Manufacturing method of laminated film

Abstract

To provide a method for manufacturing a laminated film, capable of suppressing the occurrence of a red stripe.SOLUTION: A method for manufacturing a laminated film comprises: introducing a first film 3 including a polarizer layer between a pair of rotating bonding rolls 1a and 1b, a second film 2a arranged so as to face the first film and a third film 2b arranged so as to face the surface of the first film 3 on the opposite side of the second film 2a with an adhesive supplied respectively between the first film 3 and the second film 2a and between the first film 3 and the third film 2b by discharge nozzles 5a and 5b to bond the respective films to each other; and supplying the adhesive while maintaining the state of positioning the tips of the discharge nozzles 5a and 5b in the insides of adhesive reservoirs 6a and 6b respectively formed between the first film 3 and the second film 2a and between the first film 3 and the third film 2b.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a laminated film.

Background Art

[0002] Conventionally, a method of bonding films together with an adhesive using a pair of bonding rolls is known (for example, Patent Document 1). In Patent Document 1, in order to prevent the liquid adhesive supplied to the center of the bonding surface from leaking from both ends in the width direction of the film, excess adhesive is removed by suction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When bonding a film including a polarizer layer and another film using a pair of bonding rolls, when the adhesive is discharged from a nozzle and supplied, red streaks extending in the MD direction may be observed in the quality inspection after bonding. An object of the present invention is to provide a method for manufacturing a laminated film capable of suppressing the occurrence of such red streaks.

Means for Solving the Problems

[0005] According to the study by the present inventor, it has been found that the red streaks occur at positions corresponding to the arrangement positions of the nozzles. Therefore, considering that the adhesive supply method has some influence, intensive studies were conducted, and the present invention was completed.

[0006] The present invention provides a method for manufacturing a laminated film, comprising introducing a first film containing a polarizer layer, a second film positioned to face the polarizer layer of the first film, and a third film positioned to face the side of the first film opposite to the second film side, between a pair of rotating laminating rolls, along with adhesive supplied to the space between the first film and the second film, and between the first film and the third film, by discharge nozzles, thereby laminating the first film, the second film, and the third film, wherein the adhesive is supplied while maintaining a state in which the tip of each discharge nozzle is positioned inside the adhesive reservoir formed between the first film and the second film, and between the first film and the third film, respectively.

[0007] By positioning the tip of the discharge nozzle inside the adhesive reservoir, the flow pressure of the discharged adhesive is absorbed by the reservoir. This prevents localized physical stress on each film, thereby suppressing film damage caused by the adhesive supply method.

[0008] In this invention, the introduction angle of the first film to the pair of laminating rolls may be set to 5° to 30° with respect to the horizontal plane, and the second film may be positioned above the first film. In this arrangement, the polarizer layer is located below the discharge nozzle, and the discharged adhesive tends to put stress on the polarizer layer, which has relatively low physical strength. In this invention, the occurrence of red streaks can be suppressed even in such cases.

[0009] In this invention, the adhesive may be a water-based adhesive. Furthermore, in this invention, at least one of the second and third films may be a triacetylcellulose film. Water-based adhesives may produce gel-like precipitates after drying, and these precipitates may damage the polarizer layer. This tendency is particularly pronounced in highly hygroscopic films such as triacetylcellulose films. In this invention, the occurrence of red streaks can be suppressed even in such cases.

[0010] In this invention, the adhesive may be supplied such that, in a side view cross-section with respect to the introduction direction of each film at the adhesive supply point, the distance between the midpoint of the rotation centers of a pair of laminating rolls and the liquid surface of the adhesive reservoir is 10 mm to 100 mm. Furthermore, the length of the portion of the discharge nozzle located inside the adhesive reservoir may be 3 mm to 15 mm.

[0011] Furthermore, the present invention provides a method for manufacturing a laminated film, comprising introducing a first film containing a polarizer layer and a second film positioned to face the polarizer layer of the first film between a pair of rotating laminating rolls, together with an adhesive supplied between the first film and the second film by a discharge nozzle, thereby laminating the first film and the second film, wherein the adhesive is supplied while maintaining a state in which the tip of the discharge nozzle is positioned inside the adhesive reservoir formed between the first film and the second film. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for manufacturing a laminated film that can suppress the occurrence of red streaks. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows how three films are bonded together, as an embodiment of the present invention. [Figure 2] This is a plan view of Figure 1. However, some components have been omitted. [Figure 3] This is a magnified section of Figure 1. [Figure 4] Figures (A) and (B) both show embodiments that are not part of the present invention. [Modes for carrying out the invention]

[0014] The present invention manufactures a laminated film by bonding multiple long films together with an adhesive while they are being transported using a conveyor roll. Laminated films manufactured using a predetermined adhesive supply method of the present invention have suppressed occurrence of red streak defects. Preferred embodiments of the present invention will be described in detail below with reference to the drawings. In each figure, the same parts or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted.

[0015] As one embodiment, a polarizing plate (laminated film) is manufactured by laminating protective films to both sides of a film containing a polarizer layer. Figure 1 shows the process of laminating three films (2a, 3, 2b) using a pair of laminating rolls 1a, 1b that can press against each other, viewed from the axial direction of the laminating rolls 1a, 1b. The laminating rolls 1a, 1b are arranged vertically, and all three films are long and are transported with their surfaces facing vertically, and they converge at the laminating rolls 1a, 1b. Figure 2 is a plan view of Figure 1. However, the film located at the top in Figure 1 is not shown in Figure 2.

[0016] In this embodiment, the first protective film (second film) 2a, the film containing a polarizer layer (first film; hereinafter referred to as "polarizing film") 3, and the second protective film (third film) 2b are introduced between the laminating rolls 1a and 1b in the order of being laminated from the top in the vertical direction. Here, it is assumed that the polarizer layer contained in the polarizing film 3 faces the first protective film 2a. Each film is conveyed from left to right in the figure, and the laminated film 4 formed by lamination by the laminating rolls 1a and 1b is then conveyed to the next process. The width of each film is, for example, 1000 mm to 2500 mm. In this embodiment, the widths of the first protective film 2a and the second protective film 2b are wider than the width of the polarizing film 3, resulting in excess length on both sides in the width direction of the first protective film 2a and the second protective film 2b.

[0017] The polarizing film 3 may consist of a polarizer layer alone, or it may have other layers laminated on top of the polarizer layer. The polarizer layer is a stretched film, for example, a polyvinyl alcohol film on which iodine or a dichroic dye is adsorbed and oriented. The thickness of the polarizer layer may be 1 μm to 50 μm, or 3 μm to 15 μm. Thinner thicknesses tend to cause red streak defects, making them suitable for application of the manufacturing method of this embodiment.

[0018] The materials constituting the first protective film 2a and the second protective film 2b are, for example, cellulose ester films such as triacetylcellulose (TAC) film; cyclic olefin films; polyester films such as polyethylene terephthalate (PET) film; and (meth)acrylic films such as polymethyl methacrylate (PMMA) film. The materials constituting the first protective film 2a and the second protective film 2b may be the same or different. At least one of the first protective film 2a and the second protective film 2b may be a triacetylcellulose film.

[0019] The materials constituting the first protective film 2a and the second protective film 2b preferably have a water contact angle of 5° to 50° on the side that is bonded to the polarizing film 3, more preferably 7° to 40°, and even more preferably 10° to 35°. The water contact angle can be measured by the following method. A measurement sample is prepared by bonding the protective film to a glass substrate using an adhesive, with the surface to be measured facing outwards. This measurement sample is placed horizontally in a contact angle meter (image processing type contact angle meter "FACE CA-X" manufactured by Kyowa Interface Science Co., Ltd.) with the surface to be measured facing upwards, and 1 microliter of water is dropped onto the surface to be measured to measure the contact angle with respect to the water.

[0020] Particularly when the polarizing film 3 is a polyvinyl alcohol film, the smaller the water contact angles of the first protective film 2a and the second protective film 2b, the higher the adhesion between them, and the less likely they are to peel off. Although a small water contact angle tends to cause red streaks, according to the manufacturing method of the present embodiment, the occurrence of red streaks can be suppressed even when the water contact angle is small. In particular, when at least one of the first protective film 2a and the second protective film 2b is a highly hygroscopic triacetyl cellulose film, the effect of the present embodiment can be significantly confirmed when the water contact angle is within the above range.

[0021] The introduction angle of the second protective film 2b with respect to the laminating rolls 1a and 1b is approximately 0° with respect to the horizontal plane. In contrast, the introduction angle of the polarizing film may be 5° to 30° with respect to the horizontal plane, or may be 10° to 20°. The introduction angle of the first protective film may be 10° to 60° with respect to the horizontal plane, or may be 20° to 50°. The introduction angle of at least one film may be 0° to ±45° with respect to the horizontal plane, may be ±5° to ±35°, or may be ±10° to ±25°.

[0022] Between the first protective film 2a and the polarizing film 3, and between the polarizing film 3 and the second protective film 2b, rod-shaped discharge nozzles 5a and 5b for discharging an adhesive are respectively arranged. The discharge nozzles 5a and 5b are arranged at the center in the width direction of the laminating rolls 1a and 1b so that their rod-shaped shapes extend in the conveyance direction of each film. The arrangement angles of the discharge nozzles 5a and 5b with respect to the horizontal direction are appropriately adjusted so as not to contact each film.

[0023] As the adhesive, an aqueous adhesive, an active energy ray curable adhesive, or a thermosetting adhesive can be used. From the perspective of application to the present embodiment, an aqueous adhesive is preferred. Examples of the aqueous adhesive include an adhesive composed of an aqueous solution of a polyvinyl alcohol-based resin, an aqueous two-component urethane-based emulsion adhesive, etc. Among them, an aqueous adhesive composed of an aqueous solution of a polyvinyl alcohol-based resin is suitable.

[0024] Suction nozzles 7, 7 are positioned on both sides in the width direction of the bonding rolls 1a, 1b and on the upstream side of the conveying process to remove excess adhesive. The suction nozzles 7, 7 are positioned in the excess portions of the first protective film 2a and the second protective film 2b.

[0025] During the lamination of each film, adhesive is discharged from the discharge nozzles 5a and 5b and supplied between the polarizing film 3 and the first protective film 2a, and between the polarizing film 3 and the second protective film 2b. The supplied adhesive spreads to both sides in the width direction of the lamination rolls 1a and 1b, covering the entire lamination area of ​​each film. If the amount of adhesive supplied is increased, the excess that cannot be introduced between the lamination rolls 1a and 1b accumulates on the upstream side of the lamination rolls 1a and 1b, forming adhesive reservoirs 6a and 6b. In this embodiment, the tips of the discharge nozzles 5a and 5b are positioned inside the adhesive reservoirs 6a and 6b, respectively, and the lamination of each film is performed while maintaining this state (Figure 1).

[0026] At the adhesive supply point, the distance between the midpoint of the rotation centers of the bonding rolls 1a and 1b and the liquid surface of the adhesive reservoirs 6a and 6b (depth of the adhesive reservoir) may be 5 mm to 100 mm, preferably 10 mm to 100 mm, and more preferably 20 mm to 70 mm. The amount of adhesive supplied is adjusted so that this distance is ensured. Here, "distance" more specifically refers to the distance measured by a straight line parallel to the surface of the first protective film 2a or second protective film 2b, assuming a side view cross-section with respect to the introduction direction of each film at the adhesive supply point (where the discharge nozzles 5a and 5b are located in the width direction of the laminating rolls 1a and 1b) (Figure 3). The starting point is the midpoint P3 of the line segment connecting the rotation center P1 of laminating roll 1a and the rotation center P2 of laminating roll 1b, and the ending point is the part of the contact area between the adhesive reservoir 6a or adhesive reservoir 6b and the first protective film 2a or second protective film 2b that is furthest from the laminating roll 1a or laminating roll 1b (indicated by D1 and D2 in Figure 3. In Figure 3, the dashed lines drawn at both ends of the double arrows labeled D1 or D2 are parallel to each other).

[0027] Distances D1 and D2 may or may not be the same. At least one of distances D1 and D2 may be within the above numerical range, or both may be within the above numerical range. Distances D1 and D2 are strictly distances on a side view cross section at the locations where the discharge nozzles 5a and 5b are positioned as shown in Figure 3, but the adhesive reservoirs 6a and 6b may have a predetermined distance in the width direction of the bonding rolls 1a and 1b centered on the locations where the discharge nozzles 5a and 5b are positioned. Here, "predetermined distance" has the same definition as distances D1 and D2, and decreases as you move toward both sides in the width direction of each film, starting from the locations where the discharge nozzles 5a and 5b are positioned.

[0028] The length of the portion of the discharge nozzles 5a and 5b that is located inside the adhesive reservoirs 6a and 6b (indicated by symbols G1 and G2 in Figure 3), that is, the length of the portion of the discharge nozzles 5a and 5b that is always wet with adhesive during the lamination of each film, is preferably 3 mm to 15 mm, and more preferably 5 mm to 10 mm.

[0029] Conventionally, in film lamination in the manner shown in Figure 1, if adhesive reservoirs 6a and 6b are not created, or if the tips of the discharge nozzles 5a and 5b are not positioned inside the adhesive reservoirs 6a and 6b (for example, the tip of the discharge nozzle is in contact with the surface of the adhesive reservoir as shown in Figure 4(A), or the tip of the discharge nozzle is completely separated from the adhesive reservoir as shown in Figure 4(B)), red streaks extending in the MD direction were sometimes observed during quality inspection of the laminated film after lamination. According to the inventor's research, these red streaks are more likely to occur when using a water-based adhesive that can produce gel-like precipitates after drying, when using a highly hygroscopic triacetylcellulose film as the protective film, and when the film receiving the supplied adhesive (the film located on the lower side during lamination) is a polarizing film. Furthermore, it was found that the location where the red streaks occur corresponds to the location where the discharge nozzle is positioned.

[0030] In this embodiment, by positioning the tips of the discharge nozzles 5a and 5b inside the adhesive reservoirs 6a and 6b, the flow pressure of the discharged adhesive is absorbed by the adhesive reservoirs 6a and 6b. For example, in the embodiment shown in Figure 4(B), the discharged adhesive comes into contact with the polarizing film 3 in droplet or linear form before joining the adhesive reservoirs 6a and 6b. However, in this embodiment (Figure 2), the adhesive is supplied to the adhesive reservoirs 6a and 6b from the beginning, and the adhesive does not leave the adhesive reservoirs 6a and 6b before coming into contact with the polarizing film 3. This prevents localized physical stress from the adhesive on each film, including the polarizing film 3, and suppresses damage that causes red streaks.

[0031] In particular, in this embodiment, the polarizing film 3, which has relatively low physical strength, is located below the discharge nozzle 5a, but as described above, it is less susceptible to damage from the discharged adhesive, thus suppressing the occurrence of red streaks.

[0032] When a water-based adhesive is used as the bonding agent, the laminated film 4 is dried after bonding to remove the water contained in the water-based adhesive. At this time, a gel-like precipitate may form, and this precipitate may damage the polarizing film 3. This tendency is particularly pronounced when a highly hygroscopic film such as a triacetylcellulose film is used as the first protective film 2a or the second protective film 2b. In this embodiment, the occurrence of red streaks can be suppressed even in these cases.

[0033] Although preferred embodiments of the present invention have been described above, the present invention is not limited in any way to the above embodiments. For example, in the above embodiments, one discharge nozzle is arranged in the center of the film in the width direction, but a configuration in which multiple discharge nozzles are equally distributed in the width direction of the film is also possible.

[0034] Furthermore, although the above embodiment shows a configuration in which three films are bonded together, a configuration in which two films are bonded together is also possible. That is, a first film containing a polarizer layer and a second film positioned to face the polarizer layer of the first film are introduced between a pair of rotating bonding rolls, together with adhesive supplied between the first and second films by a discharge nozzle, thereby bonding the first and second films together. Here, the adhesive is supplied while maintaining a state in which the tip of the discharge nozzle is positioned inside the adhesive reservoir formed between the first and second films. [Examples]

[0035] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

[0036] (Materials used) • Polarizing film: Stretched polyvinyl alcohol film (12 μm thick) • Second protective film: Triacetylcellulose film (30 μm thick, water contact angle 15°) • First protective film…cyclic olefin film (thickness 13μm) • Adhesive: Water-based adhesive consisting of an aqueous solution of polyvinyl alcohol resin.

[0037] (Example 1) Three films were laminated in the manner shown in Figures 1 and 2. Specifically, the first protective film, polarizing film, and second protective film were arranged from top to bottom and introduced into the lamination roll. A discharge nozzle was positioned at the center of the film's width. Adhesive was supplied from the discharge nozzle, and the position of the discharge nozzle and the supply amount were adjusted so that the tip of the discharge nozzle was located inside the adhesive reservoir. Here, the depth of the adhesive reservoir was 7 mm, and the length of the adhesive-soaked portion of the discharge nozzle was 5 mm. The three films were successfully laminated to obtain a laminated film.

[0038] (Comparative Example 1) The three films were laminated in the same manner as in Example 1, except that the tip of the discharge nozzle was brought into contact with the surface of the adhesive reservoir when supplying the adhesive using the discharge nozzle (Figure 4(A)). The three films were successfully laminated, and a laminated film was obtained.

[0039] (Comparative Example 2) The three films were laminated in the same manner as in Example 1, except that the tip of the discharge nozzle was positioned 24 mm away from the adhesive reservoir when supplying the adhesive using the discharge nozzle (Figure 4(B), L=24 mm). The three films were successfully laminated, and a laminated film was obtained.

[0040] (Quality inspection) Each obtained laminated film was cut to 1290 mm x 500 mm and subjected to quality inspection. A white light source (special inspection lighting device ("S-light", manufactured by Japan Technical Center)) and a polarizing plate were prepared, and the laminated film to be inspected was placed between the light source and the polarizing plate. The laminated film and the polarizing plate were in a cross-transmission state, and visual inspection was performed at the angle of specular reflection. As a result of the inspection, no red streaks were observed in the laminated film obtained in Example 1, almost no red streaks were observed in the laminated film obtained in Comparative Example 1, and red streaks were clearly observed in the laminated film obtained in Comparative Example 2. These red streaks were not observed under fluorescent or green lamps. [Industrial applicability]

[0041] This invention can be used to improve the quality of laminated films. [Explanation of symbols]

[0042] 1a,1b...Laminating roll, 2a...First protective film (second film), 2b...Second protective film (third film), 3...Polarizing film (first film), 4...Laminated film, 5a,5b...Discharge nozzle, 6a,6b...Adhesive reservoir, 7,7...Suction nozzle, D1,D2...Distance, G1,G2...Length, L...Distance, P1,P2...Center of rotation, P3...Midpoint.

Claims

1. A method for manufacturing a laminated film, comprising introducing a first film containing a polarizer layer, a second film positioned to face the polarizer layer of the first film, and a third film positioned to face the side of the first film opposite to the side facing the second film, between a pair of rotating laminating rolls, along with adhesive supplied to the space between the first film and the second film, and between the first film and the third film, by a discharge nozzle, thereby laminating the first film, the second film, and the third film, The adhesive is supplied while maintaining a state in which the tip of each discharge nozzle is positioned inside the adhesive reservoir formed between the first film and the second film, and between the first film and the third film, respectively. A manufacturing method wherein the length of the portion of the discharge nozzle located inside the adhesive reservoir is 3 mm to 15 mm.

2. The introduction angle of the first film to the pair of laminating rolls is set to 5° to 30° with respect to the horizontal plane. The manufacturing method according to claim 1, wherein the second film is placed above the first film.

3. The manufacturing method according to claim 1 or 2, wherein the adhesive is a water-based adhesive.

4. The manufacturing method according to any one of claims 1 to 3, wherein at least one of the second film and the third film is a triacetylcellulose film.

5. The manufacturing method according to any one of claims 1 to 4, wherein the adhesive is supplied such that, in a side view cross-section with respect to the introduction direction of each film at the adhesive supply point, the distance between the midpoint of the rotation centers of the pair of laminating rolls and the liquid surface of the adhesive reservoir is 10 mm to 100 mm.

6. A method for manufacturing a laminated film, comprising introducing a first film containing a polarizer layer and a second film positioned to face the polarizer layer of the first film between a pair of rotating laminating rolls, together with an adhesive supplied between the first film and the second film by a discharge nozzle, thereby laminating the first film and the second film, The adhesive is supplied while maintaining a state in which the tip of the discharge nozzle is positioned inside the adhesive reservoir formed between the first film and the second film. A manufacturing method wherein the length of the portion of the discharge nozzle located inside the adhesive reservoir is 3 mm to 15 mm.

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