JP7112430B2 - Stretched porous film and manufacturing method thereof - Google Patents

Description

The present invention relates to stretched porous films and methods of making the same.

Conventionally, personal care products such as diapers are required to allow passage of air and steam, but not liquid, in order to prevent stuffiness. Therefore, personal care products such as diapers are required to be breathable and water resistant. In order to meet this demand, a porous film is used in which a water-repellent resin such as a polyolefin resin is formed into a film and fine pores are formed therein. Such a porous film allows passage of air and the like, but has a structure that does not allow passage of liquid.

Patent Document 1 discloses a breathable film obtained by melt-molding a resin composition containing a polyethylene resin, liquid paraffin, and an inorganic filler.

Japanese Unexamined Patent Publication "JP-A-62-250038"

However, the aforementioned breathable film has room for improvement in terms of flexibility.

One aspect of the present invention has been made in view of the above problems, and the object thereof is to realize a stretched porous film having air permeability, water resistance and flexibility suitable for personal care products such as diapers. That is.

In order to solve the above-mentioned problems, the present inventors conducted extensive research and found that a polyolefin resin having a specific melt mass flow rate was used, and liquid paraffin was added to the polyolefin resin at a specific mass ratio. The inventors have found that a stretched porous film having air permeability, water resistance and flexibility can be realized by using a resin composition containing a resin composition and adjusting the moisture permeability to a specific range. That is, the present invention includes the following configurations.

a polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less; , an inorganic filler, and a melt mass flow rate of the resin composition measured at 190° C. according to JIS K 7210 of 2.0 g/10 min. A stretched porous film characterized by having a moisture permeability of 1400 g/m ² ·24 h or more measured under conditions of 40°C and 60% relative humidity according to ASTM E96.

a polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less; , a mixing step of obtaining a resin composition by mixing an inorganic filler, a molding step of molding the resin composition into a film, and stretching the film obtained by the molding step at least in the machine direction. and a porosification step of making the resin composition porous, wherein the melt mass flow rate of the resin composition measured at 190° C. according to JIS K 7210 is 2.0 g/10 min. A method for producing a stretched porous film characterized by the above.

According to one aspect of the present invention, there is an effect that a stretched porous film having air permeability, moisture permeability and flexibility can be obtained.

An embodiment of the invention will be described below, but the invention is not limited thereto.

As a result of intensive studies by the inventors of the present invention, it has been found that the above-described prior art has the following problems. For example, the film shown in Patent Document 1 is considered to have poor flexibility because it uses a polyethylene resin with a low melt index.

Therefore, the stretched porous film according to one embodiment of the present invention solves the above-described problems of the prior art, and has air permeability, moisture permeability and flexibility. A detailed description will be given below.

[1. Stretched porous film]
The stretched porous film according to one embodiment of the present invention comprises a polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less, and 5.5 parts per 100 parts by mass of the polyolefin resin. A resin composition containing 0 parts by mass or more and 20 parts by mass or less of liquid paraffin and an inorganic filler, and the melt mass flow rate of the resin composition measured at 190 ° C. according to JIS K 7210 is 2.0g/10min. Thus, the moisture permeability measured under the conditions of 40° C. and 60% relative humidity according to ASTM E96 is 1400 g/m ² ·24 h or more. By combining liquid paraffin in a specific mass ratio with a polyolefin resin having specific physical properties, water resistance and desired flexibility can be obtained. Moreover, desired air permeability can be obtained by setting the moisture permeability to a specific range. Therefore, a stretched porous film having air permeability, water resistance and flexibility can be realized.

The stretched porous film may be made of a resin composition containing a polyolefin resin, liquid paraffin, and an inorganic filler. It may be one that has been

<1-1. Polyolefin Resin>
The polyolefin resin has a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less, more preferably 0.905 g/cm ³ or more and 0.935 g/cm ³ or less. When the density is within the above range, a stretched porous film having the desired flexibility can be obtained by combining with liquid paraffin, which will be described later. Also, density and melting point are correlated to some extent. When the density is within the above range, the heat setting temperature is somewhat apart from the melting point, so that it is possible to prevent the pores of the stretched porous film from being clogged due to melting of the polyolefin resin at the same time as the heat setting. Therefore, deterioration of air permeability can be prevented.

The polyolefin resins include linear low density polyethylene (LLDPE) and branched low density polyethylene (LDPE). In addition, it is preferable to use a plurality of types of polyolefin-based resins because the melt mass flow rate can be easily adjusted. A combination of linear low-density polyethylene and branched low-density polyethylene may be used as the polyolefin resin. From the viewpoint of improving heat resistance, a polyolefin resin having a density of 0.930 g/cm ³ or more and 0.970 g/cm ³ or less may be included with respect to 100 parts by mass of the polyolefin resin. In that case, the density of the entire polyolefin resin used (the density of a mixture of a plurality of types of polyolefin resin) should be 0.940 g/cm ³ or less. More preferably, all the polyolefin resins used have a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less.

<1-2. Liquid paraffin>
Liquid paraffin is a mixture of hydrocarbons having a wide range of carbon numbers of about 15 to 35 that is liquid at room temperature obtained from crude oil, and has a density of 0.790 g/cm ³ or more and 0.920 g/cm ³ or less. say something

Liquid paraffin is added for the purpose of improving flexibility. The content of liquid paraffin is preferably 5.0 parts by mass or more and 20 parts by mass or less, more preferably 7.0 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the polyolefin resin. preferable. When the liquid paraffin content is 5.0 parts by mass or more, the stretched porous film can be made more flexible. Moreover, if the content of liquid paraffin is 20 parts by mass or less, the strength of the stretched porous film can be increased. Moreover, since the occurrence of the draw resonance phenomenon can be suppressed, the productivity can be improved.

<1-3. Inorganic filler>
Inorganic fillers are added to make the film porous. Known inorganic fillers can be used without limitation, for example, inorganic salts such as calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide and aluminum hydroxide, and inorganic oxides such as zinc oxide, magnesium oxide and silica. , silicates such as mica, vermiculite and talc, and organometallic salts. Among the inorganic fillers, calcium carbonate is preferable from the viewpoint of cost performance and dissociation with the polyolefin resin.

In the resin composition, the mixing ratio of the inorganic filler is preferably 80 parts by mass or more and 200 parts by mass or less, and 85 parts by mass or more and 150 parts by mass or less with respect to the total of 100 parts by mass of the polyolefin resin and liquid paraffin. is more preferable. When the blending ratio of the inorganic filler is 80 parts by mass or more, the frequency of occurrence of voids per unit area caused by separation between the polyolefin resin and the inorganic filler can be increased. Therefore, adjacent voids are easily communicated with each other, and air permeability is improved. If the blending ratio of the inorganic filler is 200 parts by mass or less, the elongation at the time of film stretching is good and the stretching is easy.

<1-4. Other Ingredients>
The resin composition may further contain additives that are commonly used in resin compositions. Such additives include antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizers, lubricants, antifog agents, antiblocking agents, antistatic agents, slip agents, colorants, plasticizers, and the like. mentioned. The resin composition may contain a small amount of resin components other than the polyolefin-based resin and the liquid paraffin as long as the effects of the present invention are not impaired. Specifically, other resin components may be blended within 5.0 parts by mass, more preferably within 2.5 parts by mass, per 100 parts by mass of polyolefin resin and liquid paraffin in total. be. Note that the stretched porous film and the resin composition according to one embodiment of the present invention may not contain a thermoplastic elastomer.

<1-5. Physical Properties of Stretched Porous Film>
The moisture permeability of the stretched porous film is preferably 1400 g/m ² ·24h or more, more preferably 1600 g/m ² ·24h or more. When the moisture permeability is within the above range, air permeability and moisture permeability are excellent. For example, when the stretched porous film is used as the back sheet of a paper diaper, it can prevent the diaper from getting stuffy when worn. The upper limit of moisture permeability is preferably 10,000 g/m ² ·24h or less, more preferably 4,000 g/m ² ·24h or less, from the viewpoint of mechanical properties, water resistance, and liquid leakage resistance. By setting the upper limit of the moisture permeability to 4000 g/m ² ·24 h or less, the diaper using the stretched porous film is less likely to leak when worn. In addition, since the moisture permeability of all the films disclosed in Patent Document 1 exceeds 4000 g/m ² ·24 h, it is thought that liquid leakage may occur when used for diapers or the like.

The moisture permeability is measured according to ASTM E96 under the conditions of 40° C., 60% relative humidity, 24 hours of measurement time, and the pure water method. In this specification, the moisture permeability is the average value of 10 samples of 10 cm×10 cm taken from the stretched porous film.

The 5% tensile strength of the stretched porous film is preferably 0.3 N/25 mm or more and less than 2.5 N/25 mm, more preferably 0.5 N/25 mm or more and 2.3 N/25 mm or less. The lower the 5% tensile strength, the more flexible. If the 5% tensile strength is less than 2.5 N/25 mm, more flexibility can be imparted. If the 5% elongation strength is 0.3 N/25 mm or more, the elongation of the film against the line tension applied in the machine direction during secondary processing can be suppressed.

The 5% tensile strength was measured according to JIS K 7127 by subjecting the sample to a chuck distance of 50 mm and a tensile speed of 200 mm/min. is measured as the strength in the machine direction when the sample is stretched by 5%. That is, the 5% tensile strength is measured as the stress in the machine direction when the chuck-to-chuck distance is extended by 2.5 mm. In this specification, the 5% tensile strength is a value measured for a sample of 25 mm width and 150 mm length in the machine direction taken from the stretched porous film.

The melt mass flow rate of the resin composition was 2.0 g/10 min. 2.0 g/10 min. Above, 6.0g/10min. It is more preferably 2.0 g/10 min. Above, 5.0g/10min. More preferably: If the melt mass flow rate is within the above range, it is possible to form a more stable film. A melt mass flow rate of 2.0 g/10 min. If it is above, the resin pressure of the extruder at the time of film formation can be suppressed, and an adverse effect on film formation can be prevented. Also, the melt mass flow rate is 6.0 g/10 min. If it is below, it is possible to further suppress neck-in when forming a film with a T-die. Therefore, the required product width can be easily obtained. Also, melt mass flow rate and 5% tensile strength tend to correlate. When the melt mass flow rate is decreased, the 5% tensile strength is increased, and therefore the stretched porous film tends to be poor in flexibility. The melt mass flow rate of the resin composition is measured by A method at 190° C. according to JIS K 7210.

The air permeability of the stretched porous film is preferably 300 seconds/100 mL or more and 2000 seconds/100 mL or less, more preferably 400 seconds/100 mL or more and 1600 seconds/100 mL or less, 400 seconds/100 mL or more, It is more preferably 1100 seconds/100 mL or less. The smaller the air permeability, the easier it is for gas to pass through. If the air permeability is within the above range, when the stretched porous film is used as the back sheet of a paper diaper, stuffiness during wearing can be prevented. Air permeability is measured according to JIS P 8117 by the Oken test method.

The heat shrinkage of the stretched porous film in the machine direction is preferably 5.0% or less, more preferably 3.5% or less. If the 5% elongation strength is high and the heat shrinkage rate in the machine direction is 5.0% or less, the elongation of the film against the line tension applied in the machine direction during secondary processing can be further suppressed. Although the heat shrinkage in the machine direction is preferably close to 0%, it is practically 0.5% or more.

The heat shrinkage in the machine direction is measured by the following method. A 15 cm x 15 cm sample is taken from the stretched porous film. The sample is marked with 10 cm between the marks in the machine direction. After leaving this sample at 50° C. for 24 hours, it is cooled to room temperature and the length between marked lines is measured. The heat shrinkage rate in the machine direction is obtained from Formula I below.
Formula I: Heat shrinkage (%) in the machine direction={(10 cm-Length between marked lines after cooling (cm))/10 cm}×100.

The basis weight is preferably 10 g/m ² or more and 35 g/m ² or less, more preferably 11 g/m ² or more and 32 g/m ² or less, and 12 g/m ² or more and 30 g/m ² or less. It is even more preferable to have When the basis weight is within the above range, a stretched porous film having excellent air permeability, moisture permeability and mechanical strength can be obtained. If the basis weight is 10 g/m ² or more, the mechanical strength of the film can be enhanced. Also, if the basis weight is 35 g/m ² or less, sufficient moisture permeability can be obtained.

[2. Method for producing stretched porous film]
A method for producing a stretched porous film according to an embodiment of the present invention comprises a polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less, and , a mixing step of mixing 5.0 parts by mass or more and 20 parts by mass or less of liquid paraffin and an inorganic filler to obtain a resin composition; a molding step of molding the resin composition into a film; and a porosification step of stretching the film obtained by the forming step at least in the machine direction to make the film porous. By combining liquid paraffin at a specific mass ratio with a polyolefin resin having specific physical properties, a stretched porous film having water resistance and desired flexibility can be obtained. A resin composition having a melt mass flow rate within a specific range has good fluidity, and a stretched porous film having flexibility can be obtained. Also, by stretching a film containing a resin composition having a specific composition to make it porous, a stretched porous film having desired air permeability can be obtained. Therefore, a stretched porous film having air permeability, water resistance and flexibility can be realized. In addition, [1. Stretched porous film] will be omitted below, and the above description will be incorporated as appropriate.

<2-1. Mixing process>
In the mixing step, a polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less and 5.0 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the polyolefin resin. This is a step of mixing a certain liquid paraffin and an inorganic filler to obtain a resin composition. First, a polyolefin resin, liquid paraffin, an inorganic filler, and, if necessary, additives are mixed. A mixing method is not particularly limited, and a known method can be adopted. For example, it is preferable to mix for about 5 minutes to 1 hour using a mixer such as a Henschel mixer, a super mixer, or a tumbler mixer.

The resulting mixture is generally kneaded by a method such as strand cutting, hot cutting, or underwater cutting using a kneader such as a high kneading type twin-screw extruder or a tandem kneader, and pelletized. Mixing, kneading, and pelletizing in advance is preferable because uniform dispersion of the resin composition can be promoted. Moreover, depending on the formulation of the resin composition, the resin composition can be directly put into a kneader without mixing and pelletized.

<2-2. Molding process>
The molding step is a step of molding the resin composition into a film. It is preferable to form the pellets obtained as described above into a film by using a circular die or a T-die attached to the tip of the extruder. At this time, the cooling method when using the T-die method is not particularly limited, and a known method such as a nipple roll method, an air knife method, or an air chamber method can be employed. Depending on the composition of the resin composition, the resin composition can be directly charged into an extruder without mixing and kneading to form a film.

<2-3. Porosification step>
The porous-making step is a step of stretching the film obtained by the forming step at least in the machine direction to make the film porous. By stretching the film obtained by the molding step, the interfaces between the resin components (the polyolefin resin and the liquid paraffin) and the inorganic filler are separated. Then, minute voids are formed at the peeled interface, and the voids form continuous pores penetrating in the thickness direction of the film to form a stretched porous film. Stretching can be performed by a known method such as a roll stretching method or a tenter stretching method. Moreover, the stretching may be uniaxial stretching or biaxial stretching.

In addition, the draw ratio in the machine direction in the porosification step is preferably represented by the following formula II:
1.4≦Y≦0.075X+1.8 (formula II)
(In the formula, X represents the blending ratio (parts by mass) of liquid paraffin with respect to 100 parts by mass of polyolefin resin, and Y represents the draw ratio (fold).

By performing the stretching under the condition that the above formula II is established, the obtained film is sufficiently stretched while maintaining flexibility, is less likely to have thickness unevenness, and has good tear strength and sufficient A number and size of holes are formed. Therefore, with such a draw ratio, a stretched porous film having air permeability, moisture permeability and flexibility can be obtained more easily. The stretching may be single-stage stretching or multi-stage stretching.

The stretching temperature is preferably in the temperature range of normal temperature or higher and lower than the softening point of the resin composition. If the stretching temperature is room temperature or higher, uneven stretching is less likely to occur, and the thickness tends to be uniform. Also, if the stretching temperature is lower than the softening point, it is possible to prevent the stretched porous film from melting. Therefore, it is possible to prevent the pores of the stretched porous film from being crushed and the air permeability and moisture permeability to decrease. The stretching temperature can be appropriately adjusted by combining the physical properties of the resin composition to be used and the stretching ratio.

<2-4. Heat setting process>
The manufacturing method may include a heat setting step. The heat setting step is a step of heat setting the stretched porous film after stretching in order to suppress heat shrinkage in the stretching direction. Heat setting is a heat treatment performed in an environment where the stretched film is maintained in a tensioned state due to stretching and the dimensions are not changed. As a result, the thermal fixation can suppress elastic recovery during storage and shrinkage, winding, and the like due to heat.

As a heat setting method when a roll stretching method is employed as the stretching method, a method of heating the stretched film with a heated roll (annealing roll) can be mentioned. Moreover, as a heat setting method when the tenter stretching method is adopted as the stretching method, there is a method of heating the film after stretching near the exit of the tenter.

The heat setting temperature is preferably 70° C. or higher and 95° C. or lower, and preferably 80° C. or higher and 95° C. or lower. If the heat setting temperature is 70° C. or higher, thermal shrinkage can be suppressed by sufficient heat setting. Moreover, if the heat setting temperature is 95° C. or less, it is possible to further prevent the pores of the stretched porous film from being crushed by heat.

The heat setting time is preferably 0.2 seconds or longer, more preferably 0.5 seconds or longer, and even more preferably 1.0 seconds or longer. If the heat setting time is 0.2 seconds or more, thermal shrinkage can be suppressed by sufficient heat setting. Moreover, the heat setting time is preferably 20 seconds or less, more preferably 15 seconds or less. Although it depends on the combination with the heat setting temperature, it cannot be generalized, but if the heat setting time is 20 seconds or less, it is possible to further prevent the pores from being crushed due to melting of the stretched porous film. Therefore, it is possible to prevent deterioration of air permeability and moisture permeability.

The heat setting time is the time the stretched porous film is held at the heat setting temperature. For example, when the roll stretching method is adopted, it refers to the time during which the film is in contact with the annealing roll. The number of annealing rolls is not particularly limited, but when there are two or more, the heat-setting time is the sum of the times during which the stretched porous film is in contact with each annealing roll. Further, when the tenter stretching method is employed, the heat setting time indicates the time during which the film is heated at the heat setting temperature at the exit of the tenter and maintained. When heat setting is divided into multiple times and heated, it is the sum of each heating time.

The present invention is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims, and can be obtained by appropriately combining technical means disclosed in different embodiments. is also included in the technical scope of the present invention.

EXAMPLES The present invention will be described in more detail based on examples below, but the present invention is not limited to the following examples.

〔Evaluation method〕
The physical properties of the stretched porous films of Examples and Comparative Examples described later were measured by the methods described below.

(1) Melt mass flow rate The melt mass flow rate of the resin composition was measured according to JIS K 7210, selecting 190°C as the measurement temperature and using the A method. The melt mass flow rate is hereinafter also referred to as MI (melt index).

(2) Fabric weight A sample of 10 cm x 10 cm was cut from the stretched porous film, and the mass was measured with a balance. The basis weight was obtained from the area and weight of this sample.

(3) Moisture Permeability Ten samples of 10 cm×10 cm were taken from the stretched porous film. The moisture permeability of these samples was measured according to ASTM E96 under the conditions of 40° C., 60% relative humidity, 24 hours of measurement time, and the pure water method, and the average value was obtained.

(4) Air permeability The air permeability was measured according to JIS P 8117 by the Oken test method.

(5) 5% tensile strength According to JIS K 7127, a sample having a width of 25 mm and a length of 150 mm in the machine direction was taken from the stretched porous film. This sample was pulled at a chuck-to-chuck distance of 50 mm and a pulling speed of 200 mm/min. The strength in the machine direction when the sample was stretched by 5% was measured as the 5% tensile strength. That is, the stress in the machine direction was measured when the chuck-to-chuck distance was extended by 2.5 mm.

(6) Heat Shrinkage in Machine Direction A 15 cm×15 cm sample was taken from the stretched porous film. The sample was marked with 10 cm between the marks in the machine direction. After leaving this sample at 50° C. for 24 hours, it was cooled to room temperature and the length between marked lines was measured. The heat shrinkage rate in the machine direction was obtained from the following formula (Formula I).
Formula I: Heat shrinkage (%) in the machine direction={(10 cm-Length between marked lines after cooling (cm))/10 cm}×100.

[Ingredients Used]
A: Linear low-density polyethylene [manufactured by Dow Chemical Co., trade name: Dowlex 2047, density: 0.917 g/cm ³ , MI: 2.3 g/10 min. ]
B: Linear low-density polyethylene [manufactured by Dow Chemical Co., trade name: Dowlex 2035G, density: 0.919 g/cm ³ , MI: 6.0 g/10 min. ]
C: linear low-density polyethylene [manufactured by Dow Chemical Co., trade name: Dowlex 2036P, density: 0.935 g/cm ³ , MI: 2.5 g/10 min. ]
D: Linear low-density polyethylene [manufactured by Dow Chemical Co., trade name: Dowlex 2045G, density: 0.920 g/cm ³ , MI: 1.0 g/10 min. ]
E: branched low-density polyethylene [manufactured by DuPont Mitsui Polychemicals, trade name: Milathon 16P, density: 0.917 g/cm ³ , MI: 3.7 g/10 min. ]
F: ultra-low density polyethylene [manufactured by Dow Chemical Co., Ltd., trade name: Attain 4607GC, density 0.904 g/cm ³ , MI: 4.0 g/10 min. ]
G: High-density polyethylene [manufactured by Tosoh Corporation, trade name: Nipolon Hard 4200, density: 0.961 g/cm ³ , MI: 2.3 g/10 min. ]
H: Liquid paraffin [manufactured by Wako Pure Chemical Industries, Ltd., trade name: liquid paraffin, density: 0.860 to 0.890 g/cm ³ ]
I: Liquid paraffin [manufactured by Wako Pure Chemical Industries, Ltd., trade name: liquid paraffin, density: 0.825 to 0.850 g/cm ³ ]
J: Liquid paraffin [manufactured by Wako Pure Chemical Industries, Ltd., trade name: liquid paraffin, density: 0.800 to 0.835 g/cm ³ ]
K: paraffin [manufactured by Wako Pure Chemical Industries, Ltd., trade name: paraffin, melting point: 42 to 44°C, density: 0.900 g/cm ³ ]
L: Hydrogenated polybutadiene [manufactured by Nippon Soda Co., Ltd., trade name: Nisso-PB BI-2000, density: 0.860 g/cm ³ ]
M: polybutene [manufactured by NOF Corporation, trade name: polybutene 3N, density: 0.880 g/cm ³ ]
N: Hydrogenated polybutene [manufactured by NOF Corporation, trade name: Pearlream 4, density: 0.793 g/cm ³ ]
O: Calcium carbonate [manufactured by Imerys Minerals Co., Ltd., trade name: FL-520]
P: additive [titanium oxide (manufactured by Huntsman Co., Ltd., trade name: TR28) 50% by mass, hindered phenol-based heat stabilizer (manufactured by Ciba Japan Co., Ltd., trade name: IRGANOX3114) 20% by mass, A mixture with 30% by mass of a phosphorus-based heat stabilizer (manufactured by Ciba Japan Co., Ltd., trade name: IRGAFOS168)].

[Example 1]
A resin composition was prepared by mixing the polyolefin resin, hydrocarbon, inorganic filler and additive shown in Table 1. It was granulated and then film-formed.

Granulation (preparation of pellets) was performed as follows. Using a vented φ30 mm twin-screw extruder, the resin composition was extruded in a strand at a cylinder temperature of 160° C. and cooled in a water tank. After that, the extruded resin composition was cut into pieces of about 5 mm and dried to produce pellets.

Next, a film was formed from the pellets using a φ400 mm T-die film forming machine. Here, lip clearance: 1.5 mm, die temperature: 200°C, air gap: 105 mm, take-up speed: 10 m/min. , Cast roll temperature: 20°C. The obtained film was further uniaxially stretched (stretch ratio: 1.8 times) only in the machine direction with a roll stretching machine set at 40°C, and then in-line annealed with heat set rolls set at 90°C (heat setting time: 4 seconds). The heat shrinkage in the machine direction during heat setting was 8%.

In Examples 2 to 13 and Comparative Examples 1 to 8, the blending ratio of each component or the stretching conditions (stretch ratio or heat setting temperature) were changed as shown in Tables 1 and 2. A film was formed in the same manner.

なお、「ポリオレフィン系樹脂：配合割合（質量％）」は樹脂組成物に含まれるポリオレフィン系樹脂１００質量％に対する各ポリエチレン系樹脂の配合割合を表す。「炭化水素：配合割合（質量部）」は、ポリオレフィン系樹脂１００質量部に対する炭化水素の配合割合を表す。炭酸カルシウムおよび添加剤の配合割合は、ポリオレフィン系樹脂と炭化水素との合計１００質量部に対する配合割合として記載されている。

"Polyolefin-based resin: mixing ratio (% by mass)" represents the mixing ratio of each polyethylene-based resin to 100% by mass of the polyolefin-based resin contained in the resin composition. "Hydrocarbon: compounding ratio (parts by mass)" represents the compounding ratio of the hydrocarbon to 100 parts by mass of the polyolefin resin. The blending ratio of calcium carbonate and additives is described as a blending ratio with respect to a total of 100 parts by mass of the polyolefin resin and the hydrocarbon.

In addition, stretching conditions *1 represent a stretching ratio of 1.8 times and a heat setting temperature of 90°C. Stretching condition *2 represents a stretching ratio of 3.2 times and a heat setting temperature of 90°C. Stretching condition *3 indicates a stretching ratio of 2.5 times and a heat setting temperature of 90°C. Stretching condition *4 indicates a stretching condition of 1.3 times and a heat setting temperature of 90°C.

〔result〕
The basis weight, moisture permeability, air permeability, 5% tensile strength and thermal shrinkage of the stretched porous films obtained in Examples 1 to 13 and Comparative Examples 1 to 8 were measured.

実施例１～１３の延伸多孔性フィルムは、いずれも１４００ｇ／ｍ^２・２４ｈ以上の良好な透湿度を示すとともに、良好な風合いを有していた。また、実施例１～８、および１０～１２の延伸多孔性フィルムは、５％伸張強度および熱収縮率について低い値を保持していた。さらに、本実施例１～８、および１０～１２の延伸多孔性フィルムは、いずれの延伸倍率も式ＩＩを満たす。

The stretched porous films of Examples 1 to 13 all exhibited good moisture permeability of 1400 g/m ² ·24 h or more and had good texture. Also, the stretched porous films of Examples 1-8 and 10-12 retained low values for 5% tensile strength and heat shrinkage. Furthermore, the stretched porous films of Examples 1 to 8 and 10 to 12 satisfy formula II at any stretch ratio.

In Examples 3 and 4, polyolefin resins having different densities were used. In Example 4, polyethylene with a density of 0.961 g/cm ³ was used. Example 4, in which high-density polyethylene is added, has higher moisture permeability and lower air permeability than Example 3. In addition, although Example 4 had a high 5% elongation strength, it was better than Comparative Examples.

Comparing Examples 6 to 8, it can be seen that as the density of liquid paraffin decreases, air permeability decreases, and moisture permeability and 5% tensile strength increase.

In addition, Examples 9 and 13, in which the draw ratio does not satisfy Formula II, have a 5% tensile strength higher than Examples 1 to 8 and 10 to 12, which satisfy Formula II, but the moisture permeability is higher than that in Comparative Examples. , air permeability, 5% tensile strength and heat shrinkage were well balanced.

In Examples 2, 9, and 12, stretch ratios of stretched porous films of the same composition were changed. From these, it can be seen that by increasing the draw ratio, the moisture permeability increases, and the air permeability and the heat shrinkage decrease.

In Comparative Example 1, no hydrocarbon was used. As a result, the obtained stretched porous film had a high tensile strength of 5% and poor flexibility.

In Comparative Examples 2 to 5, hydrocarbons other than liquid paraffin were used as hydrocarbons. As a result, in Comparative Example 2 using paraffin as the hydrocarbon and Comparative Example 5 using hydrogenated polybutene as the hydrocarbon, stretched porous films with high 5% tensile strength and poor flexibility were obtained. In Comparative Example 3, in which hydrogenated polybutadiene was used as the hydrocarbon, and in Comparative Example 4, in which polybutene was used as the hydrocarbon, stretched porous films with low moisture permeability and easy to get stuffy were obtained.

In Comparative Example 6, 75% by mass of polyethylene having a density of 0.961 g/cm ³ was used with respect to 100 parts by mass of the polyolefin resin. As a result, a stretched porous film having low air permeability, high moisture permeability and high 5% tensile strength and poor flexibility was obtained.

In Comparative Example 7, a polyolefin resin with a low melt mass flow rate was used. As a result, the obtained stretched porous film had a low moisture permeability and was easily stuffy.

Comparative Example 8 had a low water vapor permeability, so that the stretched porous film was inferior in air permeability.

〔summary〕
[1] A polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less, and 5.0 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the polyolefin resin. It is composed of a resin composition containing liquid paraffin and an inorganic filler, and the melt mass flow rate of the resin composition measured at 190° C. according to JIS K 7210 is 2.0 g/10 min. A stretched porous film characterized by having a moisture permeability of 1400 g/m ² ·24 h or more measured under conditions of 40°C and 60% relative humidity according to ASTM E96.

[2] According to JIS K 7127, the distance between chucks is 50 mm, the pulling speed is 200 mm/min. The stretched porosity according to [1], wherein the strength in the machine direction when the chuck-to-chuck distance is stretched by 5% is 0.3 N/25 mm or more and less than 2.5 N/25 mm. the film.

[3] The air permeability of 300 seconds/100 mL or more and 2000 seconds/100 mL or less as measured by the Oken type tester method according to JIS P 8117. [1] or [2] Stretched porous film.

[4] A polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less, and 5.0 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the polyolefin resin. A mixing step of mixing liquid paraffin and an inorganic filler to obtain a resin composition, a molding step of molding the resin composition into a film, and stretching the film obtained by the molding step at least in the machine direction. a melt mass flow rate of the resin composition measured at 190° C. according to JIS K 7210 is 2.0 g/10 min. A method for producing a stretched porous film characterized by the above.

[5] The method for producing a stretched porous film according to [4], wherein the draw ratio in the machine direction in the porosification step is represented by the following formula II:
1.4≦Y≦0.075X+1.8 (formula II)
(In the formula, X represents the blending ratio (parts by mass) of liquid paraffin with respect to 100 parts by mass of polyolefin resin, and Y represents the draw ratio (fold).

INDUSTRIAL APPLICABILITY The present invention can be suitably used, for example, in personal care products such as diapers.

Claims (4)

a polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less;
A liquid paraffin that is 5.0 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the polyolefin resin;
Consists of a resin composition containing an inorganic filler,
The melt mass flow rate of the resin composition measured at 190° C. according to JIS K 7210 is 2.0 g/10 min. and
The moisture permeability measured under the conditions of 40° C. and 60% relative humidity according to ASTM E96 is 1400 g/m ² · 24 h or more ,
According to JIS K 7127, the distance between chucks is 50 mm, the pulling speed is 200 mm/min. and having a strength in the machine direction of 0.3 N/25 mm or more and 2.5 N/25 mm or less when the chuck-to-chuck distance is elongated by 5% . 2. The stretched porous film according to claim 1 , which has an air permeability of 300 seconds/100 mL or more and 2000 seconds/100 mL or less, as measured by the Oken type tester method according to JIS P 8117. A method for producing a stretched porous film, comprising:
a polyolefin resin having a density of 0.900 g/cm ³ or more and 0.940 g/cm ³ or less; , an inorganic filler, and a mixing step of obtaining a resin composition;
A molding step of molding the resin composition into a film;
a porosification step of stretching the film obtained by the forming step at least in the machine direction to make the film porous,
The melt mass flow rate of the resin composition measured at 190° C. according to JIS K 7210 is 2.0 g/10 min. and
The stretched porous film has a moisture permeability of 1400 g/m ² · 24 h or more measured under conditions of 40 ° C. and 60% relative humidity according to ASTM E96 ,
The stretched porous film was stretched according to JIS K 7127 with a distance between chucks of 50 mm and a pulling speed of 200 mm/min. and the strength in the machine direction when the distance between chucks is elongated by 5% is 0.3 N/25 mm or more and 2.5 N/25 mm or less . 4. The method for producing a stretched porous film according to claim 3 , wherein the draw ratio in the machine direction in the porosification step is represented by Formula II below:
1.4≦Y≦0.075X+1.8 (formula II)
(In the formula, X represents the blending ratio (parts by mass) of liquid paraffin with respect to 100 parts by mass of polyolefin resin, and Y represents the draw ratio (fold).