Polystyrenic stretched film and process for producing the polystyrenic stretched film

There are disclosed a polystyrenic stretched film which comprises a styrenic resin composition containing 70 to 100% by weight of a styrenic polymer having a high degree of the syndiotactic configuration, has a crystallinity of 35% or more, and contains 200 ppm or less of residual monomer components and 1000 or less of particles of foreign substances having a size of 9 .mu.m or larger in 1 cm.sup.3, and a process for producing the polystyrenic stretched film which comprises extruding the styrenic resin composition in a specific amount in combination with melt filtration of the composition, cooling the extruded composition, biaxially stretching the cooled composition, and heat treating the stretched composition under the condition that the degree of heat treatment is 10.sup.-1 or more and less than 5.times.10.sup.2. According to the present invention, a stretched film having excellent printing property and other properties, such as a high peeling strength after vapor deposition, and a process for efficiently producing the polystyrenic stretched film having the excellent properties are provided.

TECHNICAL FIELD 
The present invention relates to a polystyrenic stretched film and a 
process for producing said film. More particularly, the present invention 
relates to a polystyrenic stretched film which is advantageously used as a 
base material for condenser films, FPC electric insulation films, 
photographic films, process films for printing, films for over-head 
projectors, packaging films, and the like, and a process for producing 
said film. 
BACKGROUND ART 
Styrenic polymers having the syndiotactic configuration have excellent 
mechanical properties, heat resistance, appearance, solvent resistance, 
and electric properties, and are expected to be used in various 
applications. Therefore, various technologies for extrusion of films, 
sheets, and fibers, various molded articles, and various applications have 
been proposed. 
In the field of films, a material is frequently used for practical 
applications in the form of laminates, as a film treated with vapor 
deposition, or as a film having printing thereon. Therefore, it is 
necessary that a material has excellent properties for printing or vapor 
deposition. Stretched films having various physical properties which use 
the styrenic polymers having the syndiotactic configuration described 
above as a material, processes for producing stretched films, and various 
applications using the stretched films have been disclosed in Japanese 
Patent Application Laid-Open No. 182348/1989, Japanese Patent Application 
Laid-Open No. 182346/1989, Japanese Patent Application Laid-Open No. 
67328/1990, Japanese Patent Application Laid-Open No. 143851/1990, 
Japanese Patent Application Laid-Open No. 74437/1991, Japanese Patent 
Application Laid-Open No. 86707/1991, Japanese Patent Application 
Laid-Open No. 124750/1991, Japanese Patent Application Laid-Open No. 
131843/1991, Japanese Patent Application Laid-Open No. 261485/1992, 
Japanese Patent Application Laid-Open No. 200858/1993, Japanese Patent 
Application Laid-Open No. 57013/1994, Japanese Patent Application 
Laid-Open No. 57014/1994, Japanese Patent Application Laid-Open No. 
57015/1994, Japanese Patent Application Laid-Open No. 57016/1994, Japanese 
Patent Application Laid-Open No. 57017/1994, Japanese Patent Application 
Laid-Open No. 64036/1994, Japanese Patent Application Laid-Open No. 
64037/1994, Japanese Patent Application Laid-Open No. 65399/1994, Japanese 
Patent Application Laid-Open No. 65400/1994, Japanese Patent Application 
Laid-Open No. 65401/1994, Japanese Patent Application Laid-Open No. 
65402/1994, Japanese Patent Application Laid-Open No. 80793/1994, Japanese 
Patent Application Laid-Open No. 91748/1994, Japanese Patent Application 
Laid-Open No. 91749/1994, Japanese Patent Application Laid-Open No. 
91750/1994, Japanese Patent Application Laid-Open No. 99485/1994, Japanese 
Patent Application Laid-Open No. 100711/1994, Japanese Patent Application 
Laid-Open No. 106616/1994, Japanese Patent Application Laid-Open No. 
107812/1994, Japanese Patent Application Laid-Open No. 107813/1994, 
Japanese Patent Application Laid-Open No. 114924/1994, and Japanese Patent 
Application Laid-Open No. 114925/1994. 
However, films of conventional styrenic polymers having the syndiotactic 
configuration are not satisfactory with respect to the printing property 
including the setting property in the printing operation (adhesion of ink 
and the like) and other properties, such as peeling strength after vapor 
deposition. This causes problems when the films are used in various 
applications. 
DISCLOSURE OF THE INVENTION 
As the result of intensive studies made by the present inventors to solve 
the above problems, it has been found that a film having excellent 
properties, such as an excellent printing property and high peeling 
strength after vapor deposition, can be obtained when the content of 
residual monomers which are volatile components in the film and the 
content of foreign substances are decreased to or below specific values, 
and crystallinity is increased to or above a specific value. It has also 
been found by the present inventors that, even when the retention time is 
increased and the content of residual monomers are increased by using a 
melt filter to decrease the content of foreign substances, it is possible 
to decrease the content of residual monomers by a specific heat treatment. 
The present invention was completed on the basis of the discoveries 
described above with the object of providing a film having excellent 
printing property and other properties, such as a high peeling strength 
after vapor deposition. 
Accordingly, the present invention provides a polystyrenic stretched film 
which comprises a styrenic resin composition containing 70 to 100% by 
weight of a styrenic polymer having a high degree of the syndiotactic 
configuration, has a crystallinity of 35% or more, preferably 37% or more, 
and contains 200 ppm or less, preferably 150 ppm or less, of residual 
monomers, and 1000 or less particles, preferably 800 or less particles, of 
foreign substances having a size of 9 .mu.m or larger in 1 cm.sup.3. 
The present invention also provides a process for producing a polystyrenic 
stretched film which comprises extruding a styrenic resin composition 
containing 70 to 100% by weight of a styrenic polymer having a high degree 
of the syndiotactic configuration at 330.degree. C. or lower in 60 minutes 
or less in combination with melt filtration of the styrenic resin 
composition, cooling the extruded styrenic resin composition, biaxially 
stretching the cooled styrenic resin composition, and heat treating the 
biaxially stretched styrenic resin composition under the condition that 
the degree of heat treatment A expressed by the following equation (I) is 
1.times.10.sup.-1 or more and less than 5.times.10.sup.2, preferably 
5.times.10.sup.-1 or more and 3.times.10.sup.2 or less: 
EQU A=.SIGMA.T.times.t/d.sup.2 ! (I) 
wherein T represents temperature of the heat treatment (K), t represents 
time of the heat treatment (second), and d represents thickness of the 
film (pm). 
In the present invention, it is particularly preferred that the styrenic 
polymer contains 80 to 100% by mol of the repeating unit of styrene and 0 
to 20% by mol of the repeating unit of p-methylstyrene.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION 
The material used for the polystyrenic stretched film is described in the 
following. 
In the present invention, the styrenic polymer which has a high degree of 
the syndiotactic configuration means that its stereochemical structure is 
of high degree of the syndiotactic configuration, i.e., the 
stereo-structures in which phenyl groups or substituted phenyl groups as 
side chains are located alternately at opposite directions relative to the 
main chain consisting of carbon-carbon bonds. The tacticity thereof is 
quantitatively determined by the nuclear magnetic resonance method 
(.sup.13 C-NMR method) using a carbon isotope. The tacticity as determined 
by the .sup.13 C-NMR method can be indicated in terms of proportions of 
structural units continuously connected to each other, i.e., a diad in 
which two structural units are connected to each other, a triad in which 
three structural units are connected to each other, and a pentad in which 
five structural units are connected to each other. The styrenic polymer 
having a high degree of the syndiotactic configuration used in the present 
invention means polystyrene, a poly(alkylstyrene), a poly(halogenated 
styrene), a poly(alkoxystyrene), a poly(vinylbenzoic acid ester), a 
hydrogenation product of a polymer described above, a mixture of polymers 
described above, or a copolymer containing the units of the above polymers 
as main components, having such a syndiotacticity that the proportion of 
racemic diad is at least 75%, preferably at least 85%, or the proportion 
of racemic pentad is at least 30%, preferably at least 50%. Examples of 
the poly(alkylstyrene) include poly(methylstyrene), poly(ethylstyrene), 
poly(propylstyrene), poly(butylstyrene), poly(phenylstyrene), 
poly(vinylnaphthalene), poly(vinylstyrene), poly(acenaphthylene), and the 
like. Examples of the poly(halogenated styrene) include 
poly(chlorostyrene), poly(bromostyrene), poly(fluorostyrene), and the 
like. Examples of the poly(alkoxystyrene) include poly(methoxystyrene), 
poly(ethoxystyrene), and the like. Particularly preferred styrenic 
polymers among the polymers described above are copolymers of styrene and 
p-methylstyrene, polystyrene, poly(p-methylstyrene), 
poly(m-methylstyrene), poly(p-tertiary-butylstyrene), 
poly(p-chlorostyrene), poly(m-chlorostyrene), and poly(p-fluorostyrene) 
(refer to Japanese Patent Application Laid-Open No. 187708/1987). 
Examples of the comonomer used for the copolymer containing the units of 
the styrenic polymers as main components thereof include monomers for the 
styrenic polymers described above; olefin monomers, such as ethylene, 
propylene, butene, hexene, octene, and the like; diene monomers, such as 
butadiene, isoprene, and the like; cyclic diene monomers; and polar vinyl 
monomers, such as methyl methacrylate, maleic anhydride, acrylonitrile, 
and the like. 
Styrenic polymers containing 80 to 100% by mol of the repeating unit of 
styrene and 0 to 20% by mol of the repeating unit of p-methylstyrene are 
particularly preferably used. 
The molecular weight of the styrenic polymer is not particularly limited. 
The styrenic polymer having a weight-average molecular weight of 10,000 or 
more and 3,000,000 or less, more preferably 50,000 or more and 1,500,000 
or less, is preferably used. When the weight-average molecular weight is 
less than 10,000, sufficient stretching cannot be achieved sometimes. The 
molecular weight distribution of the styrenic polymer is not particularly 
limited, and polymers having various molecular weight distribution can be 
used. It is preferred that the ratio of the weight-average molecular 
weight (Mw) to the number-average molecular weight (Mn) is 1.5 or more and 
8 or less. The styrenic polymer having the syndiotactic configuration has 
the heat resistance remarkably superior to that of styrenic polymers 
having the conventional atactic configuration. 
The styrenic polymer having a high degree of the syndiotactic configuration 
described above is contained in the polystyrenic stretched film of the 
present invention in an amount of 70 to 100% by weight, preferably 80 to 
100% by weight. 
To the styrenic polymer having a high degree of the syndiotactic 
configuration of the present invention, lubricants, other thermoplastic 
resins, antioxidants, inorganic fillers, rubbers, compatibilizing agents, 
colorants, crosslinking agents, crosslinking aids, nucleating agents, 
plasticizers, and the like, may be added to form a composition to the 
extent that the object of the present invention is not impaired thereby. 
As the lubricant, for example, inorganic particles can be used. The 
inorganic particles include oxides, hydroxides, sulfides, nitrides, 
halides, carbonates, sulfates, acetates, phosphates, phosphites, salts of 
organic acids, silicates, titanates, and borates of elements of IA, IIA, 
IVA, VIA, VIIA, VIII, IB, IIB, IIIB, and IVB Groups, hydrates of these 
compounds, complex compounds based on these compounds, and natural mineral 
particles. 
Specific examples of the inorganic particles include compounds of elements 
of IA Group, such as lithium fluoride, borax (a hydrate of sodium borate), 
and the like; compounds of elements of IIA Groups, such as magnesium 
carbonate, magnesium phosphate, magnesium oxide (magnesia), magnesium 
chloride, magnesium acetate, magnesium fluoride, magnesium titanate, 
magnesium silicate, a hydrate of magnesium silicate (talc), calcium 
carbonate, calcium phosphate, calcium phosphite, calcium sulfate (gypsum), 
calcium acetate, calcium terephthalate, calcium hydroxide, calcium 
silicate, calcium fluoride, calcium titanate, strontium titanate, barium 
carbonate, barium phosphate, barium sulfate, barium phosphite, and the 
like; compounds of elements of IVA Group, such as titanium dioxide 
(titania), titanium monooxide, titanium nitride, zirconium dioxide 
(zirconia), zirconium monooxide, and the like; compounds of elements of 
VIA Group, such as molybdenum dioxide, molybdenum trioxide, molybdenum 
sulfide, and the like; compounds of elements of VIIA Group, such as 
manganese chloride, manganese acetate, and the like; compounds of elements 
of VIII Group, such as cobalt chloride, cobalt acetate, and the like; 
compounds of elements of IB Group, such as copper (I) iodide, and the 
like; compounds of elements of IIB Group, such as zinc oxide, zinc 
acetate, and the like; compounds of elements of IIIB Group, such as 
aluminum oxide (alumina), aluminum hydroxide, aluminum fluoride, 
aluminosilicates (aluminum silicate, kaolin, and kaolinite), and the like; 
compounds of elements of IVB Group, such as silicon oxides (silica, silica 
gel), graphite, carbon, glass, and the like; and particles of natural 
minerals, such as carnallite, kernite, mica (phlogopite), pyrolusite, and 
the like. 
The average diameter of the inorganic particles is not particularly 
limited, and is preferably 0.01 to 3 .mu.m. The inorganic particles are 
contained in the molded product in an amount of 0.001 to 5% by weight, 
preferably 0.005 to 3% by weight. The inorganic particles are contained in 
the finished molded product, and the method of incorporating the inorganic 
particles into the molded product is not particularly limited. For 
example, a method in which the inorganic particles are added or formed by 
precipitation at a desired step during polymerization, or a method in 
which the inorganic particles are added at a desired step during melt 
extrusion, may be used. 
As the other thermoplastic resins which may be added to the styrenic resin 
described above in the present invention, various types of thermoplastic 
resin may be used. Examples of the thermoplastic resin include styrenic 
resins having the atactic configuration, styrenic resins having the 
isotactic configuration, polyphenylene ethers, and the like. These resins 
described above are easily compatible with the styrenic polymer having the 
syndiotactic configuration described above, and is effective for 
controlling crystallization in the preparation of a preliminary molded 
product for stretching. Therefore, the stretching property can be 
improved, and the conditions of the stretching can be easily controlled. 
Thus, a film having excellent mechanical properties can be obtained. When 
a styrenic resin having the atactic configuration and/or the isotactic 
configuration are added to the styrenic polymer having a high degree of 
the syndiotactic configuration, it is preferred that the added resins 
comprise monomer units similar to those of the styrenic polymer having a 
high degree of the syndiotactic configuration. The content of the 
compatible resin component in the styrenic resin composition is 1 to 70% 
by weight, preferably 2 to 50% by weight. The content of the compatible 
resin component more than 70% by weight is not preferable because the 
advantageous properties of the styrenic polymer having the syndiotactic 
configuration, such as heat stability, are impaired. 
As other types of resins which can be added to the styrenic resin used in 
the present invention and are not compatible with the styrenic resin, any 
types of resin other than the compatible resins described above, such as 
polyolefins like polyethylene, polypropylene, polybutene, polypentene, and 
the like, polyesters like polyethylene terephthalate, polybutylene 
terephthalate, polyethylene naphthalate, and the like, polyamides like 
nylon-6, nylon-6,6, and the like, polythioethers like polyphenylene 
sulfide and the like, polycarbonates, polyarylates, polysulfones, 
polyether ether ketones, polyether sulfones, polyimides, polymers of 
halogenated vinyl compounds like teflon and the like, acrylic polymers 
like polymethyl methacrylate and the like, polyvinylalcohol, and the like 
other resins, crosslinked resins containing the compatible resins 
described above, can be used. Because these resins are not compatible with 
the styrenic polymer having the syndiotactic configuration used in the 
present invention, these resins can be dispersed in the styrenic resin 
having the syndiotactic configuration in the form of islands when these 
resins are added in small amounts. Therefore, these resins are effective 
for providing good gloss after stretching and for improving lubricating 
property of the surface. The content of the incompatible resin component 
is preferably 2 to 50% by weight when the incompatible resin component is 
added in order to improve gloss, and 0.001 to 5% by weight when the 
incompatible resin component is added in order to control the surface 
properties. When the product is used at high temperatures, it is preferred 
that a relatively heat resistant incompatible resin is used. 
As the antioxidant, an antioxidant containing phosphorus, a phenolic 
antioxidant, or an antioxidant containing sulfur can be used. Polystyrenic 
resin compositions having good heat stability can be obtained by using 
such antioxidants. 
As the antioxidant containing phosphorus, various types of antioxidant 
including monophosphites and diphosphites can be used. Examples of the 
monophosphite include tris(2,4-di-t-butylphenyl) phosphite, tris(mono- and 
di-nonylphenyl) phosphites, and the like. As the diphosphite, phosphites 
represented by the general formula: 
##STR1## 
wherein R.sup.1 and R.sup.2 each represent an alkyl group having 1 to 20 
carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or an aryl 
group having 6 to 20 carbon atoms, and may the same or different, can be 
used. Specific examples of the diphosphite include 
distearylpentaerythritol diphosphite, dioctylpentaerythritol diphosphite, 
diphenylpentaerythritol diphosphite, 
bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, 
bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite, 
diclyohexylpentaerythritol diphosphite, tris(2,4-di-t-butylphenyl) 
phosphite, tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene phosphonite, 
and the like. Among these compounds, 
bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, 
bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite, 
tris(2,4-di-t-butylphenyl) phosphite, and 
tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene phosphonite are preferably 
used. 
As the phenolic antioxidant, various types of phenolic antioxidant can be 
used. Specific examples of the phenolic antioxidant include 
dialkylphenols, trialkylphenols, diphenylmonoalkoxyphenols, 
tetraalkylphenols, and the like. 
Examples of the dialkylphenol include 
2,2'-methylenebis(6-t-butyl-4-methylphenol), 
1,1-bis(5-t-butyl-4-hydroxy-2-methylphenyl)butane, 
2,2'-methylene-bis(4-methyl-6-cyclohexylphenol), 
4,4'-thio-bis(6-t-butyl-3-methylphenol), 
2,2'-bis(5-t-butyl-4-hydroxy-2-methylphenyl)-4-n-dodecylmercaptobutane, 
and the like. Examples of the trialkylphenol include 
2,6-di-t-butyl-4-methylphenol, 
2,2'-methylene-bis(6-t-butyl-4-ethylphenol), 2,2'-methylenebis4-methyl-6- 
(.alpha.-methylcyclohexyl)phenol!, 
2,2'-methylenebis(4-methyl-6-nonylphenol), 
1,1,3-tris(5-t-butyl-4-hydroxy-2-methylphenyl)butane, ethylene 
glycol-bis3,3-bis(3-t-butyl-4-hydroxyphenyl)butyrate!, 
1,1-bis(3,5-dimethyl-2-hydroxyphenyl)-3-(n-dodecylthio)butane, 
1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)-2,4,6-trimethyl benzene, 
2,2-bis(3,5-di-t-butyl-4-hydroxybenzyl)malonic acid dioctadecyl ester, 
n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl) propionate, 
tetrakismethylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)!methane, 
3,9-bis1,1-dimethyl-2-(.beta.-(3-t-butyl-4-hydroxy-5-methylphenyl)propion 
yloxy)ethyl 2,4,8,10-tetraoxaspiro5,5!undecane, 
tris(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, and the like. Examples 
of the diphenylmonoalkoxyphenol include 2,6-diphenyl-4-methoxyphenol and 
the like. Examples of the tetraalkylphenol include 
tris(4-t-butyl-2,6-dimethyl-3-hydroxybenzyl) isocyanurate and the like. 
As the antioxidant containing sulfur, thioether antioxidants are 
preferable. Specific examples of the thioether antioxidant include 
dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, 
distearyl-3,3'-thiodipropionate, pentaerythritol-tetrakis(.beta.-lauryl 
thiopropionate), 
bis2-methyl-4-(3-n-alkylthiopropionyloxy)-5-t-butylphenyl! sulfides, 
2-mercaptobenzimidazol, and the like. Among these compounds, 
pentaerythritol-tetrakis(.beta.-lauryl thiopropionate) is particularly 
preferable. 
In the polystyrenic stretched film of the present invention, an organic 
compound having an--NH-- group and a molecular weight lower than 10,000 
may be contained when necessary. As the organic compound, a compound 
having an electron-attracting group adjacent to the--NH-- group is 
preferable. As the electron-attracting group, a group having an aromatic 
ring, such as a benzene ring, a naphthalene ring, an anthracene ring, a 
pyridine ring, a triazine ring, an indenyl ring, or a derivative of these 
rings, or a group having a carbonyl group is preferable. As the organic 
compound described above, an organic compound having a heat decomposition 
temperature of 260.degree. C. or higher is preferable. Specific examples 
of the organic compound include 
2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, 
N,N'-hexamethylene-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamide), 
N,N'-bis3-(3,5-di-t-butylhydroxyphenyl)propionyl!hydrazine, 
3-(N-salicyloyl)amino-1,2,4-triazole, decamethylenedicarboxylic acid 
disalicyloyl hydrazide, isophthalic acid (2-phenoxypropionyl hydrazide), 
2,2-oxamido-bisethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate!, 
oxalyl-bis(benzylidene hydrazide), N-formyl-N'-salicyloylhydrazine, 
2-mercaptobenzimidazole, N,N'-di-2-naphthyl-p-phenylenediamine, 
4,4'-bis(.alpha.,.alpha.-dimethylbenzyl)diphenylamine, 
2-mercaptomethylbenzimidazole, diphenylamine modified with styrene, 
diphenylamine modified with octyl group, N-phenyl-1-naphthylamine, 
poly(2,2,4-trimethyl-1,2-dihydroquinoline), 
6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, 
N,N'-diphenyl-p-phenylenediamine, 
N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, 
N-phenyl-N'-(3-methacryloxy-2-hydroxylpropyl)-p-phenylenediamine, 
thiodiphenylamine, paminodiphenylamine, N-salicyloyl-N'-aldehyde 
hydrazine, N-salicyloyl-N'-acetylhydrazine, N,N'-diphenyloxamide, 
N,N'-di(2-hydroxyphenyl)oxamide, 
6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, 
N-phenyl-N'-isopropyl-p-phenylenediamine, and the like. 
The compound having an --NH-- group and a molecular weight lower than 
10,000 described above is contained in the polystyrenic stretched film of 
the present invention in an amount less than 30% by weight when necessary. 
The physical properties of the polystyrenic stretched film of the present 
invention are described in the following. 
The polystyrenic stretched film of the present invention has a 
crystallinity (Xc) of 35% or more, preferably 37% or more. A crystallinity 
less than 35% is not preferable because the degree of heat shrinkage is 
increased to cause a larger deformation by heating. The content of 
residual monomers in the polystyrenic stretched film of the present 
invention is 200 ppm or less, preferably 150 ppm or less. A content of 
residual monomers more than 200 ppm is not preferable because the printing 
property deteriorates and the peeling strength after vapor deposition 
decreases. The number of particles of foreign substances having a size of 
9 .mu.m or larger in the polystyrenic stretched film of the present 
invention is 1000 or less in 1 cm.sup.3, preferably 800 or less in 1 
cm.sup.3. When the number of particles of foreign substances having a size 
of 9 .mu.m or larger in 1 cm.sup.3 is more than 1000, the printing 
property of the stretched film deteriorates. Therefore, this condition is 
not preferable. 
The properties of the stretched film described above can be evaluated, for 
example, in accordance with the following methods. 
(1) Crystallinity (Xc): Crystallinity (Xc) is measured by using a 
differential scanning calorimeter or the like apparatus. 
Crystallinity (%)={(enthalpy of fusion (J/g)-enthalpy of crystallization by 
cooling (J/g))/53 (J/g)}.times.100 
As the enthalpy of fusion at the crystallinity of 100%, the value of 53 J/g 
is used for the styrenic polymer having the syndiotactic configuration. 
(2) Content of residual monomers: A piece of film was dipped into 
dimethylformamide at 100.degree. C. for 3 hours. The content of residual 
monomers is quantitatively determined by measurement of the obtained 
extract using the gas chromatography. 
(3) Number of foreign substances: Number of foreign substances in a film in 
an amount corresponding to the volume of 1 cm.sup.3 is continuously 
counted by using a CCD camera or the like. An average value is calculated 
from the results of 10 measurements. 
The polystyrenic stretched film of the present invention described above 
has excellent printing property and other properties, such as a high 
peeling strength after vapor deposition. The polystyrenic stretched film 
of the present invention can be produced by various processes which have 
conventionally been used. However, in order to efficiently obtain a 
stretched film having the properties described above, it is preferred that 
the process for producing a polystyrenic stretched film of the present 
invention is used. 
The process for producing the polystyrenic stretched film of the present 
invention is described in the following. 
In the process for producing the polystyrenic stretched film of the present 
invention, the styrenic resin composition containing 70 to 100% by weight 
of a styrenic polymer having a high degree of the syndiotactic 
configuration is extruded at 330.degree. C. or lower in 60 minutes or less 
in combination with melt filtration of the styrenic resin composition. The 
extruded styrenic resin composition is cooled, and the cooled styrenic 
resin composition is treated with biaxial stretching. 
More specifically, the preliminary molded product (a film, a sheet, or a 
tube) is prepared generally by the extrusion molding using the styrenic 
polymer having a high degree of the syndiotactic configuration as the 
material. In the extrusion molding, the melted and kneaded material for 
molding described above is molded to form a specified shape by using an 
extruder in combination with melt filtration of the styrenic resin 
composition. As the extruder, any of a single screw extruder and a twin 
screw extruder may be used. An extruder having or not having a vent may be 
used. For the melt filtration of the styrenic resin composition, it is 
preferred that a filter consisting of sintered metal fiber is used. The 
pore size of the filter is preferably 5 to 50 .mu.m. The number of 
particles of foreign substances can be decreased by the melt filtration. 
However, a part of the styrenic polymer described above is decomposed by 
the heat history, and the content of volatile matter (residual monomers) 
increases. Even though the content of the volatile matter can be decreased 
by the heat treatment which is subsequently conducted, it is preferred 
that the temperature of the filtration is kept in the range of 330.degree. 
C. or lower, more preferably in the range of 250.degree. to 320.degree. 
C., and the retention time is kept below 60 minutes in order to suppress 
the increase in the content of volatile matter as much as possible. 
The conditions for the extrusion are not particularly limited, and can be 
suitably determined in accordance with the situation. It is preferred that 
the temperature is selected in the range which is higher than the melting 
point or the decomposition temperature of the material for molding by 
50.degree. C. or more, and that the shearing force is selected in the 
range of 5.times.10.sup.6 dyne/cm.sup.2 or less. A T-die or a circular die 
can be used as the die. 
In the process for producing the polystyrenic stretched film of the present 
invention, the obtained preliminary molded product for stretching is 
solidified by cooling after being molded by the extruder. As the medium 
for the cooling, various media, such as a gas, a liquid, a metal roll, and 
the like, can be used. When a metal roll is used, it is effective for 
decreasing the dispersion of thickness and preventing the formation of 
waviness that a method using an air knife, an air chamber, a touch roll, 
an electrostatic pinning, or the like, is adopted. 
The temperature of cooling for solidification is generally in the range 
which is from 0.degree. C. to the temperature higher than the glass 
transition temperature of the preliminary molded product for stretching by 
30.degree. C., preferably in the range which is from the temperature lower 
than the glass transition temperature of the preliminary molded product 
for stretching by 70.degree. C. to the glass transition temperature. The 
rate of cooling can be suitably selected in the range of 200.degree. to 
3.degree. C./sec. 
The preliminary molded product which has been solidified by cooling is 
biaxially stretched. In the stretching, the product may be stretched 
simultaneously in the longitudinal direction and in the transverse 
direction, or may be stretched consecutively in the two directions in any 
order. The stretching may be conducted in a single step or in a plurality 
of steps. The stretching ratio by area is 2 or more, preferably 3 or more. 
As the method of stretching, various types of method, such as a method 
using a tenter, a method of stretching between rolls, a method using 
bubbling utilizing a gas pressure, a method of rolling, and the like, may 
be used. A suitable method or a combination of suitable methods can be 
selected from these methods. The temperature of stretching can be 
generally selected in the range from the glass transition temperature to 
the melting point of the preliminary molded product. The rate of 
stretching is generally 1.times.10 to 1.times.10.sup.5 %/minute, 
preferably 1.times.10.sup.3 to 1.times.10.sup.5 %/minute. 
In the present invention, the styrenic resin composition which has been 
extruded, cooled, and stretched under the conditions described above is 
heat treated under the condition that the degree of heat treatment A 
expressed by the following equation (I) is 1.times.10.sup.-1 or more and 
5.times.10.sup.2 or less, preferably 5.times.10.sup.-1 or more and less 
than 3.times.10.sup.2 or less: 
EQU A=.SIGMA.T.times.t/d.sup.2 ! (I) 
wherein T represents temperature of the heat treatment (K), t represents 
time of the heat treatment (second), and d represents thickness of the 
film (.mu.m). 
The heat treatment can be conducted in accordance with a conventional 
process. More specifically, the heat treatment can be conducted by holding 
the extruded, cooled, and stretched styrenic resin composition under a 
tense condition, a relaxed condition, or a condition of limited shrinkage 
at a temperature in the range which is from the glass transition 
temperature to the melting point of the film, preferably from a 
temperature lower than the melting point by 100.degree. C. to a 
temperature immediately below the melting point, for 0.5 to 120 seconds. 
It is possible that the heat treatment is conducted in separate two or 
more steps under different conditions within the range described above. 
The heat treatment may also be conducted in an atmosphere of an inert gas, 
such as argon gas, nitrogen gas, or the like. 
According to the process for producing the polystyrenic stretched film of 
the present invention, the polystyrenic stretched film of the present 
invention which has been described above can be efficiently produced, and 
the polystyrenic stretched film having excellent printing property and 
other properties, such as a high peeling strength after vapor deposition, 
can be obtained. 
The present invention is described in more detail with reference to 
examples in the following. However, the present invention is not limited 
by the examples. 
Reference Example 1 
A glass vessel of a 500 ml inner volume which had been purged with argon 
was charged with 17 g (71 mmol) of copper sulfate pentahydrate 
(CuSO.sub.4.5H.sub.2 O), 200 ml of toluene, and 24 ml (250 mmol) of 
trimethylaluminum, and the resultant mixture was allowed to react at 
40.degree. C. for 8 hours. After the reaction was finished, solid parts 
were removed from the reaction product, and 6.7 g of a catalyst product 
was obtained. The catalyst product had the molecular weight of 610 which 
was measured by the freezing point depression. 
Preparation Example 1 
Preparation of a styrenic polymer having the syndiotactic configuration! 
A reactor of a 2 liter inner volume was charged with the catalyst product 
obtained in Reference Example 1 described above in such an amount that 7.5 
mmol of aluminum atom was contained, 7.5 mmol of triisobutylaluminum, 
0.038 mmol of pentamethylcyclopentadienyltitanium trimethoxide, 0.95 liter 
of purified styrene, and 0.05 liter of p-methylstyrene, and polymerization 
of the resultant mixture was allowed to proceed at 90.degree. C. for 5 
hours. After the reaction was finished, the catalyst components were 
decomposed by a methanol solution of sodium hydroxide. The resultant 
product was repeatedly washed with methanol and dried to obtain 446 g of a 
polymer. 
The weight-average molecular weight of the obtained polymer was measured by 
the gel permeation chromatography using 1,2,4-trichlorobenzene as the 
solvent at 130.degree. C., and was found to be 305,000. The ratio of the 
weight-average molecular weight to the number-average molecular weight was 
2.67. It was confirmed by the measurement of the .sup.1 H-NMR that the 
content of p-methylstyrene in the obtained polymer was 7% by mol. It was 
also confirmed by the measurements of the melting point and the .sup.13 
C-NMR that the obtained polymer was polystyrene having the syndiotactic 
configuration. 
Preparation Example 2 
Preparation of a styrenic polymer having the syndiotactic configuration! 
A reactor of a 2 liter inner volume was charged with the catalyst product 
obtained in Reference Example 1 described above in such an amount that 7.5 
mmol of aluminum atom was contained, 7.5 mmol of triisobutylaluminum, 
0.038 mmol of pentamethylcyclopentadienyltitanium trimethoxide, 0.97 liter 
of purified styrene, and 0.03 liter of p-methylstyrene, and polymerization 
of the resultant mixture was allowed to proceed at 90.degree. C. for 5 
hours. After the reaction was finished, the catalyst components were 
decomposed by a methanol solution of sodium hydroxide. The resultant 
product was repeatedly washed with methanol and dried to obtain 466 g of a 
polymer. 
The weight-average molecular weight of the obtained polymer was measured by 
the gel permeation chromatography using 1,2,4-trichlorobenzene as the 
solvent at 130.degree. C., and was found to be 318,000. The ratio of the 
weight-average molecular weight to the number-average molecular weight was 
2.51. It was confirmed by the measurement of the .sup.1 H-NMR that the 
content of p-methylstyrene in the obtained polymer was 4% by mol. It was 
also confirmed by the measurements of the melting point and the .sup.13 
C-NMR that the obtained polymer was polystyrene having the syndiotactic 
configuration. 
Preparation Example 3 
Preparation of a styrenic polymer having the syndiotactic configuration! 
A reactor of a 2 liter inner volume was charged with the catalyst product 
obtained in Reference Example 1 described above in such an amount that 7.5 
mmol of aluminum atom was contained, 7.5 mmol of triisobutylaluminum, 
0.038 mmol of pentamethylcyclopentadienyltitanium trimethoxide, 0.90 liter 
of purified styrene, and 0.10 liter of p-methylstyrene, and polymerization 
of the resultant mixture was allowed to proceed at 90.degree. C. for 5 
hours. After the reaction was finished, the catalyst components were 
decomposed by a methanol solution of sodium hydroxide. The resultant 
product was repeatedly washed with methanol and dried to obtain 466 g of a 
polymer. 
The weight-average molecular weight of the obtained polymer was measured by 
the gel permeation chromatography using 1,2,4-trichlorobenzene as the 
solvent at 130.degree. C., and was found to be 312,000. The ratio of the 
weight-average molecular weight to the number-average molecular weight was 
2.73. It was confirmed by the measurement of the .sup.1 H-NMR that the 
content of p-methylstyrene in the obtained polymer was 12% by mol. It was 
also confirmed by the measurements of the melting point and the .sup.13 
C-NMR that the obtained polymer was polystyrene having the syndiotactic 
configuration. 
EXAMPLE 1 
The styrenic polymer having the syndiotactic configuration obtained in 
Preparation Example 1 was melt extruded at 300.degree. C., and then formed 
into pellets. The obtained pelletized material was melt extruded by an 
extruder equipped with a melt filter of a filtration accuracy of 10 .mu.m 
(a product of Nippon Seisen Co., Ltd.; a filter of sintered metal fiber; a 
leaf disk type), and then brought into tight contact with a cooling roll 
of 50.degree. C. by the electrostatic pinning method to prepare a 
preliminary molded sheet for stretching having a thickness of 1400 .mu.m. 
The temperature of melt filtration was 280.degree. C., and the average 
retention time was 30 minutes. 
The obtained preliminary molded sheet for stretching was continuously 
stretched at 110.degree. C. to the stretching ratio of 3.5 in the 
longitudinal direction. The part of stretching was heated by an infrared 
heater. Then, the longitudinally stretched sheet was stretched at 
115.degree. C. to the stretching ratio of 4.0 in the transverse direction. 
The stretched sheet was subsequently heat treated at 245.degree. C. for 15 
seconds while the width of the sheet is held unchanged, and then heat 
treated at 245.degree. C. for 15 seconds under the limited shrinkage of 6% 
to obtain a film having a thickness of 100 .mu.m. The degree of heat 
treatment A obtained by the equation (I) was 1.6. 
The properties of the obtained film were evaluated in accordance with the 
following methods. 
(1) Crystallinity (Xc): Crystallinity (Xc) was measured by using a 
differential scanning calorimeter. 
##EQU1## 
(2) Content of residual monomers: The film was cut into a square piece 
having edges of 3 mm. The obtained piece of the film was extracted with 
dimethylformamide at 100.degree. C. The content of residual monomers were 
quantitatively determined by measurement of the obtained extract using the 
gas chromatography. 
(3) Number of foreign substances: The film was fed into a clean room lower 
than Class 1000 at a speed of 3.0 m/min while an ionized air was blown to 
the film, and passed between a stroboscope attached with a light diffusion 
plate and a CCD camera. The number of foreign substances having a size of 
9 .mu.m or larger was counted by an image treatment of the image captured 
by the CCD camera. The frequency of flashing of the stroboscope was 1200 
shots/min. The area of the film corresponding to 1 cm.sup.3 of the film 
was continuously observed in the view area of 2.0.times.2.5 mm. This 
measurement was repeated 10 times, and the number of foreign substances in 
1 cm.sup.3 was obtained as the average of the values from the 10 
measurements. 
(4) Peeling strength after vapor deposition: The obtained film was coated 
with aluminum to the thickness of about 80 nm by the vacuum vapor 
deposition. Lines were cut into the coated surface of the film in the form 
of a lattice having a distance between lines of 1 mm by using a cutter. A 
pressure sensitive adhesive tape was attached to the cut surface and then 
peeled off. The number of lattice elements peeled off from the surface per 
100 lattice elements was counted. 
(5) Printing property: A stamp of an area of 140 cm.sup.2 was used for 
printing lines of a lattice having a distance between lines of 10 mm. The 
lines were printed on the film by the stamp using an oil ink. The number 
of position where the line is discontinuous or diffuse was counted. 
The results are shown in Table 1. 
FIG. 1 illustrates a schematic diagram showing the outline of the apparatus 
for evaluation of the number of foreign substances in a clean room lower 
than Class 1000. 
EXAMPLE 2 
The styrenic polymer obtained in Preparation Example 2 was melt extruded at 
300.degree. C., and then formed into pellets. The obtained pelletized 
material was melt extruded by an extruder equipped with a melt filter of a 
filtration accuracy of 10 .mu.m (a product of Nippon Seisen Co., Ltd.; a 
filter of sintered metal fiber; a leaf disk type), and then brought into 
tight contact with a cooling roll of 50.degree. C. by the electrostatic 
pinning method to prepare a preliminary molded sheet for stretching having 
a thickness of 700 .mu.m. The temperature of melt filtration was 
280.degree. C., and the average retention time was 48 minutes. 
The obtained preliminary molded sheet for stretching was continuously 
stretched at 110.degree. C. to the stretching ratio of 3.5 in the 
longitudinal direction. The part of stretching was heated by an infrared 
heater. Then, the longitudinally stretched sheet was stretched at 
115.degree. C. to the stretching ratio of 4.0 in the transverse direction. 
The stretched sheet was subsequently heat treated at 255.degree. C. for 15 
seconds while the width of the sheet is held unchanged, and then heat 
treated at 255.degree. C. for 15 seconds under the limited shrinkage of 6% 
to obtain a film having a thickness of 50 .mu.m. The degree of heat 
treatment A obtained by the equation (I) was 6.3. 
The properties of the obtained film were measured in accordance with the 
same methods as those used in Example 1. 
EXAMPLE 3 
The styrenic polymer obtained in Preparation Example 3 was melt extruded at 
300.degree. C., and then formed into pellets. The obtained pelletized 
material was melt extruded by an extruder equipped with a melt filter of a 
filtration accuracy of 10 .mu.m (a product of Nippon Seisen Co., Ltd.; a 
filter of sintered metal fiber; a leaf disk type), and then brought into 
tight contact with a cooling roll of 50.degree. C. by the electrostatic 
pinning method to prepare a preliminary molded sheet for stretching having 
a thickness of 2400 .mu.m. The temperature of melt filtration was 
290.degree. C., and the average retention time was 17 minutes. 
The obtained preliminary molded sheet for stretching was continuously 
stretched at 110.degree. C. to the stretching ratio of 3.5 in the 
longitudinal direction. The part of stretching was heated by an infrared 
heater. Then, the longitudinally stretched sheet was stretched at 
115.degree. C. to the stretching ratio of 4.0 in the transverse direction. 
The stretched sheet was subsequently heat treated at 220.degree. C. for 20 
seconds while the width of the sheet is held unchanged, and then heat 
treated at 220.degree. C. for 20 seconds under the limited shrinkage of 6% 
to obtain a film having a thickness of 175 .mu.m. The degree of heat 
treatment A obtained by the equation (I) was 0.6. 
The properties of the obtained film were measured in accordance with the 
same methods as those used in Example 1. 
EXAMPLE 4 
The styrenic polymer obtained in Preparation Example 2 was melt extruded at 
300.degree. C., and then formed into pellets. The obtained pelletized 
material was melt extruded by an extruder equipped with a melt filter of a 
filtration accuracy of 10 .mu.m (a product of Nippon Seisen Co., Ltd.; a 
filter of sintered metal fiber; a leaf disk type), and then brought into 
tight contact with a cooling roll of 50.degree. C. by the electrostatic 
pinning method to prepare a preliminary molded sheet for stretching having 
a thickness of 140 .mu.m. The temperature of melt filtration was 
280.degree. C., and the average retention time was 55 minutes. 
The obtained preliminary molded sheet for stretching was continuously 
stretched at 110.degree. C. to the stretching ratio of 3.5 in the 
longitudinal direction. The part of stretching was heated by an infrared 
heater. Then, the longitudinally stretched sheet was stretched at 
115.degree. C. to the stretching ratio of 4.0 in the transverse direction. 
The stretched sheet was subsequently heat treated at 255.degree. C. for 15 
seconds while the width of the sheet is held unchanged, and then heat 
treated at 255.degree. C. for 15 seconds under the limited shrinkage of 6% 
to obtain a film having a thickness of 10 .mu.m. The degree of heat 
treatment A obtained by the equation (I) was 158.4. 
The properties of the obtained film were measured in accordance with the 
same methods as those used in Example 1. 
Comparative Example 1 
The styrenic polymer obtained in Preparation Example 1 was melt extruded at 
300.degree. C., and then formed into pellets. The obtained pelletized 
material was melt extruded by an extruder equipped with a melt filter of a 
filtration accuracy of 10 .mu.m (a product of Nippon Seisen Co., Ltd.; a 
filter of sintered metal fiber; a leaf disk type), and then brought into 
tight contact with a cooling roll of 50.degree. C. by the electrostatic 
pinning method to prepare a preliminary molded sheet for stretching having 
a thickness of 1400 .mu.m. The temperature of melt filtration was 
280.degree. C., and the average retention time was 80 minutes. 
The obtained preliminary molded sheet for stretching was continuously 
stretched at 110.degree. C. to the stretching ratio of 3.5 in the 
longitudinal direction. The part of stretching was heated by an infrared 
heater. Then, the longitudinally stretched sheet was stretched at 
115.degree. C. to the stretching ratio of 4.0 in the transverse direction. 
The stretched sheet was subsequently heat treated at 180.degree. C. for 2 
seconds while the width of the sheet is held unchanged to obtain a film 
having a thickness of 100 .mu.m. The degree of heat treatment A obtained 
by the equation (I) was 0.09. 
The properties of the obtained film were measured in accordance with the 
same methods as those used in Example 1. 
Comparative Example 2 
The styrenic polymer obtained in Preparation Example 2 was melt extruded at 
300.degree. C., and then formed into pellets. The obtained pelletized 
material was melt extruded by an extruder equipped with a melt filter of a 
filtration accuracy of 10 .mu.m (a product of Nippon Seisen Co., Ltd.; a 
filter of sintered metal fiber; a leaf disk type), and then brought into 
tight contact with a cooling roll of 50.degree. C. by the electrostatic 
pinning method to prepare a preliminary molded sheet for stretching having 
a thickness of 100 .mu.m. The temperature of melt filtration was 
280.degree. C., and the average retention time was 90 minutes. 
The obtained preliminary molded sheet for stretching was continuously 
stretched at 110.degree. C. to the stretching ratio of 3.5 in the 
longitudinal direction. The part of stretching was heated by an infrared 
heater. Then, the longitudinally stretched sheet was stretched at 
115.degree. C. to the stretching ratio of 4.0 in the transverse direction. 
The stretched sheet was subsequently heat treated at 190.degree. C. for 65 
seconds while the width of the sheet is held unchanged, and then heat 
treated at 190.degree. C. for 55 seconds under the limited shrinkage of 6% 
to obtain a film having a thickness of 10 .mu.m. The degree of heat 
treatment A obtained by the equation (I) was 556. 
The properties of the obtained film were measured in accordance with the 
same methods as those used in Example 1. 
Comparative Example 3 
A film was prepared and evaluated in accordance with the same procedures as 
those used in Example 1 except that the styrenic polymer was extruded by 
the extruder not equipped with a melt filter. 
The properties of the obtained film were measured in accordance with the 
same methods as those used in Example 1. 
TABLE 1 
______________________________________ 
(Part 1) 
film 
degree of content of 
heat average residual 
melt treatment 
thickness 
crystallinity 
monomers 
filter 
A .mu.m % ppm 
______________________________________ 
Example 1 
10 1.6 100 44 31 
Example 2 
10 6.3 50 45 23 
Example 3 
10 0.6 175 41 47 
Example 4 
10 153 10 46 &lt;20 
Comparative 
10 0.09 100 33 350 
Example 1 
Comparative 
10 556 10 47 220 
Example 2 
Comparative 
none 1.6 100 44 20 
Example 3 
______________________________________ 
TABLE 1 
______________________________________ 
(Part 2) 
film 
number of 
number of 
peeled 
foreign element printing property 
substances/ 
after vapor 
diffuse discontinuous 
cm.sup.3 
deposition 
line line 
______________________________________ 
Example 1 
457 0 none none 
Example 2 
333 0 none none 
Example 3 
519 9 none none 
Example 4 
483 0 none none 
Comparative 
498 7 12 none 
Example 1 
Comparative 
461 5 &gt;8 none 
Example 2 
Comparative 
6754 8 none 35 
Example 3 
______________________________________ 
INDUSTRIAL APPLICABILITY 
As described in the above, the polystyrenic stretched film of the present 
invention has excellent printing property and other properties, such as a 
high peeling strength after vapor deposition. According to the process for 
producing the polystyrenic stretched film of the present invention, the 
polystyrenic stretched film having the excellent properties can be 
efficiently produced. 
Therefore, the polystyrenic stretched film of the present invention can be 
advantageously used as a base material for condenser films, electric 
insulation films, photographic films, process films for printing, optical 
films such as films for over-head projectors, and packaging films and is 
remarkably valuable in the industrial applications.