JP2005511838A - Breathable film - Google Patents

Abstract

For the purpose of increasing the water vapor permeability of the film, the use of a powdered granular calcium carbonate material having a d ₅₀ of less than 1.0 μ as an inorganic filler in a stretched thermoplastic polyolefin film is provided. Also disclosed is a method for increasing the water vapor permeability of a stretched, inorganic filled thermoplastic polyolefin film, including using powdered calcium carbonate having a d ₅₀ of less than 1.0 μ as the inorganic filler.

Description

  The present invention relates to a breathable film, its use and its production method.

Alkaline earth metal carbonates, particularly calcium carbonate, are used as particulate fillers in end products, such as breathable film products, including compositions comprising thermoplastic polymers. Such films are used for many consumer products, such as backing materials, plastic paper, household wrapping paper, roofing membranes, shopping bags, diapers, adhesive bandages, training pants, sanitary napkins, surgical drapes and surgical clothing. It is manufactured for use. The compositions that make up these films contain two basic components, the first component being a thermoplastic polymer, usually a polyolefin polymer that is mostly linear, such as linear low density polyethylene. And the second component is an inorganic particulate filler such as calcium carbonate. A third component, i.e. a binder or an adhesive, may optionally be present. These components are mixed and compounded together to form a compound or concentrate, which is a film using any one of the film manufacturing methods known to those skilled in the film manufacturing field, including casting or blowing. Molded into layers (usually in sequential steps). Alternatively, the film may be placed on a substrate such as paper or board in a manner known as extrusion coating.
After the film has been processed to its desired form, the film is then processed in a manner well known in the art, such as hydraulic pressure, pinch rolls moving at different speeds, interfacing, and the like. The film is stretched uniaxially or biaxially by a digital roll or a tenter ring.

  Nago et sl. (Journal of Applied Polymer Science, Vol. 45, 1527-1535) is a polypropylene sheet containing 59% by mass of calcium carbonate having a particle size of 0.08-3.0% as a filler. Discloses a method for producing a microporous polypropylene sheet by biaxial stretching.

One aspect of the present invention provides the use of powdered granular calcium carbonate having a d ₅₀ of less than 1.0 μm as an inorganic filler in a stretched thermoplastic polyolefin film for the purpose of increasing the water vapor permeability of the film. .
In accordance with another aspect of the present invention, a method for increasing the water vapor permeability of a stretched inorganic filled thermoplastic polyolefin film comprising the use of powdered calcium carbonate having a d ₅₀ of less than 1.0 μm as an inorganic filler. Is provided.

An object of the present invention is to increase the water vapor permeability (or “breathability”) of a stretched inorganic filled polyolefin film. This is achieved by the present invention using powdered calcium carbonate filler having a d ₅₀ of less than 1.0 μm as the inorganic filler.
When such a powder of calcium carbonate is used, be compared with the conventional inorganic filler polyolefin film inorganic filler is filled with a 1.0μm greater than d _50, breathable stretched polyolefin film is increased I understood.

The designation “d ₅₀ ” for the inorganic filler used here is defined as the particle size value at which less than 50% by weight of the particles are present.

For the purposes of the present invention, the film, U.S. least 100g / m ^2/24 hr water vapor permeability of is calculated using the test method described in Patent No. 5,695,868 ( A film is “breathable”.
In this specification, “film” means a sheet or layer of material having an average thickness of less than about 250 μm. The general thickness dimensions and properties of the film will be described later. The film of the present invention is a breathable film, that is, a breathable film having fine continuous pores (generally smaller) having a size of about 30 μm or less. Such a film, for example, allows atmospheric water vapor on one side of the film to penetrate into the atmosphere on the other side without liquid water permeating through the film.

The calcium carbonate used in the present invention may be a carbonate obtained from a mineral resource, and may include a carbonate processed by a processing method including refining and a pulverizing step for obtaining an appropriate particle size distribution. The milling step can be carried out in a dry state, generally without the addition of hygroscopic or hydrophilic chemicals, or after the dispersant used has been minimized and / or subsequently known from the filler in a known manner. It may be carried out in a wet state in an aqueous medium to be removed. The wet milled material is then dried to the extent that the particulate material has an appropriate moisture content. The particles of the granular product of the present invention are treated (coated) with an aliphatic carboxylic acid hydrophobized surface treating agent commonly used to coat carbonates.
The calcium carbonate used in the present invention may be obtained from natural resources such as marble, chalk or limestone. Desirably at least 95% by weight of the calcium carbonate filler, although other inorganic additives in small amounts, such as one or more of kaolin, calcined kaolin, wollastonite, bauxite, talc or mica can be present with the carbonate. Preferably, at least 99% by weight contains the carbonate itself. At least 95% by mass to 99% by mass may be calcium carbonate obtained by a well-known method of processing natural calcium carbonate obtained from mineral resources.

The granular product of the present invention preferably has one or more of the following particle size characteristics.
i. Top cut of less than about 10 μm, desirably less than about 8 μm (at least 99% of the particles of material have a size with a smaller particle size value).
ii. Less than about 0.35 wt%, more preferably less than about 0.2 wt%, most preferably less than about 0.1 wt% moisture capture.
All particle size values specified here are used in the field of sedimentation of particles in a fully dispersed state in an aqueous medium using a Micromeritics Corp. USA SEDIGRAPH 5100 device. It is measured by a well-known usual method.
The powdered calcium carbonate used in the present invention may have a d ₅₀ of at least 0.3 μm, for example, a d ₅₀ greater than 0.5 μm. Furthermore, the calcium carbonate may have a d ₅₀ of less than 0.8 μm.
The calcium carbonate used in the present invention preferably has a total surface moisture content of less than about 0.1% by weight even after exposure to humid air at 80% relative humidity for 40 hours at 20 ° C. Desirably, the surface moisture content is less than about 0.1% by weight even after exposure to air at 97% relative humidity for 40 hours at 20 ° C.
The calcium carbonate filler used in the present invention is ground to obtain an appropriate particle size distribution. The grinding method may be substantially dry from the filler in a dry state without the addition of hygroscopic or hydrophilic chemicals, or after the dispersant used has been minimized and / or subsequently known. It may be performed in a wet state in an aqueous medium. The wet milled material is then dried to the extent that the particulate material has an appropriate moisture content.

The calcium carbonate used in the present invention is treated by, for example, a known purification method, a fine powder method, and a particle size sorting method in order to give an appropriate shape before use to form the granular product of the present invention. May be. However, after such treatment, the amount of hygroscopic or hydrophilic additive present preferably removes such additive used, for example in a water washing treatment, as described above. Minimized by things.
The calcium carbonate used in the present invention is treated with a hydrophobizing surface treating agent, and this treatment may be performed by addition to the thermoplastic polymer material before use.
Alternatively, the hydrophobizing agent (sometimes referred to as an antagonist) may be added directly to the thermoplastic polymer compounded with calcium carbonate before, during or after addition of the particulate product of the present invention. In order to maximize the action and effect of this hydrophobizing agent, it is preferable that the complete surface treatment of calcium carbonate is performed before addition to the thermoplastic polymer.
When the calcium carbonate filler used in the present invention is surface treated, the d ₅₀ of the treated filler is within the range defined above (may be slightly different from the d ₅₀ before the treatment). Should.
The use of surface treatments that promote the dispersion of inorganic particulate materials in hydrophobic polymer materials when added to dry inorganic particulate materials is well known. Suitable surface treatment agents include aliphatic carboxylic acids having 10 to 30 carbon atoms in the chain, such as stearic acid, behenic acid, palmitic acid, arachidic acid, montanic acid, capric acid, lauric acid, myristic acid. , But not limited to, isostearic acid and serotic acid and mixtures thereof.
Further details regarding the surface treatment of calcium carbonate for polymer compositions are found in WO 99/61521, the contents of which are hereby incorporated by reference for all purposes.

The production method employed to produce the calcium carbonate used in the present invention can be selected from many methods known to those skilled in the art. Further details regarding the production of particulate calcium carbonate inorganic materials suitable for use in the present invention are found in WO 99/61521, the contents of which are hereby incorporated by reference for all purposes. The
The polymeric material to which calcium carbonate is added to form the composition may include, for example, a continuous thermoplastic polyolefin polymer matrix.
Granular calcium carbonate, together with the thermoplastic polyolefin material and any other conventional additives such as binders or adhesives, forms an intermediate product that is stretched to form a stretched final product. May be introduced into the applied composition.
This method used to form an intermediate product from a thermoplastic material and particulate calcium carbonate and then to form a stretched polyolefin film is one or more of the methods well known in the art described below. Also good.
In the intermediate film product and the subsequent stretched product, the thermoplastic polyolefin polymer may form from 20% to 80% by weight and the filler may be from 30% by weight of the composition, i.e. the polymer and filler combination. 80% by weight is formed. More preferably, the thermoplastic polymer forms from about 30% to about 55% by weight of the composition and the filler forms from about 45% to about 65% by weight of the composition.
Preferred thermoplastic polymers in the present invention are thermoplastic polyolefins, such as those containing more than about 50% by weight olefin units and referred to as polyolefin resins.

Examples of the polyolefin polymer (or resin) that can be used to give the polyolefin resin include, as a main component, monoolefin polymers such as ethylene, propylene, and butene, or copolymers thereof. Common examples of polyolefin resins include low density polyethylene, linear low density polyethylene (ethylene-α-olefin copolymers), polyethylene resins such as medium density polyethylene and high density polyethylene, polypropylene and ethylene-polypropylene copolymers. Polypropylene resin, poly (4-methylpentene), polybutene, ethylene-vinyl acetate copolymer, and mixtures thereof. These polyolefin resins may be obtained by polymerization in a known manner, for example by using a Ziegler catalyst, or by using a single site catalyst such as a metallocene catalyst. In particular, polyethylene resin is preferable, and linear low density polyethylene (ethylene-α-olefin copolymer) and low density polyethylene are most preferable. Furthermore, from the viewpoint of fluidity, film stretchability, etc., the melt index of the polyolefin resin is preferably in the range of about 0.5 to 5 g / 10 min.
Other thermoplastic polymers that may be used in the practice of the present invention are thermoplastic elastomers such as SBS.
Desirably, when one or more other fillers are used with the granular product of the present invention, the filler comprises at least 50% by weight, for example 80% to 99% by weight calcium carbonate.

Examples of other fillers include calcium carbonate (not according to the invention), barium sulfate, calcium sulfate, barium carbonate, magnesium hydroxide, aluminum hydroxide, zinc oxide, calcium oxide, magnesium oxide, titanium oxide, silica And talc.
The average particle diameter of the other fillers is preferably 20 μm or less, preferably 10 μm or less, preferably 0.5 to 5 μm. In order to improve the dispersibility of other fillers in the polyolefin resin, other fillers that may be subjected to a surface treatment to impart hydrophobicity to the surface may be used. Examples of suitable surface treatment agents include fatty acids such as stearic acid specified above.
The composition ratio between the thermoplastic polymer and the calcium carbonate filler has an effect on the formability and stretchability of the film and the breathability and water vapor permeability of the resulting film. When the amount of the filler is insufficient, the adjacent micropores obtained by interfacial separation between the polymer and calcium carbonate are not continuous, and the porous film has good gas permeability and water vapor permeability. Cannot be obtained. On the other hand, if the amount of calcium carbonate is too large, defective molding occurs during the film formation process, the stretchability deteriorates, and sufficient stretching cannot be performed. In view of these limiting factors, the composition ratio between the polymer and the calcium carbonate filler is from 25 to 70 parts by weight of polymer per 70 to 30 parts by weight of calcium carbonate, for example 70 to 40 parts by weight. It may be 30 to 60 parts by weight of polymer per part of calcium carbonate.
In the production of the breathable film of the present invention, the concentrate of the polyolefin polymer resin and calcium carbonate filler, i.e. the masterbatch, may be first produced by mixing and compounding prior to the film production process.

In addition to the polymer and filler, the mixture of components blended by compounding can be any other commonly known optional components used in thermoplastic films, such as binders, plasticizers, lubricants, antioxidants. One or more of an ultraviolet absorber, a dye, and a colorant may be included. When used, the binder or pressure-sensitive adhesive promotes bonding of the formed film to other members, such as a nonwoven fibrous layer or one or more non-porous layers.
The thermoplastic polymer, filler and, if necessary, other optional additives are mixed and kneaded by a suitable compounding machine / or mixer such as a Henschel mixer, super mixer, tumbler mixer, etc. For example, it may be pelletized by use of a single screw extruder or a twin screw extruder that forms strands that may be cut into pellets.
The masterbatch in pellet form, i.e. the concentrate, is melted and the intermediate film (i.e. the film before stretching) by the use of molding and film forming equipment well known in the art
Molded or formed. Typically, the masterbatch is dropped to the appropriate calcium carbonate content using the same or different polymer as the masterbatch polymer prior to the film forming process. For example, the masterbatch may be formed with an inorganic filler content on the order of 70% by weight, which is dropped, for example, to an inorganic filler content of 55% by weight.
The intermediate may be a blown film, cast film or extruded film. Also, other types of films are considered to be within the scope of the present invention to provide a molding method that is compatible with the filled film. Suitable methods for producing the films of the present invention will be readily apparent to those skilled in the art.

The intermediate film is then heated to a temperature about 5 ° C. or more below near the melting point of the thermoplastic polymer, and then at least about 1 of its original length to thin the film and make it porous. .2 times, preferably at least 2.5 times.
A further feature of this thinning method is the change in opacity of the film. When molded, the film is relatively transparent, but after stretching, the film becomes opaque. Furthermore, when the film is oriented during the stretching process, the film also becomes soft. Taking these factors into consideration, and in order to have a water vapor transmission rate of at least 100 g ² per per 24 hours 1 m, the film is, for example, film, approximately per 1 m ² with respect to the absorbent product applications of personal care 35g less it has a mass per unit area of, for other applications of certain species may be reduced to a range having a mass per unit area of less than about per 1 m ² 18 g.
The molding device and the film molding device may include, for example, an extruder equipped with a T-die or an inflation molding device equipped with a circular die, as in the prior art. Film production may be performed at a later time after the master batch production, and if possible, in another production plant. In some cases, the masterbatch can be formed directly into a film without producing an intermediate product.
A roll method in which the film is brought about in at least uniaxial direction, from room temperature to the temperature of the softening point of the thermoplastic polymer, in a known manner, for example interfacial separation between the polymer and the inorganic filler, whereby a porous film can be prepared The film can be stretched by an interdigitizing method or a tenter method. Stretching may be performed in one step or in several steps. Since the draw ratio determines the film breakage at high stretch and the air permeability and water vapor permeability of the obtained film, it is desirable to avoid an excessively high stretch ratio and an excessively low stretch ratio. The draw ratio is preferably in the range of 1.2 to 5 times, more preferably 1.2 to 4 times, at least in the uniaxial direction. When biaxial stretching is performed, for example, the first direction of stretching is applied in the machine direction, i.e., perpendicular to the machine, and then the second direction of stretching is perpendicular to the first direction. It is possible to apply to. Alternatively, biaxial stretching may be performed simultaneously in the machine direction and in a direction perpendicular thereto. In order to produce a film by the method according to this aspect of the present invention, a conventionally known method or a method developed thereafter can be applied.

If necessary to stabilize the shape of the obtained holes after stretching, a heat-fixing treatment may be performed. The heat fixing treatment may be, for example, a heat fixing treatment for 0.1 to 100 seconds at a temperature in the range from the softening point of the resin to the vicinity of the melting point of the resin.
There is no restriction | limiting in particular about the thickness of the air permeable film product of this invention. The thickness should be such that a film with suitable flexibility and good feel is obtained without tearing or breaking.
Usually, the thickness of the breathable film is in the range of 5 μm to 100 μm, preferably 10 μm to 70 μm.
Generally, once a film is formed, it has a mass per unit area of less than about 100 g / m ² , and after stretching and thinning, its mass per unit area is less than about 35 g / m ² , desirably less than about per 1 m ² 18 g.
The breathable film can be suitably used for applications that require flexibility, such as a disposable diaper backing sheet.
As used herein, “porous” includes, but is not limited to, “breathable” films.
The breathable film of the present invention having such properties includes disposable diapers, body fluid absorption pads and bed sheets, medical materials such as surgical gowns and base materials such as hot compresses, jumpers, clothing materials such as rain gear, Building materials such as wallpaper and water-resistant materials such as roofs and house wraps, desiccants, dehumidifiers, deoxidizers, packaging materials to pack disposable body warmers, various articles and foods to maintain freshness It may have suitable breathability, water vapor permeability and feel, and excellent mechanical properties and long-term adhesion for proper use in products such as packaging materials, cell separators and the like. Breathable films are particularly desirable as materials used in products such as disposable diapers and body fluid absorbent pads. Breathable films are one of the methods well known in the art in such products to form one or more other layers, such as nonwoven fiber layers, and composites or laminates with, for example, adhesives or binders. It may be formed.

  Embodiments of the present invention are described with reference to the following examples, in the form of examples only.

Example 1

Ground calcium carbonate without chemicals produced by low solid sand milling means was used. The calcium carbonate had a d ₅₀ of 0.6 μm.
A 3 ton sample (dry weight) of carbonate was dehydrated, dried, and stearate coated with the addition of a stearate dose of 2.1% by weight (corresponding to 1% by weight per 4.5 m ² / g of surface area). . The coated material was then passed through a Nissin air classifier to remove material present at ad ₅₀ above 10 μm so that the product did not cause off-size aggregation.
Two tons of coated final product was produced. The physical analysis of uncoated and coated products is shown in Tables 1 and 2 below, respectively. The physical properties of the coated product are for three representative samples collected from a 2 ton bulk sample.

Table 1

Physical analysis of uncoated products

Table 2

Physical analysis of coated products (carbonate A)

Coated calcium carbonate materials referred to above (hereinafter referred to as carbonate A) Commercially available calcium carbonate having a d ₅₀ of the sample and 1.27 (hereinafter referred to as carbonate B) the performance of, the filling of 65% Agent (including 1500 ppm Irganox 1010 anti-oxidant) and compared with various LLDPE resins of different densities.
The following masterbatch compositions were prepared as shown in Table 3 showing the single viscosity (MI) and stiffness (density) of the resin employed (prior to the addition of processing additives).

Table 3

The LLDPE used in compounds D and E contained 10% by weight polyethylene wax processing additive.
These compositions were compounded with a Werner and Pfiddler ZSK40 compounder operating at a die temperature of 220 ° C., an extrusion rate of 300 rpm, and a discharge rate of 80 kg / h.
Compounds containing polyethylene wax processing additives (compounds D and E) were compounded with a Baker-Perkins MP2030 compounder operating at an extrusion rate of 300 rpm, a discharge rate of 80 kg / h and a die temperature of 220 ° C.
The resulting masterbatch sample was then lowered to nominal 50 or 55% calcium carbonate content and then maintained at the following temperatures: 190 ° C, 200 ° C, 200 ° C, 210 ° C, 220 ° C. Extruded at a cast film pilot line with a heated zone and a die temperature of 220 ° C., followed by stretching in the machine direction. The extruder feed rate and stretch roller speed were selected to produce a stretched film with a nominal thickness of 25 μm.
The results obtained are shown in Table 4 below. Water vapor permeability of the film _{(MVTR) (g · H 2} O.m -2. Days measured in ^-1) at 37 ° C., the ASTM E-96 (weight loss method) as (as control two sets Sample Measured using a porous membrane). The calcium carbonate content of the film was measured by ashing at 450 ° C. for 1 hour. The comments are about the quality of the film produced with respect to its thickness uniformity and tear resistance.

Table 4

Many of the films obtained were non-uniform due to the limitations of the stretching equipment used, and were thus “failed”. Some of these films were taken as samples for MVTR, but the results obtained for these films are limited comparison values.

Example 2

Ground calcium carbonate without chemicals produced by low solid sand milling means was used. To remove the coarse material, the slurry is hydrocyclized, dewatered, dried and stearized with the addition of a stearate dose of 1.25 wt% (equal to 1 wt% per surface area 4.5 m ² / g). It was. The product had a d ₅₀ of 0.81 μm as measured by sedigraph (hereinafter referred to as carbonate C).
Performance of carbonate C in the LLDPE resin with various fillers levels content, commercially available calcium carbonate having a d ₅₀ of 1.27 (hereinafter referred to as carbonate D) were compared to the performance of the.
A 60 wt% (filler) masterbatch of carbonates C and D was prepared on a Werner and Pfiddler ZSK40 twin screw extruder. The apparatus was operated at 170 ° C, 190 ° C, 200 ° C, 210 ° C barrel temperature and 220 ° C die temperature and 50% drive torque at a feed rate of 100 kg masterbatch / hour. The masterbatch also contained 1500 ppm Irganox 1010.

The resulting masterbatch was diluted with virgin LLDPE to achieve the required nominal level of 45, 50, or 55 wt% filler, 190 ° C, 200 ° C, 200 ° C, 210 ° C, 220 ° C, respectively. Extruded in a cast film pilot line with 5 heated barrels maintained at a temperature of 属 C and a die maintained at a temperature of 220 属 C. The extruded film was stretched sequentially in the machine direction. The extruder speed and draw roller speed were selected to produce a microporous film with a nominal thickness of 25 μm.
The water vapor transmission rate (MVTR) (g.H ₂ O.m ⁻² .day ⁻¹ ) of the film was determined as ASTM E-96 (mass loss method) at 37 ° C. in duplicate (using a microporous membrane as a control). ). The results are shown in Table 5. The actual proportion of filler in the film was measured by loss on ignition at 400 ° C. It is therefore possible to standardize all MVTR values for nominal filler loading levels of 45, 50 and 55% by weight. These values are shown in Table 5.

Table 5

  Table 5 shows that for most stretch ratios and filler loading, carbonate C provides a higher breathability increase than carbonate D.

Claims (18)

Use of a powdered calcium carbonate material having a d ₅₀ of less than 1.0 μm as an inorganic filler in a stretched thermoplastic polyolefin film intended to increase the water vapor permeability of the film. Powdered particulate calcium carbonate material has a 0.3μm greater than d _50, Use according to claim 1. Use according to claim 2, wherein the powdered granular calcium carbonate material has a d ₅₀ of greater than 0.5 µm. Powdered particulate calcium carbonate material has a d ₅₀ of less than 0.8 [mu] m, use according to any one of claims 1 to 3.   Use according to any one of claims 1 to 4, wherein the powdered granular calcium carbonate material has a surface treated with a hydrophobizing agent.   6. Use according to claim 5, wherein the hydrophobizing agent is an aliphatic carboxylic acid having 10 to 30 carbon atoms.   Use according to claim 6, wherein the hydrophobizing agent is stearic acid.   Use according to any one of claims 1 to 7, wherein the polyolefin is polyethylene.   Use according to claim 8, wherein the polyethylene is linear low density polyethylene or low density polyethylene. A method for increasing the water vapor permeability of a stretched inorganic-filled thermoplastic polyolefin film, characterized in that a powdered granular calcium carbonate material having a d ₅₀ of less than 1.0 μm is used as the inorganic filler. The method of claim 10, wherein the powdered granular calcium carbonate material has a d ₅₀ of greater than 0.3 μm. The method of claim 11, wherein the powdered granular calcium carbonate material has a d ₅₀ of greater than 0.5 μm. Powdered particulate calcium carbonate material has a d ₅₀ of less than 0.8 [mu] m, method according to any one of claims 10 to 12.   14. A method according to any one of claims 10 to 13, wherein the powdered granular calcium carbonate material has a surface treated with a hydrophobizing agent.   15. A method according to claim 14, wherein the hydrophobizing agent is an aliphatic carboxylic acid having 10 to 30 carbon atoms.   The method of claim 15, wherein the hydrophobizing agent is stearic acid.   The method according to any one of claims 10 to 16, wherein the polyolefin is polyethylene.   The method according to claim 17, wherein the polyethylene is linear low density polyethylene or low density polyethylene.