density polyethylene (m-LLDPE) has a density of 0.880 to 0.930 g. / cm 3, the porous film according to claim 1 having a melting point 85 ~ 130 ° C., the amount 5-30 parts by weight.
3. The porous film according to claim 1, wherein the polyethylene resin composition is further blended with high density polyethylene having a density of 0.940 to 0.970 g / cm 3 and a melting point of 125 to 145 ° C.
The porous film according to any one of claims 1 to 3, wherein the basis weight is 10 to 100 g / m 2 .
The difference between the minimum fusion temperature MD (min) in the machine flow direction (MD) and the maximum fusion temperature TD (max) in the transverse direction (TD) is TD (max) −MD (min) of 1 ° C. or more. The porous film according to any one of claims 1 to 4.
6. The porous film according to any one of claims 1 to 5, wherein the porous film is made porous at a stretch ratio of 2.5 to 5.0 times in total in at least one uniaxial direction.
A ventilating exothermic substance storage bag comprising at least one layer of the porous film according to any one of claims 1 to 6 and having an opening edge bonded by heat sealing.
The ventilating and exothermic substance storage bag according to claim 7, which is a disposable storage bag for warmers.