JP2017132266A - Method for producing optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method capable of producing a high-quality film free from streak-like defects in a melt film-forming method.SOLUTION: In a method for producing an optical film including discharging a resin plasticized by melting means in a film-like shape from a die, a joining part on a resin flow passage from the leading edge on the downstream side of the melting means to the die is configured so that R of the edge part, brought into contact with the flow passage, in the cross section of the joining part is 40 μm or less, and further, the maximum deviation of the flow passages in the joining part cross sections of both members to be joined is set at 50 μm or less.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an optical film with reduced streak defects.

  As a film forming method, a melt film forming method is known in which a thermoplastic resin is heated and melted by an extruder or the like, and then discharged into a film using a T-die and cooled and solidified. Although this method is superior in productivity to a solution casting method in which a resin composition is dissolved in an organic solvent and the solution is cast into a sheet / film form and then dried to produce a film, the T-die is used. There was a problem that streaky defects occurred in the flow direction in the discharged film. Moreover, when using a film especially for an optical film use, since a stripe defect is detected as an optical distortion, it is requested | required to reduce a stripe defect with higher precision.

  On the other hand, by adding a heat stabilizer to the resin, an attempt has been made to improve the raw material resin formulation by suppressing the generation of eyes and eyes, which is one of the causes of streak defects.

  Various attempts have also been made in melt film-forming methods and apparatuses. For example, in Patent Document 1, a die line is smoothed by pressing a film after discharging a T die with a forming roll. Further, in Patent Document 2, streak-like defects caused by lip edges are suppressed by defining T die edge accuracy. It has been proposed.

JP 2009-166290 A JP 2005-173072 A

  As described above, several manufacturing methods and apparatuses have been proposed in order to eliminate streak-like defects, but they have not completely eliminated streak-like defects.

  In Patent Document 1, it has been proposed to reduce vertical stripes by controlling the pinching pressure by the touch roll, the film temperature at the time of contact with the cooling roll, and the film temperature at the time of stretching, but in the process of heating the film after the stretching process, etc. Since heat return occurs and vertical stripes are generated again, for example, in an optical film manufacturing method in which a stretching process is often necessary to develop optical characteristics, it is not a fundamental solution.

  Moreover, although the countermeasure by the recessed part and convex part reduction of T-die edge part in patent document 2 is improved about the stripe-like defect resulting from a lip edge part, there are still many stripe-like defects which are not solved (because of a lip edge part) Not effective against streak-like defects.)

  The present invention has been made in view of the problems of film quality and productivity that have not been solved by such conventional techniques, and particularly suppresses the occurrence of streak-like defects in the optical film manufacturing method (melt film forming method). An object of the present invention is to provide a method for producing a high-quality optical film.

  As a result of diligent investigations to solve the above problems, we noticed that the streaks of the melt-flowing resin before the resin flows into the die (upstream of the die) is one of the causes of streak-like defects. The present inventors have found out that a portion where a streak-like defect has occurred is a joint that connects each member, and that the occurrence of the streak-like defect can be further reduced by suppressing this occurrence, leading to the present invention. In particular, it is possible to take measures against fine streak defects that are problematic when the film is used for optical applications.

  That is, the present invention relates to a method of manufacturing an optical film in which a resin plasticized by a melting means is discharged from a die into a film shape, and the joining portion on the resin flow path from the downstream end of the melting means to the die is a joining portion. A method for producing an optical film by melt film formation, characterized in that R of an edge portion in contact with the flow path in the cross section is 40 μm or less, and further, the maximum deviation of the flow path in the cross section of the joint portion of both members to be joined is 50 μm or less. Provided.

  Further, both members to be joined have a male-female structure or a structure in which the position is fixed by a key, and the tolerance of the fitting part of the male-female structure or the key is 50 μm or less. Provided.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress the stripe defect which the molten resin had before resin flowed into die | dye, to reduce a stripe defect, and to provide a high quality optical film. In particular, it is possible to take measures against fine streak defects that are problematic in optical films.

  The present invention relates to a method for producing an optical film in which a resin plasticized by a melting means is discharged from a die into a film shape. The present invention relates to a method for producing an optical film by melt film formation, characterized in that R of the edge portion in contact with the flow path is 40 μm or less, and further, the maximum deviation of the flow path in the section of the joint portion of both members to be joined is 50 μm or less is there.

  Here, various methods can be used as a means for melting the resin (thermoplastic resin). However, as is generally done, an extruder is used and the resin is heated and kneaded to be melted. These facilities are preferable.

  In the present invention, as an extruder, a single-screw extruder, a co-directional meshing twin-screw extruder, a co-directional non-meshing twin-screw extruder, a different-direction meshing twin-screw extruder, a different-direction non-meshing twin-screw extruder Various extruders such as a multi-screw extruder can be used. Among them, the single-screw extruder is preferable because the resin staying portion in the extruder is small, so that it is possible to prevent thermal deterioration of the resin during extrusion and the equipment cost is low. Moreover, it is preferable to use an extruder having a vent mechanism in order to remove residual volatile components in the resin and heating products in the extruder.

  As a form of the raw material such as a thermoplastic resin to be fed into the extruder, it is preferable to use a solid state resin, preferably a 3 mm square pellet shape. For example, the pellet-shaped resin is supplied into the extruder through a hopper attached to the raw material supply port of the extruder. This hopper preferably has a drying mechanism, and it is preferable that the hopper capacity be designed in consideration of the necessary drying time and resin consumption time so that it can be supplied into the extruder with moisture in the resin removed.

  As a screw used in a single screw extruder or the like, a general full-flight configuration with a compression ratio of about 2-3 for an extruder with a vent can be used, but a special so as not to leave unmelted material. A kneading mechanism may be provided.

  In the present invention, the extrusion conditions when using an extruder as the melting means must be adjusted according to the thermoplastic resin used. For example, when a polycarbonate resin is used, the resin temperature at the outlet of the extruder is 220. It is preferable to set the temperature of each cylinder part so that it may become -320 degreeC, More preferably, it is preferable that it is 240-290 degreeC. If the resin temperature is less than 220 ° C, the melt viscosity becomes very large and it may become difficult to torque the extruder or form the film. There is a possibility that.

  The molten resin obtained by melting means such as an extruder is then preferably supplied to the die using a gear pump. By using a gear pump, the discharge amount fluctuation in the extruder is absorbed, the quantitativeness of the supply is remarkably improved, and the stability of the film thickness with time is improved.

  Thus, when the gear pump is disposed between the melting means and the die, the joint portion on the resin flow path extending from the downstream end of the gear pump to the die has an R of the edge portion in contact with the flow path in the joint cross section of 40 μm or less, Furthermore, it is preferable that the maximum deviation of the flow path in the cross section of the joint portion between both members to be joined is 50 μm or less. In this case, it is preferable that the joint on the resin flow path from the downstream end of the melting means to the downstream end of the gear pump also has the characteristics of the above-mentioned joint, but the streak defect generated upstream of the gear pump is Since it can be expected to disappear when passing through, it is not always necessary (however, since it may cause resin-derived foreign matter, defects, coloring, etc. due to resin stagnation even upstream of the gear pump, it is particularly downstream of the melting means. It is preferable that the joint from the tip to the downstream tip of the gear pump is also a joint having the characteristics of the joint.

  The molten resin quantitatively supplied from the gear pump or directly supplied from the melting means is supplied to the die through, for example, a tubular flow path, and is discharged from the die into a film. It is preferable to provide a foreign substance removing device in the resin flow path from the gear pump to the die or in the resin flow path from the melting means to the die when no gear pump or the like is used. Thereby, the foreign material contained in the raw material resin or the foreign material generated by the extruder or the gear pump can be trapped, and the foreign material defect in the film can be reduced. As the foreign matter removing device, a leaf disk type filter is preferable in terms of filtration accuracy, filtration area, pressure resistance, and time until filter clogging with foreign matter. In the case of optical use, the filter filtration accuracy is preferably 1 to 20 μm, preferably 3 to 10 μm.

  When the foreign substance removing device is arranged between the melting means and the die in this way, the joint portion on the resin flow path from the downstream end of the foreign matter removing apparatus to the die is connected to the edge portion R which is in contact with the flow path in the joint section. Is preferably 40 μm or less, and further, the maximum deviation of the flow path in the cross section of the joint portion of both members to be joined is preferably 50 μm or less. In this case, it is preferable that the joint portion on the resin flow path from the downstream end of the melting means to the downstream end of the foreign substance removing device also has the characteristics of the above joint portion. This is not always necessary because it can be expected to disappear when passing through the filter medium etc. in the foreign substance removal device (however, even if it is upstream of the foreign substance removal device, resin-derived foreign matter, defects, coloring, etc. occur due to resin retention. Since there is a possibility, it is preferable that the joint part from the downstream end of the melting means to the downstream end of the foreign substance removing device is also a joint part having the characteristics of the joint part.

  Thus, in this invention, the form of the junction part which joins the resin flow path of each member is prescribed | regulated. Examples of members to be joined include melting means (such as an extruder), gear pump, foreign matter removing device (such as a filter), die, and piping. In general, only the fact that the joining portion connects the flow paths of the respective members so that there is no leakage of the resin is considered, but in the production of a film for a specific application, its fine form may be a problem. In particular, when used in optical film applications, fine streak defects that have not been a problem in other applications become a problem, and it is important to deal with such fine streak defects. On the other hand, by designing and managing the shape of the joint so as to satisfy the range specified in the present application, the occurrence of streak defects in the flow resin is suppressed and the streak defects including fine ones are reduced. An optical film can be provided.

  Specifically, R of the edge portion in contact with the flow path in the joint section is 40 μm or less, and the maximum deviation of the flow paths in the joint section of both members to be joined is 50 μm or less.

  Regarding the R of the edge portion, if the R of the edge portion exceeds 40 μm, the flow path is recessed at the joint surface, and a streak-like result is produced when the fluid resin passes through the portion. Not only that, but resin stagnation occurs in the part, and thus resin-derived foreign matter / defects are generated in the film. R of this edge part is 40 micrometers or less, More preferably, it is 30 micrometers or less, More preferably, it is 15 micrometers or less.

  Furthermore, in order to prevent defects on the film, it is preferable that there are no steps having a width of 50 μm or more and a depth of 50 μm or more due to scratches or dents on the joint edge. More preferably, the step has a width of 20 μm or more and a depth of 20 μm or more, and more preferably has a size of 10 μm or more and a depth of 10 μm or more.

  On the other hand, even if the joint portion alone is in the specified range, if the joint portion is shifted and connected, the flow paths to be joined are displaced from each other, resulting in a streak-like defect. Therefore, it is necessary to make the maximum deviation of the flow paths in the joint cross section of both members to be joined to be 50 μm or less. In order to suppress this displacement of the joint portion, both members to be joined have a male-female structure or a structure in which the position is fixed by a key (for example, the key is installed on the mating surface of the flange where the joint portion is located). It is preferable. Among these, it is preferable that both the members to be joined have a male-female structure, since the surfaces that are brought into close contact with each other during connection are less likely to be displaced. About this male-female structure, it is also possible to install a short ring that is male at both ends between both members of the female. The tolerance of the fitting part of the male / female part is preferably 50 μm or less. If the tolerance of the fitting portion exceeds 50 μm, a step is generated due to the fitting of the male and female, which is not preferable. In addition, it is preferable that the fitting portion having a structure in which the position is fixed by the key also has a tolerance of 50 μm or less.

  As the die used in the present invention, those having various structures can be used, but a T die is preferable, and for example, a general coat hanger die can be used. As the width direction thickness adjusting mechanism, a mechanism capable of adjusting a gap in an arbitrary portion in the width direction of the lip by pushing a bolt or the like is preferable.

  Even when a specific joint is used as in the present invention, streaky defects caused by die scratches may remain separately. Therefore, it is more preferable to process the lip edge accuracy within the range of the edge bright line width of 1 to 30 μm. The die lip portion is preferably subjected to hard chrome plating or ceramic spraying because the bright line width accuracy can be improved.

  On the other hand, the resin discharged in the form of a film from the die can be cooled by various methods. For example, the resin is cast on a temperature-controlled roll (hereinafter referred to as a first roll), and the temperature is further adjusted while being taken. Can be brought into contact with a roll (hereinafter referred to as a second roll) and cooled and solidified. Further, at this time, the film can be sandwiched and formed by a temperature-controlled roll (hereinafter, sandwiching roll) provided separately and the first roll. In this case, the roll landing position of the film is stabilized and the quality of the thickness is improved, and the film is smoothed by pressing, and the unevenness of the streak defect becomes thin. Moreover, electrostatic application, an air knife, etc. can also be used separately for landing position stabilization.

  The cooling temperature is usually set based on the glass transition temperature. The first roll with which the film first comes into contact is the glass transition temperature ± 30 ° C. of the thermoplastic resin, and the second roll is glass transition temperature ± 30 ° C. preferable.

  The film can be taken out by various methods. For example, the film can be taken up by a nip roll installed after the second roll, wound around a take-up core, and obtained as a film original. At this time, since both ends of the film become thick due to the influence of neck-in, the film may be trimmed with a cutter or the like.

  The film raw film thus obtained may be used as it is, or may be stretched by a stretching machine and obtained as an optical film such as a retardation film.

  On the other hand, various resins can be used as the thermoplastic resin in the present invention. For example, norbornene resin, polycarbonate resin, polysulfone resin, polyethersulfone resin, polymethyl methacrylate, and the like are polymerized and copolymerized. Or acrylic resins obtained by modification (including acrylic resins having a ring structure in the main chain), polyarylate resins, polystyrene resins, polyvinyl chloride resins, and the like. Among these, it is preferable to use a polycarbonate resin and an acrylic resin (especially an acrylic resin having a ring structure in the main chain that can also be used for applications requiring heat resistance), which are particularly excellent in transparency and workability. .

  In particular, when used as a light-transmitting layer of an optical recording medium, the light-transmitting layer and the substrate on which the light-transmitting layer is bonded are made of the same material in order to prevent warping or distortion due to the difference in dimensional change rate from the substrate. Therefore, polycarbonate which is widely used as a substrate material for optical recording media is preferable. Among them, an aromatic polycarbonate composed of a repeating unit composed mainly of 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) is particularly preferred because it is mass-produced and inexpensive. The main component here refers to a repeating component composed of a compound occupying 50 mol% or more of the dihydroxy compound which is a raw material of polycarbonate. Therefore, even if 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) is used alone, other dihydroxy compounds are added or copolymerized or mixed within a range not exceeding 50 mol%. Can be used. Although it does not specifically limit as a dihydroxy compound used by copolymerizing or mixing, As an example, 1, 1-bis (4-hydroxy 2, 2-bis (4-hydroxy-3-methylphenyl) propane, 1, 1-, Bis (4-hydroxy-3-tert-butylphenyl) propane, 2,2-bis (4-hydroxy-3-tert-butylphenyl) propane, 2,2-bis (4-hydroxy-3-bromophenyl) propane, Bis (hydroxyaryl) alkanes such as 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 1,1-bis (4-hydroxyphenyl) ethylbenzene, 1,1-bis (4- Bis such as hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane Hydroxylaryl) cyclohexanes, fluorenes such as 9,9-bis (4-hydroxyphenyl) fluorene, dihydroxyaryls such as 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxy-3,3′-dimethylphenyl ether Ethers, 4,4'-dihydroxydiphenyl sulfide, dihydroxyaryl sulfides such as 4,4'-dihydroxy-3,3'-dimethylphenyl sulfide, 4,4'-dihydroxydiphenyl sulfoxide, 4,4'-dihydroxy- And dihydroxyaryl sulfoxides such as 3,3′-dimethylphenyl sulfoxide, and compounds derived from the above compounds, which are suitable for the main component of the repeating unit consisting of bisphenol A. However, bisphenol A can be used in combination as long as it does not impair transparency, but since bisphenol A is a cheap and readily available raw material, the more bisphenol A component is used, the cheaper the optical film The repeating unit of bisphenol A is preferably 80 mol% or more, more preferably 90% or more, and particularly preferably 100 mol% (that is, alone).

  The present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, the measuring method of each physical property measured in the following examples and comparative examples is as follows.

(1) Edge part inspection The edge part was observed at a magnification of 150 times from an angle of 45 ° with respect to the cross section of the joint part with a digital microscope, the bright line width was obtained, and R of the edge part was calculated by the following formula.
(R of edge portion) = (bright line width) / √2

(2) Streaky defects The obtained stretched film was projected onto a screen with a point light source, and streaks appearing as shadows in the flow direction of the projected image were defined as streak defects, and the number of the strips was confirmed. In addition, it was judged that the number of streak defects was 5 or less.

(3) Foreign matter / defect The defect is visually detected on the obtained stretched film, the detected part is magnified up to 500 times with a digital microscope, the core such as burnt foreign matter is not seen, and between the two polarizing plates In the crossed Nicol state in which the film was placed on and observed, a product having no change in color was regarded as an acceptable product without foreign matter / defects.

Example 1
Polycarbonate (Iupilon H-4000 manufactured by Mitsubishi Gas Chemical Co., Ltd., glass transition temperature 148 ° C.) was used as the thermoplastic resin, dried at 100 ° C. for 4 hours with a drying hopper, and supplied to a φ40 mm extruder. The resin was heated and melted so as to have a resin temperature of 280 ° C. with an extruder, and the molten resin was extruded through a gear pump to a leaf disk filter and a T die of 4 inches and 5 μm cut. At this time, each member is connected from the extruder to the die by arranging piping having joints at both ends between the members. All of these joints have a male-female structure with a fitting part tolerance of 30 μm (the maximum deviation of the flow path is 30 μm or less), and the R of each edge is 20 μm. T-die is 400mm wide, cooled and solidified with a cast roll adjusted to 140 ° C and a cooling roll adjusted to 135 ° C, taken up at 9m / min with a take-up roll, and film thickness at the take-up core A film original of 70 μm was obtained.

  The obtained polycarbonate film was stretched in the machine direction by a stretching machine to obtain a final stretched polycarbonate film.

  The obtained stretched polycarbonate film was in a good state with no streak-like defects and resin-derived foreign matter / defects observed.

(Example 2)
Example except that all joints have a male-female structure with a fitting part tolerance of 30 μm (maximum deviation of the flow path is 30 μm or less), and R of the edge part contacting the flow path in the joint cross section is 40 μm 1 was carried out in the same manner.

  In the obtained stretched polycarbonate film, very thin but three streak defects were observed per 10 cm width. Resin-derived foreign matter / defects were not seen.

(Example 3)
It was carried out in the same manner as in Example 1 except that the joint R on the upstream side of the filter, specifically, the edge R of the joint between the gear pump and the upstream pipe was 150 μm (that is, the above-mentioned one joint is located). All other joints are the same as in Example 1.) In the obtained polycarbonate stretched film, one very thin streak defect was observed per 10 cm width. Moreover, 5 resin / m ^{2 of} resin-derived foreign matters / defects were observed.

(Comparative Example 1)
The same operation as in Example 1 was performed except that all the edges R of the joint portion were 150 μm. In the obtained stretched polycarbonate film, 10 very thin streak defects were observed per 10 cm width. Further, 10 resin / m ^{2 of} resin-derived foreign matters / defects were observed.

(Comparative Example 2)
The same method as in Example 1 was performed except that the edge R of all the joints was 50 μm. Although the obtained polycarbonate stretched film was very thin, seven streak defects were observed per width of 10 cm. Resin-derived foreign matter / defects were not seen.

Claims (1)

  A method for suppressing streak-like defects in an optical film by melt film formation, wherein R of an edge portion in contact with a flow passage in a cross section of a joint portion on a resin flow passage extending from a downstream end of a melting means to a die is adjusted to a predetermined value or less. The suppression method characterized by suppressing the said streak-like defect.