JP2004331944A - Porous film and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low cost film which is opaque white before wetting with water (in a dry state) and is turned to transparent by wetting with water (in a wet state), and to provide its production method. <P>SOLUTION: The porous film is obtained by at least uniaxially stretching a film which is composed of a polyolefin resin composition containing 0.1-10 pts.wt. hydrophilic agent based on 100 pts.wt. composition consisting of (A) 25-80 wt.% polyolefin resin and (B) 75-20 wt.% filler. Wherein the hydrophilic agent is preferably a fatty acid ester compound. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a porous film and a method for producing the same. More specifically, the present invention relates to a porous film which shows an opaque white color before being wet with water (when dry) and becomes transparent after being wet with water (when wet), and a method for producing the same.

  2. Description of the Related Art In recent years, porous films that are effective in preventing urine leakage and diaper rash are often used as backsheets of disposable diapers. The porous film has an infinite number of micropores formed therein, and light is irregularly reflected at an interface inside the porous film, so that the porous film has an opaque white color. For this reason, when used for a backsheet of a disposable diaper, the inside of the diaper is difficult to see from the outside. In particular, there has been a problem that it is difficult to distinguish a light color such as urine, and it is difficult for the wearer to visually recognize whether or not the urine has been excreted. Therefore, it was necessary to actually remove the diaper and check it by hand, which caused inconvenience.

  Therefore, a material in which white fine particles that become transparent when water is absorbed are fixed to a hydrophilic base material such as paper together with a resin binder has been disclosed as an indicator means for informing urine excretion (Patent Document 1, Patent Document 2, etc.). reference). If printing is performed on the back surface of this base material, the white fine particles on the front surface and the base material become transparent when wet with water, and the printing on the back surface can be seen through. This utilizes a physical change in that the refractive index of white fine particles is close to that of water, and when the fine particles become wet with water, diffuse reflection of light on the surface of the fine particles is reduced and the fine particles become transparent.

  However, paper that is often used as a base material has a hard touch feeling, and is not preferable for applications such as disposable diapers that directly touch the skin. In addition, due to the high manufacturing cost, it is not suitable for disposable uses such as disposable diapers. Further, for the same reason as above, there is also a problem that the display area cannot be increased and visibility is poor.

No. 3-58416 JP-A-9-299401

  Therefore, an object of the present invention is to provide a low-cost film which is opaque white before being wet with water (when dry) and becomes transparent when wet with water (when wet), and a method for producing the same.

  The present inventors have found that, in a composition comprising a specific amount of a polyolefin resin and a filler, a porous film obtained from a polyolefin resin composition containing a specific amount of a hydrophilic agent can achieve the above object, The present invention has been reached.

  That is, the porous film of the present invention comprises 0.1 to 10 parts by weight of a hydrophilic agent based on 100 parts by weight of a composition comprising (A) 25 to 80% by weight of a polyolefin resin and (B) 75 to 20% by weight of a filler. It is obtained by stretching a film made of a polyolefin resin composition containing at least one part in at least a uniaxial direction.

  In the present invention, a porous film in which the hydrophilic agent is a surfactant is a preferred embodiment.

  Further, a porous film in which the hydrophilic agent is a fatty acid ester compound is a preferred embodiment of the present invention.

  Further, a porous film in which the fatty acid ester compound is an ester of polyethylene glycol and a fatty acid is a preferred embodiment of the present invention.

  Further, a porous film in which the polyethylene glycol has an average molecular weight of 150 to 750 is a preferred embodiment of the present invention.

  Further, a porous film in which the fatty acid has 12 to 16 carbon atoms is a preferred embodiment of the present invention.

  According to the present invention, there is provided a water detection film comprising the porous film having a total light transmittance of less than 50% when dry and a total light transmittance of 50% or more when wet.

  Further, according to the present invention, the polyolefin resin (A) is blended in a ratio of 25 to 80% by weight and the filler (B) is blended in a ratio of 75 to 20% by weight. There is provided a method for producing a porous film, comprising forming a film using a mixture to which 1 to 10 parts by weight is added, and then stretching the film in at least one direction.

  The porous film of the present invention has much higher flexibility than conventional films, is more inexpensive, has lower total light transmittance when dry, and has higher total light transmittance when wet. Therefore, it has a function of detecting moisture such as urine equivalent to the conventional one, and can be suitably used as a water detection film.

Hereinafter, the present invention will be described in detail.
The porous film of the present invention is obtained by melt-forming a resin composition containing a specific amount of a polyolefin resin, a specific amount of a filler, and a specific amount of a hydrophilic agent to form a film, and stretching the film in at least one direction. Can be manufactured.

((A) polyolefin resin)
The polyolefin resin (A) used in the present invention is mainly composed of, for example, homopolymers of olefins such as ethylene, propylene and butene and copolymers thereof, and specifically, low-density polyethylene, Linear low-density polyethylene (ethylene-α-olefin copolymer), medium-density polyethylene, polyethylene resin such as high-density polyethylene, polypropylene, polypropylene resin such as propylene-ethylene copolymer, poly4-methylpentene, polybutene, Examples include an ethylene-vinyl acetate copolymer, an ethylene-butene copolymer, and a mixture thereof.

  The polyolefin resin (A) may be a resin produced using a Ziegler catalyst or a resin produced using a single-site catalyst such as a metallocene catalyst. Of these, polyethylene-based resins are preferable, and linear low-density polyethylene, which is an ethylene-α-olefin copolymer, and low-density polyethylene are particularly preferable.

  Further, in consideration of the moldability and stretchability of the film, the melt index of the polyolefin resin (A) is preferably in the range of 0.5 to 10 g / 10 min.

((B) filler)
As the filler (B), an inorganic filler or an organic filler can be used. Examples of the inorganic filler include calcium carbonate, barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide, aluminum hydroxide, zinc oxide, magnesium oxide, titanium oxide, silica, talc, glass beads, and the like. Of these, barium sulfate and calcium carbonate are preferred. In consideration of low cost and the like, calcium carbonate is more preferable. As the organic filler, resin beads such as polystyrene, polymethyl methacrylate, and phenol resin are preferable.

  The composition ratio between the polyolefin resin (A) and the filler (B) affects the moldability and stretchability of the film, the total light transmittance of the obtained film when dry and when wet, and the like. If the amount of the filler is small, the number of fine pores obtained by peeling off the interface between the polyolefin resin and the filler decreases, and the light transmittance in a dry state increases, which is not preferable. On the other hand, when the amount of the filler is large, it is not preferable because sufficient stretching cannot be performed due to poor molding or poor stretchability when forming a film. From such a viewpoint, the composition ratio of the polyolefin resin (A) and the filler (B) is preferably 25 to 80% by weight of the polyolefin resin and 75 to 20% by weight of the filler. More preferably, the polyolefin resin is 30 to 70% by weight and the filler is 70 to 30% by weight, and further preferably, the polyolefin resin is 30 to 65% by weight and the filler is 70 to 45% by weight.

  The average particle size of the filler is preferably 20 μm or less, more preferably 10 μm or less, and most preferably 0.5 to 5 μm.

  The filler may have been subjected to a surface treatment in order to improve the dispersibility with the polyolefin resin. As the surface treatment agent, those capable of making the surface hydrophobic by coating the surface of the filler are preferable, and examples thereof include higher fatty acids such as stearic acid and lauric acid, and metal salts thereof.

(Hydrophilic agent)
The porous film of the present invention is characterized by comprising a polyolefin resin composition in which a specific amount of a hydrophilic agent is contained in a composition comprising a polyolefin resin (A) and a filler (B).

  The amount of the hydrophilic agent affects the total light transmittance when wet. If the amount of the hydrophilic agent is small, water is less likely to penetrate into the pores when wet with water, and the total light transmittance when wet is undesirably low. On the other hand, when the addition amount of the hydrophilic agent is large, the light transmittance in a wet state is increased, but it is not preferable because the bleed out of the hydrophilic agent occurs during storage or the extrusion performance deteriorates. In consideration of such points, the amount of the hydrophilic agent is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the composition containing the polyolefin resin (A) and the filler (B). More preferably, it is 0.5 to 5 parts by weight.

  The hydrophilic agent is preferably a surfactant. Examples of the surfactant include an anionic surfactant, a cationic surfactant, a nonionic surfactant, and an amphoteric surfactant. Activators are preferred.

  The hydrophilic agent is preferably at least one compound selected from fatty acid ester compounds. Fatty acid esters include, for example, esters of polyhydric alcohols or polypolyhydric alcohols with fatty acids. Examples of polyhydric alcohols and polyhydric alcohols include glycerin, polyglycerin, sorbitan, ethylene glycol, polyethylene glycol, propylene glycol, and polypropylene glycol. Examples of the fatty acid include coconut fatty acid, tallow fatty acid, caprylic acid, lauric acid, myrislic acid, palmitic acid, stearic acid, behenic acid, and oleic acid. Among these, polyethylene glycol fatty acid esters are most preferable in consideration of bleed out of the hydrophilic agent during storage, migration of the hydrophilic agent during use, and moldability of the film.

  The average molecular weight of polyethylene glycol constituting the polyethylene glycol fatty acid ester affects bleed-out of the hydrophilic agent during storage, migration of the hydrophilic agent during use, and film formability. If the average molecular weight of the polyethylene glycol is too small, the hydrophilic agent tends to bleed out during storage and is easily denatured with time, which is not preferable. In addition, the hydrophilic agent easily migrates during use, and is particularly not preferable because the hydrophilic agent is washed away by water and diffuses around. Further, it is not preferable because smoke is easily generated at the time of melt extrusion molding. If the average molecular weight of the polyethylene glycol is too large, the extrusion amount at the time of melt extrusion tends to decrease, and the film productivity decreases, which is not preferable. Therefore, the average molecular weight of polyethylene glycol constituting the hydrophilic agent is preferably from 150 to 750. More preferably, it is 300 to 500. The average molecular weight can be measured by a known mass spectrometer.

  The carbon number of the fatty acid constituting the polyethylene glycol fatty acid ester affects bleed-out of the hydrophilic agent during storage, migration of the hydrophilic agent during use, and film formability. If the carbon number of the fatty acid is too small, the hydrophilic agent tends to bleed out during storage, and is undesirably denatured with time. In addition, the hydrophilic agent easily migrates during use, and particularly, the hydrophilic agent is easily washed away by moisture, and the hydrophilic agent is undesirably diffused around. Further, the extrusion performance at the time of melt extrusion molding is liable to decrease, which is not preferable. If the carbon number of the fatty acid is too large, the hydrophilicity tends to decrease, and the total light transmittance in the wet state of the present invention cannot be increased. Therefore, the fatty acid preferably has 12 to 16 carbon atoms.

  Specific examples of the above fatty acid ester include "TB-202" and "TB1259" (trade names, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) and "Likemar O-71-DE" (trade name, manufactured by Riken Vitamin Co., Ltd.).

  In the porous film of the present invention, other additives such as a stretching aid, a stabilizer, an antioxidant, a coloring agent, an ultraviolet absorber, and a dispersant may be added as long as the object of the present invention is not hindered. Good.

(Method for producing porous film)
Next, a method for producing the porous film of the present invention will be exemplified.
First, the polyolefin resin (A), the filler (B), the hydrophilic agent, and if necessary, other additives are mixed using a Henschel mixer, a super mixer, a tumbler type mixer, or the like, and the mixture is uniaxially or biaxially mixed. The mixture is supplied to a screw extruder, kneaded and pelletized. An extruder equipped with a T-die or the like, or an inflation molding machine equipped with a circular die, at a temperature in the range of the melting point of the polyolefin resin (A) or higher, preferably higher than the melting point + 20 ° C. and lower than the decomposition temperature. Melting and film formation using a known molding machine such as If necessary, it is also possible to form a film directly with a molding machine without pelletizing.

  The formed film is heated at a temperature in the range of room temperature to the softening point of the polyolefin resin (A) (a value measured by a method specified in JIS K6760) by a known method such as a roll method, a tenter method, and a gear method. A porous film is produced by stretching in at least one direction and causing interfacial separation between the polyolefin resin and the filler.

  Stretching may be performed in one step or may be performed in multiple steps. Since the stretching ratio is related to the film tear during stretching and the total light transmittance of the obtained film when dry, it is not preferable that the ratio is too high or too low. From such a viewpoint, the stretching ratio is preferably at least 1.2 to 6 times in one axis direction, and more preferably 1.4 to 5 times.

  In the case of biaxial stretching, a method of first performing uniaxial stretching in the machine direction or a direction perpendicular to the machine direction, and then performing second axis stretching in a direction perpendicular to the machine direction, and a machine direction, and There is a method in which biaxial stretching is performed simultaneously in directions perpendicular to each other. Either method can be applied. After the stretching, a heat setting treatment may be performed, if necessary, in order to stabilize the form of the obtained opening. Examples of the heat setting treatment include a method in which a heat treatment is performed for 0.1 to 100 seconds at a temperature within a range from the softening point of the polyolefin resin (A) to the melting point.

(Porous film)
The porous film of the present invention may be subjected to a printing process as needed. In particular, when used as an indicator for notifying urine excretion, by performing a printing process on the back surface, it is possible to obtain an effect that a printed pattern cannot be seen when dry, but can be seen through when wet. Printing is not particularly limited, such as flexographic printing or gravure printing, and the ink used is not particularly limited, such as oiliness or aqueousness.

  Although there is no particular limitation on the printed pattern, water tends to hardly permeate from the solid printed portion into the holes inside the film, and the solid printed portion tends to take a long time to be transparent when wet. Conversely, the dot printing portion is relatively easy for water to permeate into the holes inside the film, and becomes transparent in a short time. It is preferable to use solid printing and dot printing depending on the application. In addition, it is also possible to perform double-sided printing according to the application so as to provide a function difference between the front surface and the back surface.

  The porous film of the present invention can be formed into a laminated film by laminating other members as needed, or can be formed into a multilayer film by a multilayer extrusion process. The function may be imparted by lamination with a member such as a film, a nonwoven fabric, a woven fabric, a tissue, or pulp, or by multilayering with a porous film using the same or different materials.

  If the porous film of the present invention is extremely thick, it is not preferable because the total light transmittance when wet is low and the flexibility and the cost are poor. Also, when the film is extremely thin, it is not preferable because the film is broken at the time of forming the film. In consideration of these, the normal thickness is about 5 to 100 μm. It is preferably from 7 to 70 μm, and more preferably from 8 to 50 μm.

  When the porous film of the present invention produced as described above is used as a film for water detection, it is preferable that the film exhibit an opaque white color when dry and become transparent when wet. Therefore, if the total light transmittance in the dry state is too high, the difference in transmittance between the dry state and the wet state is reduced, and the difference due to being wet with water becomes difficult to perceive. Absent. On the other hand, if the total light transmittance in a wet state is too low, a pattern printed on the back surface, for example, becomes difficult to see through in a wet state, which is not preferable as a water detection film. Therefore, the total light transmittance of the porous film is preferably less than 50% when dry and 50% or more when wet. More preferably, the dry time is less than 45% and the wet time is 55% or more. The difference between the total light transmittance between the dry state and the wet state is preferably 15% or more, more preferably 20% or more.

  The stiffness of the porous film of the present invention measured by a 45 ° cantilever method according to JIS L1096 is preferably 80 mm or less, thereby having an appropriate flexibility. Therefore, it is suitably used as an indicator for notifying urinary excretion for disposable diapers, for example, applications requiring flexibility. The lower limit of the rigidity is not particularly specified, but is usually about 10 mm by the cantilever method.

  The present invention will be more specifically described by the following examples. The present invention is not limited to these examples.

The melt index (hereinafter referred to as MI), the total light transmittance when dry, the total light transmittance when wet, the film thickness, and the rigidity shown in the examples are values measured by the following methods.
(1) Melt index (g / 10min)
The measurement was performed under the conditions of a temperature of 190 ° C. and a load of 2160 g by the method specified in ASTM D1238-57T (E).

(2) Total light transmittance when dry (%)
It was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: NDH-300A) based on the method specified in JIS K7105. Two arbitrary points were measured for one sample of a porous film having a size of 50 mm in the machine direction (hereinafter, referred to as MD) and a direction of 100 mm in a direction perpendicular to the machine direction (hereinafter, referred to as TD). Was averaged and calculated.

(3) Total light transmittance when wet (%)
A sample was collected in the same manner as in (2) above, the film was immersed in pure water for 1 minute, and the water droplets on the surface were wiped off. Each sample was measured with a haze meter in the same manner as in (2), and the average value was calculated. I asked.

(4) Film thickness Ten samples of 10 cm in MD and 10 cm in TD were collected from the porous film, and a thickness measuring device (UPAIGHT DIAL GUAGE NO.25, manufactured by PEACOCK Co., Ltd.) was measured at any five points of each sample. The film thickness was determined by averaging the measured values at a total of 50 points.

(5) Rigidity (mm)
The measurement was performed according to the method (45 ° cantilever method) specified in JIS L1096. After winding a 200 mm film on the TD and a 300 mm film on the MD on a TD with a width of 25 mm on the TD, the sample was pulled out, and the obtained flat roll (25 mm in width and 300 mm in length) weighed 1 kg. The roller was pressed by one reciprocation with a roller.

(6) Transfer of hydrophilic agent A 200 mm square porous film without a hydrophilic agent (the porous film not using the hydrophilic agent of Example 1), a 200 mm square porous film according to the present invention, and two 100 mm square filter papers were used. In this order, 5 ml of ink-colored water is dropped on the filter paper. Next, a 10 kg weight (100 mm square) is placed on the filter paper, and after 5 minutes, whether or not the ink has leaked out to the bottom surface (the back surface of the porous film without the hydrophilic agent) is visually observed within an area of 100 mm square, and the following criteria are used. evaluated.
：: no exudation,
Δ: Exuded in a range of half or less of the area,
×: Exudation was observed over half the area.

(7) Formability The state when the film was formed under the conditions of the examples was evaluated according to the following criteria.
：: Can be molded without generating smoke, a decrease in extrusion rate, and film breakage.
△ Smoke: Smoke is seen from the extruder, but actual production is possible.
× Smoke: Smoke from the extruder is intense; trial production is possible or actual production is not possible.
△ Decrease in extrusion rate: The extrusion rate from the extruder decreases, but molding is possible,
× Decrease in extrusion rate: The extrusion rate from the extruder drops extremely, making molding impossible.
X Film tear: The film is broken during stretching.

[Example 1]
38 parts by weight of linear low-density polyethylene (manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name: Ultzex 2021L, density: 0.920 g / cm ³ , MI: 2.1 g / 10 min) [LLDPE1] 38 parts by weight and low-density polyethylene ( Made by Mitsui Petrochemical Industry Co., Ltd., trade name: Mirason 27, density: 0.918 g / cm ³ , MI: 2.0 g / 10 min) [LDPE] 2 parts by weight, calcium carbonate (Dowa Calfine Co., Ltd.) (Trade name: SST-40, average particle diameter: 1.0 μm) [CaCO ₃ ] 60 parts by weight, hydrophilic agent (Matsumoto Yushi Co., Ltd., trade name: TB-202) [A] 3 parts by weight are added. After mixing with a tumbler mixer, the mixture was uniformly kneaded at 200 ° C. using a tandem type extruder and processed into pellets. This pellet was melt-formed at 240 ° C. using an extruder equipped with a T-die, and then stretched in the machine direction at a stretch ratio of 4.0 times between a preheating roll and a stretch roll heated to 70 ° C. The film was uniaxially stretched to obtain a porous film having a thickness of 25 μm. The total light transmittance in a dry state, the total light transmittance in a wet state, the film thickness, and the rigidity of the obtained porous film were measured by the methods described above. Table 1 shows the obtained results.

[Examples 2 to 17, Comparative Examples 1 to 4]
A porous film was produced in the same manner as in Example 1, except that the polyolefin resin, the filler, the hydrophilic agent, the compounding ratio (parts by weight) thereof, and the stretching ratio were changed as shown in Tables 1 to 3. Each property of the obtained porous film was evaluated in the same manner as in Example 1, and the results are shown in Tables 1, 2 and 3.

The raw materials used are as follows.
LLDPE2: linear low-density polyethylene, manufactured by Mitsui Petrochemical Industry Co., Ltd., trade name Evolu SP3040, density 0.930 g / cm ³ , MI 4.0 g / 10 min,
PP: polypropylene, manufactured by Grand Polymer Co., Ltd., trade name: F103WH, density: 0.910 g / cm ³ , MI (measured at 230 ° C.): 2.4 g / 10 min,
BaSO ₄ : barium sulfate, manufactured by Barite Industry Co., Ltd., trade name HD, average particle size 1 μm,
PS beads: crosslinked polystyrene, manufactured by Mitsui Chemicals, Inc., 1 μm grade, average particle size 1 μm,
C: polyethylene glycol (average molecular weight 200) fatty acid (carbon number 12) ester,
D: polyethylene glycol (average molecular weight 600) fatty acid (C12) ester,
E: polyethylene glycol (average molecular weight 400) fatty acid (carbon number 14) ester,
F: Polyethylene glycol (average molecular weight 400) fatty acid (carbon number 16) ester.

  According to the present invention, a water detection film that can be suitably used in the fields of sanitary materials, medical materials, clothing materials, building materials, packaging materials, and the like can be provided. This film can be suitably applied to an indicator for notifying urine excretion in an absorbent article such as a disposable diaper.

Claims (8)

(A) 25 to 80% by weight of a polyolefin resin,
(B) 75-20% by weight of filler
A porous film obtained by stretching a film of a polyolefin resin composition containing 0.1 to 10 parts by weight of a hydrophilic agent with respect to 100 parts by weight of a composition of at least one axis.   The porous film according to claim 1, wherein the hydrophilic agent is a surfactant.   The porous film according to claim 1, wherein the hydrophilic agent is a fatty acid ester compound.   The porous film according to claim 3, wherein the fatty acid ester compound is an ester of polyethylene glycol and a fatty acid.   The porous film according to claim 4, wherein the polyethylene glycol has an average molecular weight of 150 to 750.   The porous film according to any one of claims 3 to 5, wherein the fatty acid has 12 to 16 carbon atoms.   The water detection film comprising the porous film according to any one of claims 1 to 6, wherein the total light transmittance when dry is less than 50%, and the total light transmittance when wet is 50% or more.   The polyolefin resin (A) is blended in a ratio of 25 to 80% by weight and the filler (B) is blended in a ratio of 75 to 20% by weight. A method for producing a porous film, comprising forming a film using the added mixture, and then stretching the film at least uniaxially.