Method for manufacturing thermoplastic polyolefin films

Abstract

To provide a method for producing a polyolefin film containing cellulose fibers with good film-forming properties. [Solution] A method for producing a thermoplastic polyolefin film, comprising the steps of: preparing a kneaded product by pre-kneading a resin composition containing a thermoplastic polyolefin and a fibrous filler while melting the thermoplastic polyolefin, wherein the fibrous filler mainly contains cellulose fibers; and forming a film from the kneaded product by calendering.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a thermoplastic polyolefin film.

Background Art

[0002] As an environmentally considerate fibrous filler, cellulose fiber, which is a biomass material, has been attracting attention. Since cellulose fiber can improve the mechanical strength, dimensional stability, oxygen barrier property, etc. of resin products, for example, research is underway to utilize a member obtained by adding this to polyolefin and injection molding it for automotive applications (for example, Patent Document 1).

[0003] On the other hand, not only for injection molded members, but also in polyolefin films for packaging materials and the like, it is expected that the improvement of functions by cellulose fiber is useful. As a method for manufacturing a resin film to which a fibrous filler such as cellulose fiber is added, the T-die method is known. For example, Patent Document 2 discloses a method for manufacturing a conductive film by extruding a resin composition such as polyolefin containing a conductive filler by a T-die and then cooling it with a cooling roll.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, it was found that when attempting to form a polyolefin film containing a certain amount of cellulose fiber by following the manufacturing method described in Patent Document 1, film formation defects such as cracking and uneven thickness are likely to occur. Furthermore, even if the die opening width of the T-die is narrowed, die swells occur, making it difficult to achieve stable film formation.

[0006] This disclosure is made in view of the above circumstances and aims to provide a method for producing a polyolefin film containing cellulose fibers with good film-forming properties. [Means for solving the problem]

[0007] The aspects of this disclosure are, for example, as follows: [1] A step of preparing a compound by pre-kneading a resin composition containing a thermoplastic polyolefin and a fibrous filler while melting the thermoplastic polyolefin, wherein the fibrous filler mainly contains cellulose fiber, A process of forming a film from the compound by the calendering method, A method for producing a thermoplastic polyolefin film, comprising the features described above. [2] The manufacturing method according to [1], wherein the average fiber diameter of the fibrous filler is 0.05 to 50 μm. [3] The method for producing the thermoplastic polyolefin according to [1] or [2], wherein the thermoplastic polyolefin comprises a propylene homopolymer or a propylene copolymer. [4] The method for producing the thermoplastic polyolefin according to any one of [1] to [3], wherein the thermoplastic polyolefin comprises a ternary polymer of propylene-ethylene-butene. [5] The method for producing the resin composition according to any one of [1] to [4], further comprising a maleic acid-modified polyolefin. [6] The thermoplastic polyolefin further comprises a propylene-ethylene-butene random copolymer elastomer, The manufacturing method according to [3], wherein the content of the propylene-ethylene-butene random copolymer elastomer in the resin composition is 20% by mass or less. [7] The manufacturing method according to any one of [1] to [6], wherein the content of the fibrous filler in the resin composition is 1% by mass or more. [8] The manufacturing method according to any one of [1] to [7], wherein the temperature of the kneaded material when forming the film is 200°C or lower. [Effects of the Invention]

[0008] This disclosure provides a method for producing a polyolefin film containing cellulose fibers that has good film-forming properties. [Modes for carrying out the invention]

[0009] Preferred embodiments of this disclosure are described in detail below. However, this disclosure is not limited to the embodiments described below.

[0010] <Resin composition> The resin composition comprises a thermoplastic polyolefin and a fibrous filler. The fibrous filler mainly consists of cellulose fibers.

[0011] (Thermoplastic polyolefin) The resin composition contains thermoplastic polyolefins. Thermoplastic polyolefins are non-crosslinked polyolefins.

[0012] Examples of thermoplastic polyolefins include linear polyolefins such as homopolymers of olefins like polyethylene, polypropylene, and polybutene; copolymers of ethylene and one or more α-olefins (ethylene-based copolymers); copolymers of propylene and one or more α-olefins (propylene-based copolymers); or copolymers of two or more α-olefins. The copolymers may be block copolymers or random copolymers. The thermoplastic polyolefin may be any one of these, or a mixture of any multiple thereof, but it is preferable that it contains a propylene homopolymer or a propylene-based copolymer.

[0013] Examples of α-olefins include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 9-methyl-1-decene, 11-methyl-1-dodecene, and 12-ethyl-1-tetradecene.

[0014] From the viewpoint of economic rationality and the stability of calendered film formation, propylene copolymers are preferred as thermoplastic polyolefins. Specifically, these include copolymers of propylene and one or more α-olefins selected from the group consisting of ethylene, 1-butene, 1-hexene, and 1-octene, propylene-based binary copolymers (propylene copolymers (propylene-α-olefin copolymers)), or propylene-based terpolymers (propyleneter polymers). Among these, propylene-based binary copolymers (propylene copolymers (propylene-α-olefin copolymers)) or propylene-based terpolymers (propyleneter polymers) are preferred. The thermoplastic polyolefin contains a propylene-ethylene binary copolymer, preferably a random copolymer thereof, which facilitates calendering. The thermoplastic polyolefin contains a propylene-ethylene-butene ternary copolymer, preferably a random copolymer thereof, which lowers the melting point and makes calendering easier.

[0015] When the thermoplastic polyolefin contains a propylene-based binary copolymer (propylene copolymer (propylene·α-olefin copolymer)) or a propylene-based terpolymer (propylene terpolymer), its amount in the resin composition may be 99% by mass or less, may also be 70% by mass or less, or may be 50% by mass or less. As the proportion of the propylene copolymer decreases, the crystallinity increases and the melting point also increases, resulting in a decrease in processing stability in calender film formation. Also, the above amount may be 1% by mass or more, may also be 5% by mass or more, or may be 9% by mass or more.

[0016] In addition to the propylene homopolymer and propylene-based copolymers, the thermoplastic polyolefin preferably further contains a propylene·ethylene·butene random copolymer elastomer. By further containing the propylene·ethylene·butene random copolymer elastomer, it is easier to obtain better impact resistance. When the thermoplastic polyolefin contains the propylene·ethylene·butene random copolymer elastomer, its amount in the resin composition may be 1% by mass or more, may also be 5% by mass or more, or may be 9% by mass or more, and may also be 20% by mass or less from the perspective of the molding resin.

[0017] When the thermoplastic polyolefin contains both a propylene·ethylene·butene terpolymer and a propylene·ethylene·butene random copolymer elastomer, the content of the propylene·ethylene·butene random copolymer elastomer may be more than 0 part by mass to 20 parts by mass or less, or may be more than 0 part by mass to 10 parts by mass or less with respect to 100 parts by mass of the propylene·ethylene·butene terpolymer. When the content of the propylene·ethylene·butene random copolymer elastomer is below the above upper limit, it is easy to suppress the adhesion of the resin to the calender roll and stabilize the film formation.

[0018] In the resin composition, the amount of the thermoplastic polyolefin may be 20% by mass or more, may also be 30% by mass or more, or may be 50% by mass or more, and may also be 99% by mass or less, or may be 95% by mass or less. When the amount of thermoplastic polyolefin is above the lower limit, the film-forming properties of the film are easily improved, and when it is below the upper limit, it is easier to improve the film's functionality with fibrous fillers.

[0019] In this disclosure, thermoplastic polyolefins are a concept that does not include maleic acid-modified polyolefins as described below.

[0020] (Maleic acid-modified polyolefin) The resin composition preferably further contains maleic acid-modified polyolefin. Examples of maleic acid-modified polyolefin include maleic anhydride-modified polypropylene.

[0021] The inclusion of maleic acid-modified polyolefin in the resin composition improves the miscibility between the thermoplastic polyolefin and the fibrous filler, making it easier for the fibrous filler to disperse in the resin composition. This not only improves film-forming properties but also reduces variations in the physical properties and characteristics of the film. In particular, when maleic acid-modified polyolefin is added to the resin composition in a range such that the fibrous filler:maleic acid-modified polyolefin ratio is 99:1 to 10:90 (by mass), or 95:5 to 10:90, the miscibility between the thermoplastic polyolefin and the fibrous filler is more easily improved.

[0022] In the resin composition, the amount of maleic acid-modified polyolefin may be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 10% by mass or less. When the amount of maleic acid-modified polyolefin is above the lower limit, the mixability between thermoplastic polyolefin and fibrous filler tends to improve, and when it is above the upper limit, it tends to suppress the deterioration of various physical properties of the polyolefin film.

[0023] (Fibrous filler) The resin composition contains a fibrous filler. The fibrous filler mainly consists of cellulose fibers. Cellulose fibers are fibers obtained by defibrating pulp fibers. Cellulose fibers can also be called cellulose nanofibers.

[0024] Cellulose fiber may contain at least one of hemicellulose and lignin in addition to cellulose. Cellulose may account for 50% or more by mass of the cellulose fiber, and may account for 70% or more by mass. Cellulose fibers may be modified with hydrophobic functional groups such as fluorene.

[0025] The fibrous filler may include, in addition to cellulose fiber, plant fibers (cotton), regenerated fibers (rayon or cupro), acetate fibers (acetate fibers, diacetate fibers, or triacetate fibers), pulp fibers, hemicellulose, lignin, etc. However, in the fibrous filler, the amount of cellulose fiber, which is the main component, is 50% by mass or more, may be 70% by mass or more, or may be 100% by mass.

[0026] The average fiber diameter of the fibrous filler may be 0.05 to 50 μm, or it may be 1 to 10 μm. When the average fiber diameter is above the lower limit, the improvement in mechanical strength due to the resin reinforcement effect of cellulose fibers is more likely to occur, and when it is below the upper limit, it is easier to achieve an improvement in mechanical strength while minimizing the decrease in impact resistance.

[0027] The average fiber length of the fibrous filler may be 1 to 1000 μm, or it may be 1 to 100 μm. When the average fiber length is above the lower limit, the improvement in mechanical strength due to the resin reinforcement effect of cellulose fibers is more likely to occur, and when it is below the upper limit, it is easier to obtain a film with fewer aggregates or fewer appearance defects originating from cellulose fibers.

[0028] The average aspect ratio of the fibrous filler may be 50 or more, 500 or more, 700 or more, 1000 or less, or 950 or less. If the average aspect ratio is above the lower limit, the mechanical strength and thermal expansion stability of the film tend to improve, and if it is below the upper limit, it is easier to obtain a film with fewer aggregates or fewer appearance defects originating from cellulose fibers. The average aspect ratio of fibrous fillers is defined as the ratio of the average fiber length to the average fiber diameter (average fiber length / average fiber diameter).

[0029] The average fiber diameter and average fiber length of fibrous fillers can be calculated by measuring the fiber diameter and fiber length of any 20 fibers in transmission electron microscope images of the resin composition or film and taking the average value.

[0030] In the resin composition, the amount of fibrous filler may be 1 to 70% by mass, 1 to 50% by mass, or 9 to 20% by mass. In the resin composition, the amount of fibrous filler may be 10 to 100 parts by mass, 20 to 80 parts by mass, or 30 to 70 parts by mass per 100 parts by mass of thermoplastic polyolefin. If the amount of fibrous filler is above the lower limit, it is easier to improve the film's functionality with the fibrous filler, and if it is below the upper limit, it is easier to improve the film's film-forming properties.

[0031] According to this disclosure, even resin compositions containing a large amount of fibrous fillers with a high aspect ratio can be successfully formed into films.

[0032] (Other ingredients) The resin composition may contain other components besides thermoplastic polyolefins, maleic acid-modified polyolefins, and fibrous fillers. These other components may include colorants, elastomers, UV absorbers, light stabilizers, inorganic materials such as calcium carbonate, mica, and talc, flame retardants such as metal hydrates, pigments, foam regulators, lignin, hemicellulose, antioxidants, nucleating agents, antistatic agents, processing stabilizers, slip agents, and foaming agents. In the resin composition, the amounts of other components may be 10% by mass or less.

[0033] <Method for manufacturing thermoplastic polyolefin film> The method for manufacturing a thermoplastic polyolefin film is: A resin composition containing thermoplastic polyolefin and fibrous filler is pre-kneaded while melting the thermoplastic polyolefin to prepare a kneaded product; The process of forming a film from a compound using the calendering method, It is equipped with.

[0034] The calendering method allows for film formation without the influence of draw resonance seen in the T-die method. Furthermore, because the influence of draw resonance does not need to be considered, a larger amount of fibrous filler can be added in the calendering method. In addition, since the shear force applied to the resin (thermoplastic polyolefin) and cellulose fibers is small in the calendering method, resin heat generation can be kept low, and discoloration of the film caused by the hemicellulose component present in the cellulose fibers can be suppressed.

[0035] The temperature during pre-mixing, that is, the temperature at which the thermoplastic polyolefin is melted, can be, for example, in the range of the melting point of the thermoplastic polyolefin + 50°C, and may be, for example, 100 to 200°C, or 100 to 170°C.

[0036] The pre-mixing time may be, for example, 1 to 20 minutes, or 2 to 10 minutes. The shear force (shear rate) applied to the resin composition during pre-mixing is, for example, 1 to 1000 seconds. -1 It may be, and for 10-500 seconds -1 That's fine.

[0037] While there are no particular limitations on the pre-mixing equipment (mixer), examples include mixing rolls, intensive mixers (e.g., Banbury mixers, kneaders), etc.

[0038] The compound prepared by pre-mixing is formed into a film (thermoplastic polyolefin film) by the calendering process. A calendering machine is used for the calendering process. The temperature conditions during calendering, that is, the temperature of the compound used to form the film, may be, for example, 100-200°C or 100-140°C. If the temperature conditions are below the above upper limit, it is easier to suppress discoloration of the film caused by the thermal decomposition of hemicellulose.

[0039] <Thermoplastic polyolefin film> Because thermoplastic polyolefin films contain cellulose fibers, they exhibit improved mechanical strength, dimensional stability, and oxygen barrier properties compared to films that do not contain cellulose fibers. Furthermore, since cellulose fibers are biomass materials, these films can be considered more environmentally friendly and sustainable. In this disclosure, such polyolefin films can be referred to as cellulose fiber composite films.

[0040] The film thickness may be 20 to 2000 μm, or 50 to 500 μm. When the film thickness is above the lower limit, the mechanical strength improvement effect of cellulose fibers is more easily realized, and when it is below the upper limit, sufficient cooling of the resin occurs during calendering, making it easier to stabilize the physical properties.

[0041] Thermoplastic polyolefin films can be suitably used in applications such as various food packaging materials, food and non-food trays, decorative sheets, transport bags, and anti-static films. [Examples]

[0042] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0043] <Preparation of materials to be used> Propylene-ethylene-butene (C3-C2-C4) ternary random polypropylene: Novatec PP FX4EA, manufactured by Japan Polyethylene Corporation. Propylene-ethylene-butene (C3-C2-C4) ternary random copolymer elastomer: Toughmer PN-2070, manufactured by Mitsui Chemicals. Maleic acid-modified polypropylene: Yumex 1010, manufactured by Sanyo Chemical Industries. Cellulose fiber masterbatch 1: Average fiber diameter 0.5 μm, average fiber length 125 μm, average aspect ratio 250 (cellulose fiber content 30% by mass, remainder mainly PP) Cellulose fiber masterbatch 2: Average fiber diameter 1.0 μm, average fiber length 160 μm, average aspect ratio 160 (cellulose fiber content 30% by mass, remainder mainly PP) Cellulose fiber masterbatch 3: Average fiber diameter 5.0 μm, average fiber length 550 μm, average aspect ratio 110 (cellulose fiber content 30% by mass, remainder mainly PP) Cellulose fiber masterbatch 4: Average fiber diameter 10 μm, average fiber length 900 μm, average aspect ratio 90 (cellulose fiber content 30% by mass, remainder mainly PP) Cellulose fiber masterbatch 5: Average fiber diameter 12 μm, average fiber length 750 μm, average aspect ratio 50 (cellulose fiber content 30% by mass, remainder mainly PP)

[0044] <Film Formation> (Examples, Comparative Examples 3) Resin compositions were prepared by dry blending various materials according to the formulations in Table 1 or 2. The numerical values ​​for each material in Tables 1 and 2 represent parts by mass of that material. This was placed in a mixer and pre-mixed at 120°C for 5 minutes using two rollers to obtain the mixed product. Using a small calender film-forming machine (manufactured by Nippon Roll Manufacturing Co., Ltd.), films were formed from the obtained kneaded material at the temperatures listed in Tables 1-2 (resin mixture temperature: 120-200°C) to obtain a film thickness of 50 μm, resulting in the films (thermoplastic polyolefin films) shown in each example.

[0045] (Comparative Examples 1 and 2) Resin compositions were prepared by dry blending various materials according to the formulations in Table 2. This was fed into a twin-screw extruder, melted and mixed at a cylinder temperature of 138°C, extruded from a strand die, and solidified with water cooling. This was then cut into 3mm lengths with a strand cutter to produce mixed pellets. We attempted to form films from the resulting kneaded pellets using a T-type die extruder and an inflation extruder (cylindrical die) under conditions of a film thickness of 50 μm. However, in both extruders, film breakage and uneven thickness in the film formation direction occurred, making it impossible to obtain films suitable for evaluation.

[0046] <Film Evaluation> The following evaluations were performed on each example film. The results are shown in Tables 1 and 2.

[0047] (Film appearance - perforated) We visually inspected each example of film to check for holes. ○: There were no holes. ×: There was a hole.

[0048] (Film appearance and color) The color of the film in each example was visually inspected. ○: White. △: Pale cream color. △△: Light brown.

[0049] (Tensile modulus of elasticity in the MD direction) A dumbbell-shaped test specimen was prepared with a width of 10 mm in the effective test area, so that the direction of film formation during film formation was the same as the direction of the load during testing. Then, a tensile test (23°C) was performed with a chuck distance of 40 mm and a tensile speed of 50 m / min, and the tensile modulus of elasticity (MPa) of the test specimen was measured.

[0050] (Elongation at break, TD direction) A dumbbell-shaped test specimen was prepared with a width of 10 mm in the effective test area, so that the direction of film formation during film formation was perpendicular to the direction of the load during testing. A tensile test (23°C) was then performed with a chuck distance of 40 mm and a tensile speed of 50 m / min, and the elongation rate (%) before fracture was measured.

[0051] (Impact resistance) The dumbbell test specimens used for evaluating the elongation at break were bent into an arc shape, the ends of the dumbbells were joined together with double-sided tape, and the ring was left standing for 1 hour in environments of -10°C, 0°C, and +10°C. Then, 1 kg / cm² was applied to the R portion. 2 The bending section along the arc was bent 180° by applying a load, and the cracks in the 180° bend were visually evaluated. ○: It didn't break. △: Some cracks were observed. ×: It's completely broken.

[0052] [Table 1]

[0053] [Table 2]

Claims

1. A step of preparing a kneaded product by pre-kneading a resin composition containing a thermoplastic polyolefin and a fibrous filler while melting the thermoplastic polyolefin, wherein the fibrous filler mainly contains cellulose fiber, A process of forming a film from the compound by the calendering method, A method for producing a thermoplastic polyolefin film, comprising the features described above.

2. The manufacturing method according to claim 1, wherein the average fiber diameter of the fibrous filler is 0.05 to 50 μm.

3. The method for producing a thermoplastic polyolefin according to claim 1 or 2, wherein the thermoplastic polyolefin comprises a propylene homopolymer or a propylene copolymer.

4. The method for producing a thermoplastic polyolefin according to claim 1 or 2, wherein the thermoplastic polyolefin comprises a ternary copolymer of propylene, ethylene, and butene.

5. The manufacturing method according to claim 1 or 2, wherein the resin composition further comprises a maleic acid-modified polyolefin.

6. The thermoplastic polyolefin further comprises a propylene-ethylene-butene random copolymer elastomer, The manufacturing method according to claim 3, wherein the content of the propylene-ethylene-butene random copolymer elastomer in the resin composition is 20% by mass or less.

7. The manufacturing method according to claim 1 or 2, wherein the content of the fibrous filler in the resin composition is 1% by mass or more.

8. The manufacturing method according to claim 1 or 2, wherein the temperature of the kneaded material when forming the film is 200°C or lower.

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