WO2017175878A1

WO2017175878A1 - Stretched porous film, and production method therefor

Info

Publication number: WO2017175878A1
Application number: PCT/JP2017/015207
Authority: WO
Inventors: 田中　伸幸
Original assignee: 株式会社トクヤマ
Priority date: 2016-04-08
Filing date: 2017-04-06
Publication date: 2017-10-12
Also published as: JPWO2017175878A1; JP6859324B2; CN108779279A

Abstract

Provided is a stretched porous film comprising a resin composition which includes 80-200 parts by mass of an inorganic filler per 100 parts by mass of a polyolefin which comprises 85-50 mass% of a linear low-density polyethylene, 10-35 mass% of a branched low-density polyethylene, and 5-25 mass% of polypropylene. The stretched porous film has a strength at 5% elongation in the machine direction of at least 3.5 N/25mm, a moisture vapour transmission rate of at least 2000 g/m²∙24h, and a mass per unit area of 10-35 g/m². The stretched porous film exhibits excellent pitch printing suitability and film texture.

Description

Stretched porous film and method for producing the same

The present invention relates to a stretched porous film and a method for producing the same. More specifically, the present invention relates to a polyolefin stretched porous film having a high machine direction low strain extension strength, suitable for pitch printing, and having good moisture permeability, and a method for producing the same.

Conventionally, there is a method of producing a stretched porous film by stretching a film in which an inorganic filler is added to a polyolefin resin at least in a uniaxial direction and generating microvoids by causing interfacial peeling between the inorganic filler and the polyolefin. Many have been proposed. Since these stretched porous films have a large number of minute voids inside, these voids are connected to each other to form communication holes. Therefore, the liquid does not permeate while having high moisture permeability. Because of this property, stretched porous polyolefin films are used for sanitary materials such as disposable diapers and sanitary napkins, functional packaging materials such as desiccants and disposable warmers, simple clothing such as disposable gloves and rain feathers, waterproof building materials such as house wrap, and multi-agricultural methods. It is widely used for agricultural applications such as industrial sheets and waste disposal applications such as compost-coated sheets.
For example, in the case of disposable diapers, the stretched porous film used for the sanitary material application is not only moisture-permeable and breathable, but also has water resistance and contradictory properties. Liquid leakage resistance and flexibility in accordance with movement during wearing are required. On the other hand, mechanical properties such as strength in the machine flow direction, tensile elastic modulus, and tensile elongation necessary for producing a disposable diaper are also required.
By the way, such a stretched porous film for paper diapers, when used as a moisture-permeable film for a back sheet of children's disposable diapers, enhances the brand and added value of the product, and further increases the consumer's willingness to purchase. For the purpose, printing with high design and design with characters and characters arranged is usually applied. When such a printing is performed on the stretched porous film, if the fluctuation of the printing pitch (interval) is large, the yield of the diaper is deteriorated at the time of commercialization, and thus the stability of the printing pitch is required. Even if the fluctuation of the printing pitch is small, if the printed film is wound up and stored as a roll, the roll shape of the roll will change during storage and the central part of the roll will be tightened. It has also been known that the beginning and end of the pattern become loose, which causes a change in the printing pitch later, which also changes the yield of the diaper. The fluctuation of the printing pitch is likely to occur when the line tension applied in the machine direction during printing is large and requires a film with little elongation, but any property of the film greatly affects the change in roll shape during storage. It was not known in the past.
Conventionally, polyethylene has been used as a polyolefin resin from the viewpoint of flexibility as a raw material for stretched porous films for paper diapers, but such a film is excellent in flexibility but is stretched during printing. There were drawbacks.
In JP-A-2002-249622, as a polyolefin resin, (1) at least one kind of high-density polyethylene and polypropylene is 10 to 70% by mass, (2) linear low-density polyethylene is 88 to 15% by mass, and (3) A porous film obtained by stretching a resin composition containing 3 to 15% by weight of branched low density polyethylene and an inorganic filler is shown. In this stretched porous film, (1) high-density polyethylene and polypropylene components are blended to improve the low strain elongation represented by 5% tensile strength in the machine direction and prevent printing pitch deviation. In order to fully exhibit this effect, in the examples, it is blended in the amount of 30 to 45% by mass in terms of the content in the polyolefin. As a result, the obtained stretched porous film has a considerably high 5% tensile strength, but it is still the highest at 31 g / 25 mm (3.2 N / 25 mm). With this strength, the printing pitch is stable. I wasn't satisfied with my sex at a practical level.
Therefore, in order to further improve the physical properties, if more (1) high-density polyethylene and polypropylene components are blended, this time, as shown in Comparative Example 1 of JP-A-2002-249622, the rigidity of the film is increased. Softness increases too much and the film feels worse. Further, in the stretching step of the resin composition, it may be possible to improve the 5% stretching strength by increasing the stretching ratio. However, as the stretching ratio is increased, the thermal shrinkage rate of the film may be deteriorated. JP 2002-249622 A shows only a draw ratio in a low range of 1.5 to 3.0 times. In fact, the draw ratio specifically adopted in the examples is only a low point of 2.0 times (see [0039]). Further, according to the knowledge of the present inventors, performing a high-magnification stretching with a composition containing a large amount of the polypropylene component in this way also causes a problem of reducing the moisture permeability of the obtained stretched porous film. It has become clear. Based on such prior art and knowledge, it has been impossible to find a measure for improving the 5% tensile strength to a sufficient value while satisfying other properties at a practical level.
On the other hand, JP-A-2015-229719 discloses (A) 20 to 80 parts by mass of a linear polyethylene resin having a density of 0.910 to 0.929 g / cm ³ and (B) a density of 0.930 to 0.965 g / cm ^3. 10 to 40 parts by mass of a polyethylene resin of cm ³ , (C) 5 to 20 parts by mass of low-density polyethylene having a density of 0.910 to 0.929 g / cm ³ , and (D) 5 to 20 parts by mass of a propylene homopolymer It is shown that a stretched porous film is produced from a resin composition containing a resin component containing a part, (E) an inorganic filler, and (F) a plasticizer. In this stretched porous film, it can be seen that the blending amount of the (D) propylene homopolymer is relatively small.
However, on the other hand, (B) polyethylene resin with a density of 0.930 to 0.965 g / cm ³ includes some of the category of low density polyethylene, but most of them correspond to high density polyethylene. Therefore, when using high-density polyethylene as the component (B), it functions as a component that increases the 5% stretch strength of the stretched porous film, similarly to the propylene homopolymer (D). In the examples, only one example with a low draw ratio of 2.5 times was specifically performed (see [0065]), and it was also disclosed that the 5% stretch strength could be improved to a sufficient value. Absent. The reason for this is that even if the total amount of the high-density polyethylene and the polypropylene component is increased to improve the 5% stretch strength and the stretch ratio is increased, the film as disclosed in JP-A-2002-249622 is used. This is because there is concern about an increase in the bending resistance and deterioration of the texture of the film.

Therefore, the object of the present invention is to have high moisture permeability and excellent texture, small variation in printing pitch during printing, and small variation in printing pitch of printed film rolls during storage, The object is to provide a stretched polyolefin porous film.
Another object of the present invention is to use a resin composition having a special composition with a relatively small amount of polypropylene as a polyolefin resin, and to produce a stretched porosity having the above-mentioned properties, which is produced by employing a large stretch ratio. To provide a film.
Still another object of the present invention is to provide a stretched porous film having a 5% stretch strength in the machine direction at a level not known in the prior art and having a low printing pitch while maintaining high moisture permeability and excellent texture. There is.
It is still another object of the present invention to provide a polyolefin stretched porous film that provides a printed film roll excellent in winding shape during storage.
Still another object of the present invention is to provide a printed film roll excellent in winding shape during storage.
Still other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, the above objects and advantages of the present invention are:
First, a resin composition containing 100 parts by mass of a polyolefin comprising 85 to 50% by mass of linear low density polyethylene, 10 to 35% by mass of branched low density polyethylene, and 5 to 25% by mass of polypropylene, and 80 to 200 parts by mass of an inorganic filler. A stretched porous film comprising 5% elongation strength in the machine direction of 3.5 N / 25 mm or more, moisture permeability of 2000 g / m ² · 24 h or more, and basis weight of 10 to 35 g / m ² Achieved.

Hereinafter, the present invention will be described in detail. The stretched porous film of the present invention comprises (1) 85 to 50% by mass of linear low density polyethylene, (2) 10 to 35% by mass of branched low density polyethylene, and (3) 5 to 25% by mass of polypropylene (PP). And 100 parts by mass of a polyolefin and 80 to 200 parts by mass of an inorganic filler.
(1) Linear low density polyethylene (hereinafter sometimes referred to as LLDPE), which is a polyolefin, is composed of a copolymer of ethylene and a small amount of an α-olefin, and has a linear polyethylene main chain and a carbon number of 2 to It has about 6 short chain branches. The density of LLDPE is preferably 0.910 to 0.950 g / cm ³ , more preferably 0.915 to 0.945 g / cm ³ . The melt index (MI) of LLDPE is preferably 1 to 8 g / 10 min. And particularly preferably 2.0 to 7.5 g / 10 min. It is. When the density, or more preferably, the density and the melt index are in the above ranges, the stretched porous film is excellent in flexibility, air permeability, and liquid leakage resistance.
Here, the said density is a density measured by JISK7112, and the measuring method of the density of other resin is also the same as this. The melt index is a value measured by the A method at 190 ° C. in accordance with JIS K 7210, and the melt index measurement methods for other resins are the same.
Specific examples of the linear low density polyethylene include ethylene-propylene, ethylene- (1-butene), ethylene- (1-hexene), ethylene- (4-methyl-1-pentene), and ethylene- (1- Octene) and the like.
(1) The amount of linear low density polyethylene used is required to be 85 to 50% by mass of the total amount of polyolefin in order to greatly affect the strength and stiffness of the obtained stretched porous film. 80 to 55% by mass. When the amount used exceeds the above range, the strength of the stretched porous film and mechanical strength such as stiffness are lowered, and when it is less, the stiffness of the stretched porous film increases.
(2) Branched low-density polyethylene (hereinafter sometimes referred to as LDPE) is generally called low-density polyethylene (PE-LD), and the density of LDPE having long chain branches is preferably 0.910-0. 940 g / cm ³ . LDPE can be usually synthesized by polymerizing ethylene in the presence of a radical polymerization catalyst under high pressure. Among these, those having a density of 0.915 to 0.930 g / cm ³ are preferable. The melt index is 1 to 8 g / 10 min. In particular, 2.0 to 7.0 g / 10 min. It is preferable that When the density, more preferably the melt index is within the above range, the resin composition can have the extrusion characteristics and moldability of the film and the mechanical strength required for the stretched porous film.
(2) The amount of branched low density polyethylene (LDPE) used needs to be 10 to 35% by mass of the total amount of polyolefin. Preferably, it is 13 to 35% by mass of the total amount of polyolefin. The amount used affects the uniformity of the thickness of the resulting stretched porous film. If the amount of LDPE used exceeds the above range, the frequency of pinholes in the film will increase. On the other hand, if the amount is small, the uniformity of the film thickness is deteriorated, and draw resonance is likely to occur in the film.
(3) Polypropylene constituting the polyolefin is not particularly limited, but has a density of 0.890 to 0.940 g / cm ³ and a melt index of 1 to 8 g / 10 min. It is preferable that When the density and melt index are within the above ranges, the resin composition can have the extrusion characteristics and moldability of the film, and the mechanical strength required for the stretched porous film.
Polypropylene is a homopolymer of propylene or a copolymer of propylene and a small amount of other α-olefins. Specific examples include a propylene homopolymer, a propylene-ethylene copolymer, and a propylene-ethylene-EPR (ethylene-propylene rubber) copolymer. Of these, the propylene unit content of the propylene-ethylene copolymer is preferably 60 mol% or more.
(3) The amount of polypropylene used is 5 to 25% by mass of the total amount of polyolefin. Preferably, it is 7 to 22% by mass of the total amount of polyolefin. Polypropylene is an important component for increasing the 5% tensile strength in the machine direction of the obtained stretched porous film, but when this is blended in a large amount exceeding the above upper limit, the stretched porosity obtained as described above. In the conductive film, the moisture permeability is lowered and the texture is also deteriorated. If polypropylene is blended in less than the lower limit, the 5% tensile strength cannot be increased to the value specified by the present invention.
The three types of polyolefins used in the present invention may be resins manufactured using a multisite catalyst such as a Ziegler catalyst, or a resin manufactured using a single site catalyst such as a metallocene catalyst. Also good.
In the present invention, the melt index of polyolefin comprising (1) linear low density polyethylene, (2) branched low density polyethylene, and (3) polypropylene is 1-8 g / 10 min. It is preferable that
In the present invention, known inorganic fillers can be used without limitation, for example, inorganic salts such as calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide, aluminum hydroxide, zinc oxide, magnesium oxide, Examples thereof include inorganic oxides such as silica, silicates such as mica, vermiculite and talc, and organic metal salts. Of these, calcium carbonate can be particularly preferably used because of cost performance and releasability from the polyethylene resin.
The average particle size of the inorganic filler is preferably 10 μm or less, more preferably 0.5 to 5.0 μm, and even more preferably 0.7 to 3.0 μm. When the average particle size is in the above range, it is excellent in dispersibility, it is easy to form communication holes during stretching, and it is possible to efficiently produce a stretched porous film that hardly causes film breakage during molding. It is. If the average particle size of the inorganic filler is larger than the above range, it tends to cause pinholes, and if it is smaller, it tends to cause draw resonance during film formation.
The inorganic filler is preferably one that has been surface-treated in order to improve dispersibility in the resin. As the surface treating agent, those capable of hydrophobizing the surface by coating the surface of the inorganic filler are preferable, and examples thereof include fatty acids, higher fatty acids, metal salts thereof, waxes and the like. The amount of the surface treatment agent is not particularly limited, but is preferably about 0.5 to 2.0% by mass, more preferably 1.5% by mass or less, and 1.0% by mass with respect to the inorganic filler. It is particularly preferred that
The polyolefin resin composition in the present invention includes the polyolefin and an inorganic filler, and the composition thereof is 80 to 200 parts by mass of the inorganic filler with respect to 100 parts by mass of the polyolefin, and preferably 100 parts by mass of the polyolefin. The inorganic filler is 85 to 150 parts by mass. If the mass ratio of the inorganic filler to the polyolefin is smaller than the above range, the interface between the polyolefin and the inorganic filler is peeled off, and the void generation frequency per unit area is reduced, so adjacent voids are difficult to communicate with each other. The air permeability deteriorates. When it is larger than the above range, elongation at the time of film stretching is lost, it becomes difficult to stretch, and it becomes difficult to obtain high 5% stretch strength.
It is not always necessary to add a plasticizer to the polyolefin resin composition in the present invention. The plasticizer content is preferably less than 2 parts by mass, and more preferably less than 1 part by mass. In the present invention, the plasticizer is a general term for compounds that improve the plasticity of the film and impart flexibility to the film. When the content of the plasticizer increases, the melt index of the resin composition increases and it becomes difficult to obtain a high 5% tensile strength. The type of the plasticizer is not particularly limited, and examples thereof include fatty acids, higher fatty acids, low molecular weight polyethylene, epoxidized soybean oil, polyethylene glycol, and fatty acid esters.
Moreover, you may mix | blend the additive currently used for the normal resin composition with the resin composition in this invention. Examples of such additives include antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, neutralizers, lubricants, antifogging agents, antiblocking agents, antistatic agents, slip agents, and coloring agents. . A small amount of a resin component other than that constituting the polyolefin may be blended in the resin composition as long as the effects of the present invention are not impaired. Specifically, if it is within 5 parts by mass, more preferably within 2.5 parts by mass with respect to 100 parts by mass of polyolefin, it is allowed to blend other resin components.
In the present invention, the melt index of the resin composition is 2 g / 10 min. Preferably, it is 2 g / 10 min. 5 g / 10 min. Or less, preferably 2 g / 10 min. 4 g / 10 min. The following is more preferable. By being in the above range, stable film formation can be performed. When it is larger than the above range, neck-in occurs when forming a film with a T-die, and the required product width cannot be obtained, and when it is small, the resin pressure of the extruder during film formation increases, It will have an adverse effect. Also, the smaller the melt index value, the greater the 5% stretch strength.
In the present invention, the 5% stretch strength in the machine direction of the stretched porous film is 3.5 N / 25 mm or more, preferably 3.7 N / 25 mm or more, and more preferably 4.0 N / 25 mm or more. . The larger the 5% stretch strength in the machine direction, the better the low strain stretch strength in the machine direction, and the elongation of the film can be kept small relative to the line tension applied in the machine direction during printing. Therefore, the fluctuation of the printing pitch (interval) is small, and it is possible to suppress a decrease in yield when a product such as a diaper is commercialized. In the stretched porous film of the present invention, the 5% tensile strength in the machine direction is preferably 10.0 N / 25 mm or less, more preferably 6.0 N / 25 mm or less. If it exceeds the above range, the bending resistance increases and the texture becomes insufficient. The 5% tensile strength in the machine direction can be determined according to JIS K 7127.
In the present invention, the moisture permeability of the stretched porous film is 2000 g / m ² · 24 h or more, and preferably 2100 g / m ² · 24 h or more. When the moisture permeability is in the above range, the breathability and moisture permeability are excellent. For example, when used for a back sheet of a disposable diaper, the stuffiness at the time of wearing is prevented. Although the upper limit is not particularly limited moisture permeability, mechanical properties, water resistance, and liquid leakage resistance reasons, preferably 10000g ^/ m 2 · 24h, and most preferably, 5000g ^/ m 2 · 24h It is. The moisture permeability can be determined by ASTM E96B.
In the present invention, the heat shrinkage rate (%) after treatment for 24 hours at 50 ° C. in the machine direction of the stretched porous film is preferably 3.0% or less, and more preferably 2.5% or less. The fact that the thermal shrinkage rate in the machine direction is small makes it possible to suppress the elongation of the film to be small relative to the line tension applied in the machine direction during printing, in addition to increasing the 5% elongation strength. Therefore, the smaller the heat shrinkage rate (%) in the machine direction, the smaller the printing pitch deviation can be suppressed, but practically 0.5% is the lower limit. In the stretched porous film of the present invention, the heat shrinkage rate (%) in the machine direction is expressed as a ratio of shrinkage of the film length in the machine direction before and after being left at a temperature of 50 ° C. for 24 hours. Specifically, a 15 cm × 15 cm sample is cut out from the stretched porous film, and marked lines are inserted so that the distance between marked lines is 10 cm in the machine direction. After being allowed to stand at a temperature of 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 of the present invention is calculated from the following formula (I).
Heat shrinkage in machine direction (%) =
{(10 cm—measured length cm) / 10 cm} × 100 (100) (I)
In the present invention, the basis weight of the stretched porous film is 10 to 35 g / m ² . It is preferably 11 to 32 g / m ² , and more preferably 12 to 30 g / m ² . By setting the basis weight within the above range, a stretched porous film excellent in air permeability, moisture permeability and mechanical strength can be obtained. If it is larger than this range, it will be difficult to satisfy the moisture permeability of the film, and if it is smaller, the mechanical strength of the film will be lowered.
Below, the manufacturing method of the stretched porous film of this invention is demonstrated.
The stretched porous film of the present invention is not limited by its production method, but is usually (1) 85 to 50% by mass of linear low density polyethylene and (2) 10 to 35 of branched low density polyethylene. A resin composition comprising 100% by mass of polyolefin and 100% by mass of (3) 5-25% by mass of polypropylene and 80-200 parts by mass of an inorganic filler is formed into a film, and the resulting film is machined. The film is preferably stretched 2.6 to 5.0 times in the direction and then preferably at a temperature in the range of 70 to 95 ° C., preferably at least 0 while maintaining the shrinkage in the machine direction preferably at 3 to 20%. It can be manufactured by heat setting for 2 seconds.
First, the polyolefin and the inorganic filler, and further, the additive to be blended as necessary are mixed. As a mixing method, a known method can be employed. For example, the mixing is preferably performed for about 5 minutes to 1 hour using a mixer such as a Henschel mixer, a super mixer, or a tumbler mixer.
The obtained mixture is preferably melt-kneaded and pelletized. As a kneading method, a known method can be adopted. For example, a kneading machine such as a high kneading type twin screw extruder or a tandem kneading machine is used to knead by a method such as strand cut, hot cut or underwater cut. And pelletizing. Premixing, kneading and pelletizing as described above are preferable because uniform dispersion of the resin composition can be promoted. Depending on the composition of the resin composition, it can be directly put into a kneader without mixing and pelletized.
Subsequently, the obtained pellets are formed into a film with a circular die or a T die attached to the tip of the extruder. At this time, as a cooling method when the T-die method is used, a known method such as a nip roll method, an air knife method, or an air chamber method can be employed. Depending on the blending of the resin composition, the film can be formed by directly feeding the resin composition into an extruder without mixing and kneading.
The film obtained by forming the film is stretched by a known method such as a roll stretching method or a tenter stretching method to obtain a stretched porous film. Here, in the obtained stretched porous film, in order to make the 5% stretch strength in the machine direction a high value specified by the present invention, the stretch ratio should be at least 2.6 to 5 times in the machine direction. is important. That is, the constituent resin composition is such that the amount of the polypropylene component is small and the 5% tensile strength is difficult to increase. In the present invention, however, the film made of the resin composition is stretched in this way. By carrying out at such a specific high magnification, a high value of 3.5 N / 25 mm or more can be achieved as the physical property value.
The draw ratio in the machine direction is preferably 2.8 times or more, more preferably 3.1 times or more. When the said draw ratio is too large, tear strength will become low and practicability will be lacking. The upper limit is preferably 4.5 times, more preferably 4.0 times. Further, by increasing the draw ratio, unevenness in thickness does not become a problem despite the inclusion of polypropylene, and it is not always necessary to add a dispersant.
In the present invention, the stretching may be single-stage stretching or multi-stage stretching, but is preferably single-stage stretching in order to improve the low strain elongation strength. Therefore, specifically, it is particularly preferable to perform one-stage stretching in the machine direction.
The stretching temperature is not particularly limited as long as it is at room temperature or higher and lower than the softening point of the resin composition. If the stretching temperature is too lower than the above range, unevenness of stretching tends to occur, and the thickness tends to be non-uniform. If the temperature is too high, the resin melts and air permeability and moisture permeability deteriorate. The stretching temperature can be appropriately adjusted depending on the desired physical properties and in combination with the stretching ratio.
Subsequently, the stretched porous film of the present invention heat-fixes the stretched porous film after stretching as a method of suppressing thermal shrinkage in the stretching direction. The heat setting is a heat treatment performed in an environment in which a dimensional change is not caused in a state where a stretched film is maintained in a tensioned state due to stretching. The heat fixation can suppress elastic recovery, shrinkage due to heat, squeezing and the like during storage.
As a heat setting method, when a roll stretching method is adopted, a method of heating the stretched film with a heated roll (annealing roll) can be mentioned. Moreover, when the tenter stretching method is employed, a method of heating the film in the vicinity of the tenter outlet can be mentioned.
The heat setting temperature is 70 to 95 ° C, and preferably 80 to 95 ° C. When the heat setting temperature is too lower than the above range, the heat shrinkage of the film increases, and when the temperature is too high, blocking occurs.
The heat setting time is 0.2 seconds or more, preferably 0.5 seconds or more, and more preferably 1 second or more. The time is a time during which the film is held at the above temperature. For example, in the case where the film is heated by an annealing roll, it means the time during which the film is in contact with the annealing roll. The number of annealing rolls is not particularly limited, but the heat setting time in the case of two or more rolls is the sum of the time during which the film is in contact with each roll. Similarly, in the case of the tenter stretching method, the time is heated at the tenter outlet and maintained at the above temperature, and when divided and heated in multiple times, it is the sum of the times of heating. If the heat setting time is not 0.2 seconds or more, heat setting is insufficient and heat shrinkage is increased. Further, the fixing time is preferably 20 seconds or shorter, and more preferably 15 seconds or shorter. If the heat fixing time is too long, it cannot be generally described because it depends on the combination with the heat fixing temperature, but damage due to heat increases, and air permeability and moisture permeability may be reduced.
In the present invention, the shrinkage in the machine direction at the time of heat setting is 3 to 20%, preferably 5 to 15%. If the roll stretching method is adopted, the shrinkage rate is determined by the speed difference between the anneal roll and the subsequent roll. If the tenter stretching method is adopted, the clip width at both ends after heating is narrowed. It is decided by. If the shrinkage rate is too small, the heat-shrinkage of the resulting stretched porous film becomes large. If the shrinkage rate is too large, the film is slackened during production, and stable production cannot be performed.
The stretched porous film produced as described above has a 5% elongation strength in the machine direction in addition to the physical properties conventionally required for sanitary material applications such as paper diapers, and is particularly suitable for printing. Since the pitch does not shift and a clear pattern or the like can be obtained, it is preferably used as a back sheet of a paper diaper to be printed. The stretched porous film of the present invention is usually wound up as a roll and provided as a roll for printing. The stretched porous film on which printing has been performed is again wound up as a roll and supplied for final use.
For example, a roll subjected to printing does not change its winding shape even during long-term storage for more than one month, and the printing pitch does not fluctuate later during storage. Can be used with good yield. In addition, the stretched porous film of the present invention is suitably used for moisture permeable waterproof sheets that require weather resistance and light resistance, such as building material use, agricultural use, and waste treatment use, by laminating with a breathable reinforcing material. it can.
The breathable reinforcing material is not particularly limited, and for example, a nonwoven fabric, a woven fabric, a split fabric, a mesh, a net, a filter, paper, a fabric, or the like can be used. In addition, the material of the breathable reinforcing material is not particularly limited, and polyolefin-based, polyester-based, and nylon-based materials can be used. However, when laminating with the stretched porous film of the present invention, a heat fusion method is used. In view of the fact that it can be easily laminated, it is preferable that the surface layer contains a polyethylene resin having a melting point peak of 130 ° C. or lower.

Examples and Comparative Examples are shown below, but the present invention is not limited to these Examples.
In addition, the physical-property value described in the Example and the comparative example was measured by the method shown below.
1) Melt index Measured by method A at 190 ° C. according to JIS K 7210.
2) It was cut off with a basis weight of 10 cm × 10 cm and measured by measuring the mass with a balance.
3) Ten samples (10 cm × 10 cm) were taken from the moisture-permeable stretched porous film, measured according to ASTM E96B at a temperature of 40 ° C., a relative humidity of 60%, and a pure water method, and the average value was calculated. And asked. The measurement time was 24 hours.
4) A sample having a width of 25 mm and a length (machine direction) of 150 mm was cut from a 5% stretch strength stretched porous film. According to JIS K 7127, the distance between chucks is 50 mm, and the pulling speed is 200 mm / min. Then, the strength (stress) in the machine direction was measured when the sample (distance between chucks) was extended by 5% (2.5 mm).
5) Heat shrinkage in machine direction (%)
A 15 cm × 15 cm sample is cut out from the stretched porous film, and marked lines are inserted so that the distance between marked lines is 10 cm in the machine direction. After being allowed to stand at a temperature of 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 of the present invention is calculated from the following mathematical formula (I).
Heat shrinkage in machine direction (%) =
{(10 cm-measurement length cm) / 10 cm} × 100 (I)
Example 1
Linear low density polyethylene A [manufactured by Dow Chemical Co., Ltd., trade name: Dourex 2035G, density: 0.919 g / cm ³ , melt index: 6.0 g / 10 min. ] 34% by mass, B [(Dow Chemical Co., Ltd., product name: Dow Rex 2036P, density: 0.935 g / cm ³ , melt index: 2.5 g / 10 min.] 42% by mass, branched low density Polyethylene C [made by Mitsui DuPont Polychemical Co., Ltd., trade name: Mirason 16P, density: 0.917 g / cm ³ , melt index: 3.7 g / 10 min.] 18% by mass, and polypropylene E [Co., Ltd. Prime polymer, product name: F-704NP, density: 0.900 g / cm ³ , MI: 2.8 g / 10 min.] In addition to 100 parts by mass of polyolefin, the average particle size is 2.0 μm Calcium carbonate G (product name: FL-520, manufactured by Imeris Minerals Co., Ltd.) 102 parts by mass, additive H [titanium oxide (Huntsman Co., Ltd., product name: TR28) 50% by mass, hindered phenol-based heat stabilizer (Ciba Japan Co., Ltd., product name: IRGANOX 3114) 20% by mass, phosphorus-based heat stabilizer (Ciba Japan Co., Ltd.) A resin composition containing 2 parts by mass of a product, product name: IRGAFOS168) 30% by mass mixture] was granulated, and film forming was performed.
For granulation, a φ30 mm twin screw extruder with a vent was used to extrude into a strand at a cylinder temperature of 180 ° C., cooled in a water bath, cut and dried to about 5 mm to obtain pellets. Next, the pellet was formed into a film using a φ400 mmT die film forming machine. At this time, lip clearance = 1.5 mm, die temperature = 230 ° C., air gap = 105 mm, take-up speed = 10 m / min. The cast roll temperature was 20 ° C. Furthermore, it was uniaxially stretched only in the machine direction with a roll stretching machine set at 60 ° C. (stretching ratio: 3.2 times), and then in-line annealed with a heat set roll set at 90 ° C. (heat setting time 4 seconds). The shrinkage in the machine direction during the heat setting was 8%.
The obtained stretched porous film was evaluated for basis weight, moisture permeability, 5% stretch strength, and heat shrinkage rate. The results are shown in Table 2. The obtained stretched porous film had good moisture permeability of 2000 g / m ² · 24 h or more and good texture. Further, the 5% tensile strength maintained a high value.
Examples 2-6, 10-13
A film was molded and evaluated in the same manner as in Example 1 except that the composition (Table 1) was changed. The results are shown in Table 2. All of the obtained stretched porous films had good moisture permeability and good texture of 2000 g / m ² · 24 h or more. Further, the 5% stretch strength was kept high and the heat shrinkage rate in the machine direction was kept low.
Example 7
A film was molded and evaluated in the same manner as in Example 2 except that the stretching ratio was 2.8 times as the stretching condition. The results are shown in Table 2. The obtained stretched porous film had good moisture permeability of 2000 g / m ² · 24 h or more and good texture. Further, the 5% stretch strength was kept high and the heat shrinkage rate in the machine direction was kept low.
Example 8
A film was molded and evaluated in the same manner as in Example 2 except that the stretching ratio was 2.6 times as the stretching condition. The results are shown in Table 2. The obtained stretched porous film had good moisture permeability of 2000 g / m ² · 24 h or more and good texture. Further, the 5% stretch strength was kept high and the heat shrinkage rate in the machine direction was kept low.
Example 9
A film was molded and evaluated in the same manner as in Example 2 except that the stretching ratio was 3.8 times as the stretching condition. The results are shown in Table 2. The obtained stretched porous film had good moisture permeability of 2000 g / m ² · 24 h or more and good texture. Further, the 5% stretch strength was kept high and the heat shrinkage rate in the machine direction was kept low.
Comparative Examples 1-4
A film was molded and evaluated in the same manner as in Example 1 except that the composition was changed to the composition shown in Table 1. The results are shown in Table 2.
Comparative Example 5
A film was molded and evaluated in the same manner as in Example 1 except that the stretching ratio was 1.7 times as the stretching condition. The results are shown in Table 2.
Comparative Example 6
A film was molded and evaluated in the same manner as in Example 2 except that the stretching ratio was 2.0 times as the stretching conditions. The results are shown in Table 2.
From the results of Comparative Examples 1 to 6, the moisture permeability was 2000 g / m ² · 24 h or less, the 5% tensile strength was a low value, and there were many pinholes, and physical properties could not be evaluated.

Explanation of symbols in Table 1 (Polyolefin resin, raw material)
A: Linear low density polyethylene [manufactured by Dow Chemical Co., Ltd., trade name: Dow Rex 2035G, density: 0.919 g / cm ³ , melt index: 6.0 g / 10 min. ]
B: Linear low density polyethylene [manufactured by Dow Chemical Co., Ltd., trade name: Dow Rex 2036P, density: 0.935 g / cm ³ , melt index: 2.5 g / 10 min. ]
C: Branched low density polyethylene [Mitsui DuPont Polychemical Co., Ltd., trade name: Mirason 16P, density: 0.917 g / cm ³ , melt index: 3.7 g / 10 min. ]
D: Branched low density polyethylene [manufactured by Asahi Kasei Chemicals Corporation, trade name: L1850K, density: 0.918 g / cm ³ , melt index: 6.7 g / 10 min. ]
E: Polypropylene [manufactured by Prime Polymer Co., Ltd., trade name: F-704NP, density: 0.900 g / cm ³ , MI: 2.8 g / 10 min. ]
F: polypropylene [manufactured by Nippon Polypro Co., Ltd., trade name: Wintech WFX4M, density: 0.900 g / cm ³ , MI: 2.8 g / 10 min. ]
G: Calcium carbonate [Product name: FL-520, manufactured by Imerizu Minerals Co., Ltd.]
H: Additive [Titanium oxide (manufactured by Huntsman Co., Ltd., trade name: TR28) 50% by mass, hindered phenol thermal stabilizer (manufactured by Ciba Japan Co., Ltd., trade name: IRGANOX3114) 20% by mass, phosphorus system Thermal Stabilizer (Ciba Japan Co., Ltd., trade name: IRGAFOS168) 30% by mass mixture]
(Extension conditions)
* 1: Uniaxial stretching (stretching ratio: 3.2 times) was performed only in the machine direction with a roll stretching machine set at 60 ° C., and then in-line annealing was performed with a heat set roll set at 90 ° C.
* 2: Uniaxial stretching was performed only in the machine direction with a roll stretching machine set at 60 ° C. (stretching ratio: 2.8 times), and then in-line annealing was performed with a heat set roll set at 90 ° C.
* 3: Uniaxial stretching (stretching ratio 2.6 times) was performed only in the machine direction with a roll stretching machine set at 60 ° C., and then in-line annealing was performed with a heat set roll set at 90 ° C.
* 4: Uniaxial stretching (stretching ratio 3.8 times) was performed only in the machine direction with a roll stretching machine set at 60 ° C., and then in-line annealing was performed with a heat set roll set at 90 ° C.
* 5: Uniaxial stretching (stretching ratio 1.7 times) was performed only in the machine direction with a roll stretching machine set at 60 ° C., and then in-line annealing was performed with a heat set roll set at 90 ° C.
* 6: Uniaxial stretching was performed only in the machine direction with a roll stretching machine set at 60 ° C. (stretching ratio: 2.0 times), and then in-line annealing was performed with a heat set roll set at 90 ° C.

Effect of the Invention The stretched porous film of the present invention is highly excellent in 5% stretch strength in the machine direction. Therefore, when printing is performed on the stretched porous film, there is no shift in the print pitch, and the printed pattern is It becomes clear and the yield at the time of commercialization is improved. Furthermore, the texture and moisture permeability are good, and it can be usefully used for various applications of the porous film to which the printing is applied, including for disposable diapers.

Claims

A resin composition comprising 100 parts by mass of polyolefin comprising 85 to 50% by mass of linear low density polyethylene, 10 to 35% by mass of branched low density polyethylene, and 5 to 25% by mass of polypropylene, and 80 to 200 parts by mass of an inorganic filler,
A stretched porous film having a 5% tensile strength in the machine direction of 3.5 N / 25 mm or more, a moisture permeability of 2000 g / m 2 · 24 h or more, and a basis weight of 10 to 35 g / m 2 .
The melt index of the polyolefin is 1-8 g / 10 min. The stretched porous film according to claim 1, wherein
The stretched porous film according to claim 1 or 2, wherein the inorganic filler is calcium carbonate.
The melt index of the resin composition is 2 g / 10 min. The stretched porous film according to any one of claims 1 to 3, which is as described above.
A resin composition containing 100 parts by mass of a polyolefin comprising 85 to 50% by mass of linear low density polyethylene, 10 to 35% by mass of branched low density polyethylene, and 5 to 25% by mass of polypropylene, and 80 to 200 parts by mass of an inorganic filler The film obtained was stretched 2.6 to 5 times in the machine direction, and then maintained at a shrinkage rate in the machine direction of 3 to 20%, at least in the temperature range of 70 to 95 ° C. The method for producing a stretched porous film according to claim 1, wherein the film is heat-fixed for 2 seconds.