Inflation film and manufacturing method thereof

Abstract

To provide an inflation film having high haze and an excellent high-speed thin film forming property, and a manufacturing method thereof.SOLUTION: There is provided an inflation film that comprises a laminate including three layers, in order of a layer (A), a layer (B), and a layer (C). The layer (A) and the layer (C) are made of a high-pressure low-density polyethylene satisfying the following requirements (a) to (c), the layer (B) is made of a high-pressure low-density polyethylene satisfying the following requirements (d) to (e), and a ratio of the layer (B) to the entire laminate is 50 mass% or more. The inflation film has a thickness of 10 to 18 μm and a haze of 15 to 25%. Requirement (a): a melt flow rate (hereinafter referred to as MFR) measured at 190°C and a load of 21.18 N is 1.5 to 4.0 g / 10 min. Requirement (b): density is 919 to 930 kg / m3. Requirement (c): a swell ratio measured at 235°C is 2.0 or more. Requirement (d): MFR is 5.0 to 10 g / 10 min. Requirement (e): density is 919 to 930 kg / m3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a polyethylene film and a method for forming an inflation film, and in particular to a polyethylene film suitable for an optical film or a protection film for a dry film resist, and a method for forming the same. [Background technology]

[0002] In blown film molding, molten resin is extruded from the annular outlet of a circular die to form a tubular bubble, which is then expanded by air (expansion air) blown inward to form a tubular film with a desired diameter and thickness, and is widely used as a method for obtaining various resin films including polyethylene. In a molding device that performs this type of blown film molding, an external cooling device (hereinafter referred to as an "air ring") that cools the resin bubble from the outer periphery during the expansion process is disposed above the die.

[0003] The air ring is equipped with at least one or more cooling air outlets, and the opening degree and the air volume can be appropriately adjusted depending on the properties and temperature of the molten resin, the molding speed, etc. In the molding of polyethylene inflation films, it is generally known that the more the bubbles are cooled rapidly, the better the transparency (the lower the haze) and the worse the high-speed moldability and thin film moldability become (for example, see Non-Patent Document 1).

[0004] In recent years, protective films for dry film resists have been attracting attention as films obtained by blown film molding of polyethylene. High haze is required for this film, but slow cooling of bubbles alone is not sufficient, so polyethylene with a high swell ratio is often used to scatter light by utilizing the surface roughness caused by melt fracture.

[0005] However, polyethylene with a high swell ratio has a high viscosity and its fluidity deteriorates during thin film moldability, resulting in insufficient high-speed thin film moldability. A method was therefore sought that would achieve both high haze and high-speed thin film moldability.

[0006] Under these circumstances, a manufacturing method has been proposed in which an air ring is devised to enhance cooling of the molten resin near the die in order to obtain a film that has high haze and is suitable for high-speed, thin-film molding (see, for example, Patent Document 1). However, the maximum thickness of the film that can be molded is 19 μm, and the market demands further cost reduction and thinner films. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Toshitaka Kanai, "Film Molding," J-Stage Publishing, 1993, pp. 752-757 [Patent documents]

[0008] [Patent Document 1] JP 2023-077154 A Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an inflation film having high haze and excellent high-speed and thin-film formability, and a method for producing the same. [Means for solving the problem]

[0010] As a result of intensive research into solving the above-mentioned problems, the inventors discovered that the above-mentioned problems could be solved by a laminated film of resin that exhibits specific melting characteristics, and by the number and position of air outlets for cooling the tubular molten resin extruded from a die in the production of an inflation film, thereby completing the present invention.

[0011] That is, the respective aspects of the present invention are as follows [1] to [4]. [1] An inflation film comprising a laminate composed of three layers, in the order of Layer A, Layer B, and Layer C, wherein Layer A and Layer C are made of high-pressure low-density polyethylene satisfying the following requirements (a) to (c), Layer B is made of high-pressure low-density polyethylene satisfying the following requirements (d) to (e), the ratio of Layer B to the entire laminate being 50 mass% or more, the thickness being 10 to 18 μm, and the haze being 15 to 25%. (a) The melt flow rate (hereinafter referred to as MFR) measured at 190°C and a load of 21.18 N is 1.5 to 4.0 g / 10 min. (b) Density is 919-930 kg / m 3 (c) Swell ratio measured at 235°C is 2.0 or more. (d) MFR is 5.0 to 10 g / 10 min. (e) Density is 919-930 kg / m 3 [2] A dry film resist comprising a protective film, a resist layer and a substrate, wherein the protective film is the inflation film described in [1]. [3] A method for producing an inflation film comprising melt-extruding high-pressure low-density polyethylene through an annular die to form a tubular film, and supplying gas into the inner space of the tubular film while cooling it to expand it, the method comprising the steps of: (1) providing an air ring having one cooling air outlet for the molten resin adjacent to the annular die and having a distance (L) between the top of the die and the cooling air outlet of 30 mm or less; and (2) blowing cooling air onto the tubular film from the outside. [4] The method for producing an inflation film according to [3], further comprising a step of winding up the cooled tubular film with a winding device, the winding speed of the film being 75 m / min or more. Effect of the Invention

[0012] According to the present invention, it is possible to provide an inflation film forming method that achieves both high haze and high-speed thin film formability in an inflation film, which have been difficult to achieve together until now. This not only improves the productivity of dry film resist protect films, but also contributes to reducing waste. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing an example of an inflation film forming machine used in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in detail below.

[0015] The inflation film, which is one embodiment of the present invention, includes a laminate film composed of three layers, Layer (A), Layer (B), and Layer (C), in this order.

[0016] The high-pressure low-density polyethylene constituting layers (A), (B) and (C) is polyethylene produced by high-pressure radical polymerization. There are two types of polymerization reactors for high-pressure low-density polyethylene: tubular type (also called pipe type) and autoclave type (also called tank type or vessel type). It is known that high-pressure low-density polyethylene polymerized in an autoclave type reactor has a wider molecular weight distribution and more long chain branches than high-pressure low-density polyethylene polymerized in a tubular type reactor. The high-pressure low-density polyethylene can be conveniently selected from commercially available products, and is commercially available, for example, from Tosoh Corporation under the trade name Petrocene.

[0017] The high-pressure low-density polyethylene constituting Layer (A) and Layer (C) has an excellent inflation film formability when its MFR, measured according to JIS K6922-1, is 1.5 to 4.0 g / 10 min, and preferably 3.0 to 4.0 g / 10 min. If the high-pressure low-density polyethylene has an MFR of less than 1.5 g / 10 min, high-speed thin film forming may become difficult due to melt fracture, and if it is more than 4.0 g / 10 min, the haze of the film may decrease.

[0018] The high-pressure low-density polyethylene constituting layers (A) and (C) has a density of 919 to 930 kg / m according to JIS K6922-1. 3 When the film is in the range of 922 to 927 kg / m, the film has high rigidity and is excellent in static friction coefficient. 3 The density of high-pressure low-density polyethylene is 919 kg / m 3 If it is smaller than this, the frictional force at the contact surface between the film surfaces will increase, making it difficult to move or deform, and wrinkles may easily occur. 3 If it is larger, deformation may be restricted due to lack of flexibility, and wrinkles may easily occur.

[0019] Furthermore, the high-pressure low-density polyethylene constituting layers (A) and (C) has a swell ratio (SR) of 2.0 or more measured at 235°C. If the SR of the high-pressure low-density polyethylene is 2.0 or more, the static friction coefficient is low and wrinkles are less likely to occur. SR is obtained by using a melt indexer used in JIS K6922-1, collecting a strand-shaped extrudate in a measuring cylinder containing isopropanol placed directly under the orifice, and dividing the diameter (D) of the strand by the orifice diameter (D0) of the melt indexer.

[0020] The high-pressure low-density polyethylene constituting layer B has an MFR of preferably 5.0 to 10 g / 10 min, since this provides excellent inflation film formability, and more preferably 8.0 to 10 g / 10 min. If the MFR of the high-pressure low-density polyethylene is less than 5.0 g / 10 min, high-speed thin film molding may become difficult due to melt fracture, while if it is more than 10 g / 10 min, molding start-up may become difficult due to insufficient melt tension.

[0021] The high-pressure low-density polyethylene constituting layer (B) has a density of 919 to 930 kg / m 3 When the film has a high rigidity, the film has a high rigidity, and the preferable range is 924 to 927 kg / m 3 The density of high-pressure low-density polyethylene is 919 kg / m 3 If it is smaller than this, the film may be prone to wrinkling due to insufficient rigidity. 3 If it is larger, deformation may be restricted due to lack of flexibility, and wrinkles may easily occur.

[0022] Other resins may be added to the high-pressure low-density polyethylene constituting Layer (A), Layer (B) and Layer (C), such as copolymers of ethylene and α-olefins having 3 to 12 carbon atoms, high-density polyethylene, propylene polymers, 1-butene copolymers and polyolefins such as 4-methyl-1-pentene.

[0023] Furthermore, known additives that are commonly used in polyethylene, such as antioxidants, ultraviolet protection agents, dispersants, foaming agents, lubricants, pigments, and flame retardants, may be added within the limits that do not impair the object of the present invention.

[0024] When the haze of the inflation film is 15 to 25%, the film has excellent appearance as a protective film for a dry film resist and excellent peelability from the film roll, and is preferably 16 to 20%. If the haze of the film is less than 15%, the surface becomes smooth and the friction coefficient increases, which may cause wrinkles to easily occur, whereas if the haze is more than 25%, the film may have poor adhesion to the resist layer when used as a protective film for a dry film resist and may easily peel off.

[0025] From the viewpoints of economy and environmental protection, the thickness of the film is 10 to 18 μm, and preferably 10 to 17 μm. If the thickness of the film is less than 10 μm, the bubbles are likely to burst.

[0026] One embodiment of the present invention relates to a method for producing an inflation film, which comprises melt-extruding high-pressure low-density polyethylene through an annular die to form a tubular film, and supplying gas into the inner space of the tubular film while cooling it to expand it. The method comprises providing an air ring having one cooling air outlet for the molten resin adjacent to the annular die and with a distance (L) between the die top and the cooling air outlet of 30 mm or less, and producing an inflation film by blowing cooling air onto the tubular film from the outside.

[0027] A multi-layer inflation molding machine is used for inflation molding. The inflation molding machine can be one with a general device configuration, for example, one equipped with an extruder, a die, an inflation / cooling section, a clamping roll, and a winder.

[0028] The die of the molding machine is an annular metal mold that shapes the molten resin extruded from the extruder of the inflation film molding machine into a ring shape and discharges it. In the present invention, high-pressure low-density polyethylene is melt-extruded from the annular die to form a tubular film.

[0029] In the inflation and cooling section, the molten resin is expanded by air injected into the die, and then the resin bubbles in the expanding process are cooled by an external cooling device (air ring) that cools the outer periphery. In other words, this is the section where the air ring is installed. In the present invention, the melt-extruded tubular film is expanded by supplying gas into its inner space while being cooled.

[0030] The cooling air outlet refers to the part from which air is discharged in an air ring, a device that blows cooling air from the outside of the cylindrical molten resin (bubble) discharged from an annular die in inflation film molding. In inflation molding, it is usually necessary to cool the molten resin bubble by blowing air from all around it, so the outlet is ring-shaped. In the present invention, the cylindrical film is cooled by blowing cooling air from the outside.

[0031] The number of cooling air outlets is usually one or more. Having one cooling air outlet is preferable because it has a large effect of increasing haze and is excellent in terms of high speed and thin film formability.

[0032] Furthermore, it is preferable to arrange the die and the air ring so that the distance (L) between the die top and the cooling air outlet is 30 mm or less, as this has a large effect of increasing haze and provides excellent high-speed and thin-film formability.

[0033] The method for producing an inflation film further includes a step of winding the cooled tubular film with a winding device. From the viewpoint of excellent high-speed formability, the film winding speed is preferably 75 m / min or more.

[0034] The inflation film is used for various applications such as various packaging, construction and civil engineering materials, and agricultural applications, and is particularly suitable as a protective film for dry film resists and the like.

[0035] The dry film resist according to one embodiment of the present invention is a dry film resist including a protective film, a resist layer, and a substrate, and the above-mentioned inflation film is used as the protective film.

[0036] The resist layer is made of a composition containing a photoinitiator, a photocrosslinking agent, and an acrylic resin.

[0037] The substrate is a polyester (PET) film. EXAMPLES

[0038] The present invention will be described in more detail below by showing examples, but the present invention is not limited to these examples. (1) Melt flow rate (MFR) The MFR of the polyethylene resin was measured at 190°C and a load of 21.18 N in accordance with JIS K6922-1:2018 using a melt indexer (manufactured by Takara Kogyo Co., Ltd.). (2) Density Measurements were performed in accordance with JIS K6922-1:2018.

[0039] Example 1 The inner and outer layer extruders of an air-cooled multi-layer inflation molding machine manufactured by Sumitomo Heavy Industries Modern Co., Ltd. were used to extrude layers (A) and (C), respectively, with a melt flow rate (MFR) of 3.5 g / 10 min and a density of 922 kg / m 3 A high-pressure low-density polyethylene (manufactured by Tosoh Corporation under the trade name Petrothene 17M01E) produced by the autoclave method with a swell (SR) of 2.02 was fed into the extruder for the intermediate layer as layer (B). 3A high-pressure low-density polyethylene (manufactured by Tosoh Corporation, product name Petrothene 14M01A) manufactured by the autoclave method was supplied and extruded at a temperature of 165°C for all layers so that the ratio of (A layer) / (B layer) / (C layer) was 25 / 50 / 25 (mass%). The air ring had one outlet (single air ring) and the distance (L) between the die top and the cooling air outlet was 26 mm, and molding was performed while cooling the extruded resin by blowing air at 15°C. The molding conditions for the inflation film are shown in Tables 1 and 2.

[0040] The high-speed thin film formability was evaluated by increasing the winding speed and recording the speed and film thickness just before breakage.

[0041] The haze of the obtained film was measured using a haze meter (NDH7000) manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K7136.

[0042] The static friction coefficient of the obtained film was measured in accordance with JIS K7125 using a tensile tester (RTE-1210) manufactured by A&D Co., Ltd.

[0043] The presence or absence of wrinkles was judged by visual inspection. The evaluation results are shown in Table 2. In the table, "◯" indicates that no wrinkles were formed, and "×" indicates that wrinkles were formed.

[0044] Example 2 The same processing as in Example 1 was carried out except that the ratio of the molding conditions in Table 1 was (A layer) / (B layer) / (C layer) = 20 / 60 / 20 (mass%). The results of high-speed thin film molding, haze, static friction coefficient, and wrinkles are shown in Table 2.

[0045] Example 3 The same processing as in Example 1 was carried out except that the ratio of the molding conditions in Table 1 was (A layer) / (B layer) / (C layer) = 17 / 66 / 17 (mass%). The results of high-speed thin film molding, haze, static friction coefficient, and wrinkles are shown in Table 2.

[0046] Example 4 The (B) layer in Table 1 is molded under the following conditions: MFR 8.0 g / 10 min, density 924 kg / m 3 The treatment was carried out in the same manner as in Example 1, except that the polyethylene used was a high-pressure low-density polyethylene produced by an autoclave method (manufactured by Tosoh Corporation, product name Petrothene 23M01A). The results of high-speed thin film molding, haze, static friction coefficient, and wrinkles are shown in Table 2.

[0047] Example 5 The treatment was carried out in the same manner as in Example 2, except that the (B) layer in the molding conditions in Table 1 was replaced with the high-pressure low-density polyethylene used in Example 4. The results of high-speed thin film molding, haze, static friction coefficient, and wrinkles are shown in Table 2.

[0048] Example 6 The treatment was carried out in the same manner as in Example 3, except that the (B) layer in the molding conditions in Table 1 was made of the high-pressure low-density polyethylene used in Example 4. The results of high-speed thin film molding, haze, static friction coefficient, and wrinkles are shown in Table 2.

[0049] Example 7 The (B) layer in Table 1 is molded under the following conditions: MFR 8.0 g / 10 min, density 925 kg / m 3 The treatment was carried out in the same manner as in Example 1, except that the polyethylene used was a high-pressure low-density polyethylene produced by the tubular method (manufactured by Tosoh Corporation, product name Petrothene 230). The results of high-speed thin film molding, haze, static friction coefficient, and wrinkles are shown in Table 2.

[0050] Comparative Example 1 The same treatment as in Example 1 was carried out except that the ratio of the molding conditions in Table 1 was (A layer) / (B layer) / (C layer) = 33 / 34 / 33 (mass%). The results are shown in Table 3, and the lower limit thickness of the film that can be formed was thick.

[0051] Comparative Example 2 The molding conditions for layers (A) and (C) in Table 1 are MFR 1.1 g / 10 min and density 931 kg / m 3The treatment was carried out in the same manner as in Example 6, except that the polyethylene used was a high-pressure low-density polyethylene (manufactured by Tosoh Corporation, product name Petrothene 220K) produced by an autoclave method with an SR of 1.53. The results are shown in Table 3. The lower limit thickness of the film that can be formed was large, the haze of the obtained film was low, and wrinkles were observed.

[0052] Comparative Example 3 The treatment was carried out in the same manner as in Example 3, except that the high-pressure low-density polyethylene used in the layers (A) and (C) of Comparative Example 2 was used for the layer (B) in the molding conditions in Table 1. The results are shown in Table 3, with the lower limit thickness of the film that could be formed being thick, and wrinkles being observed in the obtained film.

[0053] Comparative Example 4 The (B) layer in Table 1 is molded under the following conditions: MFR 13g / 10min, density 919kg / m 3 The treatment was carried out in the same manner as in Example 3, except that the high-pressure low-density polyethylene (manufactured by Tosoh Corporation, product name Petrothene 349) produced by the autoclave method was used. The results are shown in Table 3. The bubbles could not be pulled up due to insufficient melt tension, and a film could not be formed.

[0054] Comparative Example 5 The molding conditions for layers (A) and (C) in Table 1 are MFR 8.0 g / 10 min and density 918 kg / m 3 The treatment was carried out in the same manner as in Example 6, except that the polyethylene used was a high-pressure low-density polyethylene (manufactured by Tosoh Corporation, product name Petrothene 213) produced by an autoclave method with an SR of 1.90. The results are shown in Table 3, and the obtained film had a low haze and a high static friction coefficient.

[0055] Comparative Example 6 The treatment was carried out in the same manner as in Example 3, except that the high-pressure low-density polyethylene used in the layers (A) and (C) of Comparative Example 5 was used for the layer (B) in the molding conditions in Table 1. The results are shown in Table 3, and wrinkles were observed in the obtained film.

[0056] Comparative Example 7 The molding conditions for layers (A) and (C) in Table 1 are MFR 4.0 g / 10 min and density 922 kg / m3 The treatment was carried out in the same manner as in Example 6, except that the polyethylene used was a high-pressure low-density polyethylene (manufactured by Tosoh Corporation, product name Petrothene 190) produced by a tubular process with an SR of 1.47. The results are shown in Table 3, and the haze of the obtained film was low.

[0057] Comparative Example 8 The same treatment as in Example 3 was carried out, except that a double air ring with two blowing ports was used as in the molding conditions in Table 1. The results are shown in Table 3, and the haze of the obtained film was low.

[0058] Comparative Example 9 The same treatment as in Example 6 was carried out, except that a double air ring with two blowing ports was used as in the molding conditions in Table 1. The results are shown in Table 3, and the haze of the obtained film was low.

[0059] Comparative Example 10 The same treatment as in Example 3 was carried out, except that an air ring with L of 40 mm was used in the molding conditions in Table 1. The results are shown in Table 3, and the haze of the obtained film was low.

[0060] Comparative Example 11 The same treatment as in Example 6 was carried out, except that an air ring with L of 40 mm was used in the molding conditions in Table 1. The results are shown in Table 3, and the haze of the obtained film was low.

[0061] [Table 1]

[0062] [Table 2]

[0063] [Table 3]

[0064] [Table 4] [Explanation of symbols]

[0065] A Air Ring for Blown Film Forming B. Blown film molding die C Annular outlet D Cooling air outlet L Distance between the top of the die and the bottom of the cooling air outlet

Claims

1. An inflation film comprising a laminate constituted of three layers, namely, an (A) layer, a (B) layer, and a (C) layer, in this order, wherein the (A) layer and the (C) layer are made of high-pressure low-density polyethylene satisfying the following requirements (a) to (c), the (B) layer is made of high-pressure low-density polyethylene satisfying the following requirements (d) to (e), the ratio of the (B) layer to the entire laminate is 50 mass% or more, the thickness is 10 to 18 μm, and the haze is 15 to 25%. (a) A melt flow rate (hereinafter referred to as MFR) measured at 190° C. and a load of 21.18 N is 1.5 to 4.0 g / 10 min. (b) Density is 919 to 930 kg / m ３ (c) A swell ratio measured at 235° C. of 2.0 or more (d) MFR is 5.0 to 10 g / 10 min. (e) density is 919 to 930 kg / m ３

2. A dry film resist comprising a protective film, a resist layer and a substrate, wherein the protective film is the inflation film according to claim 1.

3. 2. The method for producing an inflation film according to claim 1, comprising melt-extruding high-pressure low-density polyethylene through an annular die to form a tubular film, and supplying gas into the inner space of the tubular film while cooling it to expand it, wherein an air ring is provided adjacent to the annular die and the distance (L) between the die top and the cooling air outlet is 30 mm or less, and cooling air is blown onto the tubular film from the outside.

4. 4. The method for producing an inflation film according to claim 3, further comprising a step of winding the cooled tubular film with a winding device, the winding speed of the film being 75 m / min or more.

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