KR19990004212A - Manufacturing method of breathable film - Google Patents

Abstract

The present invention is a composition comprising 50 to 200 parts by weight of an inorganic filler coated with stearic acid and 0.1 to 30 parts by weight of polyethylene wax based on 100 parts by weight of polyethylene resin composed of low density polyethylene resin, linear low density polyethylene resin and medium density polyethylene resin. It is related with the manufacturing method of the breathable film characterized by extending | stretching the disc sheet melt-molded by 1.5 times-36 times area draw ratio. The breathable film prepared by the manufacturing method of the present invention has a soft touch, excellent film processability, excellent dispersibility of various inorganic fillers and additives, has an appropriate strength and moisture permeability, and is suitable for use in diaper back sheets, waterproof clothing, and the like.

Description

Manufacturing method of breathable film

The present invention relates to a manufacturing method of a breathable film having excellent softness and excellent strength, proper moisture permeability, and excellent biaxial stretching processability.

Breathable film is used for various purposes such as disposable diapers, waterproof clothing, packaging materials, sanitary materials. In particular, a disposable diaper, which has been used in large quantities recently, is widely used as a backsheet for a breathable film having proper moisture permeability in order to prevent a so-called diaperlash phenomenon, such as a skin bite caused by obstruction of skin respiration when worn for a long time.

Conventionally breathable film is added to the polyolefin resin mainly polyethylene-based polyolefin resin as a specific ratio as disclosed in Japanese Patent Laid-Open Publication Nos. 58-149303, 60-185803, 59-69906 and 4,472,328, etc. Thereafter, a number of methods for producing a breathable film have been proposed in which a sheet obtained by forming a melt film by a known method is stretched uniaxially or biaxially so that fine pores are continuously formed at the interface between the resin and the inorganic filler.

However, because the breathable film is used in infant diapers sensitive to the touch, a soft touch is required, and because of the fine porosity, the mechanical properties, in particular, the tensile strength in the width direction when uniaxial stretching are used compared to the conventional non-breathable film. However, there is a big problem that the strength such as tear strength in the stretching direction is very poor, and the improvement has been urgently requested.

In particular, the disposable diaper structurally pulls the diaper's ear in the width direction of the breathable film to adhere the tape to the tape, and thus the tensile strength and tear strength in the width direction need to be improved. Consumers who use diapers have experienced many inconveniences, such as the physical properties of the fragrances are so low that they tear when using the ear portion of the diaper. However, the breathable biaxially stretched article has good mechanical properties in the width direction and can eliminate the discomfort of the ear portion when used as a diaper cover. Therefore, biaxial stretching processing of the breathable film has been attempted for the mechanical properties of the breathable film.

There are two main methods for biaxial stretching of breathable film, one of which is to form a double blown film and to perform biaxial stretching at about the same time, and the other is a sequential stretching method. It is a biaxial stretching method in which longitudinal stretching is performed, and in the second direction, width stretching is performed in a tenter. There are some difficulties in biaxial stretching of the breathable film, the most difficult of which is to make the thickness of the processed film constant and to suppress the occurrence of rupture during film processing.

In particular, in the case of sequential stretching using a roll and a tenter, a number of finely formed on the film at the time of primary roll stretching, when longitudinal stretching by the roll speed difference first and then entering the tenter in the width direction, Small pores serve as a weak point that causes rupture, resulting in rupture of the entire film produced by the tenter stretching machine, which makes it difficult to produce a normal film.

In order to solve this problem, a number of methods for adding a low melting polymer, a plasticizer, a surfactant, etc. as a third component, in addition to the polyethylene resin and the inorganic filler have been proposed. For example, European Patent Publication No. 66672 describes processing aids containing liquid or waxy hydrocarbon polymers, US Pat. No. 4,432,28 contains liquid polybutadiene or liquid polybutadiene polymers, and Japanese Patent Application Laid-Open No. 57-47334 Polybutadiene or polybutene is disclosed in Japanese Patent Laid-Open No. 58-15538, polyhydroxy saturated hydrocarbon, Japanese Patent Laid-Open No. 61-144331, polyester or epoxy plasticizer, and Japanese Patent Laid-Open No. 62-144. In 129321, silicone oils are disclosed in Japanese Patent Application Laid-Open No. 61-235439, No. 62-18435, No. 62-27438, No. 62-280233, No. 62-280234, No. 62-280235, No. 62- 288640, So 63-22844, Pyeong 1-56744, Pyeong 1-96229, Pyeong 1-249840, Pyeong 5-5253, etc., for example, esters such as dipentaerythritol ester are added as third components. Excellent strength and soft touch Eggplant was intended to obtain a breathable film.

However, the third component adopted in the prior art is very expensive, so the cost is greatly increased, there is a problem that the breakage of the breathable film and the thickness is not constant, it is urgently needed to improve it.

The present inventors have intensively studied to improve the above problems, and using the novel polyethylene-based resin composition, it is possible to prevent the film rupture phenomenon during the stretching process by the roll and tenter, the process instability, such as thickness instability The present invention has been developed a method of manufacturing a breathable film that can be suitably used for diaper back sheets and the like, while having a soft touch and excellent strength while eliminating problems.

An object of the present invention is to provide a novel polyethylene-based breathable film manufacturing method having a soft touch and excellent strength and an appropriate moisture permeability.

In order to achieve the above object, the present invention stretches the breathable film by stretching 50 to 200 parts by weight of the inorganic filler and 0.1 to 30 parts by weight of the polyethylene wax with respect to 100 parts by weight of the resin mixture mixed with three different polyethylene resins in an appropriate ratio. It is characterized by manufacturing.

More specifically, the present invention is a 100 weight polyethylene resin composed of a low density polyethylene resin of 0.916 to 0.922 g / cc, a linear low density polyethylene resin of 0.923 to 0.930 g / cc and a medium density polyethylene resin of 0.931 to 0.940 g / cc The present invention relates to a method for producing a breathable film by stretching an original sheet obtained by melt-molding a composition comprising 50 to 200 parts by weight of an inorganic filler coated with stearic acid and 0.1 to 30 parts by weight of polyethylene wax.

Hereinafter, the present invention will be described in more detail.

In the present invention, the polyethylene resin is used by mixing three or more kinds of ethylene homopolymers or copolymers such as low density polyethylene, linear low density polyethylene, and medium density polyethylene, and the copolymers include copolymers with propylene, butene, hexene, octene, and the like. Can be.

The melt index of the low density polyethylene, linear low density polyethylene, and the medium density polyethylene for extrusion coating suitable for the present invention is suitably in the range of 0.02 to 20 g / 10 minutes (measured at 190 ° C and 2.16 Kg or less according to ASTM D 1238-70). . When the melt index is less than 0.02 g / 10 minutes, abnormal flow occurs when the original sheet is produced by extrusion melting, and it is difficult to obtain a uniform film, and when it exceeds 20 g / 10 minutes, the uniform stretchability is deteriorated.

In addition, the polyethylene resin of the present invention is a mixture of low density polyethylene having a density of 0.916 to 0.922 g / cc, linear low density polyethylene having a density of 0.923 to 0.930 g / cc, and medium density polyethylene having a density of 0.931 to 0.940 g / cc in an equal ratio. It is preferable to use.

When the low density polyethylene is used alone, the film is inferior in strength, biaxially ruptured, and when the linear low density polyethylene is used alone, problems such as uneven thickness of the breathable film and low moisture permeability occur. In addition, the use of medium-density polyethylene alone improves the strength and moisture permeability, but the film thickness is nonuniform and the film ruptures during biaxial stretching.

In addition, even if only two kinds of the resin is used, the object of the present invention can not be achieved. In other words, when a mixture of low density polyethylene and linear low density polyethylene is used, the processability of the film is improved, but the strength and moisture permeability are decreased. When the mixture of low density polyethylene and medium density polyethylene is used, the processability and strength of the film are increased, but the film ruptures during biaxial stretching. When a mixture of linear low density polyethylene and medium density polyethylene is used, it is possible to prevent the rupture of the film during biaxial stretching and increase the strength of the film, but the thickness of the film is uneven and the neck-in phenomenon during the processing of the film This occurs and there is a problem that the productivity of the film is lowered.

Therefore, in order to achieve the object of the present invention, must be used by mixing the three or more kinds of polyethylene resins.

Inorganic fillers suitable for the present invention include calcium carbonate, silica, barium equivalents, magnesium sulfate, calcium sulfate, talc, kaolin, aluminum hydroxide, magnesium hydroxide, zinc oxide, alumina, titanium oxide, mica, zeolite, diatomaceous earth, magnesium carbonate, cray or Mixtures of these are used. Forms of the inorganic fillers include plate, peak, spherical and the like, but spherical is most preferred, and the average particle diameter is in the range of 0.1 to 5 탆, preferably 0.5 to 3 탆. If the average particle diameter is less than 0.1 µm, the inorganic filler is difficult to disperse in the resin, so that the mechanical properties deteriorate. If the average particle diameter is more than 5 µm, the surface appearance of the stretched breathable film is poor.

In the present invention, the inorganic filler is coated with stearic acid. Inorganic fillers coated with stearic acid synergize with polyethylene waxes to increase dispersibility in polyethylene resins and significantly reduce breakage of the resulting film during biaxial stretching. The inorganic filler is preferably used 50 to 200 parts by weight of the inorganic filler coated on 100 parts by weight of polyethylene resin. If the amount is less than 50 parts by weight, the interface between the polyethylene resin and the inorganic filler is peeled off, and thus the hole that is expressed does not penetrate continuously, resulting in poor breathability. If it exceeds 200 parts by weight, the physical properties such as elongation after stretching of the film are exceeded. There is a risk of deterioration.

In the present invention, an inorganic filler coated with stearic acid may be used by a known method, but the method developed by the present inventors, that is, a method of dispersing molten stearic acid in a state in which a finely ground inorganic filler is suspended with air at a high pressure. It is more preferable to use the inorganic filler prepared by the above. This coating method is more efficient than the conventional method in which stearic acid and inorganic filler particles are passed through a heated drum. For example, the coating method of the present invention can coat about 95% calcium carbonate with about 0.8 wt% stearic acid, which can coat 90-95% calcium carbonate with about 2.0 wt% stearic acid. It is more efficient than the conventional method. In addition, since there is almost no residual stearic acid as compared with the conventional method in which a large amount of stearic acid that is not completely coated on the inorganic filler remains, the side effect of processing with residual stearic acid, that is, die-build up (extrusion die exit) Accumulation of foreign matter in the vicinity) and reduction of melt pressure in the extruder cylinder can be significantly reduced.

In the present invention, as the polyethylene wax, an ethylene homopolymer or copolymer having a weight average molecular weight of about 200 to 5,000 and a weight average molecular weight / number average molecular weight of 1.0 to 5.0 is used.

If the weight average molecular weight of the polyethylene wax is less than about 200, the dispersibility to the inorganic filler is excellent and good for the soft touch, but the strength is very poor, and there is a possibility of disadvantages such as increased roll contamination and thickness instability during extrusion processing. If it is more than 5,000, the dispersibility is reduced and the soft touch is degraded.

In addition, when the weight average molecular weight / number average molecular weight, which is the molecular weight distribution, is 5.0 or more, there is a problem in that gas generation due to thermal decomposition during processing increases.

In the present invention, the polyethylene wax is preferably added in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of polyethylene resin, and more preferably 0.5 to 25 parts by weight. If it is less than 0.1 part by weight, the softness tends to be remarkably inferior, and if it is more than 30 parts by weight, the amount of wax may be excessive, resulting in poor breathability.

In the present invention, it is also possible to add ordinary additives such as lubricants, antioxidants, antistatic agents, processing aids and the like to the resin composition used in the production of the breathable film.

According to the present invention, due to the strong adhesiveness and dispersibility of the polyethylene wax as well as the soft touch due to the polyethylene wax, the polyethylene wax serves as an additive such as a dispersant, which is conventionally used, and also becomes a polymer. As a result, processing problems such as stretching roll contamination due to elution of additives having low molecular weight, thickness instability due to abnormal flow during extrusion processing, and excellent softness and excellent breathability with proper moisture permeability Films can be produced.

Hereinafter, the manufacturing method of the polyethylene-based breathable film of this invention is demonstrated in detail.

Polyethylene resins, inorganic fillers, and usual additives and polyethylene waxes are adjusted in an appropriate amount and mixed in a conventional blender or mixer. As the mixer, a drum dumbler type mixer, a ribbon blender, a Henschel mixer, a super mixer, or the like may be used. A high speed stirring mixer such as a Henschel mixer is preferable.

Next, the mixture is kneaded, which is suitably carried out by a conventionally known apparatus such as a conventional single screw extruder, a twin screw extruder, a mixing roll, a balbar mixer, a twin screw kneader, and the like. The kneaded resin composition is then pelletized. The resin composition pellets are put into a hopper and the film is molded according to a conventional film forming apparatus and molding method by extrusion processing. In-flation molding using a round die, and a die-die extrusion molding using a tee die are appropriately employed. May be carried out.

Next, the sheet formed by the extrusion method is stretched in the traveling direction (MD) in the range of 1.2 times to 6.0 times, preferably 1.5 times to 5.0 times, at a temperature between the glass transition point and the melting point or less. In this case, when the temperature is lower than the glass transition point, the film cannot be stretched because the film breaks before the elongation exceeds the yield point, and when the temperature exceeds the melting point, satisfactory aeration amount during stretching in the driving direction due to the flow of the molecular chain is reached. It is impossible to get In addition, when the draw ratio is less than 1.2 times, sufficient aeration amount is not obtained, and when the draw ratio exceeds 6 times, cutting phenomenon occurs frequently during stretching and a film cannot be stably obtained. Subsequently, the film calculated in the running direction is stretched in the width direction (TD) under the conditions and the draw ratio of the above temperature range to obtain a biaxially stretched breathable film.

Moreover, it is also possible to carry out only uniaxial stretching, without performing biaxial stretching as mentioned above. That is, the manufacturing method of the breathable film by this invention can be manufactured by either uniaxial or biaxial stretching, and it is preferable to extend | stretch so that the total area draw ratio may be 1.5 to 36 times. If the area stretching ratio is less than 1.5 times, sufficient air permeability cannot be obtained. If the area stretching ratio is more than 36 times, air permeability is obtained, but the strength is significantly worse. In order to improve the dimensional stability, the film after extending | stretching may heat-fix.

Physical properties of the polyethylene-based breathable film prepared according to the present invention, the type and physical properties of the polyethylene-based resin, the type and particle diameter of the inorganic filler, the type and physical properties of the polyethylene wax, the blending ratio, and the stretching temperature, stretching ratio, stretching method, etc. It can be freely adjusted according to the stretching conditions.

Hereinafter, the present invention will be described in more detail with reference to the following examples. The following examples are only specific examples of the present invention and do not limit or limit the protection scope of the present invention.

(Example)

Tensile strength, tear strength, moisture permeability, softness (soft feel), workability (neck-in and thickness uniformity, etc.) of the breathable films prepared according to the following Examples and Comparative Examples were measured as follows.

[The tensile strength]

In accordance with JIS P 8113, the strength (kg / cm 2) at the time of fracture of the sample was measured in the running direction (MD) and in the width direction (TD) perpendicular to the running direction (sample size: 100 mm length × 25 mm width, and tensile speed). 500mm / min, measuring temperature: 23 ± 1 ℃).

[Tear strength]

The tear strength (g) was measured according to JIS K6772 (measured temperature: 23 ± 1 ° C., tensile speed: 300 mm / min).

[Moisture permeability]

As a method of evaluating breathability, moisture permeability (g / m ² 24hr) was measured according to ASTM E 96-63 (temperature: 37.8 ° C, humidity 90% RH)

[Flexibility (soft)]

It touched by hand and evaluated the soft touch degree ((◎: very flexible and good texture, (circle): softness, (triangle | delta): slightly hard, x: hard and bad texture)).

[Dispersibility]

The dispersion state of the inorganic filler and various additives of the stretched breathable film was visually observed (◎: very good, ○: good, △: normal, ×: poor).

[Processability]

Neck Inn at T-Die

The ratio of the width (when sheet extrusion speed is 25 m / min) is reduced as the sheet extruded from the tee-die having a die width of 2000 mm touches the cooling roll during the stretching of the breathable film by the roll and tenter.

When the sheet extrusion speed is 25 m / min, the sheet extruded from the 2000 mm wide die is reduced by 300 mm when reaching the cold roll, and 300 mm / 2000 mm = 15% when the sheet is 1700 mm wide. The higher the neck-in ratio, the lower the productivity and processability.

Thickness uniformity of extruded sheet

Thickness uniformity with time change of the sheet | seat extruded from the tee-die of die width 2000mm at the time of breathable film extending | stretching by a roll and a tenter ((circle): very good, (circle): good, (triangle | delta): normal, x: bad).

Process film rupture suppression at the time of tenter biaxial stretching

In the air permeable film stretching process by roll and tenter, after extending | stretching roll in the longitudinal direction of the sheet | seat extruded from the tee die | die of 2000 mm of die widths, the burst suppression property of the processed film according to the tenter extension of the width direction (◎: Very good (24 0 to 3 bursts during time processing, ○: Good (4 to 7 bursts during 24 hours processing), △: Normal (8 to 12 bursts during 24 hours processing), ×: Poor (more than 13 times during 24 hours processing) rupture)).

Examples 1-10

Low density polyethylene (ethylene-hexene copolymer, hexene content 18%, density 0.918, LDPE 960 manufactured by Hanyang Chemical, Resin A) 33 wt%, melt index 2.5g with melt index 5.0g / 10min (190 ℃, 2.16kg) Linear low density polyethylene (ethylin-hexene copolymer, hexene content 13%, density 0.924, LL6040, Resin B) 33 weight%, melt index 0.9g / 10 for 10 minutes (190 degreeC, 2.16 kg) To 100 parts by weight of polyethylene resin composed of 34% by weight of medium density polyethylene (ethylene-hexene copolymer, hexene content 8%, density 0.935, MDPE 2037, Resin C) manufactured by Dow Corporation Calcium carbonate (average particle diameter 2.0 mu m) and polyethylene wax (number average molecular weight = 2500, weight average molecular weight = 5,000) coated with stearic acid are blended in the ratio shown in Table 1, mixed in a Henschel mixer, and the mixture is kneaded with a twin screw kneader. Then pelletized. The obtained resin composition pellets were introduced into a film forming extruder through a hopper and melt-extruded at 220 ° C. to prepare a melt as a disc sheet through a T-die. The obtained original sheet was stretched at the stretching ratio shown in Table 1 in the running direction (MD) at the stretching temperature of 60 ° C, and stretched at the stretching ratio shown in Table 1 in the width direction (TD) while maintaining the tenter temperature at 120 ° C. The polyethylene-based breathable film having a thickness of 38 μm was finally processed by heat treatment at 110 ° C. for 1 day. Tensile strength, tear strength, moisture permeability, flexibility (soft touch), dispersibility, processability (neck in, thickness uniformity, and breakage inhibiting property) of the prepared breathable film were evaluated, and the results are shown in Table 1.

Comparative Examples 1 to 6

As in Table 2, except that the type and composition of the polyethylene-based resin was changed, the same process as in Example 5 was performed, and the results are shown in Table 2.

Comparative Example 7

The same procedure as in Example 5 was carried out except for the use of calcium carbonate that was not coated in place of calcium carbonate coated with stearic acid, and the results are shown in Table 2.

Comparative Example 8

Except not adding a polyethylene wax, the same process as in Example 5, and the results are shown in Table 2.

Comparative Example 9

Except for using a liquid polybutadiene instead of a polyethylene wax was carried out in the same manner as in Example 5, the results are shown in Table 2.

Example Composition and Properties of Film

TABLE 1

Composition and Properties of Comparative Film

TABLE 2

Claims (5)

100 parts by weight of a polyethylene resin composed of a low density polyethylene resin having a density of 0.916 to 0.922 g / cc, a linear low density polyethylene resin of a density of 0.923 to 0.930 g / cc and a medium density polyethylene resin of a density of 0.931 to 0.940 g / cc is coated with stearic acid. A method of producing a breathable film, comprising stretching the composition comprising 50 to 200 parts by weight of the inorganic filler and 0.1 to 30 parts by weight of polyethylene wax at a melt sheet-molded original sheet area draw ratio of 1.5 to 36 times. The method for producing a breathable film according to claim 1, wherein the polyethylene resin is an ethylene polymer or a copolymer of molten resin of 0.02 to 20 g / 10 minutes (measured at 190 ° C and 2.16 kg according to ASTM D 1238-70). The method of claim 1, wherein the inorganic filler is calcium carbonate, silica, barium sulfate, magnesium sulfate, calcium sulfate, talc, kaolin, aluminum hydroxide, magnesium hydroxide, zinc oxide, alumina, titanium oxide, mica, zeolite, diatomaceous earth, magnesium carbonate, Method for producing a breathable film, characterized in that the cray or a mixture thereof. The method of manufacturing a breathable film according to claim 1, wherein the inorganic filler is coated by dispersing the molten stearic acid in a state where the finely ground inorganic filler is suspended with air of strong pressure. The method for producing a breathable film according to claim 1, wherein the polyethylene wax has a weight average molecular weight of 200 to 5,000 and a weight average molecular weight / number average molecular weight of 1.0 to 5.0.