JP2003012842A - Fine porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fine porous film, composed of a resin composition excellent in thin-film formability and high-speed film formability, excellent in gas permeability, a balance of a mechanical property such a tear strength, flexibility and appearance. SOLUTION: A polyethylene resin composition is composed of a straight-chain and low-density polyethylene of 20-40 wt.% that is polymerized by a catalyst having a single polymerizing active site and has a density of 0.910-0.930 g/cm<3> , a straight-chain and low-density polyethylene of 5-10 wt.% having the density of above 0.930 g/cm<3> and 0.95 g/cm<3> or below, a low-density polyethylene of 2-15 wt.%, and an inorganic filler of 40-65 wt.% that is surface-treated by a glyceride based material and has the average particle diameter of 1.5 μm or below. The fine porous film is obtained by orienting a film composed of the above polyethylene resin composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a large number of fine through holes penetrating between the front and back surfaces and has excellent breathability, and is suitable for sanitary goods, packaging materials, building materials, waterproof clothing, etc. The present invention relates to a suitably used microporous film.

[0002]

2. Description of the Related Art Conventionally, there has been provided a microporous film having a large number of fine holes penetrating between the front and back surfaces. Because it has a function of allowing moisture to pass through, it is widely used for sanitary items such as disposable diapers, sanitary items, blood-proof sheets, packaging materials such as dehumidifiers and waterproof covers, battery separators, building materials such as waterproof sheets, waterproof clothing, etc. It's being used.

As the above-mentioned microporous film, specifically, JP-A-61-144331 discloses 100 to 100 parts by weight of a crystalline polyolefin resin and 20 to 100 parts by weight of a copolymer of ethylene and another α-olefin. A sheet-like product obtained by mixing 50 to 400 parts by weight of an inorganic filler and 0.1 to 20 parts by weight of a plasticizer with 100 parts by weight of a mixed resin composition containing 100 parts by weight of the resin composition at a temperature not higher than the melting point of the crystalline polyolefin resin. A microporous film obtained by stretching and then heat setting has been proposed. Further, in JP-A-9-25372, 100 parts by weight of a resin component consisting of linear low-density polyethylene, a copolymer of ethylene and another olefin, and branched low-density polyethylene is added to calcium carbonate 80-200.
There has been proposed a microporous film obtained by stretching a sheet-shaped material containing 1 part by weight and then heat-setting.

However, the air permeability of the above microporous film is still insufficient, and in order to improve the air permeability of this microporous film, the stretching ratio of the above-mentioned sheet-like material is increased, or in the mixed resin composition. It is conceivable to increase the amount of the inorganic filler compounded in the.

However, in the former method, the tear strength of the obtained microporous film along the stretching direction is reduced, the flexibility of the obtained microporous film is reduced, or the through holes become large, so that the moisture content is reduced. Another problem occurs that it becomes easier to pass through, and the latter method causes another problem that the film-forming property on a sheet is deteriorated, cutting during film formation is likely to occur, and thinning becomes difficult. However, none of them was a fundamental solution to the problem of low air permeability of the microporous film.

[0006]

An object of the present invention is to form a resin composition having excellent thin film forming properties and high-speed film forming properties, and to have excellent air permeability and mechanical strength such as tear strength. It is to provide a microporous film having an excellent balance with flexibility and an excellent appearance. Also,
In addition to the above, another object of the present invention is to provide a microporous film which is excellent in preventing leakage of body fluid such as menstrual blood.

[0007]

The microporous film of the present invention is a linear low-molecular film having a density of 0.910 to 0.930 g / cm ³ which is polymerized using a catalyst having a single polymerization active point. Density polyethylene (hereinafter referred to as "linear low-density polyethylene (A)") 20 to 40% by weight, density 0.93
5 to 10% by weight of linear low-density polyethylene (hereinafter referred to as "linear low-density polyethylene (B)") having a density of more than 0 g / cm ³ and 0.950 g / cm ³ or less, low-density polyethylene 2 to 15 %, And a film made of a polyethylene resin composition, which is surface-treated with a glyceride-based substance and comprises 40 to 65% by weight of an inorganic filler having an average particle size of 1.5 μm or less, is stretched. .

The polyethylene resin composition used in the present invention comprises a linear low-density polyethylene (A), a linear low-density polyethylene (B) and a low-density polyethylene mixed with an inorganic filler.

As the linear low-density polyethylene (A), a catalyst having a single polymerization active point is used from the viewpoint that the obtained microporous film has excellent mechanical strength such as tear strength. A polymerized product is used. Examples of the catalyst having a single polymerization active point include metallocene catalysts, single site catalysts, Kaminsky catalysts and the like.

When the linear low-density polyethylene (A) has a high density, the film-forming property of the polyethylene-based resin composition is lowered, and the stretchability of the film made of the polyethylene-based resin composition is lowered. Since the number of micropores penetrating the microporous film is insufficient and the air permeability is reduced, and when the micropore film is low, the resulting micropore film becomes too flexible and the secondary processability is reduced, so 0.910 Limited to 0.930 g / cm ³ .

If the amount of the linear low-density polyethylene (A) blended in the polyethylene resin composition is too large, the resulting microporous film becomes too flexible and the secondary processability is lowered. Since the mechanical strength such as tear strength of the porous film decreases, it is limited to 20 to 40% by weight.

The linear low density polyethylene (B)
If the density is high, the resulting microporous film will be too hard and the mechanical strength will be reduced, and if it is low, the microporous film will be too soft and the secondary processability will be decreased.
It is limited to more than 930 g / cm ³ and 0.950 g / cm ³ or less.

If the amount of the linear low-density polyethylene (B) blended in the polyethylene resin composition is large, the mechanical strength such as tear strength of the microporous film obtained will be low, and if it is small, the microporous film obtained. Since the secondary workability of is decreased, it is limited to 5 to 10% by weight.

Further, if the amount of the low-density polyethylene compounded in the polyethylene resin composition is large, the mechanical strength such as tear strength of the obtained microporous film is lowered, and if it is small, the polyethylene resin composition is formed into a film. Property is deteriorated and striped unevenness is generated in the microporous film obtained by stretching the film made of the polyethylene resin composition, and the appearance is deteriorated. Therefore, the content is limited to 2 to 15% by weight.

The inorganic filler is not particularly limited as long as it is surface-treated with a glyceride-based substance and has an average particle size of 1.5 μm or less. For example, calcium carbonate, barium sulfate, talc, clay, diatomaceous earth, silica. Etc.

The surface of the inorganic filler is treated with a glyceride-based material because the glyceride-based material is a resin composed of the linear low-density polyethylene (A), the linear low-density polyethylene (B) and the low-density polyethylene. This is because it has an appropriate affinity for the components, that is, the inorganic filler surface-treated with the glyceride-based substance is the above-mentioned linear low-density polyethylene (A), linear low-density polyethylene ( B) and the resin component consisting of the above low-density polyethylene are uniformly dispersed to improve the film-forming property of the polyethylene-based resin composition into a film, and when the film is stretched, its stretching ratio Even when the stretching ratio is low, a part of the surface of the inorganic filler is smoothly separated from the resin component, and the surface of the inorganic filler and the resin composition Smooth delamination between the films that innumerable fine holes penetrating over between both surfaces is smoothly and reliably pierced, it is possible to obtain a microporous film with excellent breathability.

Further, as described above, the obtained microporous film has excellent air permeability even if the draw ratio of the stretching treatment for expressing desired air permeability is a low draw ratio. Flexibility and mechanical strength are not impaired by performing a stretching treatment with a high stretching ratio in order to obtain desired air permeability like a porous film, therefore,
The microporous film is excellent in both mechanical strength such as tear strength and flexibility.

Examples of the glyceride-based substance that has been surface-treated with the above-mentioned inorganic filler include monoglycerides such as glycerin monostearate and glycerin monopalmitate; Examples thereof include diglyceride.

If the average particle size of the inorganic filler is large,
When a film made of a polyethylene resin composition is stretched, large holes may be formed, and since a thin film cannot be formed, the thickness is limited to 1.5 μm or less.

Further, if the water content of the inorganic filler is large, the mechanical strength of the obtained microporous film tends to decrease, and high-speed film formation of the polyethylene resin composition becomes difficult, resulting in a decrease in productivity. Therefore, it is preferably 1% by weight or less.
The water content is a value measured at a temperature of 160 ° C. by the Karl Fischer method of JIS K0068.

Further, the inorganic filler preferably contains a silicon dioxide-based clay mineral, if necessary. Silicon dioxide-based clay minerals have an excellent blood coagulation action, and the inclusion of silicon dioxide-based clay minerals in the inorganic filler significantly improves the leakproofness of body fluids such as menstrual blood in the resulting microporous film. However, it is preferably used for sanitary products such as sanitary napkins and blood-proof sheets.

The above silicon dioxide-based clay mineral contains 40% by weight or more of silicon dioxide (SiO ₂ ) and aluminum oxide (Al ₂
O ₃ ), titanium oxide (TiO ₂ ), iron oxide (Fe ₂ O ₃ ),
It is a natural clay mineral containing a metal oxide such as magnesium oxide (MgO), and specific examples thereof include kaolin, bentonite, talc, activated clay, silica sand, diatomaceous earth, and the like. Or two or more kinds may be used in combination. When the content of the silicon dioxide-based clay mineral in the inorganic filler is too high, the film-forming property of the polyethylene-based resin composition is lowered, and the mechanical strength and flexibility such as tear strength of the obtained microporous film are lowered. Then
If the amount is small, the leakproofness of the body fluid of the obtained microporous film will not be improved, so 0.5 to 70% by weight is preferably contained in the inorganic filler. In particular, when the resulting microporous film is used in a sanitary napkin, the microporous film is
Since it comes into contact with a large amount of menstrual blood in which fibrin is decomposed by plasmin, the content of the silicon dioxide-based clay mineral in the inorganic filler is 3 in order to sufficiently exert the blood coagulation promoting action.
It is preferably from 0 to 70% by weight.

If the content of the above-mentioned inorganic filler in the polyethylene resin composition is too large, the film-forming property of the polyethylene resin composition is deteriorated and it becomes impossible to obtain a thin film and a microporous film. , The resulting microporous film becomes brittle and its mechanical strength decreases, so 4
It is limited to 0 to 65% by weight.

If the melt tension of the polyethylene resin composition is large, the drawdown property of the obtained film is lowered and the film tends to be broken, and it becomes difficult to make the film thin. As the resulting film is cut, the resulting film is likely to be unevenly spread, the thickness is likely to be non-uniform, and high-speed film formation becomes difficult,
25-50 mN is preferable. The melt tension is a tension in a take-up direction when a strand obtained by extruding the melted polyethylene-based resin composition at 190 ° C. from a capillary viscometer (orifice diameter 1 mm) is continuously taken at 50 m / min.

The method for adjusting the melt tension of the polyethylene resin composition to the above range is not particularly limited, but the linear low density polyethylene (A), linear low density polyethylene (B), low density polyethylene and Since the melt tension is likely to be insufficient by simply dry blending the inorganic filler, it is preferable to use the twin screw kneader, the single screw kneader, the Banbury mixer or the like for melt kneading. Even when these kneaders are used, if the temperature, shearing force, etc. are applied too much, the entanglement of the molecular chains is unnecessarily released and the melt tension tends to be insufficient, so it is preferable to appropriately adjust and use the kneader.

It should be noted that pigments, antioxidants, ultraviolet absorbers, lubricants and the like may be added to the polyethylene resin composition as long as the physical properties are not impaired.

The microporous film of the present invention is formed by uniaxially or biaxially stretching a film made of the above-mentioned polyethylene resin composition. The method for stretching the microporous film is conventionally used when stretching the film. The stretching method is used.

A polyolefin resin nonwoven fabric may be laminated and integrated on one or both sides of the microporous film.
Examples of such a polyolefin resin non-woven fabric include a polyethylene resin non-woven fabric and a polypropylene resin non-woven fabric.

Next, a method for producing the above microporous film will be described. As a method for producing a microporous film, for example, a polyethylene-based resin composition composed of the linear low-density polyethylene (A), linear low-density polyethylene (B), low-density polyethylene and an inorganic filler can be used in an extruder. Of the linear low-density polyethylene (A), the linear low-density polyethylene (B) and the low-density polyethylene, which are supplied and extruded into a film from a T die attached to the tip of the extruder. Examples include a method of uniaxially or biaxially stretching using a general-purpose method at a temperature below the melting point.

When a polyolefin resin nonwoven fabric is laminated and integrated on one or both sides of the microporous film, the polyolefin resin nonwoven fabric and / or the microporous film is heated and then the polyolefin resin nonwoven fabric is formed. The microporous film is laminated on one side or both sides and pressure-bonded with a roller, and a polyolefin resin nonwoven fabric is laminated and integrated on one side or both sides of the microporous film, or hot-melt type on one side or both sides of the microporous film. A method may be mentioned in which an adhesive is applied in a spray form or a spiral form, and then a non-woven fabric made of a polyolefin resin is overlapped, and the non-woven fabric made of a polyolefin resin is laminated and integrated on one side or both sides of the microporous film.

[0031]

The microporous film of the present invention is polymerized with a catalyst having a single polymerization active point and has a density of 0.910 to 0.910.
Linear low density polyethylene which is 0.930 g / cm ^3, density and exceed 0.930 g / cm ³ 0.950
A linear low-density polyethylene having a g / cm ³ or less and a low-density polyethylene are mixed in a specific weight ratio, and an inorganic filler having an average particle diameter of 1.5 μm or less is surface-treated with a glyceride-based substance in the resin component. The glyceride-based substance, which is obtained by subjecting the film made of the polyethylene-based resin composition to be added to the stretching treatment, to the surface of the inorganic filler has an appropriate affinity for the resin component. There is.

Therefore, the inorganic filler surface-treated with the glyceride-based substance is smoothly and uniformly dispersed in the resin component, and the polyethylene-based resin composition is smoothly and surely formed into a film having a desired thickness. It can be formed into a film. Then, by stretching the film having the desired thickness, it is possible to easily and surely obtain a microporous film having a desired thickness, particularly a thin thickness.

Further, since the glyceride-based substance has an appropriate affinity for the resin component as described above, when the film made of the polyethylene-based resin composition is stretched, Even when the draw ratio is low, a part of the surface of the inorganic filler is smoothly separated and separated from the resin component, and the above phenomenon is caused by a separation phenomenon between the surface of the inorganic filler and the resin component. The film has a large number of fine holes penetrating both sides thereof.

Therefore, the obtained microporous film has excellent air permeability because it has a large number of fine pores penetrating both sides thereof even at a low stretch ratio, and has a low stretch ratio. Since it is a magnification, it has excellent mechanical strength such as tear strength and flexibility.

Further, by setting the melt tension of the polyethylene resin composition in the above range, high-speed film formation or thinning is possible without causing breakage or uneven spread during film formation, and microporous. A film can be efficiently and easily obtained, and the resulting microporous film has an excellent appearance.

In addition, when the above-mentioned inorganic filler contains a silicon dioxide-based clay mineral, the silicon dioxide-based clay mineral has an action of coagulating body fluid such as blood, so that the leakproof property of the obtained microporous film is improved. However, the bodily fluid does not leak even when used as a sanitary product or blood-proof sheet. In particular, when the inorganic filler contains 30 to 70% by weight of a silicon dioxide-based clay mineral, it exerts an excellent blood coagulation promoting action even on a larger amount of blood or menstrual blood, and the obtained microporous film is obtained. Even when used for sanitary products, it exhibits sufficient leakproofness.

[0037]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

In the examples and comparative examples, the following linear low-density polyethylene, low-density polyethylene and calcium carbonate were used. The melt index (hereinafter,
"MI") conforms to JIS K 7210,
It is a value measured at a temperature of 190 ° C. and a load of 21.18 N. Metallocene PE (1): Polymerized using a metallocene-based catalyst having one polymerization active point and having a density of 0.918.
Linear low-density polyethylene with g / cm ³ and MI of 3.8 g / 10 minutes (trade name “Evolue S” manufactured by Mitsui Chemicals, Inc.)
P2040 ") Metallocene PE (2): Polymerized using a metallocene-based catalyst having one polymerization active point, and a density of 0.918.
Linear low-density polyethylene with g / cm ³ and MI of 4.0 g / 10 min (manufactured by Japan Polychem, trade name “Kernel KF380”) Metallocene PE (3): Metallocene type with one polymerization active point Polymerized with a catalyst and a density of 0.935
Linear low-density polyethylene with g / cm ³ and MI of 2.1 g / 10 minutes

LLDPE (1): linear low polymerized using a Ziegler-Natta catalyst having a plurality of polymerization active points and having a density of 0.920 g / cm ³ and an MI of 4.0 g / 10 min. Density polyethylene LLDPE (2): Density 0.935 g / cm ³ , MI
Is 2.1 g / 10 min, linear low-density polyethylene (manufactured by Tosoh Corporation, trade name “Nipolon Z ZF260”) LLDPE (3): density 0.939 g / cm ³ , MI
Is 2.1 g / 10 minutes linear low density polyethylene (manufactured by Idemitsu Chemical Co., Ltd., trade name "Moretech 0278G")

LDPE: Density 0.921 g / cm ³ ,
Low density polyethylene charcoal (1) having MI of 1.0 g / 10 min: calcium carbonate surface-treated with glycerin monostearate and having an average particle diameter of 1.3 μm (containing water content 0.1% by weight) ) Calcium carbonate (2): calcium carbonate surface-treated with glycerin monostearate and having an average particle size of 4.0 μm (water content 0.1% by weight) Calcium carbonate (3): surface treated with stearic acid And calcium carbonate having an average particle diameter of 1.3 μm (water content 0.1% by weight) Kaolin: silicon dioxide (SiO ₂ ) 52% by weight, aluminum oxide (Al ₂ O ₃ ) 42% by weight and oxidation Titanium (T
clay mineral activated clay consisting of 2% by weight of iO ₂ ) and 4% by weight of other impurities: 75% by weight of silicon dioxide (SiO ₂ ), 15% by weight of aluminum oxide (Al ₂ O ₃ ), iron oxide (Fe
Clay mineral composed of 2% by weight of ₂ O ₃ ), 2% by weight of magnesium oxide (MgO) and 6% by weight of other impurities.

(Examples 1 to 13 and Comparative Examples 1 to 7) A polyethylene resin composition having a predetermined amount shown in Table 1 was supplied to an extruder, and a film was produced from a T die attached to the tip of the extruder. To obtain a film. The melt tension of the polyethylene resin composition was as shown in Table 1.

Then, the above film was uniaxially stretched 1.5 times in a state of being kept at 50 ° C., so that a large number of fine holes penetrating both sides of the film were formed so as to have a thickness of 20 μm. A microporous film of

Film-forming property of the above polyethylene resin composition,
The air permeability, tear strength, flexibility, thin film property, appearance and leakproofness of the microporous film obtained as described above were measured by the following methods, and the results are shown in Table 1.

(Film Formability) The state of the film when extruded into a film form from a T-die was visually observed continuously for 2 hours and evaluated as follows. ◯: No film break or spread unevenness occurred Δ: Film break or spread unevenness partially occurred ×: Film break or stretch unevenness occurred frequently

(Air permeability) The air permeability of the microporous film was measured according to JIS P 8117 to make it air-permeable. In Comparative Example 7, the resulting microporous film had a large number of large holes, and the air permeability could not be measured.

(Tear Strength) The trouser tear strength was measured according to JIS K7128. In addition, Table 1
In the figure, MD represents the tear strength in the stretching direction, and TD represents the tear strength in the direction perpendicular to the stretching direction.

(Flexibility) Touch the microporous film with bare hands,
The feeling was evaluated as follows. ○ ・ ・ ・ Good △ ・ ・ ・ Slightly hard × ・ ・ ・ Hard or too soft

(Thin film property) The thickness of 20 μm and 30 μm was changed by changing the draw ratio in each of the examples and comparative examples.
m and 50 μm microporous films were produced, and the appearance of the obtained microporous film was visually observed and evaluated according to the following criteria. ◯: No holes that could be visually confirmed were generated. Δ: Holes with a diameter of about 3 mm or less that could be visually confirmed were generated in places. X: Many holes that can be visually confirmed were generated.

(Appearance) The appearance of the obtained microporous film was visually observed and measured according to the following criteria. ○: Good △: Part of unevenness ×: Large amount of unevenness

(Leakproofness) From the obtained microporous film, two square samples of 100 mm in length and 100 mm in width were cut out from an arbitrary part, and 3 ml of rabbit blood was dropped on one sample, and another sample was added. A sheet of sample was placed on top of it, and the sample was heat-sealed on all sides to encapsulate the blood in the sample. After that, length 100 mm x width 10
A 0 mm flat plate weighing 300 g was placed on the sample and allowed to stand for 5 hours, and then evaluated as follows. ◯: No blood leaked on the sample surface Δ: Blood leaked on the sample surface ×: Blood leaked on the sample surface immediately after sealing

[0051]

[Table 1]

[0052]

The microporous film of the present invention is polymerized using a catalyst having a single polymerization active point and has a density of 0.91.
0~0.930g / cm ³ linear low density polyethylene 20 to 40 wt% which is a density of 0.930 g / cm ^3, greater and 0.950 g / cm linear low-density polyethylene 5 which is ³ or less 10% by weight, low-density polyethylene 2
Inorganic fillers 40 to 65 having a surface treatment of 15% by weight and a glyceride-based substance and having an average particle size of 1.5 μm or less
Since it is characterized by stretching a polyethylene resin film consisting of wt%, even at a low stretch ratio, innumerable fine through-holes penetrated over both sides thereof are provided, thus, The microporous film of the present invention has excellent air permeability, an excellent balance of mechanical strength such as tear strength and flexibility, and also an excellent thin film formability. Further, by adjusting the melt tension of the polyethylene-based resin composition constituting the microporous film of the present invention, the film forming property is improved, and it is possible to prevent film breakage and spread unevenness during melt extrusion, It is possible to reduce the thickness of microporous film and form a film at high speed. Further, in the case of containing a silicon dioxide-based clay mineral, since the silicon dioxide-based clay mineral has a blood coagulation action, the microporous film obtained has improved leakproofness, and is suitable for sanitary products, blood-proof sheets, etc. Even in applications where high leakproofness is required, bodily fluids such as menstrual blood do not leak and can be suitably used.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4F074 AA17A AA21A AC26 AC30                       AC32 AC36 AF03 AG01 CA01                       CA02 CA03 CC02Y DA10                       DA32 DA33 DA38 DA49 DA53                 4F100 AA02A AC03A AH02A AK03B                       AK06A AK63A AL05A BA02                       BA07 CA23A DG15B DJ10A                       EJ64A GB07 GB15 GB66                       GB72 JA13A JD02 JD05                       JK02A YY00A                 4J002 BB021 BB022 BB023 BB051                       BB052 DE236 DG046 DJ016                       DJ036 DJ046 EH056 FB086                       FD016 GB00 GC00 GG00                       GK00 GL00

Claims (4)

[Claims] 1. A linear low-density polyethylene having a density of 0.910 to 0.930 g / cm ³ which is polymerized by using a catalyst having a single polymerization active point and has a density of 0.2 to 20% by weight. Over 930 g / cm ³ and 0.950 g / cm ³
5-10% by weight of linear low-density polyethylene, which is
Low density polyethylene 2 to 15% by weight, and surface-treated with glyceride-based substance and average particle size is 1.5 μm
A microporous film obtained by stretching a film made of a polyethylene resin composition containing the following inorganic filler of 40 to 65% by weight. 2. The microporous film according to claim 1, wherein the polyethylene resin composition has a melt tension of 25 to 50 mN. 3. The microporous film according to claim 1, wherein the inorganic filler contains silicon dioxide clay mineral in an amount of 0.5 to 70% by weight. 4. The microporous film according to any one of claims 1 to 3, wherein a polyolefin resin nonwoven fabric is laminated and integrated on one side or both sides.