JPH0939066A - Manufacture of polystyrene film and unoriented film to be used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oriented polystyrene film having a uniform thickness and a syndiotactic structure, without causing cracks or breaking, by extruding a molten polystyrene so that the cross section of an unoriented sheet of the molten polystyrene has a maximum thickness at a width-directional central part of the sheet and has a minimum thickness at a portion between the central part and each of both ends of the sheet. SOLUTION: The extrusion operation of a heated and molten polystyrene to be extruded from a die of an extruder is performed so that the cross section of an unoriented sheet extruded has a maximum thickness at a width-directional central part of the sheet and has a minimum thickness at a portion between the central part and each of both ends of the sheet, respectively. For this purpose, a flow passage of the molten resin in the die of the extruder and a width of die lips are suitably adjusted. Further, the thickness distribution of the unoriented sheet is finely adjusted. The die lips have such a structure that a metal lip-adjusting fitting 52 is moved and a movable lip is also simultaneously moved by turning a lip adjusting bolt 51. By turning the adjusting bolt 51, a clearance between the die lips can be adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polystyrene resin film having a syndiotactic structure which is excellent in transparency and can be used as a support for photographic films, and the unstretched film used in this method. Regarding the seat.

[0002]

2. Description of the Related Art Polystyrene resins are used in various molded products and packaging materials because they are difficult to absorb moisture and have excellent transparency and gloss. Also, since it has good electric properties such as dielectric constant and insulating property, it is also used as an electric insulating material for capacitors, high frequency cables and the like. However, polystyrene-based resins generally do not have a satisfactory level of heat resistance, impact resistance, etc., and when the polystyrene-based resins are used for the above-mentioned applications, polystyrene-based resins are used in addition to other types of resins, rubbers, and inorganic filler materials. A blended product containing the above is used. That is, the styrene-based resin polymers that have been conventionally used have an atactic structure and are non-crystalline, so that they are sufficiently high in mechanical strength such as impact resistance as described above. I can't say. Further, since the polystyrene-based resin is non-crystalline as described above, improvement in physical properties due to stretching treatment (promotion of oriented crystallization) could not be expected.

Also, the blended resin of the above polystyrene resin and other resins cannot be said to be at a sufficiently satisfactory level in heat resistance, impact resistance and the like. On the other hand, other general thermoplastic resins such as polyethylene, polypropylene, polyethylene terephthalate, and polyamide are not satisfactory in heat resistance and chemical resistance, and few are not easily affected by water vapor. There is also a problem that raw materials are expensive and disadvantageous in manufacturing.

On the other hand, recently developed syndiotactic polystyrene (also referred to as SPS, for example, JP-A-62-104818) has crystallinity, a high melting point of 160 ° C. to 330 ° C., and heat resistance. Since it is excellent in chemical resistance and humidity stability, and the raw material is inexpensive and advantageous in manufacturing because it uses a styrene monomer, it is considered to be used for various purposes. For example, JP-A-3-13184
No. 3 discloses use of a photographic film as a support, and JP-A No. 2-67328 describes use as a packaging material.

In order to prepare a stretched film using the SPS resin having such excellent performance, the resin is first melt extruded to prepare an unstretched sheet (raw sheet), and then stretched in the longitudinal or longitudinal direction. good. For example, the stretching of the SPS resin in the longitudinal direction (longitudinal direction) is carried out in a temperature range higher than the glass transition temperature and lower than the melting point (JP-A-2-67328 and JP-A-1-182346). . However, it is not easy to stably carry out such a stretching operation, and there are various problems.

[0006]

That is, according to the study by the present inventors, syndiotactic polystyrene is
Since it has crystallinity and a high crystallization rate, crystallization may proceed rapidly depending on the conditions of melt extrusion and longitudinal stretching operations (cooling time, residence time, etc.), and when it is greatly bent during the process. Is susceptible to fine cracks. Also,
Since the syndiotactic polystyrene is rigid, the position of the sheet may be displaced and the sheet may be broken while passing through the plurality of rolls in the stretching operation. Further, cracks may be generated from a sheet pressure-bonded to a roll surface having a small diameter during continuous sheet conveyance, or the sheet may be broken,
It is also likely to occur when a metal fitting (sheet carrier) that holds the leading edge of the sheet is used when the sheet is passed. Further, the sheet misalignment is generally corrected by detecting the edge position of the sheet with an optical sensor or the like and automatically adjusting the angle or position of the transport roll. Is brittle, and therefore, a slight strain easily occurs at the edge portion due to a slight strain during the above-mentioned position adjustment and often breaks. On the other hand, in order to prevent the occurrence of cracks and breakage, when the heating temperature during stretching is increased, the sheet easily sticks to the roll,
The adhered sheet is torn intermittently, resulting in uneven thickness of the sheet, which prevents uniform stretching. In addition, when the sticking is remarkable, the sheet may be forced to stop around the roll, and the conditions for stable film formation cannot be said to be sufficiently studied.

At the same time as the above problem, it is important to obtain a stretched sheet having a uniform thickness. According to the study of the present inventor, it is possible to adjust the thickness of an unstretched sheet (raw sheet) during melt extrusion. It turned out to be important. In order to obtain a stretched sheet having a uniform thickness, it is considered that the die lip is adjusted to make the thickness of the unstretched sheet constant in the width direction. Further, in the stretching of polyethylene terephthalate, it is also disclosed that this polymer has the maximum thickness in the central portion of the film, is shaped so as to be tapered at both end portions, and is stretched. (Japanese Patent Publication No. 34-78).
However, it is not possible to obtain a stretched sheet having a uniform thickness, even if the thickness is made constant or the above method is applied to syndiotactic polystyrene.

An object of the present invention is to provide a method for producing a polystyrene film, which allows a stretched film of a polystyrene resin having a syndiotactic structure with a uniform thickness to be stably and continuously produced without causing cracks or breaks. To provide. Further, the object of the present invention is advantageous in a method for producing a polystyrene film, which is capable of producing a stretched film of a polystyrene resin having a uniform thickness of syndiotactic structure in a stable and continuous manner without causing cracks or breaks. The present invention is to provide an unstretched polystyrene sheet used for.

[0009]

According to the present invention, polystyrene having a syndiotactic structure is heated and melted in an extruder, and the hot-melted polystyrene is extruded from the extruder to prepare an unstretched sheet, and the unstretched sheet is then stretched. In a method for producing a polystyrene film by stretching a sheet in a longitudinal direction under heating, an extrusion operation from an extruder of the heat-melted polystyrene, a cross section of the extruded unstretched sheet is the center in the width direction of the sheet. The method for producing a polystyrene film is characterized in that it is formed to have a maximum thickness in a portion and a minimum thickness between the central portion and both end portions.

The preferred embodiment of the method for producing a polystyrene film of the present invention is as follows. 1) Passing the unstretched sheet through a roll adjusted to stretch the unstretched sheet in the longitudinal direction in a temperature range from 15 ° C. lower than the glass transition temperature of the polystyrene to 15 ° C. higher than the glass transition temperature. After making it do. 2) The cross section of the unstretched sheet immediately after being extruded has the following conditions (1) and (2): 0.7a ≦ b ≦ 0.95a (1) 0.05c ≦ d ≦ 0. 3c (2) [where a is a numerical value of the maximum thickness (unit is mm) of the central portion in the width direction of the sheet, and b is the central portion and both end portions in the width direction of the sheet. Represents the average value of each minimum thickness (unit represents mm) between, c represents the sheet width (unit represents mm), and d represents the edge of the sheet width from each end. It represents the average value of the distance (unit represents mm) to the position showing the minimum thickness. ] The shape is satisfied. 3) The polystyrene film comprises polystyrene having a syndiotactic structure and inorganic fine particles contained in the polystyrene in a proportion of 0.001 to 0.1% by weight based on the polystyrene. 4) The inorganic fine particles of 3) above are silica. 5) The primary particles of the inorganic fine particles of 3) above are 5 to 45 m ²
/ G specific surface area, 0.001-0.1 ml / g pore volume and 0.05-5.0 μm average particle size. 6) The inorganic fine particles of 3) above are pulverized products of quartz glass or natural quartz. 7) The thickness of the polystyrene film is 25 to 300
μm (preferably 50 to 200 μm). 8) The polystyrene film is for a support for a photosensitive material such as a photographic film.

Further, the present invention is a sheet made of polystyrene having a syndiotactic structure used in the above-mentioned manufacturing method, wherein the cross section has a maximum thickness in the central portion in the width direction of the sheet, and There is also an unstretched sheet having a shape having a minimum thickness between the central portion and both end portions.

The method for producing a polystyrene film of the present invention is basically such that an unstretched sheet obtained by extruding polystyrene having a syndiotactic structure by heating and then extruding it is stretched in the longitudinal direction (longitudinal direction) under heating. Or a step of further stretching in the transverse direction. The manufacturing method of the present invention will be described in detail step by step. In (1), an unstretched sheet (raw fabric) is prepared, and in (2), a uniaxially or biaxially stretched film is prepared. (1) A polystyrene pellet having a syndiotactic structure is heated and dried at 150 to 200 ° C. to crystallize the polystyrene. The obtained polystyrene was charged into a single-screw or twin-screw extruder having a die at the tip, and 280 to 3
It is heated and melted at 20 ° C., and the heated polystyrene is extruded into a sheet form from a die of an extruder. When the inorganic fine particles and the like are contained in polystyrene, the dried pellets (master pellets) and the mother pellets containing the inorganic fine particles and the like are put into a single-screw or twin-screw extruder having a die at the tip, and the temperature is adjusted to 280 to 320 ° C. The polystyrene which is melted by heating and heated is extruded into a sheet form from a die of an extruder.
The molten polystyrene extruded into the above shape is cooled on a cooling drum (casting drum) to form an unstretched sheet.

In the present invention, the extruding operation of the heat-melted polystyrene from the die of the extruder is performed such that the cross section of the extruded unstretched sheet has the maximum thickness at the central portion in the width direction of the sheet and the central portion. And both end portions are formed so as to have a minimum thickness. As a method for making the cross-sectional shape of such an unstretched sheet as described above, it can be easily carried out by appropriately adjusting the width of the flow path of the molten resin and the die lip inside the die of the extruder,
Furthermore, it is possible to continuously measure the thickness of the stretched sheet and automatically perform fine adjustment of the thickness distribution of the unstretched sheet based on the value. An example of the cross-sectional shape (thickness distribution) of the unstretched sheet of the present invention is shown in FIGS. 1 (A) and 1 (B). In FIGS. 1 (A) and 1 (B), a is the maximum thickness at the center of the sheet in the width direction,
b1 and b2 are respective minimum thicknesses between the central portion and both end portions in the width direction of the sheet (average b), c represents the sheet width, and d1 and d2 are end portions of the sheet width. To the position indicating the minimum thickness of each (average dmm). It is preferable that b1 and b2 are equal. The maximum thicknesses e1 and e2 near the edges are preferably equal. Further, it is preferable that a, e1 and e2 are all the same. The cross-sectional shape of the unstretched sheet is often the shape of FIG. 1B because the surface of the sheet on the casting drum side is pressed against the drum.

In the present invention, in particular, the above a, b, c and d
Is the condition of the following (1) and (2): 0.7a ≦ b ≦ 0.95a (1) 0.05c ≦ d ≦ 0.3c (2) [where a is It represents the numerical value of the maximum thickness (unit represents mm) of the center of the sheet in the width direction, and b represents the minimum thickness (unit: mm) between the center and both ends of the sheet in the width direction. Represents the average numerical value of the sheet width, c represents the numerical value of the sheet width (unit represents mm), and d represents the distance from the end of the sheet width to the position indicating the minimum thickness (unit: mm is represented). ] It is preferable to satisfy.

As the extruder used for preparing the unstretched sheet, it is preferable to use a twin-screw extruder so that the master pellets and the mother pellets can be efficiently mixed. An extruder having no vent may be used, but it is preferable to use an extruder having a vent in order to prevent bubbles from being generated in the film due to the generated gas. Further, it is preferable to use a gear pump (a metering pump) in order to stably discharge from the extruder and to send out the molten resin. Before the molten resin is discharged from the die into a sheet shape, it may be filtered by a filter. As a material for the filter, a metal furnace material such as a sintered fiber of stainless steel or a sintered wire net is preferable. The filtration accuracy of the filter is generally in the range of 5 to 20 μm.

The thickness of the unstretched sheet prepared above is
Generally, it is in the range of 0.8-2 mm. The temperature of the surface of the cooling drum is preferably 55 to 85 ° C. If the temperature is less than 55 ° C., the central portion of the sheet is rapidly cooled, so that the warp appears strongly at the end portion, and thus a problem easily occurs in the subsequent stretching step. 85 ° C
If it exceeds, the sheet will stick to the cooling drum, making it difficult to form an unstretched film. The cooling rate of the sheet is from 60 to 200 ° C./minute until the glass transition temperature after the molten resin discharged from the die comes into contact with the cooling drum, and the sheet is cooled at an average temperature of 30 ° C. Up to 40 to 100 ° C./min are preferably averaged. If the cooling rate after reaching the glass transition temperature is low, the haze of the finally obtained stretched film will be high.

Improvement of the smoothness of the surface of the unstretched sheet formed from the above-mentioned discharged molten resin, improvement of the smoothness of the surface,
Suppression of increase in sheet thickness at the edge, uniform sheet thickness,
In order to prevent crystallization of the sheet and the like, it is common to perform heating of the cooling drum, electrostatic application, edge pinning, cooling air blowing, air suction and water application, or combined use of calender rolls. . These can be used alone or in combination. For the same purpose, it is preferable to reduce the backlash of the gears of the variable speed reducer such as the cooling drum, the eccentricity of the pulley, the deviation of the roller interval of the driving tune, and the like. It is also important to take measures against vibration such as the die head for extrusion

(2) The unstretched sheet (raw sheet) obtained above is stretched in the longitudinal direction (longitudinal direction), and in the case of a biaxially stretched film, further stretched in the transverse direction (width direction). To do. The lengthwise stretching process of the present invention will be described with reference to FIG. FIG. 2 shows a uniaxial stretching device for stretching the unstretched sheet in the longitudinal direction. The unstretched sheet is inserted into the pair of first nip rolls 1 so that the sheet tension generated in the previous step can be cut off and the subsequent sheet handling can be performed stably. Next, the first preheating roll 2, the second preheating roll 3, and the third preheating roll 4 are sequentially conveyed and preheated. Preheating is the first drawing zone heated by the infrared heater,
It is performed so that it can be easily heated to a predetermined temperature. After passing through the second nip roll 5, the preheated sheet is heated from the upper and lower sides by the first infrared heater 10 and the second infrared heater 11 and simultaneously stretched in the longitudinal direction (first stretching zone 13). The stretched sheet is the first
After passing through the transport roll 6, it is heated from the upper side by the third infrared heater 12 and simultaneously further stretched in the longitudinal direction (second stretching zone 14). The stretching is performed by giving a difference in the rotational speed of the second nip roll 5 and the third nip roll 7. At that time, the first transport roll 6
Thus, the stretching process is divided. In addition, the first transport roll 6
Also functions to suppress the vibration and tension of the sheet at the time of stretching so that the stretching can be performed stably. The sheet stretched twice in this way passes through the third nip roll 7 and the fourth nip roll 8 and finally passes through the second transport roll 9, whereby a uniaxially stretched sheet is produced. The fourth nip roll 8 relaxes the load on the third nip roll and also functions to cool the sheet.

In the present invention, the roll (the first nip roll 1 in FIG.
The temperatures of the first to third preheating rolls 2 to 4 and the second nip roll 5) are adjusted within a range of 15 ° C. lower than the glass transition temperature of polystyrene, which is a material of the unstretched sheet, to 15 ° C. higher than the glass transition temperature. Preferably. At least, the temperature of the immediately preceding roll is preferably adjusted within the above temperature range. When the temperature of the roll is less than 15 ° C. lower than the glass transition temperature, the sheet is easily broken on the roll, and when the temperature is higher than 15 ° C. higher than the glass transition temperature, the roll is apt to stick and the thickness is increased. It is easy to cause unevenness. Infrared heater 1 installed in the drawing zone
0 to 12 are those whose distance from the seat and output can be adjusted, and those having a maximum temperature of about 600 ° C. are suitable. The adjustment is generally performed so that the temperature of the sheet in the stretching zone is not less than the glass transition temperature of the resin and not more than the cooling crystallization temperature. Further, as a method of holding the roll that passes through before stretching the unstretched sheet in the above specific temperature range, for example, the temperature of hot water, heat medium (oil), steam, etc. passed through the roll, pressure, etc. Can be mentioned.

The longitudinally stretched sheet is generally subjected to transverse stretching and heat setting by a transverse stretching device (tenter). Of course, a vertically stretched sheet may be used as the uniaxially stretched film.

The sheet stretched in the longitudinal direction (extrusion direction or longitudinal direction) under heating is preheated by holding both ends by clips fed by an endless belt for clip transport, and then transversely stretched under heating. .
That is, the distance between the clips at both ends of the sheet is gradually increased and the transverse stretching is performed. The transverse stretching is performed by heating the polystyrene used for the sheet to a temperature between the glass transition temperature (Tg ° C.) and the melting point. The laterally stretched sheet is
Subsequently, heat setting is performed in an atmosphere of a higher temperature. The distance between the clips on both ends that are widened due to the lateral stretching is maintained. The heat setting is generally carried out by heating to a temperature between the glass transition temperature (Tg ° C.) and the melting point of polystyrene. The heat set sheet is subsequently heat relaxed.
The distance between the clips at both ends of the seat is gradually reduced to provide relaxation. The thermal relaxation amount is generally 1 to 10%. Then, it is cooled by blowing air at room temperature or below, and a biaxially stretched polystyrene film is obtained.

In the longitudinal and transverse stretching of the present invention, if the stretching ratio is too low, the sheet cannot be oriented sufficiently, the sheet becomes brittle, the haze becomes high, and further uniform stretching becomes difficult. On the other hand, if the magnification is too high, the sheet is likely to tear, which is not preferable because the sheet may break in the tenter. In general, the stretching ratio is preferably 2 to 6 times in both length and width, and particularly preferably 3 to 5 times. The transverse stretching speed is preferably about 5 to 250% / sec from the viewpoint of making the amount of heat applied to the sheet uniform, controlling the orientation, and easiness of handling. The biaxially stretched sheet after the transverse stretching is completed,
As described above, it is conveyed to the heat setting treatment zone while being held by the clip. Here, the heat resistance, the dimensional stability, and the heat resistance of the stretched film obtained by subjecting the stretched film to a temperature of not less than the glass transition temperature and not more than the melting point and within the range satisfying the above conditions while applying tension (heat fixing treatment) while applying tension. Properties such as chemical resistance and gas permeability can be improved. Further, the stretched sheet may be cut at both ends (so-called ears) through a heat relaxation zone and a cooling zone and wound, or may be continuously conveyed to a coating step.

Polystyrene having a syndiotactic structure used in the present invention (hereinafter sometimes referred to as SPS)
Is a polystyrene resin whose stereoregularity is a syndiotactic structure, in which phenyl groups or substituted phenyl groups, which are side chains with respect to the main chain formed from carbon-carbon bonds, are mainly located in opposite directions. It has a three-dimensional structure. The stereoregularity (tacticity) can be quantified by a nuclear magnetic resonance method (NMR method).
The stereoregularity measured by this nuclear magnetic resonance method can be indicated by the existence ratio of a plurality of continuous constitutional units, for example, a diad in the case of 2 units, a trad in the case of 3 units, and a pen dadd in the case of 5 units. However, the syndiotactic polystyrene-based resin (SPS-based resin) referred to in the present invention means that the stereoregularity (tacticity) is 75% or more in racemic dieat or 30% or more in racemic pentad.
It has. Further, those having a syndiotactic structure of 85% or more in diat or 50% or more in pentad are preferable.

Examples of polystyrene-based resins that can be used in the present invention include polystyrene and various substituted polystyrenes such as polyalkylstyrene and polyhalogenated styrene. Examples of substituted polystyrenes are poly (o-, m- or p-methylstyrene), poly (2,4-, 2,5-3,4- or 5-
Poly (alkylstyrene) such as dimethylstyrene) and poly (pt-butylstyrene); poly (o-, m-
Or p-chlorostyrene), poly (o-, m- or p-bromostyrene), poly (o-, m- or p)
-Fluorostyrene) and poly (o-methyl-p-fluorostyrene) such as poly (halogenated styrene); poly (o-, m- or p-chloromethylstyrene) such as poly (halogen-substituted alkylstyrene); poly (O-,
m- or p-methoxystyrene) and poly (o-, m
-Or p-ethoxystyrene) or other poly (alkoxystyrene); poly (o-, m- or p-carboxymethylstyrene) or other poly (carboxyalkylstyrene); poly (p-vinylbenzylpropyl ether) or other poly (Alkyl ether styrene); poly (p-trimethylsilyl styrene) and other poly (alkyl silyl styrene); and poly (vinyl benzene dimethoxy phosphate). Further, as an example of the polystyrene-based resin, a copolymer of the above-mentioned substituted styrene and unsubstituted styrene (for example, a copolymer of styrene and p-methylstyrene) is of course preferable.

In the present invention, polystyrene is particularly preferable among the examples of the polystyrene resin. Further, the polystyrene resin having a syndiotactic structure used in the present invention does not necessarily have to be a single compound, and if the syndiotacticity is within the above range, an isotactic structure or a polystyrene resin having an atactic structure is used. It may be a mixture thereof with or incorporated into the copolymer chain.

The polystyrene resin having the syndiotactic structure can be produced by a known method.
For example, the method is described in Japanese Patent Laid-Open No. 3-74437. With respect to the molecular weight of the polystyrene resin having the syndiotactic structure, its weight average molecular weight is preferably in the range of 10,000 to 3,000,000, and particularly preferably in the range of 50,000 to 15,000,000.

The polystyrene film obtained by the present invention preferably contains inorganic fine particles.
Examples of such inorganic fine particles include silica, talc, calcium carbonate, calcium sulfate, mica, kaolin, kaolinite and the like. Of these, silica is preferred.

Preferable examples of the above silica include crushed quartz glass and crushed natural quartz. In the present invention, the silica may not be surface-treated, but surface-treated silica is preferable in order to improve the affinity with the resin and suppress the generation of voids during stretching. The surface treatment can be performed using a known surface treatment agent such as a silane coupling agent. Examples of silane coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxysilane), N- (2-aminoethyl)-.
3-aminopropylmethyldimethoxysilane, N- (2
-Aminoethyl) -3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3,4-
Epoxycyclohexyl) ethyltrimethoxysilane,
Mention may be made of 3-chloropropylmethyldimethoxysilane, 3-chloropropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane and 3-mercaptopropyltrimethoxysilane.

The average particle size of the primary particles of the above-mentioned inorganic fine particles (preferably silica) is preferably in the range of 0.1 to 5.0 μm, particularly preferably in the range of 0.2 to 2.0 μm. The specific surface area is preferably 5 to 45 m ² / g. The pore volume is preferably in the range of 0.001 to 0.1 ml / g.
With silica having a specific surface area of more than 45 m ² / g, the silica particles are likely to aggregate with each other to form secondary particles or coarse particles of higher order, which reduces the slipperiness of the resulting film. On the other hand, silica having a specific surface area of less than 5 m ² / g has a low affinity with the polymer, so that voids generated when biaxially stretched become large and the transparency of the film decreases. In the case of silica having a pore volume of more than 0.1 ml / g, silica particles tend to aggregate with each other to form secondary particles or higher coarse particles, so that the slipperiness of the obtained film is deteriorated. In addition, the quality may not be stable. On the other hand, silica having a pore volume of less than 0.001 ml / g has a low affinity with the polymer, so that the voids generated when biaxially stretched become large and the transparency of the film decreases.

Furthermore, the average particle size of the primary particles of the above-mentioned inorganic fine particles (preferably silica) is 0.05 to 5.0 μm.
m is generally, 0.1 to 3.0 μm is preferable, and 0.1 to 2.0 μm is more preferable. Average particle size is 0.05
Silica of less than μm has a small effect of imparting slipperiness,
The film containing such silica does not have sufficient lubricity, or the transparency of the film decreases when silica is contained to the extent that sufficient lubricity is obtained. Further, silica having an average particle size of more than 5.0 μm has a great effect from the viewpoint of imparting slipperiness, but when a particle having such a large particle size is used, a large void is likely to occur around the particle in a biaxially stretched film. As a result, a film having high haze and low transparency is obtained. Further, when such silica having a large particle size is aggregated and present in the film, it becomes a serious defect.

In order to balance the slipperiness and transparency of the film on a high level, the amount of silica having the above-described shape, specific surface area, pore volume, and average particle diameter is adjusted to the thickness of the film to be produced. It is preferable to optimize accordingly. For example, the optimum addition amount of the silica of the present invention to a film having a thickness of 25 to 300 μm is 0.001 to 0.1% by weight, and 0.005 to 0.1% by weight is preferable. If the amount added is less than 0.001% by weight, generally required slipperiness cannot be secured, and if the amount added exceeds 0.1% by weight, transparency is generally lowered. The film thickness is 50-200.
μm is preferred.

Further, the SPS used in the present invention may contain other resins in order to improve electrostatic adhesion, slipperiness, stretchability, processing suitability and the like, and to obtain roughening and weight reduction. Or rubber (in an amount of 10% by weight or less of SPS), a nucleating agent, a fluorescent agent,
An antioxidant, a plasticizer, a colorant, an antistatic agent or the like may be added at the time of absorbing ultraviolet rays.

[0033]

【Example】

[Example 1] As syndiotactic polystyrene, a copolymer of styrene having a syndiotactic structure and p-methylstyrene (copolymerization ratio: styrene / p-methylstyrene = 89/11 (molar ratio); Syndiotactic City (Diat): 85%; Melt Flow Index: 10; Glass Transition Temperature: 97 ° C (D
SC-50 was used in nitrogen (by temperature increase of 10 ° C./min). The resin pellets were put into a full flight type single screw extruder (diameter = 40 mm, L / D = 26) and the width was 23 cm.
A coat hanger type die was attached and melt extrusion was performed at a die lip temperature of about 310 ° C., and the mixture was cooled and solidified on a casting drum to prepare an unstretched sheet having a thickness of about 1.2 mm. The die lip of the die has the cross section shown in FIG. The die lip has a structure in which when the lip adjusting bolt 51 is turned, the lip adjusting fitting 52 moves, and at the same time, the movable lip 53 also moves. 54 is a spring portion for enabling the above movement. This adjustment bolt 5
By turning 1, the lip clearance is adjusted. A plurality of such lips are arranged in the width direction of the lip to form a die. As shown in FIG. 6, the die 61 includes a lip adjusting bolt 62, a movable lip 63, and a lip opening 64.

A cross section of the unstretched sheet prepared above is shown in FIG.
The pattern 1 is shown. One surface shape of the sheet is shown, and the other side is almost flat. The unstretched sheet,
The unstretched sheet shown in FIG. 2 was stretched in the longitudinal direction using a uniaxial stretching device for stretching the unstretched sheet in the longitudinal direction. The temperature of the first nip roll 1, the first preheating roll 2, the second preheating roll 2, the third preheating roll 3, and the second nip roll 5 was adjusted to 105 ° C., and the unstretched sheet was
These rolls were passed through the sheet carrier at a speed of 1.5 m / min. At this time, by reducing the speed of all the rolls including the other rolls (the first transport roll 6, the third, the fourth nip rolls 7, 8 and the second transport roll 9) to 1.5 m / min, The speed difference between the unstretched sheet and the roll was reduced to suppress the occurrence of scratches and distortion on the sheet surface.

Immediately after the sheet reached the second transport roll 9, the first to fourth nip rolls 1, 5, 7, 8 were started and pinched (nipped) while the sheet was removed from the sheet carrier and wound.

Next, the first to third parts that have been preheated and are on standby
After moving the infrared heaters 10 to 12 near the seat,
The rotation speeds of the first transport roll 6, the third to fourth nip rolls 7, 8 and the second transport roll 9 were increased and adjusted to 3.75 m / min after one minute. Thereby, the unstretched sheet was stretched 2.5 times in the longitudinal direction to obtain a uniaxially stretched film.

In the above steps, the unstretched sheet could be stably conveyed without cracking or breaking. The cross-sectional shape of the obtained uniaxially stretched film is shown in FIG.
The pattern 3 is shown. One surface shape of the sheet is shown, and the other side is substantially flat as shown in FIG. 1 (B). From this pattern, it can be seen that the obtained uniaxially stretched film has a uniform film thickness.

[Embodiment 2] In Embodiment 1, the rotation speed of the rolls of the first transport roll 6, the third to fourth nip rolls 7 and 8, and the second transport roll 9 was increased and reached one minute later. From 3.75 m / min to 6.0 m / min (the unstretched sheet was stretched 4.0 times in the longitudinal direction)
A uniaxially stretched film was produced in the same manner as in Example 1 except that the above was changed.

In the above steps, the unstretched sheet could be stably conveyed without cracking or breaking. The cross-sectional shape of the obtained uniaxially stretched film is shown in FIG.
The pattern 4 is shown. One surface shape of the sheet is shown, and the other side is almost flat. From this pattern, it can be seen that the obtained uniaxially stretched film has a uniform film thickness.

[Comparative Example 1] A uniaxially stretched film was prepared in the same manner as in Example 1 except that the unstretched sheet in Example 1 was changed from one having the cross section of pattern 1 in FIG. 3 to one having pattern 2. Created.

In the above steps, the unstretched sheet could be stably conveyed without cracks or breaks. The cross-sectional shape of the obtained uniaxially stretched film is shown in FIG.
The pattern 5 is shown. One surface shape of the sheet is shown, and the other side is almost flat. From this pattern, it can be seen that the obtained uniaxially stretched film does not have a uniform film thickness.

[Comparative Example 2] In Comparative Example 1, the rotational speeds of the first transport roll 6, the third to fourth nip rolls 7 and 8 and the second transport roll 9 were increased one minute and then reached. From 3.75 m / min to 6.0 m / min (which allowed the unstretched sheet to be stretched 2.5 times in the longitudinal direction)
A uniaxially stretched film was prepared in the same manner as in Comparative Example 1 except that

In the above process, the unstretched sheet could be stably conveyed without cracking or breaking. The cross-sectional shape of the obtained uniaxially stretched film is shown in FIG.
The pattern 6 is shown. One surface shape of the sheet is shown, and the other side is almost flat. From this pattern, it can be seen that the obtained uniaxially stretched film does not have a uniform film thickness.

[0045]

EFFECTS OF THE INVENTION By utilizing the production method of the present invention, a uniaxially or biaxially stretched film made of SPS resin can be obtained.
It can be continuously and stably manufactured with a uniform thickness.
Therefore, according to the present invention, the properties derived from the syndiotactic structure, heat resistance, chemical resistance, high humidity stability, excellent mechanical strength, it is possible to easily obtain a polystyrene film having a uniform thickness. it can. Further, such a film can be advantageously used as a photographic material such as a photographic film support, a packaging material such as a packaging film, a plate-making material such as a plate-making support and an electric material.

[Brief description of drawings]

FIG. 1 is a view showing a cross-sectional shape of an unstretched sheet of the present invention.

FIG. 2 is a cross-sectional view showing an outline of a longitudinal stretching device that can be used in the present invention.

FIG. 3 is a diagram showing a partial cross-sectional shape of an unstretched sheet used in Examples and Comparative Examples.

FIG. 4 is a diagram showing a partial cross-sectional shape of a uniaxially stretched film prepared in Examples and Comparative Examples.

FIG. 5 is a diagram showing a cross-sectional shape of a die lip used in an example.

FIG. 6 is a diagram showing an appearance of a die used in an example.

[Explanation of symbols]

 1 1st Nip Roll 2 1st Preheating Roll 3 2nd Preheating Roll 4 3rd Preheating Roll 5 2nd Nip Roll 6 1st Conveying Roll 7 3rd Nip Roll 8 4th Nip Roll 9 2nd Conveying Roll 10 1st Infrared Heater 11 2nd Infrared Heater 12 Third infrared heater 13 First stretching zone 14 Second stretching zone 51 Lip adjusting bolt 52 Lip adjusting metal fitting 53 Movable lip 54 Spring portion 61 Die 62 Lip adjusting bolt 63 Movable lip 64 Lip opening

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Ogura No. 200 Onakazato, Fujinomiya City, Shizuoka Prefecture Fuji Photo Film Co., Ltd.

Claims (4)

[Claims] 1. A polystyrene having a syndiotactic structure is heated and melted in an extruder, and then the hot-melted polystyrene is extruded from the extruder to prepare an unstretched sheet, and the unstretched sheet is heated in a longitudinal direction. In the method of producing a polystyrene film by stretching into a sheet, an extruding operation of the heat-melted polystyrene from an extruder is performed such that the cross section of the extruded unstretched sheet has a maximum thickness in the central portion in the width direction of the sheet. And a method for producing a polystyrene film, characterized in that it is formed so as to have a minimum thickness between the central portion and both end portions. 2. The stretching of the unstretched sheet in the longitudinal direction,
The method for producing a polystyrene film according to claim 1, which is carried out after passing the unstretched sheet through a roll adjusted to a temperature of 15 ° C. lower than the glass transition temperature of the polystyrene to 15 ° C. higher than the glass transition temperature. . 3. The cross section of the unstretched sheet immediately after being extruded has the following conditions (1) and (2): 0.7a ≦ b ≦ 0.95a (1) 0.05c ≦ d. ≦ 0.3c (2) [where a is the numerical value of the maximum thickness (unit is mm) of the central portion of the sheet in the width direction, and b is the central portion of the sheet in the width direction. Represents the average value of the respective minimum thicknesses (units represent mm) between the ends, c represents the sheet width (units represent mm), and d represents the edge of the sheet width. Represents the average value of the distance (unit is mm) from the position to the position indicating the minimum thickness. ] The manufacturing method of the polystyrene film of Claim 1 which has a shape which satisfy | fills. 4. A sheet made of polystyrene having a syndiotactic structure, the cross-section of which has a maximum thickness in the central portion in the width direction of the sheet, and between the central portion and both end portions, respectively. An unstretched sheet having a shape having a minimum thickness.