JP2014234395A - Stretch film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stretch film which is excellent in impact resistance and can control the temperature inside silage and the temperature of the contact part between silage and a film in a good balance.SOLUTION: There is provided a stretch film which has at least one resin composition layer containing 3.0 pts.wt. or more and 12.0 pts.wt. or less of a mixture in which the weight ratio (titanium dioxide pigment: carbon black) of a titanium dioxide pigment to carbon black is in a range of 5:1 to 15:1, based on 100 pts.wt. of a polyethylene-based resin.

Description

  The present invention relates to a stretch film having optimum light transmittance, light reflectance, and infrared energy shielding rate. In particular, the present invention relates to a stretch film suitable for stretch-wrapping silage made into a roll bale used as horse or cattle feed using a dedicated wrapping machine or the like, and obtaining silage with high nutritional value by fermentation.

  Conventionally, to improve the puncture resistance and impact resistance, which are the required performance for silage film, or to maintain the sealing force when sealing bale-grown raw grass etc. with silage film Various proposals have been made for improving film adhesiveness (for example, Patent Documents 1 to 4).

  In addition, in order to prevent the grass from being discolored or fermented during silage adjustment, an appropriate coloring component is added to the film to reduce the transmittance of sunlight, a white monochromatic film, Products such as black monochromatic film or green monochromatic film are on the market.

JP 05-169599 A JP 05-301328 A Japanese Patent Laid-Open No. 10-235809 JP 2003-276123 A

  Silage such as grass is wrapped with a film and sealed to make the fermentation progress (with fever), and the nutritional value becomes high. In order to obtain good silage such as grass with high nutritional value, it is necessary to suppress the temperature rise due to heat generation during fermentation as much as possible. In other words, it is important that the silage surface such as pasture and the inner surface temperature are not increased as much as possible by sunlight during the daytime.

  Under such circumstances, the currently available silage film is exposed to sunlight outdoors. For example, a white film colored with a titanium oxide pigment rises in temperature at the part that contacts the film. Although the suppression effect is high, there is a problem that the temperature inside the silage tends to rise. Moreover, the film colored green is also in the same tendency as the white film, and there is a problem in suppressing the temperature rise inside the silage. On the other hand, the black film to which carbon black or the like is added has a high effect of suppressing the temperature rise inside the silage, but there is a problem that the temperature of the portion that contacts the contact surface between the silage and the film tends to rise, and any film has a temperature. There is nothing satisfactory in terms of balance control.

  In view of the above problems, an object of the present invention is to provide a stretch film that has excellent impact resistance and can control the silage internal temperature and the temperature of the contact portion between the silage and the film in a well-balanced manner.

  As a result of intensive studies to solve the above-mentioned problems, the inventors have made a stretch film having at least one resin layer to which a specific amount of a titanium oxide pigment and carbon black are added at specific ratios, respectively. Further, it has been found that a stretch film suitable for silage can be obtained, which can control the temperature of the contact portion between the silage and the film in a well-balanced manner, has excellent piercing strength and impact strength, and has excellent adhesion. Was completed.

  That is, according to the present invention, a mixture in which the weight ratio of titanium oxide pigment to carbon black (titanium oxide pigment: carbon black) is in the range of 5: 1 to 15: 1 with respect to 100 parts by weight of the polyethylene resin is 3.0. A stretch film comprising at least one resin composition layer containing at least 1 part by weight and not more than 12.0 parts by weight.

  In the present invention, the term “mixture” means that a predetermined amount of a titanium oxide pigment and carbon black need only be mixed and contained in the resin composition layer. The present invention is not limited to the form of adding (simultaneously adding) a mixture of a titanium pigment and carbon black, and the resin composition layer may be configured by individually adding a titanium oxide pigment and carbon black.

  The stretch film according to the present invention preferably has a total light transmittance of less than 25% and a light reflectance of 18% or more at a wavelength of 400 nm to 700 nm.

  The stretch film according to the present invention preferably has an infrared energy shielding rate of 15% or more at a wavelength of 5 nm or more and 25 nm or less.

  In the stretch film according to the present invention, the polyethylene resin is at least one resin selected from a polyethylene resin (A) by an ion polymerization method and a polyethylene resin (B) by a high-pressure radical method, and the molecular weight of the resin The distribution (Mw / Mn) is preferably 1.5 or more and 5.0 or less.

  The stretch film according to the present invention has the above resin composition layer as an intermediate layer, and an outer layer and / or an inner layer composed mainly of an ethylene-α-olefin copolymer or an ethylene-vinyl acetate copolymer. It is preferable to have.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in impact resistance, the stretch film which can control a silage internal temperature and the temperature of the contact part of a silage and a film with sufficient balance can be provided.

  In the stretch film according to the present invention, a mixture in which the weight ratio of titanium oxide pigment to carbon black (titanium oxide pigment: carbon black) is in the range of 5: 1 to 15: 1 with respect to 100 parts by weight of the polyethylene resin is 3 It has at least one resin composition layer containing 0.0 part by weight or more and 12.0 parts by weight or less. By having at least one such resin composition layer, it is possible to obtain a stretch film that is excellent in impact resistance and can control the silage internal temperature and the temperature of the contact portion between the silage and the film in a well-balanced manner.

1. Polyethylene resin The polyethylene resin used in the present invention is not particularly limited as long as it is an ethylene homopolymer or a copolymer containing ethylene as a main component and applicable as a stretch film. . In particular, it is preferable to use a polyethylene resin having a melt flow rate (MFR) measured at a temperature of 190 ° C. and a load of 21.18 N of 0.5 g / 10 min to 7 g / 10 min. The lower limit of MFR is more preferably 0.7 g / 10 min or more, particularly preferably 1.0 g / 10 min or more, and the upper limit is more preferably 5.0 g / 10 min or less, particularly preferably 3.0 g / 10. Is less than a minute. If the MFR of the polyethylene resin is less than 0.5 g / 10 minutes, in addition to increasing the load on the extruder during extrusion molding, there will be problems with the dispersibility of the titanium oxide pigment and carbon black described later in the resin There is a fear. Moreover, when MFR exceeds 7 g / 10min, there exists a possibility that the problem may arise in the film-forming stability at the time of inflation film shaping | molding, and there exists a possibility that the intensity | strength of the completed film may become low.

  In particular, the polyethylene resin used in the present invention is at least one resin selected from a polyethylene resin (A) obtained by an ionic polymerization method and a polyethylene resin (B) obtained by a high-pressure radical method. Is preferred.

1.1. Polyethylene resin obtained by ion polymerization method (A)
The polyethylene resin (A) obtained by the ionic polymerization method is an ethylene polymer produced by the ionic polymerization method and having a density of 0.8 g / cm ³ or more and 0.96 g / cm ³ or less, and an ethylene homopolymer Or the copolymer with the alpha olefin which has ethylene as a main component is included. Preferably, the density 0.910 g / cm ³ or more 0.935 g / cm ³ or less of ethylene -α- olefin copolymer (linear low density polyethylene, LLDPE).

  When an ethylene-α-olefin copolymer is used as the polyethylene resin (A), the α-olefin that can constitute the copolymer includes an α-olefin having 3 to 12 carbon atoms, preferably 3 to 10 carbon atoms. Specific examples include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene and the like. The proportion of α-olefin in the copolymer is preferably 3 to 40 mol%.

  The polyethylene resin (A) can be produced by an ion polymerization method using a Ziegler catalyst, a vanadium catalyst, a Phillips catalyst, a single site catalyst (including a metallocene catalyst), or the like. Among these, those produced using a single site catalyst are preferred because of their excellent mechanical strength. Preferable examples of the single-site catalyst include those containing a metallocene compound such as a zirconium compound coordinated with a group having a cyclopentadienyl skeleton and a promoter.

  Examples of the ion polymerization method include a high pressure ion polymerization method, a gas phase method, a solution method, and a slurry method, and any method may be used.

1.2. Polyethylene resin (B) obtained by high pressure radical polymerization method
The polyethylene-based resin (B) obtained by the high-pressure radical polymerization method is a low-density polyethylene (B1) obtained by the high-pressure radical polymerization method, an ethylene-vinyl ester copolymer (B2), or ethylene and α, β-insoluble. A copolymer (B3) with a saturated carboxylic acid or a derivative thereof is included, and at least one of these is preferable.

1.2.1. Low density polyethylene (B1)
The low-density polyethylene (B1), density of 0.910 g / cm ³ or more 0.940 g / cm ³ or less, preferably 0.912 g / cm ³ or more 0.935 g / cm ³ or less, more preferably 0.915 g / It is a low density polyethylene (LDPE) of cm ³ or more and 0.930 g / cm ³ or less. In addition, when the melt tension at a temperature of 190 ° C. is 1.5 g or more and 25 g or less, preferably 3 g or more and 20 g or less, more preferably 3 g or more and 15 g or less, the film moldability is good and this is preferable.

1.2.2. Ethylene-vinyl ester copolymer (B2)
The ethylene-vinyl ester copolymer (B2) is an ethylene-vinyl ester copolymer produced by a high-pressure radical polymerization method. The main component is ethylene, vinyl propionate, vinyl acetate, vinyl caproate, It is a copolymer of vinyl ester such as vinyl caprylate, vinyl laurate, vinyl stearate, vinyl trifluoroacetate and the like and other unsaturated monomers as optional components. Among these, a copolymer (EVA) of ethylene and vinyl acetate is particularly preferable.

  The ethylene-vinyl ester copolymer (B2) is a copolymer comprising 50 to 99.5% by weight of ethylene, 0.5 to 50% by weight of vinyl ester, and 0 to 49.5% by weight of other unsaturated monomers. Is preferred. The vinyl ester content is more preferably 3 to 50% by weight, still more preferably 5 to 30% by weight.

  Examples of the other unsaturated monomer in the ethylene-vinyl ester copolymer (B2) include methyl (meth) acrylate, ethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, and 2-ethoxyethyl (meth). Examples thereof include (meth) acrylic acid ester monomers such as acrylate and phenoxyethyl (meth) acrylate, and methyl (meth) acrylate is particularly preferable.

1.2.3. Copolymer of ethylene and α, β-unsaturated carboxylic acid or derivative thereof (B3)
As a copolymer (B3) of ethylene and α, β-unsaturated carboxylic acid or derivative thereof, ethylene, α, β-unsaturated carboxylic acid or derivative thereof, and other unsaturated monomer as an optional component And copolymers thereof, and metal salts thereof (ionomers), amides, imides and the like. In this case, examples of the α, β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and maleic anhydride, and acrylic acid and methacrylic acid are particularly preferable. Other unsaturated monomers include methyl (meth) acrylate, ethyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, phenoxyethyl (meth) acrylate, and the like. Examples include (meth) acrylic acid ester monomers, and methyl (meth) acrylate is particularly preferable.

  The copolymer (B3) is a copolymer comprising 50 to 99.5% by weight of ethylene, 0.5 to 50% by weight of α, β-unsaturated carboxylic acid, and 0 to 49.5% by weight of other unsaturated monomers. Polymers are preferred. The content of α, β-unsaturated carboxylic acid is more preferably 3 to 50% by weight, still more preferably 5 to 30% by weight.

  The molecular weight distribution (Mw / Mn) of the polyethylene resin is preferably 1.5 or more and 5.0 or less. If the molecular weight distribution is smaller than 1.5, the load on the extruder during molding increases, and there is a possibility that problems such as an increase in the resin temperature due to heat generation in the extruder may occur. On the other hand, if the molecular weight distribution exceeds 5.0, the film strength is lowered, the optical properties are also lowered, and the film appearance may be deteriorated.

2. Titanium oxide pigment and carbon black In the present invention, the weight ratio of titanium oxide pigment to carbon black (titanium oxide pigment: carbon black) contained in the resin composition layer is 5: 1 to 15: 1. When the weight ratio of carbon black is too large, the light reflectance at a wavelength of 400 to 700 nm is reduced when used for silage, and the temperature at the contact portion between the silage and the film rises excessively when exposed to sunlight. Resulting in. If the weight ratio of carbon black is too small, the total light transmittance increases, and the temperature inside the silage rises excessively when exposed to sunlight.

  The total content of the titanium oxide pigment and carbon black in the resin composition layer is 3.0 parts by weight or more and 12.0 parts by weight or less with respect to 100 parts by weight of the polyethylene resin. The lower limit is preferably 5.0 parts by weight or more, more preferably 6.0 parts by weight or more, and the upper limit is preferably 10.0 parts by weight or less, more preferably 8.0 parts by weight or less. When the total content is less than 3.0 parts by weight, the total light transmittance increases, and the internal temperature of the silage rises excessively when exposed to sunlight. Moreover, when there are more total contents than 12.0 weight part, not only the reduction effect of a total light transmittance will be saturated, but the intensity | strength reduction of a film will be caused and cost will also rise.

  The titanium oxide pigment is not particularly limited as long as it is titanium oxide used as a pigment, and any of those produced by a known production method such as a sulfuric acid method or a chlorine method can be used. In particular, it is preferable to use a rutile type from the viewpoint of stability of crystal form, thermal stability, and weather resistance. Further, from the viewpoint of improving dispersibility in the stretch film and controlling the silage internal temperature and the temperature of the contact portion between the silage and the film in a more balanced manner, the average particle size of the titanium oxide pigment is 0.05 μm or more and 1.0 μm or less Is preferred. In the present application, the “average particle size” means an average particle size obtained based on laser diffraction / scattering measurement.

  Carbon black is not particularly limited, and any carbon black produced by a known production method such as a furnace method, a channel method, or an acetylene method can be used. From the viewpoint of availability, those produced by the oil furnace method are preferred. In addition, the average particle size of carbon black is preferably 40 nm or less from the viewpoint of improving dispersibility in the stretch film and controlling the silage internal temperature and the temperature of the contact portion between the silage and the film in a more balanced manner.

3. Other additive components In the resin composition layer, various known auxiliary additives used in silage films such as grasses, if necessary, such as tackifiers, ultraviolet absorbers, light stabilizers, antioxidants, You may contain an antiblocking agent, a slip agent, a neutralizing agent, a heat retention agent, etc.

  Examples of the tackifier include natural rubber, styrene isoprene styrene block copolymer (SIS), styrene butadiene rubber (SBR), butyl rubber, EVA hot melt, various tackifiers, etc., but polybutene and polyisobutylene. Are preferably used.

  Moreover, when applying the stretch film which concerns on this invention to the film for silage, it is preferable to include a light stabilizer and a ultraviolet absorber as a weather resistance agent in a resin composition layer in consideration of the use in the outdoors. For example, it is preferable to include a hindered amine compound (light stabilizer).

4). Resin Composition In the present invention, a resin composition is composed of the above-described polyethylene resin, titanium oxide pigment, carbon black, and other additives that are optional components. The resin composition can be easily obtained by mixing each component. The titanium oxide pigment, carbon black or various additives added in the resin composition may be prepared by simple blending with a Henschel mixer, an extruder or the like, such as dry blending, in a desired composition. However, it is preferably provided as a master batch that is blended in a high concentration in the base resin and melt-kneaded in an extruder. In particular, the pelletized master batch improves handling, transportation and workability, and also allows the titanium oxide pigment and carbon black to be uniformly dispersed in the resin composition. There is no unevenness of addition, and a stretch film with uniform performance can be obtained.

5. Stretch film layer structure The stretch film according to the present invention has a weight ratio of the titanium oxide pigment to carbon black (titanium oxide pigment: carbon black) of 5: 1 to 15 with respect to 100 parts by weight of the polyethylene resin. : At least one resin composition layer containing 3.0 parts by weight or more and 12.0 parts by weight or less of a mixture in the range of 1: In addition to the resin composition layer, other layers You may have. In particular, the resin composition layer (layer b) is used as an intermediate layer, and the outer layer and / or inner layer is a layer (layer a) containing ethylene-α-olefin copolymer as a main component or ethylene-vinyl acetate copolymer. What has the layer (layer c) which has coalescence as a main component is preferable.

  That is, when the stretch film according to the present invention has a three-layer structure, layer a / layer b / layer a, layer a / layer b / layer c, layer c / layer b / The layer configuration may be either layer c or layer c / layer b / layer a, and may be appropriately selected according to suitability with a silage wrapping machine, control of film adhesion, and the like. In any case, the above resin composition layer (layer b) is preferably an intermediate layer. By setting it as such a layer structure, the unevenness | corrugation roughness of the film surface by a titanium oxide pigment etc. is suppressed, and the adhesiveness of the films at the time of silage wrapping can be made favorable. Further, when the above resin composition layer containing a titanium oxide pigment or the like is used in any one of the inner layer and the outer layer, the resulting film may be curled, and the handling property at the time of lapping work is hindered. There is also a fear.

  The composition ratio (thickness ratio) of the film in the case of a three-layer structure is preferably 1: 6: 1 to 1: 1: 1, more preferably 1: 5: 1 to 1: 2: 1. More preferably, it is 1: 4: 1 to 1: 3: 1. The total thickness of the film is preferably 10 μm to 50 μm, more preferably 15 μm to 40 μm, and still more preferably 20 μm to 35 μm. If it is such thickness ratio and total thickness, it can be set as the stretch film which has sufficient mechanical strength, and can control silage internal temperature and the temperature of the contact part of a silage and a film with further balance.

6). Stretch film manufacturing method The stretch film according to the present invention can be easily manufactured by molding the above resin composition by a known molding method. As the molding method, for example, an air-cooled inflation film molding by an extruder according to the number of laminated resin layers constituting the film, and a lamination die having a feed block type, a multi-manifold type, a multi-slot type joining / merging portion, Examples include T-die film molding, and the inflation film molding method is particularly simple and economical.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, unless this invention exceeds the summary, it is not limited to a following example at all.

  The measurement and evaluation of physical properties according to Examples and Comparative Examples were performed by the following methods.

1. Evaluation method of resin physical properties (1) Melt flow rate (MFR) of resin: Measured according to JIS K6922-2: 1997 appendix (190 ° C., 21.18 N load).
(2) Density of resin: measured according to JIS K7122.
(3) Weight average molecular weight (Mw) and number average molecular weight (Mn) of the resin: measured by the following apparatus and conditions.

Apparatus: Waters GPC 150C type Detector: MIRAN 1A infrared spectrophotometer (measurement wavelength, 3.42 μm)
Column: 3 AD806M / S manufactured by Showa Denko (column calibration is made by Tosoh monodisperse polystyrene (0.5 mg / ml solution of each of A500, A2500, F1, F2, F4, F10, F20, F40, and F288) Measurements were made to approximate the logarithm of the elution volume and molecular weight by a quadratic equation, and the molecular weight of the sample was converted to polyethylene using the viscosity equation of polystyrene and polyethylene, where the coefficient of the viscosity equation of polystyrene is α = 0.723, log K = -3.967, and polyethylene has α = 0.723, log K = -3.407.)
Measurement temperature: 140 ° C
Injection volume: 0.2ml
Concentration: 20mg / 10ml
Solvent: Orthodichlorobenzene Flow rate: 1.0 ml / min

2. Stretch film physical property evaluation method (1) Total light transmittance The total light transmittance (%) was measured by a method based on JIS K7105 using a direct reading haze meter (manufactured by Toyo Seiki Seisakusho). The lower the numerical value, the better the light blocking effect and the higher the temperature rise suppression effect inside the silage.

(2) Light reflectance The light reflectance (%) of the film with respect to light having a wavelength of 400 to 700 nm was measured using a spectrophotometer (V-550 manufactured by JASCO Corporation). The maximum peak reflectance at this time was read and used as the reflectance value of the film. The higher the value, the higher the temperature rise suppression effect on the contact surface between the silage and the film.

(3) Infrared energy shielding rate The spectral radiation divergence of each wavelength obtained by Planck's radiation law is weighted by the absorption rate corresponding to each wavelength of the film obtained by the infrared spectrophotometer, and the spectrum weighted by the absorption rate The infrared energy shielding rate (%) was obtained from the ratio of the radiant divergence and the original spectral radiant divergence. The larger the numerical value, the higher the infrared absorption ability, and the lowering of the internal temperature drop rate at night can be reduced.

(4) Punching impact strength test Penetration fracture energy (punching impact strength) (J / cm) was measured using a testing machine including the following in accordance with JIS P8134 (1976).
・ A pendulum with a 90 ° arc-shaped arm that can attach a penetrating part to the tip and can vibrate freely. ・ The standard is 25.4mmφ hemispherical metal, and the surface has a specular gloss. A clamp that can be attached to the tip of the arc-shaped arm of the arm and clamps the test piece horizontally and uniformly, with an inner diameter of 50 mmφ as a standard.

(5) Measurement of temperature 14kg of commercially available fertilizer for horticultural use is put into a polystyrene foam container (410mm x 500mm x height 200mm), an evaluation film is spread on the top, and it goes to the outside of the Sanyo Kasei company site in Yokkaichi City, Mie Prefecture. Install and measure the internal temperature of the fertilizer soil (measured by embedding a sensor 5 cm below the surface of the fertilizer soil) and the inner surface temperature of the stretched film (sensor on the inner surface of the film) using a temperature measuring instrument ("Andoritori TR-71Uai" manufactured by T & D) Measurement was carried out continuously day and night.

Example 1
The following resin compositions constituting the outer layer, the intermediate layer, and the inner layer were extruded using a three-layer three-layer inflation film molding machine (die diameter: 300 mmφ) manufactured by Plako Co., Ltd. (molding temperature: outer layer 160 ° C., intermediate layer 180 ° C., inner layer) 175 ° C.) and inflation film molding was performed to obtain a stretch film according to Example 1. The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

Resin composition constituting outer layer: ethylene-vinyl acetate copolymer resin (Novatec EVA “LV440” manufactured by Nippon Polyethylene Co., Ltd., MFR 2.0 g / 10 min, vinyl acetate content 15 wt%, Mw / Mn 4.4) 100 A resin composition comprising 4 parts by weight of polybutene as an adhesive and 0.2 parts by weight of a hindered amine light stabilizer as a weathering agent. A resin composition constituting an intermediate layer: an ethylene-α-olefin copolymer resin ( Low-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd.) obtained by Dow Chemical's “DOWLEX2045G”, MFR 1.0 g / 10 min, density 0.920 g / cm ³ , Mw / Mn 3.8) by 80 parts by weight, high-pressure radical polymerization method "Novatec LD LF440B", MFR2.8g / 10 minutes, density ^{0.924g / cm 3, Mw / Mn4} . ) 20 parts by weight, titanium oxide pigment (FTR-700, Sakai Chemical Industry Co., Ltd., average particle size 0.2 μm) is 6.0 parts by weight, and carbon black (RCF, Mitsubishi Chemical Co., Ltd., average particle size 24 nm) is 0.0 part. 5 parts by weight, 4 parts by weight of polybutene as an adhesive, and 0.2 parts by weight of a hindered amine light stabilizer as a weathering agent. A resin composition constituting the inner layer: an ethylene-α-olefin copolymer (Japan) “Novatech LL UF230” manufactured by Polyethylene, 75 parts by weight of MFR 1.0 g / 10 min, density 0.920 g / cm ³ , Mw / Mn 3.6), low density polyethylene by the high pressure radical method (“Novatech LD manufactured by Nippon Polyethylene Co., Ltd.) LF440B ", MFR2.8g / 10 min, density ^{0.924g / cm 3, Mw / Mn4.5} ) 25 parts by weight, polybutylene as an adhesive 4 parts by weight of down, hindered amine light stabilizer resin composition prepared by mixing 0.2 parts by weight weathering agents

(Example 2)
In the intermediate layer, a stretch film according to Example 2 was obtained in the same manner as in Example 1 except that the content of titanium oxide pigment was 5.5 parts by weight and the content of carbon black was 1.0 part by weight. . The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

Example 3
In the intermediate layer, a stretch film according to Example 3 was obtained in the same manner as in Example 1 except that the content of the titanium oxide pigment was 2.5 parts by weight and the content of the carbon black was 0.5 parts by weight. . The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

Example 4
In the intermediate layer, a stretch film according to Example 4 was obtained in the same manner as in Example 1 except that the content of the titanium oxide pigment was 11.0 parts by weight and the content of the carbon black was 1.0 part by weight. . The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

(Comparative Example 1)
A stretch film according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the content of the titanium oxide pigment in the intermediate layer was 0 part by weight and the content of carbon black was 6.5 parts by weight. The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

(Comparative Example 2)
A stretch film according to Comparative Example 2 was obtained in the same manner as in Example 1 except that the content of the titanium oxide pigment in the intermediate layer was 6.5 parts by weight and the content of carbon black was 0 parts by weight. The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

(Comparative Example 3)
In the intermediate layer, a stretch film according to Comparative Example 3 was obtained in the same manner as in Example 1 except that the content of titanium oxide pigment was 3.5 parts by weight and the content of carbon black was 3.0 parts by weight. . The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

(Comparative Example 4)
In the intermediate layer, a stretch film according to Comparative Example 4 was obtained in the same manner as in Example 1 except that the content of titanium oxide pigment was 6.2 parts by weight and the content of carbon black was 0.3 parts by weight. . The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

(Comparative Example 5)
In the intermediate layer, a stretch film according to Comparative Example 5 was obtained in the same manner as in Example 1 except that the content of titanium oxide pigment was 1.8 parts by weight and the content of carbon black was 0.2 parts by weight. . The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

(Comparative Example 6)
In the intermediate layer, a stretch film according to Comparative Example 6 was obtained in the same manner as in Example 1 except that the content of titanium oxide pigment was 12.5 parts by weight and the content of carbon black was 2.5 parts by weight. . The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

(Comparative Example 7)
In the intermediate layer, the content of titanium oxide pigment is 3.5 parts by weight, the content of carbon black is 0 part by weight, and phthalocyanine green ("PG-7" manufactured by Dainichi Seika Kogyo Co., Ltd.) is 3.0 parts by weight. A stretch film according to Comparative Example 7 was obtained in the same manner as in Example 1 except that it was included. The obtained film had an outer layer thickness of 4 μm, an intermediate layer thickness of 17 μm, and an inner layer thickness of 4 μm. The evaluation results of the obtained film are shown in Table 1 below.

As is clear from the results shown in Table 1, in the stretch films according to Examples 1 to 4, the weight ratio of the titanium oxide pigment and carbon black in the intermediate layer and the total addition amount were within a predetermined range. The internal temperature of the film (corresponding to the temperature inside the silage) and the internal surface temperature of the film (corresponding to the temperature of the contact portion between the silage and the film) can be controlled in a well-balanced manner, and the punching impact strength is high. Specifically, in any film, the internal temperature of the film is less than 25 ° C., the increase in the internal temperature is effectively suppressed, and a temperature suitable for silage can be maintained. In addition, any film has an inner surface temperature of less than 40 ° C., and the temperature does not increase excessively even in the vicinity of the film surface. Each film has an excellent punching impact strength of about 300 J / cm.
On the other hand, in the stretch film according to Comparative Example 1, since the titanium oxide pigment was not added to the intermediate layer, the light reflectance of the film was lowered, and the surface temperature inside the film was excessively increased (40 ° C. was excellent) And increased to around 45 ° C.).
Further, in the stretch film according to Comparative Example 2, since carbon black was not added to the intermediate layer, the total light transmittance of the film increased, the infrared energy shielding rate decreased, and the film internal temperature increased. The result was too high (exceeding 25 ° C and rising to around 30 ° C).
In the stretch film according to Comparative Example 3, in the intermediate layer, carbon black was excessively added to the titanium oxide pigment, so that the light reflectance of the film was decreased and the surface temperature inside the film was excessively increased ( Well over 40 ° C).
Further, in the stretch film according to Comparative Example 4, the amount of carbon black added to the titanium oxide pigment in the intermediate layer was too small, so that the total light transmittance of the film increased and the infrared energy shielding rate was high. As a result, the internal temperature of the film increased excessively (exceeding 25 ° C.).
Further, in the stretch film according to Comparative Example 5, since the total addition amount of the titanium oxide pigment and carbon black in the intermediate layer was excessively decreased, the total light transmittance increased, the light reflectance decreased, and the infrared ray The energy shielding rate also decreases, and both the film internal temperature and the film inner surface temperature rise too much (internal temperature: well above 25 ° C, rise to around 30 ° C, inner surface temperature: well above 40 ° C, 45 Raised to ℃).
Further, in the stretch film according to Comparative Example 6, since the total amount of the titanium oxide pigment and carbon black in the intermediate layer was excessively increased, the light reflectance was lowered and the surface temperature inside the film was increased too much. As a result, the punching impact strength also decreased extremely (inner surface temperature: increased to around 40 ° C., punching impact strength: decreased to 250 J / cm).
Furthermore, in the stretch film according to Comparative Example 7, in the intermediate layer, by adding phthalocyanine green instead of carbon black, the total light transmittance increased, the infrared energy shielding rate decreased, and the film internal temperature Increased too much (well over 25 ° C).

  From the above, only when the addition ratio / addition amount of titanium oxide pigment and carbon black in the film is limited to severe, it has excellent impact resistance and the silage internal temperature and the temperature of the contact part between the silage and the film. It can be seen that the balance can be controlled in a balanced manner. Further, it can be seen that such a remarkable and unique effect is obtained when a titanium oxide pigment and carbon black are combined among a number of pigments instead of other colorants such as phthalocyanine green.

  Although the present invention has been described with reference to the most practical and preferred embodiments at the present time, the invention is not limited to the embodiments disclosed herein. However, the present invention can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification, and a stretch film accompanying such a change is also understood to be included in the technical scope of the present invention. There must be.

  The stretch film according to the present invention has an optimal light transmittance and infrared energy shielding rate. In particular, a roll bale-like silage used as horse or cattle feed is stretched using a dedicated wrapping machine or the like. It can be suitably used as a silage film that is packaged to obtain silage with high nutritional value by fermentation.

Claims (5)

  A mixture in which the weight ratio of titanium oxide pigment to carbon black (titanium oxide pigment: carbon black) is in the range of 5: 1 to 15: 1 with respect to 100 parts by weight of polyethylene resin is 3.0 parts by weight or more and 12.0 parts by weight. A stretch film comprising at least one resin composition layer containing at most 1 part by weight.   The stretch film according to claim 1, wherein the total light transmittance is less than 25%, and the light reflectance at a wavelength of 400 nm to 700 nm is 18% or more.   The stretch film according to claim 1, wherein an infrared energy shielding rate of a wavelength of 5 nm to 25 nm is 15% or more.   The polyethylene resin is at least one resin selected from a polyethylene resin (A) by an ion polymerization method and a polyethylene resin (B) by a high-pressure radical method, and the molecular weight distribution (Mw / Mn) of the resin is It is 1.5 or more and 5.0 or less, The stretch film in any one of Claims 1-3 characterized by the above-mentioned.   The resin composition layer as an intermediate layer, and an outer layer and / or an inner layer as a main component of an ethylene-α-olefin copolymer or an ethylene-vinyl acetate copolymer. The stretch film in any one of 1-4.