KR19980066536A - Breathable film - Google Patents

Abstract

The present invention provides an area stretch ratio of a disc sheet melt-molded with a composition containing 0.1-30 parts by weight of polyethylene wax, based on 100 parts by weight of a composition composed of 40 to 80% by volume of polyethylene resin and 60 to 20% by volume of an inorganic filler. It relates to a breathable film which is produced by stretching in a range of 1.5 times to 36 times. The breathable film according to the present invention has a soft touch and 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

Breathable film

The present invention relates to a breathable film or a breathable sheet having a soft touch and excellent strength, excellent 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.

Conventional breathable film is an inorganic filler is added to a polyolefin resin, mainly polyethylene-based resin at a specific magnification, as disclosed in Japanese Patent Application Laid-Open Nos. 58-14903, 60-185803, 59-59906 and 4,472,328. Thereafter, a number of methods for obtaining a breathable film have been proposed by stretching a sheet obtained by melting a film by a known method in a single axis or in a biaxial direction to form fine pores continuously 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 is very poor, such as tear strength in the stretching direction has been urgently requested to improve.

As a means for solving such a 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 liquid or waxy hydrocarbon polymers, Japanese Patent Application Laid-Open No. 57-47334 refers to liquid polybutadiene or polybutene, and Japanese Patent Publication No. 58-15538 refers to polyhydroxy saturated hydrocarbons. Japanese Patent Laid-Open No. 61-14431, a polyester or epoxy plasticizer, Japanese Patent Laid-Open No. 62-129321, silicone oil, Japanese Patent Laid-Open No. 61-235439, No. 62-18435, So 62-22844, Pyeong 1-56744, Pyeong 1-96229, Pyeong 1-249840, Pyeong 5-5253 and the like added esters such as dipentaerythritol ester as the third component It was desired to obtain a breathable film having an excellent and soft touch.

However, since the above-mentioned third components adopted in the prior art are mostly very expensive, their cost is greatly increased, and their molecular weight is only a few hundreds to thousands, they are low molecular weights. In the film processing process such as thickness instability due to abnormal flow, the improvement of this problem is urgently needed.

The present inventors have intensively researched to improve the problems described above. As a result, using a novel polyethylene resin composition, there is no problem in the process of film forming and stretching roll contamination, thickness instability, etc. It is to develop a breathable film that can be used suitably for diaper back sheet and the like, having excellent and proper moisture permeability.

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

More specifically, an object of the present invention is a disc which melt-molded a composition in which 0.1-30 parts by weight of polyethylene wax is blended with respect to 100 parts by weight of a composition composed of 40 to 80% by volume of polyethylene resin and 60 to 20% by volume of inorganic filler. It is to provide a breathable film characterized in that the sheet is produced by stretching.

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

In the present invention, the polyethylene resin is a polyethylene homopolymer or a copolymer polymerized using a conventional Ziegler-Natta catalyst, and representative examples thereof include low density polyteline, linear low density polyethylene, medium density polyethylene, and high density polyethylene. Copolymers include, for example, copolymers with propylene, butene, hexene, octene and the like.

In the present invention, one or more kinds of the above-described polyethylene homopolymer or copolymer may be used as the polyethylene resin.

The melt index of the polyethylene-based resin suitable for the present invention is suitably in the range of 0.02 to 20 g minutes / 10 minutes (measured at 190 ° C and 2.16 Kg according to ASTM D1238-70). 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 the present invention, 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, cray or Mixtures of these are used. Forms of the inorganic fillers include plate, needle, 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 composition ratio of the polyethylene resin and the inorganic filler is 40 to 80% by volume of the polyethylene resin, preferably 55 to 70% by volume, 60 to 20% by volume of the inorganic filler, preferably 45 to 30% by volume. Range. If the inorganic filler is less than 20% by volume, the interface between the polyethylene-based resin and the inorganic filler is peeled off, and there is a defect in that the hole that is expressed does not penetrate continuously, resulting in poor air permeability. Physical properties such as elongation may deteriorate.

In the present invention, the polyethylene wax is an ethylene homopolymer or an ethylene polymer having a number average molecular weight of about 200 to 5,000 by light scattering and a [weight average molecular weight / number average molecular weight] ratio of 1.1 to 5.0, which is a measure of molecular weight distribution. It consists of a copolymer with butene, hexene, and octene.

When the number-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, there is a concern that the disadvantages such as increased roll contamination, thickness instability during extrusion processing.

In this invention, it is preferable to add 0.1-30 weight part of polyethylene wax with respect to 100 weight part of compositions comprised from 40-80 volume% of polyethylene resins, and 60-20 volume% of inorganic fillers, More preferably, it is 0.5-20 weight% Wealth is the most suitable. If it is less than 0.1 part by weight, the soft touch 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 adhesion and dispersibility between the polyethylene wax and the inorganic filler, the polyethylene wax simultaneously serves as an additive such as a dispersant used in the past, and is a polymer made of a conventional additive having a low molecular weight. It is possible to prepare a breathable film having excellent softness and excellent moisture permeability without having a problem with processing agents such as stretching roll contamination due to elution and thickness instability due to abnormal flow during extrusion processing.

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, a 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 mixer, a mixing roll, a balbaric 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 the conventional film forming apparatus and molding method by extrusion processing. In-flation molding using a circular die and tee-die extrusion molding with a tee die are appropriately employed. May be carried out.

Next, the sheet molded 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, if the temperature is lower than the glass transition point, the film cannot be stretched due to the rupture of the film before the elongation exceeds the yield point.If the temperature exceeds the melting point, satisfactory aeration amount during the stretching of the driving direction due to the flow of the molecular chain is exceeded. 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 pillar stretched 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 in the range of 1.5-36 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 metalocene catalyst-based polyolefin elastomer, the blending ratio, stretching temperature, stretching ratio It can be freely adjusted according to stretching conditions such as stretching method.

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), and workability (roll contamination degree and thickness uniformity) 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).

Breathable

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% ㄲ. ㅗ.)

Flexibility (soft touch)

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)).

Machinability

Roll stretching conditions and thickness uniformity were visually measured during stretching (◎: very good, ○: good, △: normal, ×: poor).

Dispersibility

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

[Examples 1-5]

Linear low density polyethylene (ethylene-hexene copolymer, hexene content 13%, density 0.919, LL6040 made by Samsung General Chemicals, Resin A) 60 vol%, calcium carbonate with melt index 2.5g / 10min (190 ° C, 2.16Kg) (Average particle size 2.0 mu m) A content of polyethylene wax (wax: wax A having a number average molecular weight of 2,000 to 3,000 and a weight average molecular weight of 3,000 to 9,000 by weight scattering) with respect to 100 parts by weight of the composition composed of 40 volume%. Was added in different amounts (see Table 1), mixed in a Henschel mixer, and the mixture was kneaded with a twin screw kneader and 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 1.7 times in the running direction (MD) at a stretching temperature of 60 ° C., stretched 1.5 times in the width direction (TD) while maintaining the tender temperature at 120 ° C., and heat-treated at 110 ° C. for 1 day to finally obtain an area. A polyethylene-based breathable film having a thickness of 38 μm processed at a draw ratio of 2.6 was prepared. Tensile strength, tear strength, moisture permeability, flexibility (soft touch), workability (roll contamination degree and thickness uniformity), etc. of the manufactured breathable film were evaluated, and the results are shown in Table 1.

Examples 6 to 7

A polyethylene-based breathable film was prepared in the same manner as in Example 5 except that the area draw ratio was changed to 3.2 (1.9 × 1.7) and 4.0 (2.1 × 1.9). The physical properties of the prepared breathable film were evaluated in the same manner, and the results are shown in Table 1.

Example 8

Polyethylene-based breathable film was prepared in the same manner as in Example 5 except that uniaxial stretching was performed at the same area drawing ratio 2.6 as in Example 5 under the same temperature conditions. The manufactured air permeable film was evaluated in the same manner as in the same manner and the results are shown in Table 1.

[Examples 9-10]

A polyethylene-based breathable film was prepared in the same manner as in Example 5 except that the volume composition ratio of the polyethylene-based resin and calcium carbonate was changed. The physical properties of the prepared breathable film were evaluated in the same manner, and the results are shown in Table 1.

Comparative Example 1

Without adding any polyethylene wax, only linear low density polyethylene (ethylene-hexene copolymer, hexene content 13%, density 0.919, LL6040 manufactured by Samseo General Chemical, Resin A) 60% by volume, calcium carbonate (average particle size 2.0㎛) Polyethylene-based breathable film was prepared in the same manner as in Example 1 using only the composition consisting of 40% by volume. The physical properties of the prepared breathable film were evaluated in the same manner, and the results are shown in Table 2.

TABLE 1 Compositions and Compositions of Example Films

TABLE 2 Composition and Physical Properties of Comparative Film

Claims (4)

It is produced by stretching the disc sheet melt-molded composition of 0.1-30 parts by weight of polyethylene wax with respect to 100 parts by weight of the composition consisting of 40 to 80% by volume polyethylene resin and 60 to 20% by volume inorganic filler. Breathable film The breathable film of claim 1, wherein the polyethylene resin is a polyethylene homopolymer or copolymer polymerized using a Ziegler-Natta catalyst and has a melt index in the range of 0.02 to 20 g / 10 minutes. The inorganic filler according to 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, Breathable film, characterized in that the cray or a mixture thereof. The breathable film according to claim 1, wherein the polyethylene-based wax has a number average molecular weight of 200 to 5,000 by light scattering and a weight average molecular weight / number average molecular weight ratio of 1.1 to 5.0, which is a measure of molecular weight distribution. .