KR870001966B1 - Porous film and its manufacturing method - Google Patents

Abstract

Porous film is prepd. for use as waterproof sheet of a diaper. A resin composition is melted and then is molded in the form of film and then the produced film is extended. 100 wt. parts of polyolefin resin and 50-500 wt. parts of a filler are mixed to give the resin composition. The polyolefin resin is polyethylene resin and the filler is barium sulfate. The average diameter of barium sulfate particle is 0.1-7 μm.

Description

Porous film and its manufacturing method

The present invention relates to a porous film and a method for producing the same. In more detail, the present invention relates to a method for producing a porous film comprising mixing a polyolefin resin with barium sulfate as a filler, melting the resulting resin composition into a film, and stretching the film in at least one axial direction. It is about.

A number of methods are known for forming a porous film by molding a resin composition containing polyolefin resin and various immiscible fillers into a film and then stretching the resulting film. For example, Japanese Patent Laid-Open Nos. 47334 / '82 and 203520 / '82 disclose that a resin composition obtained by mixing polyethylene resin with filler and liquid rubber or hydroxylated poly-saturated hydrocarbon is melted and melted. A method for producing a porous film comprising forming a resin composition into a sheet or film and then stretching the molded sheet or film is described. Further, Japanese Patent Laid-Open Publication No. 1552 / '83 discloses melting a resin composition obtained by mixing a linear low density polyethylene resin with a filler and a liquid or waxy hydrocarbon polymer, and molding the melted resin composition into sheets or films. The manufacturing method of the porous film which consists of extending | stretching a molded sheet | seat or a film is known. However, the films produced by these processes have the disadvantage that they exhibit surface tackiness due to the mentioned components contained in addition to the olefin resin and the filler and can also be used only at relatively large thicknesses due to their low mechanical strength.

In addition, Japanese Patent Laid-Open No. 149303 / '83 discloses that such a porous film can be used as a leakproof sheet for disposable diapers. The porous film for use as a leakage preventing sheet of a disposable diaper is mixed with 100 parts by weight of polyolefin resin and 28 to 200 parts by weight of a filler and 10 to 70 parts by weight of a liquid or waxy hydrocarbon polymer, and the resulting resin composition is molded into a film. Then, the molded film is produced by stretching the film at a magnification of 1, 2 or more in at least one axial direction. However, such a method for producing a porous film has a disadvantage that it cannot provide completely homogeneous pores because the elongation is lowered depending on the type of filler, and the resulting film tends to make annoying noise. Moreover, the simultaneous use of hydrocarbon polymers makes the fraud process unsatisfactory, since hydrocarbon polymers bloom on the film surface and cause a sticky touch.

Such a porous film can also be used as a leak prevention sheet in a sanitary napkin. Conventionally, a paper sheet imparting liquid-impermeability with a synthetic resin such as polyethylene has been used for this purpose. However, sanitary napkins made from such paper sheets have the disadvantage of causing an unpleasant sensation during prolonged use due to the lack of permeability to water vapor.

It is therefore an object of the present invention to provide an improved method for producing a porous film.

Another object of the present invention is to provide a method for producing a porous film having a sufficiently high porosity while maintaining excellent water resistance and exhibiting high-moisture permeability and gas permeability.

Still another object of the present invention is to provide a method for producing a porous film having no surface tack and excellent flexibility and hardly decreasing strength.

Another object of the present invention is to provide an improved leakproof sheet for use in disposable diapers.

Another object of the present invention is to provide an improved leakproof sheet for use in a sanitary napkin.

Further objects of the present invention will be apparent from the following description.

According to the present invention, a resin composition mainly composed of 100 parts by weight of polyolefin resin and 50 to 500 parts by weight of barium sulfate is melted, the molten resin composition is molded into a film, and then the molded film is made from 1.5 to 7 in at least one axial direction. It provides a method for producing a porous film consisting of stretching at a magnification of.

In the present specification, the expression "a resin composition mainly composed of 100 parts by weight of polyolefin resin and 50 to 500 parts by weight of barium sulfate" means that the resin composition is selected from (1) normal stabilizers, antioxidants, colorants, ultraviolet absorbers and lubricants. (2) other inorganic fillers (e.g. calcium carbonate, etc.) or conventional inorganic materials, at least one additive and / or (2) barium sulfate in addition to barium sulfate usage (e.g., 20% or less based on the amount of barium sulfate used) And a resin composition which may further contain an organic modifier, but the liquid rubber and hydroxylation described in the above-mentioned Japanese Patent Publication Nos. 47334 / '82, 203520 / '82, 15538 / '83 and 149303 / '83. The poly-saturated hydrocarbon or hydrocarbon polymer should not be added to obtain a porous film without surface tack.

According to the present invention, a porous film which has no surface tack, has excellent properties and has not been obtained in the prior art, can be produced without using the above-mentioned additives which have been used in the prior art. This limits the type, amount and average particle diameter of the filler: low density polyethylene resins having a particular melt index and density, more preferably linear low density polyethylene resins having a particular melt index and density (especially ethylene and hexene and / or octene) Linear low-density polyethylene resins containing a copolymer of; And it can achieve by drawing a film in a specific ratio.

As a polyolefin resin which can be used for this invention, Homopolymers, such as a polypropylene, a low density polyethylene, a high density polyethylene, a linear low density polyethylene, a polybutylene, etc .; Copolymers such as ethylene-propylene copolymers, ethylene butylene copolymers and ethylene-vinylacetate copolymers; and mixtures thereof.

Among these resins, low density polyethylene resins having a melt index of 0.5 to 7 (0.5 to 8.5 for a linear low density polyethylene resin) and a density of 0.915 to 0.935 are preferred.

Although it is preferable to use a single resin, a blend of polyethylene resins having different densities can be used. The melt index is more preferably in the range of 1 to 5. If the melt index is less than 0.5 or greater than 7 (greater than 7 for linear low density polyethylene resins), the resin may be significantly reduced in secondary moldability into the film, making it impossible to obtain a film of small uniform thickness.

On the other hand, when the density is less than 0.915 or greater than 0.935, the resin has reduced stretchability and increased rigidity, so that a soft film cannot be obtained.

Particularly preferred polyolefin resins are linear low density polyethylene resins. The linear low density polyethylene resin is a copolymer of ethylene and one or more α-olefins, and is different from the low density polyethylene resin produced by the conventional high pressure method.

Linear low density polyethylene resins are produced by low pressure methods, and useful α-olefins include butene, hexene, octene and the like. The difference between the low density polyethylene resin produced by the high pressure method and the low density polyethylene resin produced by the low pressure method is that in the chemical structure, the former is a branched polymer while the latter is a straight chain polymer. Of these linear low density polyethylene resins, copolymers of ethylene and hexene and / or octene are particularly preferred.

In carrying out the present invention, it is preferable to use barium sulfate having an average particle diameter of 0.1 to 7 µm, more preferably 0.5 to 5 µm. When the average particle diameter is less than 0.1 mu m, well formed pores cannot be obtained. On the other hand, when the average particle diameter is larger than 7 µm, the film is poor in stretchability, and thus, as in the case where the average particle diameter is too small, well formed pores cannot be obtained.

Barium sulfate may be used in an amount of 50 to 100 parts by weight, preferably 100 to 400 parts by weight, per 100 parts by weight of the polyolefin resin. If the amount of barium sulfate used is less than 50 parts by weight, a sufficiently high porosity cannot be obtained; while if the amount used is larger than 500 parts by weight, the resulting film cannot be completely drawn due to the increased rigidity, thus resulting in a reduced porosity. Indicates.

Barium sulfate is preferably surface treated with fatty acids or metal salts thereof, silicones, silanes or resinous acids, since such treatment is effective in enhancing dispersibility in the resin and preparing well formed pores.

As long as the effects of the present invention are not impaired, other inorganic fillers such as calcium carbonate or the like, as well as ordinary inorganic and organic modifiers, may be used in addition to barium sulfate. However, these additives should be used in amounts of up to 20% based on the amount of barium sulfate used.

Hereinafter, the manufacturing method of the porous film will be described in detail.

If necessary, at least one additive selected from stabilizers, antioxidants, colorants, ultraviolet absorbers and lubricants is added to the polyolefin resin and barium sulfate. These components are mixed by Henschel mixer, Super mixer or tumbling mixer.

The resulting mixture is then kneaded and pelletized using conventional single-screw or twin-screw extruders.

Subsequently, these pellets (either alone or in combination with polyolefin resin pellets) are subjected to inflation extruder or T-die extruder at or above the melting point of the polyolefin resin (preferably above 20 ° C.) but at its decomposition temperature. It melt | dissolves at the following temperature, and forms into a film. In some cases, the mixture can be directly formed into a film by an extruder without pelletizing. Subsequently, the film is stretched at a magnification of 1.5 to 7 in at least one axial direction according to a conventional method such as roll stretching or tendering. Such stretching may be carried out in several steps and / or in two or more directions. However, in the case of biaxial stretching, it is preferable to stretch the film simultaneously in two directions. In order to enhance the morphological stability of the pores, the stretched film may be annealed by heating.

Porosity is determined by the amount of barium sulfate used and the draw ratio. When the draw ratio is less than 1.5, a sufficiently high porosity cannot be obtained, whereas when the draw ratio is larger than 7, it is impossible to continuously manufacture the porous film due to the occurrence of frequent breakage during the stretching process.

Porous films made by the process of the present invention are characterized by high porosity, excellent flexibility and low strength reduction.

Furthermore, since the affinity between the polyolefin resin and barium sulfate is good and the elongation is good, the workability is good and the pore distribution is uniform, so that the porous film can be continuously produced. In particular, when a linear low density polyethylene resin is used as the base resin, the resulting film hardly decreases in strength. Therefore, a porous film thinner (eg, about 10 μm thick) than that produced by a conventional method can be produced.

In addition, since the resin composition of the present invention does not include any of the liquid rubber, hydroxylated poly-saturated hydrocarbon and hydrocarbon polymer used in the conventional method, the resulting porous film has no surface tack.

Therefore, the porous film of the present invention can be used for coating and sanitary purposes because it has a sufficiently high porosity, and therefore has good water and gas permeability and excellent water resistance. In addition, the porous film of the present invention can be used as a filtration medium because the pore distribution is uniform.

The invention is further illustrated by the following examples. However, these examples are provided for the purpose of illustration and should not be considered as limiting the scope of the invention.

In the examples described below, the melt index (MI) is measured according to ASTM D_1238 and the density is measured according to ASTM D-1505.

In the examples described below, the properties of the film are evaluated according to the following method:

(1) strength and elongation

Using a Tensilon tensile tester, a piece of film 25 mm wide and 100 mm long is tested at an elongation rate of 20 mm / min. The strength and elongation at break are measured in the machine direction (MD) and in the transverse direction (TD).

(2) moisture permeability

Moisture permeability is tested according to ASTM E-96 (Method D).

(3) flexibility

Flexibility is assessed by texture and is rated according to the following weights:

A = very flexible and smooth

B = flexible and smooth

C = hard and rough

[Example 1-19 and Comparative Example 1-9]

Each filler shown in Table 1 was added to the corresponding base resin in the amounts shown in Table 1 and then mixed with a Henschel mixer. Thereafter, the resultant mixture was thoroughly mixed using a twin-screw mixer, and then pellets were made. These pellets were then melted at 80 ° C. higher than the melting point of the base resin to form a film using a T-die extruder.

The molded film was stretched uniaxially or biaxially (Example 3) at the magnification shown in Table 1 to obtain a porous film having the thickness shown in Table 1. However, in Comparative Example 1, the film was not stretched, and in Comparative Examples 2 and 9, the film could not be stretched. In Comparative Examples 5 and 8, the film could only be stretched at a magnification of up to two. In Comparative Examples 3 and 7, it was impossible to take samples due to frequent breakage during the stretching process.

The strength, elongation, moisture permeability and flexibility of the thus obtained porous film were evaluated in accordance with the procedure described above, and the results are shown in Table 1.

TABLE 1

Table 1 (continued)

Table 1 (continued)

Table 1 (continued)

Table 1 (continued)

Table 1 (continued)

Table 1 (continued)

Note: 1) LDPE = Low Density Polyethylene

L-LDPE = Linear Low Density Polyethylene

PP = polypropylene

EPC = ethylene-propylene copolymer

2) parts by weight of filler per 100 parts by weight of basic resin

3), 5) and 7) the maximum value at which stretching can continue

4) and 6) Samples could not be taken due to frequent breaks during stretching.

Table 1 (continued)

Table 1 (continued)

The porous film produced by the method of the present invention has a high porosity, excellent flexibility, and almost no decrease in strength, making it very suitable for use as a leakproof sheet for disposable diapers. While such anti-fogging sheets are generally used as the outermost layer of disposable diapers, materials that do not impair their water permeability (e.g., conventional perforated films or three-dimensional embossed sheets) may be used as It is superimposed on the outside to give a cloth-like appearance.

In such disposable diapers, conventional liquid absorbents including fluff (e.g., wool covered with sorbent paper, etc.) composed of pulp fibers, polymer absorbents having high water-absorbency, and the like can be used.

As the liquid-permeable sheet in direct contact with the skin, nonwoven fibers composed of polyester fibers, nylon fibers, polyolefin fibers and the like can be preferably used.

In addition, it is possible to use a pressure-sensitive tape for fixing the diaper and the elastic member (for example, rubber member) provided along the edge to prevent leakage.

Disposable diapers are made by placing a liquid absorbent on the leakproof sheet described above and laminating the liquid-permeable sheet thereon.

In a disposable diaper using the porous film of the present invention as a leakproof sheet, the outermost leakproof sheet has many pores. Since these pores pass water vapor while keeping the water in the droplet state, the skin of the infant is kept wet and dry, and there is little tendency to cause diaper rash. In addition, they have the advantage of being flexible enough not to produce an unpleasant noise and hardly torn due to their high strength.

The examples described below illustrate the use of the porous film of the present invention as a leakproof sheet for disposable diapers.

[Examples 20-22 and Comparative Examples 10-14]

Barium sulfate with an average particle diameter of 1.5 μm or each of the other fillers listed in Table 2, in the amounts shown in Table 2, low density polyethylene (LDPE) (Examples 20 and 21) of melt index 3 or linear low density polyethylene (L) of melt index 5 -LDPE) (Example 22 and Comparative Examples 10-14) were added to 100 parts by weight and then mixed with a Henschel mixer. The resulting mixture was then thoroughly mixed and then pelletized using a twin-screw mixer. Subsequently, these pellets were melted at 130 ° C and molded into a film using a T-die extruder. The molded film was uniaxially stretched at the magnification shown in Table 2 between the preheat roll and the draw roll heated to 50 ° C. to obtain a porous film having a thickness of 50 μm. The characteristics of the porous film thus recorded were evaluated, and the results are shown in Table 2. Disposable diapers were prepared by filling each porous film obtained in Examples 20-22 and 10, 13 and 14 with fluff pulp and nonwoven polyester fibers and equipped with pressure sensitive tape and a rubber member.

Disposable diapers of Examples 20-22 are superior in strength, water permeability and flexibility to those of 10, 13 and 14, with only a slight noise when used and a nice touch.

When these disposable diapers were actually used and tested on infants, the diapers of Examples 20-22 did not develop rashes on the skin of infants wearing them. In contrast, the disposable diapers of Comparative Examples 10, 13 and 14 developed extensive rashes or slight rashes (Comparative Example 13).

Example 23

Using a biaxial stretching machine heated to 2 heated to 70 ° C., the non-stretched film formed in Example 20 was simultaneously stretched at a 2 × 2 magnification in the machine direction and the transverse direction to obtain a porous film having a thickness of 50 μm. The characteristics of the porous film thus obtained were evaluated, and the results are shown in Table 2. Disposable diapers using the porous film as leakproof sheets showed as good performance as those of Example 20.

Example 24

The film was made from the same resin composition as used in Example 22. The film was uniaxially stretched at a magnification of 4 using a roll heated to 50 ° C. to obtain a porous film having a thickness of 15 μm. The characteristics of the porous film thus obtained were evaluated and the results are shown in Table 2.

On the outer side of the porous film, an LDPE film having a thickness of 70 m having a hole (20 / cm ² ) having a diameter of 1 mm over the entire surface thereof was superposed. Disposable diapers using the composite as a leakproof sheet performed as well as those of Examples 20-23.

TABLE 2

^* ) An attempt was made to stretch the film at an 8x magnification, but samples could not be taken due to frequent breakage during the stretching process.

^** ) The film could not be stretched at a magnification of 2 or more.

Table 2 (continued)

Comparative Example 15

120 parts by weight of calcium carbonate with an average particle diameter of 1.2 μm and 20 parts by weight of hydrosylated poly-saturated hydrocarbons (liquid polybutadiene GI-2000; manufactured by Nippon Soda Cup closure) linear low density polyethylene (L-LDPE) with a melt index (MI) 5 After addition to 100 parts by weight, it was mixed with a Henschel mixer. Thereafter, the mixture was thoroughly mixed using a pair-scooter mixer and pelleted.

인플레이션 압출기를 사용하여 상기 펠렛을 필름으로 성형했다. 성형된 필름을 80℃에서 3.0의 배율로 로울 연신하여 두께 50㎛의 다공성 필름을 수득했다. 수득된 다공성 필름은 부위에 따라 수분 투과성이 다르며 표면 접착성이 약간 있었다.40 mm

The pellets were molded into films using an inflation extruder. The molded film was roll drawn at a magnification of 3.0 at 80 ° C. to obtain a porous film having a thickness of 50 μm. The obtained porous film had different water permeability and slightly surface adhesion depending on the site.

Disposable diapers using the porous film as a leakproof sheet produced some rash on the skin of the infant.

[Comparative Example 16]

Same as in Comparative Example 15 except that rubber-like EPR (Toughmer P0480: manufactured by Mitsui Waste Chemical) or liquid polybutadiene (Nisso PBG; manufactured by Nippon Soda Cuppungney) was used as the hydroxylated poly-saturated hydrocarbon. The procedure was repeated. In this way, a film having a thickness of 5 µm was obtained. The porous film obtained was surface tacky and the moisture permeability changed depending on the site. Disposable diapers using each of these porous films as leakproof sheets produced some rash on the skin of the infant.

The porous film obtained by the method of the present invention has a high porosity and excellent flexibility, and despite its small thickness, hardly decreases in strength, making it very suitable for use as a leakage preventing sheet in sanitary napkins. Conventional sanitary napkins are manufactured with a structure in which a liquid absorbent such as fluff pulp, cotton or absorbent resin is partially covered with a paper film imparted with liquid-permeability by a synthetic resin treatment such as polyethylene, and the molded structure is covered with nonwoven fibers. do. As a leakproof sheet, in a sanitary napkin using the porous film of the present invention, the leakproof sheet has many pores capable of passing water vapor. Therefore, the sanitary napkins dry the user's skin and feel good even if used for a long time.

The examples described below illustrate the use of the porous film of the present invention as a leakproof sheet in a sanitary napkin.

Example 25-27

Barium sulfate having an average particle diameter of 0.8 mu m was added to 100 parts by weight of linear low density polyethylene (L-LDPE) having a melt index of 2.1 in the amounts shown in Table 3, followed by mixing in a Henschel mixer. The resulting mixture was then mixed thoroughly by a twin-screw mixer, then pellets were made. These pellets were then melted at 230 ° C. with a T-die extruder to form a film. The molded film was uniaxially stretched at the magnification shown in Table 3 between the preheat roll and the stretch roll heated to 80 ° C. to obtain a 20 μm thick porous film. The properties of the porous film thus obtained were evaluated, and the results are shown in Table 3. After the fluff pulp charge was coated with each of the porous films obtained in Examples 25-27, the sanitary napkin was prepared by covering the resulting structure with nonwoven fibers and heat sealing the overlapped portions. When compared with a commercial sanitary napkin having a liquid-permeable film of polyethylene-coated paper and the sanitary napkin of this example for a long time, the sanitary napkin of the present invention did not produce an unpleasant or smooth touch.

TABLE 3

Claims (14)

A method of producing a porous film comprising melting a resin composition composed of a polyolefin resin and a filler incompatible therewith, molding the molten resin composition into a film, and then stretching the molded film in at least one axial direction. The filler is barium sulfate, the barium sulfate is used in an amount of 50 to 500 parts by weight per 100 parts by weight of the polyolefin resin, and the film is stretched at a magnification of 1.5 to 7. The method according to claim 1, wherein the average particle diameter of barium sulfate is 0.1 to 7 µm. The method according to claim 2, wherein the average particle diameter of barium sulfate is 0.5 to 5 mu m. The method according to claim 1, wherein the barium sulfate is used in an amount of 100 to 400 parts by weight per 100 parts by weight of the polyolefin resin. The method of claim 1, wherein the barium sulfate is surface treated with a fatty acid or a metal salt thereof, silicon, silane or resin acid. The method of claim 1 wherein the polyolefin resin is polyethylene. The method of claim 6 wherein the polyethylene resin is a low density polyethylene resin having a melt index of 0.5 to 7 and a density of 0.915 to 0.935. 8. The method of claim 7, wherein the low density polyethylene resin is a single index. 8. The method of claim 7, wherein the low density polyethylene resin is a blend of polyethylene resins having different densities. 8. The method of claim 7, wherein the melt index is 1-5. The method of claim 6 wherein the polyethylene resin is a linear low density polyethylene resin. The method of claim 11, wherein the linear low density polyethylene resin has a melt index of 0.5 to 8.5 and a density of 0.915 to 0.935. 12. The process of claim 11 wherein the linear low density polyethylene resin is ethylene and a copolymer of hexene, octene or hexene and octene. In the method for producing a porous film consisting mainly of melting a resin composition composed of a polyolefin resin and a filler non-mixable thereto, molding the molten resin composition into a film, and then stretching the molded film in at least one axial direction. The water-soluble, water-permeable, prepared by the method characterized in that the mixed filler is barium sulfate, using barium sulfate in an amount of 50 to 500 parts by weight per 100 parts by weight of polyolefin resin, and stretching the film at a magnification of 1.5 to 7. And a porous film having gas permeability.