JP2024158892A - Polyethylene Film - Google Patents

Abstract

【assignment】
An object of the present invention is to provide a flexible resin film on which writing and printing can be carried out and which can be used as a packaging material or the like.
SOLUTION
The film is made of a resin composition containing 3 to 18 parts by mass of a linear low-density polyethylene (hereinafter sometimes referred to as "LLDPE (1)" in this specification) having an MFR in the range of 0.10 to 3.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190° C. and a load of 2.16 kg) (hereinafter MFR in this specification may be omitted as all MFRs are measured under the above-mentioned conditions), 40 to 90 parts by mass of a linear low-density polyethylene (hereinafter sometimes referred to as "LLDPE (2)" in this specification) having an MFR in the range of more than 3.00 and less than 20.0 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190° C. and a load of 2.16 kg), and 7 to 42 parts by mass of calcium carbonate.
[Selection diagram] None

Description

The present invention relates to a polyethylene film containing calcium carbonate.

A porous film A is known that is made of a resin composition containing 100 parts by mass of linear low density polyethylene (hereinafter sometimes referred to as "LLDPE" in the present specification) having a density of 0.93 g/ ^cm3 and a melt flow rate (hereinafter sometimes referred to as "MFR" in the present specification) of 2.1 g/10 min, 40 parts of metallocene linear low density polyethylene having a density of 0.910 g/ ^cm3 and an MFR of 5.0 g/10 min, and 150 parts of calcium carbonate (treated with fatty acid) having an average particle size of 2 μm (see Patent Document 1). The porous film A can be used as a storage bag suitable for storing a heating element, etc.

A porous film that combines high transparency and moisture permeability with excellent strength is known, which is obtained by stretching an LLDPE resin composition consisting of 30 to 50% by weight of LLDPE and 70 to 50% by weight of an inorganic filler such as calcium carbonate at least uniaxially at an areal magnification of 1.1 to 1.6 times, and is made up of 30 to 70% by weight of LLDPE having an MFR of 0.5 g/10 min or more and less than 3 g/10 min and 70 to 30% by weight of LLDPE having an MFR of 3 g/10 min or more and 20 g/10 min or less, and the difference in MFR of the LLDPE is 3 or more (see Patent Document 2). By laminating the porous film B with a breathable reinforcing material, it can be suitably used for building materials such as house wrap and roofing, agricultural applications such as mulch sheets, hygiene materials such as paper diapers and sanitary napkins, medical applications such as surgical gowns, clothing applications such as disposable raincoats, waste disposal applications, etc.

As a porous film that can exhibit excellent breathability even when used for applications involving secondary processing such as printing or lamination with nonwoven fabric, a porous film is known that is obtained by at least uniaxially stretching an unstretched film made of a resin composition containing 40 to 60% by mass of a polyethylene resin and 60 to 40% by mass of an inorganic filler such as calcium carbonate, and that is made of 40 to 70% by mass of LLDPE having an MFR of more than 3.0 g/10 min and 10 g/10 min or less and a density of 0.930 to 0.950 g/cm ³ and 60 to 30% by mass of LLDPE having an MFR of more than 0.1 g/10 min and 3.0 g/10 min or less and a density of 0.910 to 0.950 g/cm ³ (see Patent Document 3). The polyethylene porous film C can be suitably used as a waterproof and moisture-permeable sheet for sanitary materials, and can also be suitably used for medical purposes such as surgical gowns, clothing purposes such as disposable raincoats, functional packaging materials such as desiccants and disposable hand warmers, building materials such as house wraps, agricultural purposes such as mulch farming sheets, waste disposal purposes such as compost covering sheets, and the like.

As a porous film having high breathability, low heat shrinkage, and suitable for secondary processing in which heat is applied, a polyethylene-based porous film is known which is produced by forming a resin composition containing 60 to 30% by mass of a polyethylene-based resin and 40 to 70% by mass of an inorganic filler such as calcium carbonate by an inflation method, and stretching the obtained unstretched film in the flow direction of the film, in which the polyethylene-based resin is composed of 100 to 40% by mass of LLDPE having an MFR of more than 3.0 g/10 min and 10 g/10 min or less and a density of 0.930 to 0.950 g/cm ³ , and 0 to 60% by mass of LLDPE having an MFR of more than 0.1 g/10 min and 3.0 g/10 min or less, and in which the height of the frost line is adjusted to 0.5 to 4.0 times the die diameter when the unstretched film is formed (see Patent Document 4).

Japanese Patent Application Publication No. 10-168207 JP 2005-263862 A JP 2006-241276 A JP 2007-016064 A

Patent Documents 1 and 4 disclose, as a specific combination of two types of LLDPE having different MFR and calcium carbonate, a combination in which the calcium carbonate is 50 parts by mass or more per 100 parts by mass of the entire film.
Patent Documents 2 and 3 disclose, as specific combinations of two types of LLDPE having different MFRs and calcium carbonate, a combination in which the calcium carbonate is 50 parts by mass or more when the entire film is taken as 100 parts by mass, a combination of 30 parts by weight of LLDPE having an MFR of 2.1 g/min, 30 parts by weight of LLDPE having an MFR of 8 g/min, and 40 parts by weight of calcium carbonate, and a combination of 27 parts by weight of LLDPE having an MFR of 2.1 g/min, 27 parts by weight of LLDPE having an MFR of 4 g/min, and 46 parts by weight of calcium carbonate.

However, films made from the above combinations are insufficient in flexibility and are therefore inadequate as packaging materials on which writing and printing can be carried out.
An object of the present invention is to provide a flexible resin film on which writing and printing can be carried out and which can be used as a packaging material or the like.

As a result of intensive research into solving the above problems, the inventors have completed the present invention by forming a resin composition into a film by mixing two types of LLDPE with different MFRs and calcium carbonate in specific ranges of amounts.

That is, the present invention relates to a film made of a resin composition containing 3 to 18 parts by mass of a linear low-density polyethylene (hereinafter sometimes referred to as "LLDPE (1)" in this specification) having an MFR in the range of 0.10 to 3.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190° C. and a load of 2.16 kg) (hereinafter in this specification, MFR may be omitted because all MFRs are measured under the above-mentioned conditions), 40 to 90 parts by mass of a linear low-density polyethylene (hereinafter sometimes referred to as "LLDPE (2)" in this specification) having an MFR in the range of more than 3.00 and less than 20.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190° C. and a load of 2.16 kg), and 7 to 42 parts by mass of calcium carbonate.
The amount of linear low density polyethylene having an MFR in the range of 0.10 to 3.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190° C. and a load of 2.16 kg) is preferably 9 to 18 parts by mass.
It is preferable that the breaking elongation of the film in the machine direction (hereinafter sometimes referred to as "MD" in this specification) and in the direction perpendicular to the machine direction (hereinafter sometimes referred to as "TD" in this specification) is 600% or more, and that the breaking stress in MD and TD is 14.0 MPa or more.
The tensile modulus of elasticity in the MD and TD of the film is preferably in the range of 50.0 to 160.0 MPa.

The film of the present invention can be written on, printed on, etc., and is flexible, so it can be used as a packaging material, etc.

The film of the present invention is a film made of a resin composition containing 3 to 18 parts by mass of linear low-density polyethylene having an MFR in the range of 0.10 to 3.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190°C and a load of 2.16 kg), 40 to 90 parts by mass of linear low-density polyethylene having an MFR in the range of more than 3.00 and less than 20.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190°C and a load of 2.16 kg), and 7 to 42 parts by mass of calcium carbonate.

The LLDPE (1) and the LLDPE (2) have a density in the range of 0.860 to 0.925 g/ ^cm3 , and are ethylene copolymers having extremely high molecular linearity, the density of which has been reduced by copolymerizing a small amount (about a few percent) of an α-olefin having 4 to 8 carbon atoms, such as 1-butene, 1-hexene, 4-methyl-1-pentene, or 1-octene, with ethylene. In particular, those containing 4 or 6 carbon atoms as the α-olefin component are preferred.

The LLDPE (1) and the LLDPE (2) are not particularly limited as long as they satisfy the specified MFR, and can be produced by polymerization in the gas phase or liquid phase using a Ziegler-type titanium catalyst, a Phillip-type chromium oxide catalyst, or a metallocene catalyst containing, for example, a metallocene compound containing a transition metal selected from Group 4 of the periodic table and a ligand having a cyclopentadienyl skeleton, and at least one compound selected from an organoaluminum oxy compound, an organoaluminum compound, and a compound that reacts with the metallocene compound to form an ion pair.

The MFR of the LLDPE (1) is in range A of 0.10 to 3.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190°C and a load of 2.16 kg), and the lower limit of the range A is preferably 0.12 g/min or more, more preferably 0.15 g/min or more, and is 0.18 g/min or more, 0.20 g/min or more, 0.22 g/min or more, 0.25 g/min or more, 0.28 g/min or more, or 0.30 g/min or more, and the latter lower limit or more is even more preferable. In addition, the upper limit of the range A is preferably 2.80 g/min or less, more preferably 2.50 g/min or less, 2.20 g/min or less, 2.00 g/min or less, 1.80 g/min or less, 1.50 g/min or less, 1.20 g/min or less, or 1.00 g/min or less, with the latter being even more preferable.

The content of the LLDPE (1) in the resin composition is in range B of 3 to 18 parts by mass, and the lower limit of range B is preferably 4 parts by mass or more, more preferably 6 parts by mass or more, even more preferably 9 parts by mass or more, and even more preferably 12 parts by mass or more. The upper limit of range B is preferably 17.5 parts by mass or less, and more preferably 17.0 parts by mass or less.

As described above, the LLDPE (2) may be one produced by any method, but is preferably one produced by liquid phase polymerization using a metallocene catalyst.
The MFR of the LLDPE (2) is in range C of more than 3.00 and less than 20.0 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190° C. and a load of 2.16 kg). The lower limit of range C is preferably 3.30 g/min or more, more preferably 3.70 g/min or more, and is 4.00 g/min or more, 4.30 g/min or more, 4.70 g/min or more, 5.00 g/min or more, 5.30 g/min or more, or 5.70 g/min or more, and the latter lower limit or higher is even more preferable. Furthermore, the upper limit of range C is preferably 19.0 g/min or less, more preferably 18.0 g/min or less, and is 17.0 g/min or less, 16.0 g/min or less, 15.0 g/min or less, 12.0 g/min or less, 10.0 g/min or less, 8.00 g/min or less, or 7.00 g/min or less, with the latter upper limit or less being even more preferable.

The content of the LLDPE (2) in the resin composition is in a range D of 40 to 90 parts by mass, and the lower limit of the range D is preferably 41 parts by mass or more, more preferably 42 parts by mass or more, and even more preferably 43 parts by mass or more. The upper limit of the range D is preferably 85 parts by mass or less, more preferably 80 parts by mass or less, 75 parts by mass or less, 70 parts by mass or less, or 60 parts by mass or less, and the lower the latter upper limit, the more preferable it is.

The LLDPE (1) and LLDPE (2) may each be composed of one type of LLDPE, or may be composed of two or more types of LLDPE. When composed of two or more types of LLDPE, the MFR is expressed as the weighted average of the MFRs of the constituent LLDPEs.

The calcium carbonate is not particularly limited as long as it is a calcium carbonate represented by the composition formula _CaCO3, which is a main component of seashells, eggshells, limestone, chalk, etc. More specifically, examples of the calcium carbonate include heavy calcium carbonate (natural calcium carbonate) obtained by crushing and classifying limestone, and light calcium carbonate (synthetic calcium carbonate) obtained by a chemical reaction with the heavy calcium carbonate.

In the present invention, either heavy calcium carbonate or light calcium carbonate can be used, but light calcium carbonate is preferably used in consideration of the surface treatment.

The calcium carbonate can be in any of the crystal polymorphs, such as calcite crystals (trigonal rhombohedral crystals), aragonite crystals (rectangular crystals), and vaterite crystals (hexagonal crystals), but aragonite crystals are preferred.

The calcium carbonate is preferably surface-treated calcium carbonate. Here, surface-treated calcium carbonate refers to calcium carbonate whose surface is covered with a surface treatment agent, or calcium carbonate whose surface is at least in a state where a surface treatment agent is attached to the surface of the calcium carbonate.

Specific examples of surface treatment agents for calcium carbonate include fatty acids and their derivatives, resin acids and their derivatives, silica, organosilicon compounds, condensed phosphoric acid and condensed phosphate salts. Among these, metal salts of fatty acids are preferred as surface treatment agents, and fatty acid sodium salts or fatty acid potassium salts are particularly preferred.

Specific examples of the fatty acid include saturated or unsaturated fatty acids having 6 to 24 carbon atoms, preferably saturated or unsaturated fatty acids having 10 to 20 carbon atoms. Specific examples of the fatty acid include hexanoic acid (caproic acid), heptanoic acid (enanthic acid), octanoic acid (caprylic acid), nonanoic acid (pelargonic acid), decanoic acid (capric acid), dodecanoic acid (lauric acid), tetradecanoic acid (myristic acid), pentadecanoic acid (pentadecylic acid), hexadecanoic acid (palmitic acid), heptadecanoic acid (margaric acid), octadecanoic acid (stearic acid), icosanoic acid (arachidic acid), docosanoic acid (behenic acid), tetracosanoic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, myristoleic acid, palmitoleic acid, sapienic acid, eicosenoic acid, erucic acid, etc. These fatty acids and their metal salts can be used alone or in combination of two or more.

The surface-treated calcium carbonate can be produced, for example, by heating the fatty acid in an aqueous alkali metal solution such as an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution to obtain an aqueous solution of an alkali metal salt of a fatty acid, adding the aqueous solution of an alkali metal salt of a fatty acid to a slurry of calcium carbonate and water and stirring the mixture, and dehydrating the resulting calcium carbonate slurry using a filter press or the like, and drying the slurry using a box dryer or the like.

The cumulative 50% particle size (D50) on a volume basis obtained by the laser diffraction scattering method of the calcium carbonate including the surface-treated calcium carbonate is not particularly limited, but is preferably 1.0 μm or more, more preferably 1.5 μm or more, and even more preferably 2.0 μm or more. The upper limit of the cumulative 50% particle size (D50) is preferably 10.0 μm or less, more preferably 9.0 μm or less, even more preferably 8.0 μm or less, and even more preferably 6.0 μm or less.

The amount of calcium carbonate contained in the resin composition is in range E of 7 to 42 parts by mass, with the lower limit of range E being preferably 10 parts by mass or more, more preferably 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, or 30 parts by mass or more, with the latter being more preferable. The upper limit of range E is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less.

The resin composition may contain components other than the LLDPE (1), the LLDPE (2) and calcium carbonate, as long as the effects of the present invention are not impaired. Specifically, such components may include additives such as antioxidants, weathering agents, pigments, plasticizers and antistatic agents, as well as silicone oils and waxes to obtain uniform stretchability.

The method for producing the resin composition is not particularly limited, and known production methods can be used. Specifically, the components constituting the resin composition are mixed in a Henschel mixer, super mixer, tumbler mixer, or the like, and then kneaded in a high-mixing type twin-screw extruder, tandem type kneader, or the like by a method such as strand cut, hot cut, or underwater cut, and pelletized.

The film (including both stretched and unstretched polyethylene films; the same applies below) can be formed into an unstretched film by melt extruding the resin composition using a conventional film forming method such as the T-die method or the inflation method.

The unstretched film can be stretched at least uniaxially, if necessary, at a temperature range of room temperature or higher and lower than the softening point of the resin, by a known method such as roll stretching or tenter stretching. Stretching may be only uniaxial, but in order to increase the strength of the resulting stretched polyethylene film, it is preferable to stretch it biaxially. There is no particular restriction on the stretching ratio, but it is preferable that the MD stretching ratio is 1.1 to 3.0 times and the TD stretching ratio is 1.1 to 2.0 times. Stretching may be one-stage or multi-stage, and heat treatment may be performed after stretching if necessary.

The film preferably has a breaking elongation of 600% or more in the MD and TD at 23°C, and a breaking stress of 14.0 MPa or more in the MD and TD at 23°C. If the breaking elongation is 600% or less and the breaking stress is less than 14.0 MPa, the tape may break when used as a mechanical sealing tape, which is a type of packaging.

The tensile modulus of elasticity of the film in the MD and TD at 23°C is preferably in the range of 50.0 to 160.0 MPa. If the tensile modulus is less than 50.0 MPa, the film formability is poor, and if it is more than 160.0 MPa, the film lacks flexibility and there are problems with formability in secondary processing.

The thickness of the film is not particularly limited, but is preferably in the range of 2 to 200 μm, more preferably in the range of 10 to 180 μm, more preferably in the range of 50 to 160 μm, more preferably in the range of 60 to 140 μm, and particularly preferably in the range of 80 to 130 μm.

The film can be used on the entire surface or one side to form a bag. Specifically, the ends of the film can be joined to form a bag. The film ends can be joined by a heat sealing method, ultrasonic embossing method, or the like, but the fusion method is preferably used.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples in any way.

The film of the present invention was produced by extruding 10 parts by mass of the master batch resin 1 and 90 parts by mass of LLDPE (3) (MFR: 5.00 g/10 min) through a T-die at an extrusion temperature of 210°C to a film thickness of 90 μm.

[Examples 2 to 6, Comparative Examples 1 to 3]
The same procedure as in Example 1 was carried out except that the master batch resin 1 and LLDPE (3) were used in the ratio shown in Table 1, to obtain a film.

The films obtained in the examples and comparative examples were evaluated by the following methods.
[Tensile modulus (MPa)]
The films obtained in each Example and Comparative Example were cut to TD 15 mm and MD 100 mm, and TD 100 mm and MD 15 mm, and set in an apparatus with a chuck distance of 50 mm. A tensile test was performed under conditions of a pulling speed of 300 mm/min, 23°C and relative humidity of 65%, and a load-elongation curve was obtained. The tensile modulus was calculated from the tangent of the rising part (at 3% elongation) of the obtained load-elongation curve.

[Breaking elongation and breaking stress]
The breaking elongation and breaking stress were measured using a tensile tester. The films obtained in each Example and Comparative Example were cut to TD 15 mm and MD 100 mm, and TD 100 mm and MD 15 mm, and clamped and fixed between chucks set at a distance of 50 mm. The specimens were pulled at a speed of 100 mm/min, and the load was measured with a load cell attached to the tester. The load at break in the load-elongation curve was read and divided by the cross-sectional area of the sample before pulling to calculate the breaking stress (MPa). The breaking elongation was calculated from the initial chuck distance (L ₀ ) and the chuck distance at break (L ₁ ) using the following formula, and was taken as the breaking elongation (%).
Breaking elongation (%)=(L ₁ −L ₀ )/L ₀ ×100

The evaluation results are shown in Table 2.

The film of the present invention is useful as packaging bags, sealing tapes, and the like.

Claims (4)

A film made of a resin composition containing 3 to 18 parts by mass of linear low-density polyethylene with a melt flow rate in the range of 0.10 to 3.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190°C and a load of 2.16 kg), 40 to 90 parts by mass of linear low-density polyethylene with a melt flow rate in the range of more than 3.00 and less than 20.00 g/10 min (measured in accordance with JIS K 7210:1999 at a measurement temperature of 190°C and a load of 2.16 kg), and 7 to 42 parts by mass of calcium carbonate. The film according to claim 1, which contains 9 to 18 parts by mass of linear low-density polyethylene having a melt flow rate in the range of 0.10 to 3.00 g/10 min (measured according to JIS K 7210:1999 at a measurement temperature of 190°C and a load of 2.16 kg). The film according to claim 1 or 2, in which the breaking elongation of the film in the machine direction and in the direction perpendicular to the machine direction is 600% or more, and the breaking stress in the machine direction and in the direction perpendicular to the machine direction is 14.0 MPa or more. 3. The film according to claim 1, wherein the tensile modulus of the film in the machine direction and in the direction perpendicular to the machine direction is in the range of 50.0 to 160.0 MPa.