JP4530885B2 - Antistatic polyolefin film - Google Patents

Description

  The present invention relates to an antistatic polyolefin film, and particularly to an antistatic polyolefin film having stable antistatic performance.

  Polyolefin films are widely used as packaging materials because they are inexpensive, such as good processability, excellent mechanical strength, transparency, secondary processability such as bag-making property, moisture resistance, and the like. However, since it has characteristics that are very easily charged with static electricity, there are problems such as adhesion of dust and the like, electric shock to workers, and scattering of ink during printing.

  As one of the methods for solving these problems, an appropriate low molecular weight surfactant is added to the polyolefin film, and these surfactants are bleed on the polyolefin film surface, thereby providing antistatic properties on the film surface. The method of imparting has been used.

  However, such a migration type antistatic agent has the following problems (1) to (5). (1) Appearance defects (whitening phenomenon) occur due to excessive bleeding on the film surface. (2) The antistatic property tends to be poor under low humidity (it is easily influenced by humidity). (3) The bleed amount on the film surface is likely to fluctuate depending on the film forming state (conditions) (antistatic performance is difficult to stabilize). (4) The antistatic effect is reduced by wiping with water or an organic solvent. (5) Due to the low molecular weight existing on the film surface, the transferability / adhesiveness of ink, coat, etc. is hindered.

  As a means for solving the above-described problems, a high molecular weight antistatic agent is being studied in place of the low molecular weight surfactant. For example, a polyolefin film in which an antistatic resin layer made of a mixture of a polypropylene resin, a specific aromatic ring-containing polyetheresteramide and a polyamide resin, and a specific modified low molecular weight polypropylene is laminated on the surface of the polyolefin film has been proposed. (See Patent Document 1).

In addition, a block polymer having a structure in which a block of polyolefin (a) and a block of hydrophilic polymer (b) having a volume resistivity of 1 × 10 ⁵ to 1 × 10 ¹¹ Ω · cm are bonded alternately and repeatedly ( It is characterized by comprising a layer (X) having a thickness of 0.1 to 50 μm comprising an antistatic resin composition comprising A) and a polyolefin resin (B) as essential components, and a base layer (Y) comprising a thermoplastic resin. A multilayer film is also proposed (see Patent Document 2).

Further, a structure in which a block of polyolefin (a) and a block of polymer (b) having a polyoxyethylene chain having a volume resistivity of 1 × 10 ⁵ to 1 × 10 ¹¹ Ω · cm are alternately bonded. Forming an antistatic agent (A) composed of a block polymer having a dispersed phase composed of the antistatic agent (A) and a continuous phase composed of a thermoplastic resin, the number average particle diameter and number average of the dispersed phase An antistatic resin composition having a minor axis or a number average thickness of 0.01 to 1 μm has also been proposed (see Patent Document 3).

  However, in the polyolefin film using the antistatic resin layer of Patent Document 1, the compatibility between the polyolefin resin and the antistatic resin composition is insufficient. As a result, a film in which a polyolefin resin and a melt-kneaded antistatic agent resin composition are laminated conflicts with the original purpose of roll contamination during processing, poor appearance, and unstable antistatic performance due to molding conditions. It contained a defect.

  Similarly, even in the polyolefin film using the antistatic resin layer of Patent Document 2, due to the compatibility between the antistatic agent and the polyolefin and the antistatic resin composition comprising the resin and the production conditions, Appearance defects, antistatic defects, etc. are pointed out.

  Further, when the antistatic resin composition of Patent Document 3 is used and applied to a polyolefin film, the same raw material constitution is used, and the number average particle diameter, number average minor diameter or number average thickness of the dispersed phase is 0. Even when the thickness was specified within the range of 0.01 to 1 μm, variation in antistatic performance and poor appearance were confirmed.

Accordingly, the inventors diligently observed the longitudinal section of a prototype of a polyolefin film using the antistatic resin composition of Patent Document 3 with a transmission electron microscope in order to elucidate variations in antistatic performance. In the observation, the inventors have found that the difference in the cross-sectional shape of each prototype affects the antistatic performance. That is, in the prototype polyolefin film 90 in which the antistatic performance does not seem to be manifested (the surface specific resistivity is high), as shown in the vertical cross-sectional schematic diagram of FIG. It was made clear that In FIG. 5, the code | symbol 91 is the base material layer of the polyolefin film.
JP-A-11-170456 JP 2002-321314 A JP 2004-217929 A

  As described above, a close relationship is suggested between the favorable expression of the antistatic performance and the cross-sectional shape in the polyolefin film. Thereafter, as a result of further intensive studies, the inventors have found characteristics common to polyolefin films having good antistatic performance.

  The present invention has been made in view of the above points, exhibits stable antistatic properties even under low humidity, and no deterioration in antistatic properties is observed even after wiping with water or an organic solvent, In addition to eliminating processing problems such as smoke generation and roll dirt during processing, there is no variation in the development of antistatic performance between the same resin used and from production to production, charging with excellent transparency and no defects in appearance. The present invention provides a polyolefin film having preventive properties.

That is, the present invention is an antistatic polyolefin film (10) in which an antistatic layer (20) made of an antistatic resin composition (C) is laminated on a base material layer (11) made of a polyolefin resin for base layer (D). The antistatic resin composition (C) has a volume resistivity of 1 × 10 ⁵ to 1 × 10 ¹¹ Ω · cm made of a copolymer of the hydrophilic polymer (a) and the modified polyolefin (b). And the base layer polyolefin resin (D) has a melting point of 2 ° C. or more higher than the melting point of the surface layer polyolefin resin (B). a melting point, the is within the melting point ± 3 ° C. of the base layer for the polyolefin resin (D), and, in the stretching temperature to a temperature higher than the melting point of said surface layer for polyolefin resin (B), the base layer for the poly Both the permanent antistatic agent (A) and the polyolefin resin for surface layer (B) contained in the antistatic resin composition (C) are formed on the outermost layer of the base material layer (11) made of the olefin resin (D). by Rukoto be stretched in a semi-molten state or a molten state, said antistatic resin composition antistatic layer consisting of (C) (20) wherein the permanent antistatic agent (a) and the surface layer for polyolefin resin (B) The existence state forms a sea-island-like phase separation structure in which the polyolefin resin for surface layer (B) is the sea part (21), and the permanent antistatic agent (A) is a grain-shaped island part (22) , The average particle size in the vertical direction of the island portion of the grain shape made of the permanent antistatic agent (A) is 0.01 to 0.5 μm, and the maximum particle size in the vertical direction of the island portion is 1 μm or less, The permanent antistatic agent (A) The average value of the shortest adjacent distances between the island portions of the grain shape is 0.2 μm or less, and the maximum value of the shortest adjacent distances between the island portions is 0.5 μm or less, and the antistatic layer (20 ) The area fraction (SR) of the total area (S _n ) of the grain-shaped island portions made of the permanent antistatic agent (A) in the unit area (Su) of the vertical cross section with respect to the surface direction is 0.1 or more. The present invention relates to an antistatic polyolefin film.

According to the antistatic polyolefin film according to the invention of claim 1, the antistatic resin composition (C) has a volume resistivity of 1 made of a copolymer of the hydrophilic polymer (a) and the modified polyolefin (b). It contains a permanent antistatic agent (A) that is × 10 ⁵ to 1 × 10 ¹¹ Ω · cm and a polyolefin resin for surface layer (B). The melting point of the polyolefin resin for base layer (D) is the polyolefin resin for surface layer (B ) That is higher than the melting point of the polyolefin resin for the base layer (D) within a range of ± 3 ° C. and higher than the melting point of the polyolefin resin for the surface layer (B). The permanent antistatic agent (A) contained in the antistatic resin composition (C) and the surface layer layer are formed on the outermost layer of the base material layer (11) comprising the polyolefin resin for base layer (D). The permanent antistatic agent (A) of the antistatic layer (20) comprising the antistatic resin composition (C) and the polyolefin for the surface layer by stretching the olefin resin (B) in a semi-molten or molten state. The presence state with the resin (B) is a sea-island phase separation in which the polyolefin resin for surface layer (B) is the sea part (21) and the permanent antistatic agent (A) is the grain-shaped island part (22). The average particle size in the vertical direction of the island portion having a structure and comprising the permanent antistatic agent (A) is 0.01 to 0.5 μm, and the maximum particle size in the vertical direction of the island portion Is 1 μm or less, the average value of the shortest adjacent distance between the island portions of the grain shape made of the permanent antistatic agent (A) is 0.2 μm or less, and the maximum value of the shortest adjacent distance between the island portions Is less than 0.5μm The area fraction (SR) of the total area (S _n ) of the grain-shaped island portions made of the permanent antistatic agent (A) in the unit area (Su) of the cross section perpendicular to the surface direction of the antistatic layer (20) ) Is 0.1 or more, the variation in antistatic performance between the films is eliminated. Furthermore, it is excellent in transparency, and the appearance defect seen in the conventional film is improved. In addition, suitable properties are shown for printing with water-based inks.

In addition, exhibits stable antistatic properties even under low humidity, and exhibits water, further stable antistatic properties between each film such that does not also seen deterioration of antistatic properties after wiping with an organic solvent can do.

  The present invention will be described below with reference to the accompanying drawings. 1 is a schematic vertical cross-sectional view of the antistatic polyolefin film of the present invention, FIG. 2 is a schematic vertical cross-sectional view focusing on the particle size of each island portion in FIG. 1, and FIG. 3 is paying attention to the distance per island portion in FIG. FIG. 4 is a schematic vertical sectional view focusing on the area of each island portion in FIG. In any of the figures, the longitudinal section is a cut surface cut perpendicularly to the surface direction of the antistatic polyolefin film.

  As shown in FIG. 1, the basic structure of the antistatic polyolefin film 10 is that the antistatic layer 20 is laminated on the surface of the base material layer 11 (the outermost layer of the base material layer). It is a film obtained by stretching in one direction (uniaxial stretching) or biaxial stretching. Although mentioned later, the code | symbol 21 in a figure is a sea part and 22 is an island part.

  In the antistatic polyolefin film 10, the antistatic layer 20 that exhibits suitable antistatic performance is formed from the antistatic resin composition (C). This antistatic resin composition (C) is a melt kneading of a permanent antistatic agent (A) comprising a copolymer of a hydrophilic polymer (a) and a modified polyolefin (b) and a polyolefin resin for surface layer (B). Obtained by etc. On the other hand, the base material layer 11 is obtained from the polyolefin resin (D) for base layers.

  The main structure of the antistatic polyolefin film 10 can be shown as the following outline. {Antistatic polyolefin film 10 of the present invention = Antistatic layer 20 (antistatic resin composition (C)) + Base material layer 11 (polyolefin resin for base layer (D))}, {Antistatic resin composition (C) = Permanent antistatic agent (A) + polyolefin resin for surface layer (B)}, {permanent antistatic agent (A) = hydrophilic polymer (a) + modified polyolefin (b)}.

  From this, each composition component of an antistatic polyolefin film is described. The hydrophilic polymer (a) composing the permanent antistatic agent (A) is preferably generally called a polyether, such as polyether diol, polyether diamine, polyether ester amide, polyether amide imide, polyether urethane. , Polyether esters, polyether amides and modified products thereof.

  The modified polyolefin (b) composing the permanent antistatic agent (A) is a suitable polyolefin, in which a carbonyl group, a carboxyl group, an amino group, a hydroxyl group or the like is introduced as a modifying group and contains at least one end thereof. Polyolefin. Preferably, a carboxyl group-modified polyolefin is used.

The aforementioned hydrophilic polymer (a) and modified polyolefin (b) are suitably copolymerized to form the permanent antistatic agent (A). The permanent antistatic agent (A) has a volume specific resistivity of 1 × 10 ⁵ to 1 × 10 ¹¹ Ω · cm, whereby an antistatic resin composition (C) having a suitable surface specific resistivity is obtained. It is done.

Therefore, in the permanent antistatic agent (A), an acid-modified polyolefin polyether block polymer is suitable from the viewpoint of compatibility, ductility, antistatic performance and the like. Examples of the acid-modified polyolefin polyether block polymer include Sanyo Kasei Kogyo Co., Ltd .: Pelestat OP300 (volume specific resistivity: 2 × 10 ⁷ Ω · cm) and Toho Chemical Industries, Ltd .: Anstex FT-P348 ( Volume resistivity: 8 × 10 ⁸ Ω · cm) or the like is selected. Examples of the acid-modified polyolefin polyether block polymer include acid-modified polyethylene polyether block polymers.

  MFR (based on JIS-K6922-1) at 190 ° C. and 21.18 N of the above-mentioned permanent antistatic agent (A) is 1 to 50 g / 10 minutes, more preferably 2 to 20 g from the viewpoint of resin physical properties, processability and the like. / 10 minutes is preferred, and a resin satisfying the same MFR is selected. In addition, the melting point of the permanent antistatic agent (A) is preferably 100 to 170 ° C. from the viewpoints of resin physical properties, processability and the like, and a resin satisfying the same melting point is selected.

  Examples of the polyolefin resin (B) for the surface layer include homopolymers of α-olefins such as ethylene, polypropylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, Examples thereof include a polymer and a mixture thereof. Examples of the monomer other than the α-olefin copolymerizable with the α-olefin include vinyl acetate, maleic acid, vinyl alcohol, methacrylic acid, methyl methacrylate, and ethyl methacrylate. The polyolefin resin for surface layer (B) may be a combination or mixture of different resins.

  MFR (based on JIS-K-7210) at 230 ° C. and 21.18 N of the polyolefin resin for surface layer (B) is preferably 1 to 50 g / 10 minutes, more preferably considering resin physical properties and processability. Is selected from resins that are 2-20 g / 10 min.

  Moreover, the polyolefin resin (D) for base layer used as the base material layer 11 of the polyolefin film 10 of this invention is selected from the resin composition similar to the said polyolefin resin (B) for surface layers. The polyolefin resin (D) for the base layer may be a single layer made of a single resin or a mixed resin obtained by mixing different resins, or may be a laminate obtained by combining or mixing the same or different resins. it can. The melting point of the resin used as the polyolefin resin for base layer (D) is preferably about 150 ° C. or higher. This is because the workability of the subsequent processing is taken into consideration, including at the time of stretching.

  The weight ratio of the composition of the permanent antistatic agent (A) constituting the antistatic resin composition (C) to the polyolefin resin for surface layer (B) is, as will be apparent from Examples described later, (A) :( B) = Preferably within the range of 5:95 to 50:50. When the permanent antistatic agent (A) is 5 parts by weight or less, sufficient antistatic performance is not exhibited. Moreover, when a permanent antistatic agent (A) is 50 weight part or more, there exists a possibility that the external appearance defect by a compatibility fall with the polyolefin resin (B) for surface layers, or various physical properties may be impaired.

  In preparing the antistatic resin composition (C), the kneading of the permanent antistatic agent (A) and the polyolefin resin for surface layer (B) will be described. The permanent antistatic agent (A) and the polyolefin resin for surface layer (B) are dry blended by a known mixer (such as a tumbler or Henschel mixer) in parts by weight of the above-mentioned predetermined blending ratio, and a single screw extruder, twin screw It is melt-kneaded by a kneader such as an extruder or a pressure kneader. In this kneader, a twin screw extruder is preferably used in order to make the permanent antistatic agent (A) more finely dispersed.

  In producing the antistatic polyolefin film 10, a tenter method, a tubular method, a roll stretching method, or the like is used for stretching the film. As a biaxial stretching method, for example, an antistatic layer 20 made of an antistatic resin composition (C) and a base material layer 11 made of a polyolefin resin for base layer (D) are formed into a sheet by coextrusion from a T die. Is done. This sheet-like material is stretched in the longitudinal direction due to the difference in peripheral speed of the rolls, and then stretched in the transverse direction (stretching every time) by a tenter. Or, the tenter is stretched simultaneously in the longitudinal and lateral directions (simultaneous stretching). Of course, it is not limited to these stretching methods, and a stretching method and a stretching apparatus are suitably selected according to workability and resin characteristics.

  About the manufacturing conditions of an antistatic polyolefin film, it depends on the said manufacturing method. However, as specified in the invention of claim 1, in the polyolefin resin for base layer (D), a resin type having a higher melting point than that of the polyolefin resin for surface layer (B) is selected. The melting point of the polyolefin resin for base layer (D) and the polyolefin resin for surface layer (B) is mainly measured by a differential scanning calorimeter. When a mixture of a plurality of types of resins is used for the surface layer or the base layer, the melting point of the mixed resin is defined as the melting point of the mixed resin. In particular, when there are two or more melting points, the highest melting point among them is taken as the melting point of the mixed resin. When a plurality of resins are stacked, the melting point of the highest melting point resin is set. The melting point of the resin may be obtained by calculation in addition to the actual measurement by the differential scanning calorimeter as described above.

  By utilizing the difference in melting point between the polyolefin resin for base layer (D) and the polyolefin resin for surface layer (B), even if the amount of heat applied from the stretching device during stretching is uniform, the resin of the base material layer 11 And the molten state of the resin of the antistatic layer 20 are different. In particular, since the polyolefin resin for base layer (D) side has a high melting point, the polyolefin resin for surface layer (B) melts more rapidly than the base layer side. Therefore, both the permanent antistatic agent (A) and the surface layer polyolefin resin (B) contained in the antistatic resin composition (C) are formed on the outermost layer of the base material layer 11 made of the polyolefin resin for base layer (D). The film can be stretched in a semi-molten state or a molten state.

  That is, both the permanent antistatic agent (A) and the surface layer polyolefin resin (B) contained in the antistatic resin composition (C) (antistatic layer 20) that are not completely mixed together are in a semi-molten state or a molten state. Therefore, as if the mixture of water and oil was stirred, the one with the smaller amount of addition (in this case, the permanent antistatic agent (A)) was in the most stable state in terms of surface tension, that is, formed into a grain shape. The antistatic layer 20 is considered to be cooled and solidified after film formation.

  As will be apparent from the examples described later, in the film exhibiting suitable antistatic performance, the state of inhomogeneous presence of the permanent antistatic agent (A) and the polyolefin resin for surface layer (B) in the antistatic layer 20 is present. In particular, as shown in the longitudinal sectional view of FIG. 1, the surface layer polyolefin resin (B) is the sea portion 21 and the permanent antistatic agent (A) is the grain-shaped island portion 22 so that it is almost possible to distinguish each composition. A sea-island-like phase separation structure. As shown in the figure, the sea-island-like phase separation structure is such that the particle shape of the permanent antistatic agent (A) is scattered in the background of the polyolefin resin (B) for the surface layer like “islands” floating in the “sea”. It seems to be.

  As already described, by utilizing the difference in melting point between the polyolefin resin for base layer (D) and the polyolefin resin for surface layer (B), good ductility as a polyolefin film is secured. In addition, the permanent antistatic agent (A) is well dispersed as a sea island in the antistatic layer. Here, the polyolefin resin for surface layer (B) and the polyolefin resin for base layer (D) are exemplified. Sumitomo Chemical Co., Ltd. Exelen SP89E3, Nippon Polypro Co., Ltd. The company's Novatec PP FL1105C, Mitsui Chemicals Mitsui Polypro F103, and the like.

Regarding the sea-island-like phase separation structure in the antistatic layer 20 of the antistatic film, the inventors continued further analysis by paying attention to the grain-shaped island portion 22 made of the permanent antistatic agent (A). As a result , as shown in FIG. 2, the average particle diameter DV in the vertical direction of the grain-shaped island portions 22 made of the permanent antistatic agent (A) in the antistatic layer 20 is preferably 0.01 to 0.5 μm, Furthermore, it is considered that the thickness is preferably in the range of 0.05 to 0.15 μm.

When the average particle size DV in the vertical direction of the island portion is less than 0.01 μm, the island portion is finely dispersed and compatibility with the polyolefin resin (B) for the surface layer is increased. . On the other hand, when the average particle size DV in the vertical direction of the island portion exceeds 0.5 μm, the antistatic property and appearance defect are likely to occur due to the size of the average particle size. In addition , the maximum particle size DM of the grain-shaped island portion 22 made of the permanent antistatic agent (A) is preferably 1 μm or less, and more preferably 0.5 μm or less. This is because when the maximum particle size of the island portion exceeds 1 μm, appearance defects (so-called fish eyes / voids) tend to occur.

The average particle size DV in the vertical direction of the island portions of the grain shape is the particle size Dv ₁ , Dv ₂ ,. . , Dv _n , ie, DV = (Dv ₁ + Dv ₂ + ... + Dv _n ) / n. The maximum particle size DM of the island portion is the particle size Dv ₁ , Dv ₂ ,. . , Dv _n is the largest value.

Subsequently , as shown in FIG. 3, the average value LS of the shortest adjacent distances between the grain-shaped island portions 22 made of the permanent antistatic agent (A) in the antistatic layer 20 is 0.2 μm or less, more preferably. 0.1 μm or less. When the average value of the shortest adjacent distances between the island portions exceeds 0.2 μm, the antistatic defect tends to be remarkable. In addition , the maximum value LM of the shortest adjacent distance between the grain-shaped island portions 22 is 0.5 μm or less, and more preferably 0.3 μm or less. This is because when the maximum value of the shortest adjacent distance between the island portions exceeds 0.5 μm, the antistatic defect tends to be remarkable.

The average value LS of the shortest adjacent distances between the island portions is, when it is assumed that there are a plurality (n) of island portions in a certain antistatic layer, the island portion 1 based on one of the island portions. Ls ₁ is the adjacent distance (shortest adjacent distance) between the island portion 1 and the most adjacent island portion, and the reference island portions are sequentially island portion 2, island portion 3,. . . The same operation is repeated while changing the island part n. Each shortest adjacent distance is denoted by Ls ₂ , Ls ₃ . . . Refer to these average values at the time of the ls _n. That is, it is obtained as LS = (Ls ₁ + Ls ₂ + Ls ₃ + ... + Ls _n ) / n. Further, the maximum value LM of the shortest adjacent distances between the island portions is the shortest adjacent distances Ls ₁ , Ls ₂ , Ls ₃ ,. . , Ls _n corresponds to the maximum value.

Further , as shown in FIG. 4, the area fraction SR in the vertical cross section of the grain-shaped island portion 22 made of the permanent antistatic agent (A) in the vertical cross section with respect to the surface direction of the antistatic layer 20 is 0. 1 or more, and particularly preferably 0.2 or more. If the area fraction SR is less than 0.1, the antistatic property tends to be poor.

The area fraction SR is a ratio of the area of the island portion existing in the unit area in the vertical cross section of the antistatic layer. That is, assuming that there are a plurality (n) of island portions in a unit area Su of an antistatic layer, the area of the island portion 1 is S ₁ , the area of the island portion 2 is S ₂ , and the island portion 3. Are S ₃ ,. . . The area of the island portion n is _denoted as Sn. A value obtained by grading the sum of these island portions by the unit area is the area fraction SR. That is, it is obtained as SR = (S ₁ + S ₂ + S ₃ +... + S _n ) / Su.

  The average particle size, the maximum particle size, the average value of the shortest adjacent distance between the island portions, and the maximum of the island portions in the particle shape made of the permanent antistatic agent (A) described in detail with reference to FIGS. The value and the area of the island part are observed with a transmission electron microscope (TEM). The photographed electron micrograph is taken into an appropriate image analysis apparatus, and the particle size of an arbitrary number of island portions is measured based on a known image analysis method, and the average particle size in the vertical direction is calculated. Similarly, the average value and the maximum value of the shortest adjacent distance are calculated. Further, the unit area of the antistatic layer 20 and the area of each island portion are measured, and the area fraction is also calculated.

  The antistatic layer 20 made of the detailed antistatic resin composition (C) may be laminated on both surfaces of the outermost layer of the base material layer 11 made of the polyolefin resin for base layer (D), or the base material layer 11. It is good also as a lamination | stacking only to the one surface side of the outermost layer. Thus, by controlling the lamination surface of the antistatic layer 20, it is possible to provide an antistatic polyolefin film having antistatic performance corresponding to the production efficiency and the purpose of use. In addition, when laminating | stacking the antistatic layer 20 on both surfaces of the base material layer 11, it is also possible to make the antistatic layer 20 of each surface the same, or to make it mutually different.

  Although the layer thickness of the base material layer 11 is variously selected depending on applications and the like, it is 10 to 100 μm, and the layer thickness of the antistatic layer 20 laminated thereon is preferably 0.5 μm or more, particularly preferably 1 μm or more. . The above-mentioned layer thickness is preferable in consideration of sufficient antistatic properties.

  The antistatic polyolefin film of the present invention is added with various additives and fillers used for ordinary polyolefin films, including antioxidants, lubricants, colorants, and UV absorbers, as long as the object of the invention is not impaired. It can be suitably added as a component. Further, for the purpose of further improving the antistatic performance, a metal salt composed of a halide of an alkali metal or an alkaline earth metal may be added.

  Furthermore, according to the antistatic polyolefin film of the present invention, there is no change in antistatic performance due to the presence or absence of surface treatment. Therefore, when printing on this antistatic polyolefin film, prior to printing, the film surface is activated by using corona discharge treatment, flame treatment, plasma treatment, etc. And adhesion can be improved. For this reason, it is desirable to activate the film surface by any one of the methods described above.

  The antistatic polyolefin film in which the activation treatment is performed on the surface on which the antistatic layer 20 is laminated is printed with water-based ink on the outermost surface of the antistatic layer 20. If it is water-based ink printing, the kind of ink and the printing method are not particularly limited. In addition to water being used as the solvent for the water-based ink, alcohols, preferably lower alcohols such as methanol, ethanol, isopropyl alcohol, n-propyl alcohol, etc. may be used in combination, and there is no particular limitation on these.

  Also, general inorganic and organic pigments can be used as the colorant. For example, soluble and insoluble organic pigments such as azo, phthalocyanine, and naphthol, and inorganic pigments such as titanium oxide, calcium carbonate, petal, and carbon black. Is mentioned. In addition, as a resin binder for water-based inks, water-soluble or water-dispersible resins such as styrene-acrylic acid-based, styrene-maleic acid-based acrylic resins, polyurethane-based resins, rosin-modified resins, and the like can be used. It can be used as long as it can be produced, and can be used alone or in combination. As other additives, waxes, antifoaming agents, dispersing agents and the like may be used. A diluent using water / alcohols in combination may be used to adjust the viscosity of the ink during printing. Examples of the printing method include gravure printing, flexographic printing, offset printing, and ink jet printing.

  The antistatic polyolefin film of the present invention thus obtained is used alone by being laminated with packaging materials, masking materials, packaging materials for electronic parts, tape materials, and paper, nonwoven fabric, cellophane, etc. It is also possible to do. In addition, it can be used as a label on another plastic resin molded article.

[Preparation of Antistatic Agent Resin Composition]
In preparing the antistatic agent resin composition, the following permanent antistatic agent (Table 1) and polyolefin resin (Table 2) were used. In the table, A-1, A-2 are acid-modified polypropylene polyether copolymer-based permanent antistatic agents, A-3 is a polyetheresteramide-based permanent antistatic agent, A-4 is a low molecular weight type antistatic agent, B -1 to B-6 are polyolefin resins. The polyolefin resin in the table may be used for both the base material layer or the antistatic layer. Therefore, (B) is attached when used for the antistatic layer, and (D) is attached when used for the base material layer, and they are distinguished from each other for convenience. The A-1 and A-2 are made of a copolymer of the hydrophilic polymer (a) and the modified polyolefin (b) and have a volume resistivity of 1 × 10 ⁵ to 1 × 10 ¹¹ Ω · cm. It corresponds to a permanent antistatic agent (A) that satisfies certain conditions. The special order products in the table are consigned manufactured products.

  In Example 1, the tumbler is such that the permanent antistatic agent (A-1) and the polyolefin resin (B-1) satisfy the blending ratio of (A-1) :( B-1) = 10: 90 by weight ratio. Dry blended with (tumble mixer). Then, after melt-kneading with a twin screw extruder, it was extruded into a strand shape, cooled, cut into an arbitrary size and pelletized to obtain an antistatic resin composition of Example 1.

[Prototype of antistatic polyolefin film]
The above antistatic resin composition was used as an antistatic layer, and a polyolefin resin (D-5) was coextruded from a T-die using a base material layer to form a sheet. This is stretched under a stretching temperature of 158 ° C. by a tenter method biaxial stretching machine (manufactured by Mitsubishi Heavy Industries, Ltd.), and a base layer and an antistatic polyolefin film forming an antistatic layer on one side thereof are formed. Obtained (Example 1). The antistatic polyolefin film was molded with a base material layer thickness of 20 μm and an antistatic layer thickness of 1 μm. Further, the surface of the antistatic layer of the antistatic polyolefin film is subjected to corona discharge treatment (8.0 W · min / m ² ) so that the wetting test (according to JIS-K-6768) has an index of 40 mN / m. Went.

The antistatic polyolefin films of Examples 2 to 10 and Comparative Examples 1 to 4 are based on the same technique and apparatus as in Example 1. Permanent antistatic agent (A-1 to A-3) and polyolefin resin for surface layer (B-2 ~) according to the types and blending ratios of the resins shown in Table 3 (Examples) and Table 4 (Comparative Examples) below. In combination with B-6), antistatic resin compositions of Examples 2 to 10 and Comparative Examples 1 to 4 were prepared. Subsequently, an antistatic polyolefin film was obtained from each antistatic resin composition and the polyolefin resin for base layer (D) (Examples 2 to 10 and Comparative Examples 1 to 4). The antistatic polyolefin films of these examples and comparative examples were also molded with a base material layer thickness of 20 μm and an antistatic layer thickness of 1 μm (however, Example 9 is used as a reference example) .

  In Comparative Example 5, 1.0% by weight of low molecular weight type antistatic agent (A-4) was dry blended with polyolefin resin (B-5) and pelletized in the same manner as in Example 1 to obtain an antistatic agent resin composition. It was. Subsequently, this antistatic agent resin composition was extruded with a T-die to obtain a polyolefin film having a thickness of 20 μm. In both examples and comparative examples, corona discharge treatment was performed under the same conditions as in Example 1 above.

  In Tables 3 and 4 below, the melting point of each resin was measured using a differential scanning calorimeter (“DSC6200” manufactured by Seiko Instruments Inc.). Here, the melting point of the polyolefin resin for surface layer (B) of Example 6 is a value (156 ° C.) obtained by once melting and kneading the resins B-3 and B-6 and then measuring with the differential scanning calorimeter. is there. The melting point difference ((D)-(B) melting point difference (° C.)) between the base layer polyolefin resin (D) and the surface layer polyolefin resin (B) was determined from the melting point of each resin obtained.

  Regarding the antistatic polyolefin film (Examples 1 to 10 and Comparative Examples 1 to 5) of each sample, the film forming state is clearly shown, and the permanent in the antistatic layer by image analysis using a transmission electron microscope (TEM). In addition to dispersion of antistatic agent (island part), average particle size in vertical direction, average and maximum values of shortest adjacent distance, area fraction, appearance of film, surface resistivity, and water-based ink printing characteristics did. In addition, an overall comprehensive evaluation of each sample was performed. Details of the evaluation and measurement methods are shown below.

[Film formation status]
Regarding smoke generation, the smoke generation state from the extruder part, the tenter outlet part, and the exhaust port of the film forming machine was visually observed. In the evaluation, “o” indicates that no smoke is generated, “Δ” indicates that smoke is slightly generated, and “x” indicates a cloudy white cloudy part around the film forming machine.

  About roll dirt, the roll (especially extending | stretching roll) which an antistatic resin composition touches was confirmed visually, and the presence or absence of the deposit | attachment to a roll was evaluated. In the evaluation, “O” indicates that there is no contamination, “Δ” indicates that the deposit is generated within 10 minutes to 12 hours after the start of film formation, and “X” indicates that the deposit is generated within 10 minutes after the start of film formation. It was.

  When observing the shape of the film cross section with a transmission electron microscope, the antistatic polyolefin film was embedded in an epoxy resin, and an ultramicrotome was used to cut out a cross section perpendicular to the film surface direction as an ultrathin section. In order to facilitate observation of the sea-island portion, the dyeing process was performed using ruthenium tetroxide as a staining agent, and observation was performed with a transmission electron microscope (“JEM-1010” manufactured by JEOL Ltd.). The magnification at the time of observation was 20,000 times and 100,000 times.

  The taken electron micrograph was taken into an image analyzer (“SPICCA” manufactured by Nippon Avionics Co., Ltd.), the particle size of an arbitrary number of island portions was measured, and the average particle size in the vertical direction was calculated. Similarly, the maximum particle size, the shortest adjacent average distance, and the maximum distance were also calculated. Further, the unit area of the antistatic layer and the area of each island portion were measured, and the area fraction was also calculated.

  The presence state was visually observed from the photographed image. When the permanent antistatic agent forms a sea-island-like phase separation structure, it is “sea-island”, and when the permanent antistatic agent does not form a sea-island-like phase separation structure or is unclear, (See FIG. 5). In addition, those that cannot grasp the existence state are set to “not visible”.

  The average particle size was obtained by taking an electron micrograph into the image analysis apparatus, measuring the particle size in the vertical direction of an arbitrary number of island portions, and calculating the average.

  The maximum particle size was selected by measuring the particle size in the vertical direction of the island portion.

  The shortest adjacent distance and the average value thereof were obtained by measuring the distances between a certain island portion and a number of island portions adjacent to the island portion on the image captured by the image analysis apparatus. The minimum value of these distances was taken as the shortest adjacent distance. The same measurement was performed on other islands, and the shortest adjacent distance was measured. Therefore, an average value was calculated from these shortest adjacent distances.

  As the maximum value, the maximum distance was selected in the measurement of the shortest adjacent distance.

  When the area fraction is the sum of the areas of the island portions included in the entire area of the cross section of any antistatic layer on the image captured by the image analysis apparatus, the area fraction = (the area of the island portion). Calculated as (total) / (cross-sectional area of antistatic layer).

[Appearance of film]
Measurement of haze is based on JIS-K-7105, using a digital turbidimeter (“NDH-20D” manufactured by Nippon Denshoku Industries Co., Ltd.) per antistatic polyolefin film of Examples and Comparative Examples The haze was measured. The unit is (%).

  For the measurement of LSI, the transparency per antistatic polyolefin film was measured using a visual transparency tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.). The unit is (%). Incidentally, LSI is an improved index for discrepancy between visual perception and haze. The LS value indicates diffuse transmitted light at a narrow angle, and indicates a value closer to the degree of cloudiness felt by human eyes than haze.

  Appearance defects were observed visually on the surface (outermost surface of the film) on which the antistatic resin composition was laminated in the antistatic polyolefin films of Examples and Comparative Examples. A sample that was transparent over the entire surface without any irregularities was marked with “◯”, and a sample that was visually inferior in appearance such as white turbidity or surface roughness was marked with “x”.

[Surface resistivity]
The surface resistivity is in accordance with JIS-K-6911, using a high resistance-resistivity meter (“MCP-HT260” manufactured by Mitsubishi Oil Chemical Co., Ltd.), and the surface resistivity (Ω) under the following conditions: Was measured.

  The measurement immediately after film formation refers to 23 ° C. and 50% RH (hereinafter, the indicated humidity is relative humidity) for the film of each sample (Example and Comparative Example) formed from the above-mentioned tenter method biaxial stretching machine. The surface specific resistivity of the surface on which the antistatic resin composition was laminated was measured in the atmosphere of

  The measurement after standing for 1 day is a measurement of each sample film after aging in an atmosphere of 35 ° C. and 60% RH for 24 hours and then in an atmosphere of 23 ° C. and 50% RH.

  In the measurement after washing with water, the surface of the film of each sample on which the antistatic resin composition was laminated (antistatic layer) was impregnated with a neutral detergent for tableware ("Mama Lemon" manufactured by Lion Corporation). Rinse 20 times with a nylon sponge and rinse thoroughly with distilled water. After drying at 80 ° C. for 3 hours, the mixture was allowed to stand for 24 hours in an atmosphere of 23 ° C. and 50% RH, and then measured in an atmosphere of 23 ° C. and 50% RH.

  In the measurement after the solvent wiping, the surface of the film of each sample on which the antistatic agent resin composition was laminated (antistatic layer) was wiped off using a nonwoven fabric soaked with toluene so that it was rubbed 20 times. After natural drying in a 50 ° C., 50% RH atmosphere, the measurement was performed in the same atmosphere.

  In addition, the film of each sample was aged in an atmosphere of 35 ° C. and 60% RH for 24 hours, and then measured in an atmosphere of 23 ° C. and 15% RH.

[Water-based ink printability]
Toyo Ink Mfg. Co., Ltd. “JW224 Aque Ecole Black” was used as the water-based ink, and this was diluted with a dedicated diluent solvent to prepare a solid content concentration of 30% by weight and an alcohol content concentration of 10%. The obtained water-based ink was printed with a gravure printing machine on the surface of each sample (Examples 1 to 10, Comparative Examples 1 to 5) on which the antistatic agent resin composition was laminated.

  Thus, the surface of the film of the Example and comparative example in which water-based ink printing was performed was observed with the optical microscope (magnification 75 times), and the ink transfer state of each sample and the ink repellency were evaluated. In the evaluation, “o” was given when ink repelling was not observed at all and the halftone dot reproducibility was good. A case where a large number of fine repellencies were observed and halftone dots were observed was designated as “Δ”. A large repellency was observed throughout and almost no halftone dots were given as “x”.

[Comprehensive evaluation]
In the comprehensive evaluation, the applicability as an antistatic polyolefin film was evaluated in consideration of the evaluation items and indicators listed. In any case, an excellent film was designated as “◎”. A non-defective film was designated as “◯”. A film having performance problems and not suitable for use was designated as “x”.

[Results and Discussion]
From the results of evaluation and measurement detailed above, the polyolefin films of Examples 1 to 10 have good antistatic performance. In particular, the polyolefin films of Examples 1 to 8 are generally excellent in other indices. On the other hand, in the polyolefin films of Comparative Examples 1 to 5, the desired antistatic performance cannot be obtained, and other indexes have problems. In Comparative Examples 1 to 3, the presence state of the permanent antistatic agent (A) due to insufficient stretching temperature with respect to the polyolefin resin for surface layer (B) constituting the antistatic layer is a fine stripe, It causes poor appearance. In Comparative Example 4, the presence state in the polyolefin resin for the surface layer is a sea island-like phase separation structure, but lacks compatibility. For this reason, the existing particle size is large, and roll contamination due to the removal of the antistatic agent is severe and there is a problem in film formation. Moreover, the antistatic performance is also unstable. In Comparative Example 5, the problem of film formation peculiar to the low molecular weight surfactant is seen, and the antistatic performance is also unstable.

  From this knowledge, it is an essential condition that the permanent antistatic agent (A) is a copolymer of a hydrophilic polymer (a) and a modified polyolefin (b) (a block polymer having a structure in which repetitive and alternating bonds are formed). In addition to the amount of the permanent antistatic agent (A) present, it is expected that the permanent antistatic agent (A) forms a sea-island phase separation structure in the antistatic layer.

  That is, by using a resin having a higher melting point of the polyolefin resin for base layer (D) used for the base layer than the melting point of the polyolefin resin for surface layer (B) used for the antistatic layer, the permanent antistatic agent (A) and for the surface layer are used. Only the polyolefin resin (B) can be made into a semi-molten state or a molten state, that is, a semi-liquid that is not completely mixed. Therefore, as if the mixture of water and oil was stirred, the smaller addition amount (in this case, the permanent antistatic agent (A)) formed the grain shape as the most stable state in terms of surface tension, The inventor said that the state of existence of the permanent antistatic agent (A) and the surface layer polyolefin resin (B) in the antistatic layer easily formed a sea-island-like phase separation structure by cooling and solidifying as it was after forming the film. Et al.

  The permanent antistatic agent (A) and the surface layer polyolefin resin (B) in the antistatic layer have a sea-island phase separation structure, and exhibit excellent antistatic performance as a film (surface resistivity) The relationship between (reducing) is not necessarily elucidated. The inventors have speculated that the uneven distribution of the permanent antistatic agent (A) in the antistatic layer may affect the conductivity.

It is a longitudinal cross-sectional schematic diagram of the antistatic polyolefin film of this invention. It is a longitudinal cross-sectional schematic diagram paying attention to the particle size for every island part of FIG. It is a longitudinal cross-sectional schematic diagram paying attention to the distance for every island part of FIG. It is a longitudinal cross-sectional schematic diagram paying attention to the area for every island part of FIG. It is a longitudinal cross-sectional schematic diagram showing the conventional antistatic film.

DESCRIPTION OF SYMBOLS 10 Antistatic polyolefin film 11 Base material layer 20 Antistatic layer 21 Sea part 22 Island part

Claims (1)

An antistatic polyolefin film (10) obtained by laminating an antistatic layer (20) made of an antistatic resin composition (C) on a base material layer (11) made of a polyolefin resin for base layer (D),
The antistatic resin composition (C) has a permanent volume resistivity of 1 × 10 ⁵ to 1 × 10 ¹¹ Ω · cm composed of a copolymer of the hydrophilic polymer (a) and the modified polyolefin (b). Including an antistatic agent (A) and a polyolefin resin for surface layer (B),
The melting point of the polyolefin resin for base layer (D) is a melting point higher by 2 ° C. or more than the melting point of the polyolefin resin for surface layer (B),
A group comprising the polyolefin resin for a base layer (D) at a stretching temperature that is within a melting point of ± 3 ° C. of the polyolefin resin for a base layer (D) and higher than the melting point of the polyolefin resin for a surface layer (B). In the outermost layer of the material layer (11), the permanent antistatic agent (A) and the surface layer polyolefin resin (B) contained in the antistatic resin composition (C) are both stretched in a semi-molten state or a molten state. by be Rukoto,
The presence state of the permanent antistatic agent (A) and the polyolefin resin for surface layer (B) in the antistatic layer (20) comprising the antistatic resin composition (C) is the same as the polyolefin resin for surface layer (B). A sea-island-shaped phase separation structure with the sea part (21) and the permanent antistatic agent (A) as a grain-shaped island part (22) is formed.
The average particle size in the vertical direction of the grain-shaped island portion made of the permanent antistatic agent (A) is 0.01 to 0.5 μm, and the maximum particle size in the vertical direction of the island portion is 1 μm or less. ,
The average value of the shortest adjacent distance between the island portions of the grain shape made of the permanent antistatic agent (A) is 0.2 μm or less, and the maximum value of the shortest adjacent distance between the island portions is 0.5 μm or less. Yes,
The area fraction (SR) of the total area (S _n ) of the grain-shaped island portions made of the permanent antistatic agent (A) in the unit area (Su) of the cross section perpendicular to the surface direction of the antistatic layer (20 ). Is an antistatic polyolefin film characterized by having an A of 0.1 or more .

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