JPH0228131B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to polyester films. More specifically, the present invention relates to a biaxially oriented polyester film that has excellent transparency and workability and is suitable for photosensitive recording media, particularly for photography, microfilm, overhead projectors, and the like. Polyester films, such as polyethylene terephthalate films, are widely used in various fields including information recording and electrical applications due to their excellent mechanical properties, heat resistance, and electrical properties. One of the uses of such a polyester film is as a base film for use in the fields of photosensitive recording materials such as photography, microfilm, and overhead projectors. Microfilm is generally
There are silver halide films, diazo films, and vesicular films, and the usage of diazo films, vesicular films, etc. is likely to increase in the future. Both diazo film and vesicular film use diazonium salt as the photosensitive material, and their spectral sensitivity is in the ultraviolet region of 350 to 400 nm, and they are generally exposed in this wavelength range. When printing original microfilm (generally silver halide microfilm) on diazo microfilm, the base of the original microfilm
If the light transmittance of 350 to 400 nm is low, the amount of exposure to the diazo film will be insufficient, and the degree of blackening of the printed diazo microfilm image will be insufficient, resulting in a decrease in resolution and image quality. Naturally, if the amount of light is increased, the degree of blackening may increase, but this is not preferable because it often lowers the resolution or causes deterioration of the base film. Also, when printing diazo microfilm over many generations,
If the base film of the original microfilm of each generation has low light transmittance in the ultraviolet region, the image quality will deteriorate significantly. Furthermore, if there are large protrusions on the surface of the base film or large particles inside, scattering of ultraviolet rays occurs, making the copied microfilm image a blurred image that is difficult to identify. Furthermore, when microfilm is imaged using visible light from a projector or reader, if there are large protrusions on the surface, a type of frosting phenomenon occurs that makes the film surface uneven, resulting in a lack of sharpness of the image. Undesirable. Therefore, the transparency of the film in the visible region is also an important characteristic for it to be used as a base for microfilms, as is the transmittance in the ultraviolet region. On the other hand, the basic and most important characteristic of microfilms used in such applications, as in films used in other applications, is that they are excellent in workability when handling the base film and product film. That is, if the slipperiness between films or between films and metal rolls is poor, for example, when manufacturing a base film, the film is generally conveyed between a number of metal rolls, and scratches may occur due to the rolls. The produced film is generally wound into a roll and transported or subjected to post-processing. Therefore, if the slipperiness is not good, blocking of the films will occur during the winding process, making handling difficult, and surface defects such as wrinkles and lumps will occur, reducing the product value. In addition, in post-processing, for example, when coating a base material, it causes troubles such as tension fluctuation and meandering. Furthermore, a problem specific to microfilm is that when copying and printing original information from the original film onto a copy film, it is necessary to load the film into the device smoothly, and at the same time, it is necessary to avoid misalignment of the image during copying. It is also important that this does not occur. In order to improve the workability of polyester film, it is sufficient to add fine protrusions to the surface of the film.
A well-known method is to roughen the film surface by adding inert fine particles such as calcium terephthalate. Such particles tend to create voids between the particles and the polymer during the stretching film forming process, resulting in increased turbidity of the film, as well as abrasion of guide rolls and detachment of added particles during the secondary processing process. On the other hand, a method is also well known in which fine particles are precipitated in the reaction system using the residue of a metal compound used as a catalyst. This method does not require special equipment or complicated operations and can be carried out relatively easily.
There are many problems that need to be solved, such as the tendency to form agglomerated particles and the variation between batches of precipitated particles. Methods for producing such fine protrusions on the film surface have been known for some time, but attempts to improve slipperiness usually result in deterioration of transparency. In particular, as in the case of a photosensitive recording material base, strict optical requirements and workability are contradictory, and it is extremely difficult to satisfy both at the same time. As a result of intensive research into a polyester film that satisfies both of these mutually contradictory required properties, the present inventors have developed an insoluble, infusible, crosslinked polymer that has a functional group that can react with polyester and has an average particle size of 0.1 to 2μ. The present invention was completed by discovering that a film having surface roughness within a specific range by adding fine powder to polyester has excellent optical properties and workability at the same time. That is, in the present invention, the average particle size is
A roughened polyester film obtained by adding to polyester an insoluble and infusible crosslinked polymer fine powder having a functional group capable of reacting with polyester of 0.1 to 2μ, the protrusion per unit length on the surface of the film. The number N ₁ and the average height ₁ of the protrusions are the following two equations: 5≦N ₁ ≦29 (i) 0.025≦ ₁ ≦0.070 (ii) (N ₁ : Number of surface protrusions peaks per 1 mm (number/
mm) ₁ : Average height of surface protrusions (μm)) and light transmittance of 76% or more at 380 nm, 400 nm
The oriented polyester film is characterized by having a light transmittance of 78% or more. The present invention will be explained in more detail. The polyester referred to in the present invention refers to a polyester obtained using terephthalic acid or its alkyl ester and ethylene glycol as main starting materials, but other third components may be used as part of the raw materials. The third component includes one or more of isophthalic acid, naphthalene dicarboxylic acid, or their alkyl esters as an aromatic dicarboxylic acid component, and one type of polyalkylene glycol such as propylene glycol, tetramethylene glycol, and polyethylene glycol as a glycol component. Or two or more types can be used. In any case, the polyester of the present invention refers to a polyester in which at least 80% of the repeating structural units are ethylene phthalate units. The method for producing polymers usually involves a two-step process in which a transesterification reaction or an esterification reaction is performed to obtain a polyester oligomer, followed by a polycondensation reaction. In this case, a known compound such as a calcium compound is used as the transesterification catalyst. , a manganese compound, a zinc compound, a lithium compound, and the like can be used. Further, after the transesterification reaction or esterification reaction is substantially completed, one or more phosphorus compounds may be added as a regulator or stabilizer for precipitated particles. As the polycondensation catalyst, one or more of known antimony compounds, germanium compounds, titanium compounds, tin compounds, cobalt compounds, etc. can be used, but antimony compounds and germanium compounds are particularly preferred. Since the fine polymer powder used in the present invention is itself an organic substance, it has far better compatibility with polyester and transparency than inorganic compounds. However, fine polymer powders such as polytetrafluoroethylene, which do not have groups that react with polyester, do not necessarily have sufficient dispersibility and often form coarse particles. The fine polymer powder used in the present invention needs to have a functional group, and the functional group refers to a group that can react with polyester or a polyester raw material to form a covalent bond with the polyester. Examples of functional groups include ester groups, carboxyl groups, hydroxyl groups, epoxy groups, and amino groups. As the ester group, a lower alkyl ester group such as a methylcarbonyloxy group or an ethylcarbonyloxy group is preferable. Another feature of the fine polymer powder used in the present invention is that it has a crosslinked structure. That is, the fine polymer powder having the crosslinked structure is insoluble and infusible even at high temperatures during polyester synthesis or molding, and therefore can be dispersed in polyester while maintaining its original shape at the time of addition. The fine polymer powder of the present invention generally includes a compound having only one aliphatic unsaturated bond in the molecule, and a compound having two or more aliphatic unsaturated bonds in the molecule as a crosslinking agent. Examples include polymers, but the polymer is not limited thereto, and any insoluble and infusible crosslinked polymer may be used as long as it has a group that can react with polyester and form a covalent bond. Typical examples of these copolymers include:
Copolymers of methyl methacrylate and divinylbenzene or methyl acrylate and divinylbenzene can be mentioned. In addition, by saponifying these fine polymer powders having alkyl ester groups,
By carrying out copolymerization using methacrylic acid instead of methacrylic acid ester and acrylic acid instead of acrylic acid ester, it is possible to easily obtain a crosslinked polymer fine powder having carboxyl groups. Commercially available weakly acidic cation exchange resins have a crosslinked structure and carboxyl groups, and therefore can be suitably used as the crosslinked polymer used in the present invention. Further, a crosslinked polymer having an alkyl ester group, which is an intermediate raw material, may also be used. Note that the crosslinked polymer obtained from the above-mentioned monovinyl compound-divinyl compound may have pores in order to facilitate pulverization. In order to provide pores to the crosslinked polymer, a compound that can be eluted with an organic solvent after polymerization may be present during polymerization. Examples of compounds that can coexist include hydrocarbon compounds such as n-hexane, n-heptane, cyclohexane, kerosene, toluene, and xylene;
Examples include alcohols such as -butanol, n-hexanol, and n-propanol, polystyrene, polyvinyl alcohol, and polyalkylene oxide. Among these, linear polymers that are soluble in organic solvents are particularly preferred. The average particle size of the crosslinked polymer used in the present invention must be 0.1-2μ. Average particle size is 0.1μ
If it is less than this, the surface roughness of the film containing the particles is low, the slipperiness imparting effect is insufficient, and the abrasion resistance effect is also insufficient. On the other hand, the average particle size
If it exceeds 2μ, large protrusions will form on the film surface, which will reduce the light transmittance, which is undesirable. In order to obtain particles used in the present invention having an average particle size of 0.1 to 2μ, monomers used as raw materials are subjected to suspension polymerization or
There are methods to obtain it directly, such as emulsion polymerization, but
The particle size obtained varies due to slight variations in stirring, concentration, temperature, additives, etc. during the reaction, and it is difficult to obtain uniform and fine particles with good reproducibility using this method. Therefore, by pulverizing and classifying crosslinked polymers with a size of several tens of microns to several hundred microns, which can be easily obtained especially in the case of suspension polymerization, fine powder with an average particle size of 0.1 to 2 microns can be obtained. The method of obtaining it is practical.
Suitable methods for grinding the particles include, for example, jet mills, fluid energy mills, and ball mills. The particles thus pulverized are subjected to a subsequent classification step, if necessary, in order to obtain particles of a constant particle size suitable for use in the present invention. As the classification method, there are, for example, a semi-free whirlpool method, a forced whirlpool method, a hydrocyclone method, or a centrifugation method, and any of these methods may be employed. The degree of crosslinking of the fine polymer powder obtained from monovinyl compounds and divinyl compounds is preferably 8 to 50%, preferably 9 to 45%. The degree of crosslinking is a numerical value defined by the formula below, but if this value is less than 8%, it will be difficult to grind, and if it exceeds 50%, it will no longer be easy to grind, and the functional groups will Since the density decreases, the bonding force with polyester tends to become poor. Degree of crosslinking = weight of divinyl compound/total weight of monomer x 100 If the degree of crosslinking is changed, the refractive index of the resulting crosslinked polymer will also change. For example, in the case of a methacrylic acid-divinylbenzene copolymer, which is one of the polymers suitable for use as a crosslinked polymer in the present invention, the higher the crosslink density, the more the resulting crosslinked polymer and biaxially stretched polyester film. Since the refractive index of the film becomes close to that of the film and the transparency increases, it is particularly preferably used for microfilms, etc., which are the field of application of the present invention. In the present invention, by adapting raw material suitability, film forming conditions, etc. so that the surface state of the polyester film to which such crosslinked polymer fine powder is added falls within the range specified by the present invention, it is possible to It is possible to obtain an excellent film that has high light transmittance, excellent transparency, and improved handling workability. The workability and transparency of the base film for microfilm depend on the surface roughness of the base film. In other words, the peak number of surface protrusions per mm
When N ₁ (numbers/mm) is less than 5, transparency is sufficient, but the number of protrusions is insufficient, causing a problem in slipperiness. On the other hand, if the number exceeds 29, the slipperiness is good, but even for particles with a refractive index close to that of polyester, the transparency deteriorates, and the light transmittance at 400 nm becomes 78.
%, which is not desirable. In addition, if the average height ₁ of the surface projections is less than 0.025 μm, the height of the projections is too low and the resulting film has insufficient slipperiness, which may cause blocking between the films or when the film is wound up into a roll. bulge-like surface defects occur. On the other hand, if it exceeds 0.070 μm, it not only reduces the light transmittance, but also
When microfilm is processed, black spots are often observed in enlarged and reproduced images. Therefore, a film that simultaneously satisfies the two equations within the range specified by the present invention is 5≦N ₁ ≦29 (i) 0.025≦ ₁ ≦0.070 (ii). The quality of the product is excellent, with fewer scratches and no lump-like surface defects during winding into a roll. A film having a surface roughness within the range defined by the present invention as described above, and having a light transmittance of 76 at 380 nm.
% or more, the light transmittance at 400 nm is 78% or more, and preferably the light transmittance at 550 nm is 83% or more, the light transmittance is high in the ultraviolet region and the visible region,
When this film is used as an original microfilm and is printed on a diazo film or a vesicular film using ultraviolet light, the image is extremely clear. There is very little decrease in image sharpness or resolution when printing is repeated over generations, so the images produced using visible light by a projector or reader are bright and clear, making them the perfect base film for microfilm. It is excellent as. In the present invention, in the ultraviolet region, especially 380 nm and
The reason for stipulating the light transmittance at 400nm is that in recent diazo photosensitive materials, when high sensitivity is required, the maximum sensitive wavelength is designed around 400nm, whereas when high sensitivity is not required, the maximum sensitivity wavelength is designed around 400nm.
The photosensitive wavelength is designed around 380nm. Accordingly
The light transmittance at 380 nm is preferably 76% or more, more preferably 78% or more.
The light transmittance at 400 nm is preferably 78% or more, more preferably 80% or more. Generally, the light transmittance in the visible region is represented by the transmittance at 550 nm, and is preferably 83% or more, and more preferably 85% or more. The upper limit of the light transmittance at wavelengths of 380 nm and 400 nm is not particularly limited, but
Usually less than 90%. Further, the upper limit of the light transmittance at a wavelength of 550 nm is not particularly limited, but is usually 95% or less. In the present invention, the fine polymer powder is preferably added at any time during the polyester manufacturing process. If a film is formed by adding and mixing to chips or powdered polyester after completion of polymerization and extrusion, the reaction time between the fine powder and the polyester is short, and each particle of the fine polymer powder does not react sufficiently with the polyester. Therefore, the affinity is not improved, and when a stretched film is formed, voids are generated around the particles, reducing transparency. Furthermore, dispersibility is often insufficient and agglomerated particles are likely to occur. Therefore, in the present invention, the fine polymer powder is preferably added before the middle stage of polycondensation, particularly before the transesterification reaction or esterification reaction, after the transesterification reaction, or after the esterification reaction and before the start of the polycondensation reaction. As a method of adding the fine polymer powder to the polymer manufacturing process, it is preferable to add it as an ethylene glycol slurry. The slurry concentration is
Approximately 0.5 to 20% by weight is appropriate. In the present invention, the crosslinked polymer fine powder is contained in the polyester film in an amount of 0.001 to 0.2% by weight, preferably 0.005 to 0.2% by weight, more preferably 0.007 to 0.2% by weight.
Must contain 0.1% by weight. This amount
If it is less than 0.001% by weight, the effect of imparting slipperiness will be insufficient. On the other hand, if it is used in an amount exceeding 0.2% by weight, it is not preferable because the light transmittance decreases. Further, when producing the film of the present invention, the desired film can be obtained by forming the polyester containing the crosslinked polymer fine powder as it is or by diluting it with another polyester. Other polyesters used for dilution include polyesters produced by conventional precipitation methods, addition methods, and polyesters that do not contain particles, but in any case, the polymer fine powder is present in the final polyester film. body is 0.001~0.2
Must contain % by weight. In order to obtain such a film, a known film forming method is used, for example, a film is melt-extruded at 270 to 295°C, an amorphous sheet is then sequentially biaxially stretched vertically and horizontally, or simultaneously biaxially stretched, and then heat treated at 161 to 240°C. method can be adopted. The thickness of the film having the surface roughness and light transmittance within the range specified by the present invention is not particularly limited.
Films with a diameter of 25 to 250μ are suitable for microfilms due to their mechanical strength, stiffness, transparency, and ease of handling. The microfilm is prepared using diazonium salt-based photosensitizers such as P-N,N-dimethoxyaminobenzenediazonium zinc chloride, P-N,N
- Diazonium salt compounds such as diethylaminobenzenediazonium boron fluorite or P-diazo-2,5-dibutoxymorpholinobenzene boron fluoride, along with polymethyl methacrylate or acrylonitrile-vinylidene chloride copolymer, along with methyl ethyl ketone, tetrahydrofuran, and methanol. It is made by coating and drying a photosensitive liquid prepared by dissolving it in a solvent such as. For exposure, a mercury lamp, xenon lamp, chemical fluorescent lamp, etc., which contain abundant near-ultraviolet light, is used as a light source. For example, a 400W mercury lamp is used to irradiate the original image for 3 seconds to 2 minutes. A diazo microfilm can then be obtained by developing with ammonia gas. In addition to microfilms, the film is also suitable for optically and visually demanding applications, such as metallized films in which aluminum, silver, etc. are vapor-deposited on the film surface, and windows. As described in detail above, in the present invention, for the first time, a polyester film can be obtained as a stretched polyester film for photosensitive recording materials, which has both extremely excellent properties in terms of optical properties and film handling workability. The present invention will be described in more detail below with reference to Examples. In addition, the measuring method and evaluation method of the main characteristics in the present invention are shown below. 1 Surface Roughness N ₁ , ₁ The N ₁ value and ₁ value indicating surface roughness referred to in the present invention were measured by the following methods, respectively. Measurement length was approximately 60 mm and vertical magnification was 100,000 using Kosaka Institute Co., Ltd.'s ET-10 thin film step measuring machine.
Multiply the cross-sectional curve at 200x horizontal magnification. How to set the baseline Find a minimum point within a range of 80 μm starting from the first minimum point of the cross-sectional curve. The line connecting these minimum points and the first minimum point with the minimum slope is defined as the baseline. Furthermore, draw a missing baseline using the minimum point selected as the baseline as a starting point. N ₁ ; Divide the cross-sectional curve into sections every 32 μm.
Select all local maximum values in the interval. If there is a maximum value within the interval among the local maximum values, it is counted as a protrusion. The value converted to 1 mm is _N1 . ₁ ; Height of the protrusion from the baseline is hi
(μm), and the number of protrusions measured over approximately 60 mm is calculated using the following formula. 2 Light transmittance Self-recording spectrophotometer manufactured by Hitachi, Ltd.
Using Model 323, write the spectral transmittance of the film sample in the wavelength range of 350 to 750 nm on a chart.
The spectral transmittance of wavelengths of 380 nm, 400 nm, and 550 nm was read from the chart and expressed as the light transmittance of each wavelength. 3 Film haze Measured using a Nippon Denshoku turbidimeter model NDH-2A according to the method of ASTMD1003-61. 4 Average particle size: Obtained using a microscope. That is, the particles or polyester containing particles were sandwiched between cover glasses, and the maximum particle size was measured after taking a photograph. The average particle size refers to the particle size expressed as the diameter at a point where the weight fraction is 50% by calculating the weight distribution of a group of spheres with the maximum diameter as the diameter. 5 Slip property Place the film to be measured on a flat surface, wrap the same film around a core with a radius of 4 mmR, press it against each other, and make the contact width of both films 12
The coefficient of friction was measured by sliding the films together at a sliding speed of 40 mm/min with a load of 30 g. The measurements were carried out in an atmosphere with a temperature of 21±2° C. and a humidity of 65±5%. 6 Evaluation of winding workability The target film is rolled up into a roll with a hardness that does not cause ``step misalignment'' or ``sagging at the bottom of the roll'', etc., and the frequency of occurrence of lump-like surface defects that appear on the roll surface is visually observed. Observe. After winding, the film roll was cut open and the frequency of presence or absence of bulge-like surface defects was visually observed and evaluated in the following three grades. A: There are no lump-like surface defects. B: A case in which several bulge-like surface defects occur in one roll and are scattered in the width direction and longitudinal direction of the roll, and there is no practical problem. C: A large number of bulge-like surface defects (10 or more) occur in one roll, and they occur in groups, which poses a practical problem. 7 Evaluation of scratches In a dark room, shine light on the film surface at an incident angle of 45° and measure the film length.
The number of scratches was counted over a 15m area, expressed in number per square meter, and rated on the following three scales. A: No scratches or less than 10 scratches per square meter B: No scratches over 10 mm in length, but between 10 and less than 50 scratches per square meter, which is practically acceptable for normal microfilm use. C. Films that have scratches of 10 mm or more in length or have more than 50 scratches per square meter, and cannot be put to practical use as microfilms. 8 Evaluation of Image Quality A photosensitive solution having the composition described below was prepared. Butyraldehyde polyvinyl alcohol 20 parts Polyisocyanate adduct 5 parts 1,4-dioxane 180 parts p-diazo N,N-dimethylaniline zinc chloride salt 4 parts Acetonitrile 80 parts The photosensitive solution was applied to the base film and heated to 116°C for 5 minutes. It was dried. After drying, the film was placed in contact with a transparent image of reduced photographic film, and a mercury arc lamp placed 5 cm apart was used to pass the transparent image through it for 20 minutes.
Exposure for seconds. Then heat the film to 116℃ for 2 seconds.
It was heated and developed. Next, the developed film was enlarged 48 times using a projector, and the quality of the projected image was evaluated on the following three levels. A: Suitable for use with microfilm, where the image has clear contrast between black and white, no minute spots caused by the base film, and the entire screen is extremely bright. B: There are some small black spots caused by the base film, but they have almost no effect on the sharpness of the image or the contrast between black and white, the entire screen is bright, and there are no problems in practical use as a microfilm. C: Many large and small black spots are observed, and the film surface causes uneven light scattering, resulting in distorted images and lack of sharpness, which poses a practical problem for use as a microfilm. 9 Comprehensive evaluation A film with high light transmittance in the ultraviolet region, good transparency in the visible region, and good workability is ◎, a film with no practical problems is ○, a film with low light transmittance in the ultraviolet region, Is it less transparent?
Films whose workability was so significantly inferior that they could not be used were evaluated as ×. In the following examples, "parts" refer to parts by weight. Example 1 [Production of crosslinked polymer fine powder] 29.3 parts of methyl methacrylate, divinylbenzene
A homogeneous solution of 40 parts of ethylvinylbenzene, 30.7 parts of ethylvinylbenzene, 1 part of benzoyl peroxide, and 100 parts of toluene was dispersed in 600 parts of water. Next, polymerization was carried out by heating at 80° C. for 6 hours with stirring under a nitrogen atmosphere. The average particle size of the obtained polymer particles having ester groups and a degree of crosslinking of 40% is 0.1
It was warm in mm. The resulting polymer was washed with demineralized water and extracted twice with 500 parts of toluene to remove a small amount of unreacted monomer and linear polymer. Next, the polymer granules were coarsely pulverized with a hammer mill and further pulverized with a sand grinder for 5 hours to obtain crosslinked polymer fine powder with an average particle size of 0.6 μm. [Method for producing polyester film] 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.09 parts of calcium acetate hydrate were placed in a reactor, and a transesterification reaction was carried out. The reaction temperature started at 160°C at the beginning of the reaction, was increased to 200°C after 2 hours, and was increased to 230°C after another 2 hours. After the transesterification reaction was completed, an ethylene glycol slurry containing 0.063 part of phosphoric acid and 0.2 part of crosslinked polymer fine powder and 0.04 part of antimony trioxide were added to carry out a polycondensation reaction according to a conventional method. That is, the reaction temperature was gradually raised from 230°C and finally reached 280°C. On the other hand, the reaction pressure was gradually reduced from normal pressure to 0.5 mmHg. After 4 hours, the reaction was stopped and the pressure in the system was restored, and the intrinsic viscosity of the polymer was 0.66. Next, 20 parts of polyester chips containing 0.2 parts of the crosslinked polymer fine powder and 80 parts of separately prepared highly transparent polyester chips containing no particles were dry blended, and after vacuum drying at 165°C for 6 hours,
After melting at ℃ and extruding it through a T-die and quenching it, it was stretched 3.5 times in the machine direction and 3.7 times in the transverse direction.
A biaxially stretched oriented film with a thickness of 75 μm was obtained by heat treatment at 230° C. for 10 seconds. The crystallinity of this film is
It was 53%. The film was evaluated for surface roughness, transparency, workability, image quality, etc. The results are shown in Table 1. Furthermore, a photosensitive solution prepared by a conventional method (for example, the method described in Japanese Patent Publication No. 44-8402) was applied to the heat-treated biaxially stretched film obtained in this example, and
Created microfilm. The film was placed in contact with a transparency of reduced photographic film and exposed to light using a mercury arc lamp. The images were then exposed to ammonia and developed, magnified 48 times using a projector, and the resulting image quality was visually evaluated. As a result, the image had clear contrast between black and white, no minute black spots caused by the base film were observed, and the entire screen was extremely bright, making it suitable for use with microfilm. Examples 2 and 3 An example in which the amount of polymer fine powder added in Example 1 was changed is shown in Example 2, and an example in which both the particle size and the amount added are changed is shown in Table 1 as Example 3. Indicated. Examples 4 and 5 Similar synthesis reactions and pulverization operations were carried out in Example 1, except that the charging conditions were changed to 46.9 parts of methyl methacrylate, 30 parts of divinylbenzene, and 23.1 parts of ethylvinylbenzene in the production of crosslinked polymer fine powder. did. Finally, crosslinked polymer fine powder with a degree of crosslinking of 30% and an average particle size of 0.7μ was obtained. A polyester chip was prepared using this fine powder in the same manner as in Example 1, and the fine powder was added to the film in an amount of 0.03% by weight.
A 75μ film containing 0.02% by weight was prepared. The crystallinity was 52%. The evaluation results for this film are shown in Table 1. Comparative Example 1 A polyester chip was produced in the same manner as in the production of polyester chips in Example 1 by adding 0.2 parts of amorphous silica having an average particle size of 1.5 μm to 100 parts of polyester. 10 parts of the amorphous silica-containing polyester was dry-blended with 90 parts of a highly transparent polyester containing no particles, and the mixture was extruded and stretched and heat-set in the same manner as in Example 1 to obtain a 75μ film. The evaluation results for this film are shown in Table 1. As is clear from the examples in Table 1, films made using the crosslinked polymer fine powder of the present invention and having a surface roughness within the range specified by the present invention are less likely to be scratched during the manufacturing process. In addition, the film has excellent workability with almost no occurrence of bulge-like surface defects when wound up into a roll, and has excellent transparency as expressed by light transmittance and film haze. On the other hand, the film shown in Comparative Example 1 is well within the desirable range in terms of surface roughness, has a slightly high coefficient of friction, and is inferior in workability, but the results of instrumental measurements indicate that it has excellent transparency. Become. However, when the surface of the film was visually observed, a kind of uneven marbling phenomenon appeared on the surface, and image quality evaluation showed that the image lacked sharpness and could not be put to practical use as a microfilm. On the other hand, if the amount of particles is further reduced, workability will be hindered, so if such particles are used, they cannot be used in the field of optical applications. 【table】

Claims (1)

[Scope of Claims] 1. A roughened polyester film obtained by adding crosslinked polymer fine powder having a functional group and having an average particle size of 0.1 to 2μ to polyester, which shows the surface roughness of the film. N ₁ and ₁ are the following formulas: 5≦N ₁ ≦29 (i) 0.025≦ ₁ ≦0.070 (ii) [N ₁ : Number of surface protrusions per 1 mm (pieces/mm) ₁ : Average protrusion height of surface protrusions ( μm)] and has a light transmittance of 76% or more at 380 nm and a light transmittance of 78% or more at 400 nm.