JPH06123936A - Production of photographic thermoplastic resin composition - Google Patents

Abstract

PURPOSE:To produce a photographic thermoplastic resin composition reduced in microgrid by using a titanium dioxide pigment having a particle size below a prescribed range of particle size measured by the impactor method. CONSTITUTION:In a producing method for the photographic thermoplastic resin composition made of at least a thermoplastic resin and the titanium dioxide pigment, a titanium dioxide having <=1.5mum50%weigh cumulative diameter d50 and <=6mum90%weight cumulative diameter d90 in particle size distribution analysis by the impactor method is used. If the titanium dioxide pigment only has <=1.5mum d50 and <=6mum d90 obtained by measuring by the impactor method, any of rutile type and anatase type may be used as the crystal structure. Also any of a chlorine method and a sulfuric method may be also used.

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 photographic thermoplastic resin composition, and more particularly to a microgrit by providing titanium dioxide suitable for producing the resin composition in a stable manner. The present invention relates to a method for producing a photographic thermoplastic resin plastic material having a very small amount.

[0002]

2. Description of the Related Art It is known that the generation of microgrit on a resin-coated paper as a photographic support causes serious photographic problems, and an image having a resin-coated paper with microgrit as a photographic support is printed. When a person is copied on paper, microgrit will appear on the face and other parts, and the commercial value of the microgrid will be completely lost. Japanese Patent Fair 1-3829
In No. 3, it is necessary to achieve a specially defined resin pressure of less than 20 kg / cm ^{2 in} order to obtain a photographic thermoplastic resin composition having little or very little microgrit causing such serious damage. Shows.

By the way, the titanium dioxide pigment used for producing the photographic thermoplastic resin composition is generally provided according to the following process. First, in accordance with a conventional method, the surface of titanium dioxide is treated with an inorganic surface treatment agent such as aluminum oxide hydroxide, silicon oxide hydroxide, titanium oxide hydroxide, zirconium oxide hydroxide, zinc hydroxide, magnesium hydroxide, manganese compound, and phosphoric acid compound, especially a hydroxylated compound. About 0.1 to 2 wt% of aluminum or / and hydrous silicon oxide is coated.
It is generally said that the purpose of such coating treatment is to improve the light resistance of the titanium dioxide pigment and to improve the dispersibility of the titanium dioxide pigment in the resin. The titanium dioxide used may have a rutile structure or an anatase structure.

As the method for producing titanium dioxide, either the chlorine method or the sulfuric acid method can be used. As the method of surface treatment, for example, in the case of treatment with hydrous aluminum hydroxide, an aluminate such as alkali aluminate is used as a water-soluble aluminum salt in the titanium dioxide slurry, and further, for example, sodium hydroxide. ,
After adding a water-soluble alkali such as potassium hydroxide, a pH value of 6 to 8 is added to a slurry exhibiting alkalinity, and a strong acid such as sulfuric acid or hydrochloric acid or a salt exhibiting acidity is added in order to precipitate hydrous aluminum hydroxide. Surface treatment. The slurry after the surface treatment contains soluble salts and other soluble impurities by-produced during the surface treatment reaction. When such salts and impurities are brought into the next step or later, they are re-precipitated in the drying step to cause agglomeration of particles, or when they are brought into the photographic thermoplastic resin composition as a product, serious fogging or the like occurs. It may cause serious photographic problems. Therefore, cleaning and filtration are usually performed using a filtration machine such as a filter press. The cake obtained after filtration is dried using a band dryer, a flash dryer, and a fluid dryer, and further subjected to finish grinding using an impact grinder and / or a fluid energy grinder.

The titanium dioxide pigment powder obtained by such a method usually has a primary particle size of 0.15 to 0.3.
Although it is μm, generally, in the dry powder state, secondary agglomerates are formed by the cohesive force and adhesive force at various stages. The causes of secondary agglomeration include van der Waals attractive force, adhesive force due to surface moisture, electrostatic force, binding force due to surface-treated material, binding force between titanium dioxide, etc. There are weak ones that are in point contact with each other, and strong ones that are connected by face to face.

When a titanium dioxide pigment powder containing such secondary agglomeration is used in a thermoplastic resin composition for photography, the state of the secondary agglomeration of the powder, together with the surface treatment conditions of titanium dioxide, results in the dispersion of titanium dioxide in the resin. It is known to affect the degree. That is, when the secondary aggregation is intense,
In the process of kneading the pigment with the thermoplastic resin, such agglomeration does not sufficiently disentangle and remains in the thermoplastic resin composition, resulting in a high resin pressure and an increase in microgrit. The following methods are known as methods for measuring the degree of secondary aggregation of such pigments. (A) Measurement of sieve residue according to JIS K5101.22 (b) Particle size measurement by wet or dry method (c) Particle size distribution measurement by air jet sieve (developed by Alpine GmbH, Germany) (d) Particle size observation of aggregated state by microscope

[0007]

SUMMARY OF THE INVENTION In the conventional method as described above for evaluating the degree of secondary agglomeration, the quality control of the titanium dioxide pigment used in the production of the photographic thermoplastic resin composition which requires strict characteristics is required. There are many problems in evaluation. First, in the above-mentioned JIS sieve residue measurement or wet particle size distribution measurement, although the main purpose is to evaluate the agglomeration state in the dry powder state in the first place, in the state wet with a medium such as water This is a measurement, and the affinity with a solvent such as water greatly affects the degree of aggregation. However, in producing a thermoplastic resin composition for photography, the medium of titanium dioxide is a thermoplastic resin, and there is a problem with a material having a low affinity with water, and it is difficult to know the dispersion state in the thermoplastic resin. I can't.

Further, there are the following problems. That is, when a titanium dioxide pigment treated with an organic treatment such as an organopolysiloxane having a low affinity for water is produced, almost all the samples float up even if an attempt is made by these methods. The result will not be evaluated. or,
The screen residue measurement method has a problem that the objectivity of the data is poor because it is a method in which the sample on the sieve is dropped by a brush, which is very likely to vary among individuals.

Next, there are the following problems in the dry particle size measurement (for example, the dry sieving method of a low tap sieve) and the jet sieve. That is, these are excellent in that they can be measured in a dry powder state. However, if a powder such as titanium dioxide that is fine and highly cohesive is to be evaluated by such a method, there is a problem that the sieve is clogged in a very short time and the measurement cannot be performed midway.
In addition, there is a problem that the titanium dioxide pigment, which is a sample, agglomerates by the measurement itself due to vibration such as in a low tap, swirling motion, or flow due to a swirling air flow such as in a jet sheave, which makes it impossible to know what is being measured. There is. Next, in the case of microscopy, the handling method at the stage of making the observation sample may affect the aggregation state, and it is difficult to judge whether it is the result representative of the whole because the observation field of view is very limited. However, there is a problem that it is easy to make an individual difference in determining whether or not it is an aggregate in quantitative evaluation.

Due to these problems, it has hitherto been impossible to quantitatively and practically evaluate the secondary aggregation state of the titanium dioxide pigment used in the production of the photographic thermoplastic resin composition. Therefore, when trying to use a titanium dioxide pigment in a photographic thermoplastic resin composition, it is not possible to evaluate the secondary aggregation state of the pigment, which is an important index in judging whether the pigment is suitable in advance, Therefore, there is no choice but to rely on a means of determining suitability by kneading a part of the titanium dioxide pigment with the resin actually used.

[0011]

The inventor has made diligent efforts to solve the above problems, and as a result of various studies, a method for producing a thermoplastic resin composition for photography comprising at least a thermoplastic resin and a titanium dioxide pigment. At 50% weight cumulative diameter d in particle size distribution measurement by impactor method
_{The present} inventors have found a method for producing a thermoplastic resin composition for photography, which is characterized by using a titanium dioxide powder having a ₅₀ of 1.5 μm or less and a 90% weight cumulative diameter d ₉₀ of 6 μm or less.

As a result, an appropriate value of "resin pressure" at the time of extrusion molding in producing a specially defined resin composition described below,
It can be 20 kg / cm ² or less, and therefore a photographic thermoplastic resin composition having very little microgrit can be obtained. The specially defined "resin pressure" as described herein is also described in Japanese Patent Publication No. 1-38293. In an extruder, a barrel having an inner diameter of 20 mm and a length of 420 mm,
Pitch 20 mm, flight top width 3.1 mm, groove depth 3.9 mm, 8 pitch feed zone, linear inclination, 8
Pitch pressure zone, groove depth 1.6 mm, screw consisting of 5 pitch metering zone, and breaker plate and strand die with resin protrusion 3 mm in diameter and 20 mm in length. Heating control consists of 4 zones. In the extruder, set the temperature of the extruder to 180 ° C, 180 ° C, 180 ° C, 180 ° C from the resin supply side, and
Thermoplastic resin containing titanium dioxide is supplied to the resin supply port (hopper) on the extruder when the temperature of the entire zone reaches 180 ° C.
And melt-extrude at a screw rotation speed of 100 rpm. Next, set the temperature values in the 4 zones from the hopper side to 200 ° C, 25
The temperature is set to 0 ° C, 320 ° C, and 320 ° C. When all the temperature values in the 4 zones have reached the set values, the 100 mesh screen and 325 mesh screen made of stainless steel are sequentially attached to the breaker plate, and the screw rotation speed of the extruder is lowered to the minimum value, and then the 325 mesh screen is screwed. It is installed in the extruder so that it faces the. Then, the screw rotation is increased to 60 rpm, and 500 g of the thermoplastic resin in the hopper is melt-extruded. At this time, the resin pressure in the stable region which became stable with time is set to Akg / cm ² .

Next, a thermoplastic resin composition containing a titanium dioxide pigment having a predetermined concentration in each production is sampled so as to have a titanium dioxide pigment content of 750 g, which is put in a hopper and melt-extruded. The value of the maximum resin pressure at the time when 750 g of a thermoplastic resin composition as titanium dioxide pigment powder has finished passing through the extruder outlet is Bkg / cm.
^Set to ² . Here, B-Akg / cm ² is defined as the resin pressure of the thermoplastic resin composition. Further, the above-mentioned micro grit is a photographic resin-coated paper in which at least one surface of a paper or synthetic paper substrate is coated with a resin composition, and a minute foreign substance appearing on the surface of the coated resin or Refers to minute particles.

Further, the impactor method in the present invention will be described. A schematic diagram of the apparatus used for this is shown in FIG.
The particle size measuring method by the impactor method and the apparatus therefor will be described in detail with reference to FIG. The apparatus consists of two parts, a disperser part shown on the right side of FIG. 1 and a cascade impactor part on the left side. First, the disperser will be described. Quantitative paper 1 (JIS
It has a cylindrical container 2 (30 mm below the paper and 85 mm above the paper) with an inner diameter of 26 mmφ in which 5 types C and a hole diameter of 1 μm are set, and at a position 100 mm higher than the paper surface (from the upper surface of the cylindrical container 2). 15 mm) and the tip of the introduction tube 3 having an inner diameter of 4 mmφ is located at the center. 3 g of the sample to be measured was placed on one surface of the paper of this disperser, and air from the cylinder was supplied from the lower port 4 at a flow rate of 3 liter / min to form a fluidized bed of the sample, and the introduction tube The sample powder dispersed in the upper part 5 of the cascade impactor is introduced through 3.

Further, the disperser body is vibrated at a frequency of 60 Hz and an acceleration of 3 G to promote better dispersion. Next, the device portion on the cascade impactor side will be described. It has a conical introduction part 6 to which the introduction pipe 3 on the disperser side is connected,
Nine sets of a plate 7 having a nozzle outlet 9 and a collision plate 8 are provided in a cylinder having a cylinder inner diameter of 92 mmφ and a straight body portion height of 250 mm. The nozzle diameter of the plate having the nozzle outlets of each of the nine stages and the number thereof are 2.71 mmφ × 400 from the top,
1.2 mmφ x 800 pieces, 1.2 mmφ x 400 pieces,
0.9mmφ x 400 pieces, 0.7mmφ x 400 pieces,
0.5 mmφ x 400 pieces, 0.35 mmφ x 400 pieces,
0.25 mmφ x 400 and 0.25 mmφ x 20
It is 0. All nine sets of the plate 7 having the nozzle outlet 9 and the collision plate 8 are 82.4 mmφ in size, and the collision plate 8 located below the collision plate 8 at 1 mm intervals.

The powder having a particle size equal to or larger than the corresponding particle size is collected through the nozzle outlets of the respective stages and immediately below the respective collision plates 8. However, the air containing the powder which is not collected and has a particle size smaller than the corresponding particle size collides. It passes through a doughnut-shaped groove on the outside of the plate 8 and reaches the next nozzle outlet 9. The flow of air containing the measurement sample powder is carried out by the blower (or compressor) 10 at a flow rate of 28.3 l / min in a suction state.

Under the above-mentioned conditions, the nine classification plates 8 functioning as collecting plates, the smallest classified particle sizes collected respectively from the top are 12.5, 5.5, and
3.5, 2.35, 1.65, 1.05, 0.55,
0.325 and 0.215 μm. A cumulative weight distribution curve is obtained from the classified particle diameter value and the powder weight collected on each collision plate 8 in the measurement time of 15 minutes, and then 50% is obtained.
The values of the weight cumulative diameter d ₅₀ and the 90% weight cumulative diameter d ₉₀ will be determined.

Conditions other than the above, such as the conditions involved in the particle size measurement method by the impactor method, are the Andersen non-barble sampler MODEL AN- manufactured by Tokyo Direc Co., Ltd.
It is equivalent to 200. The backup filter at the bottom of the cascade impactor has a pore size of 0.
1 μm paper was used.

The titanium dioxide pigment of the present invention has a d ₅₀ of 1.5 μm or less measured by the above-mentioned impactor method,
If d ₉₀ is 6 μm or less, the crystal structure may be either rutile type or anatase type. Also, any of the chlorine method and the sulfuric acid method can be used. In the case of the chlorine method, titanium dioxide particles are generally formed by gas phase oxidative decomposition of titanium tetrachloride at a high temperature, and a rutile structure is generally easily obtained. In the case of the sulfuric acid method, hydrous titanium dioxide is formed by hydrolysis of an aqueous solution of titanyl sulfate and is fired to develop its pigmentary properties. In the case of the sulfuric acid method, those with anatase structure also
Although a rutile structure can be obtained, in the case of producing a rutile structure, a firing temperature is higher than that of an anatase structure, and a temperature for promoting the formation of a rutile structure during firing. A metal compound such as a zinc compound is allowed to coexist.

The product produced by calcination or oxidation is hereinafter referred to as titanium dioxide clinker. Titanium dioxide clinker is dry pulverized by a centrifugal roller mill (mainly Raymond mill), and the pulverized product is suspended in water to form a titanium dioxide slurry, which is further wet pulverized by a ball mill, a vibration mill, a sand grinder or the like. Use a continuous horizontal centrifuge and / or vibrating double deck screen (325 mesh U.S.P.
S. Wet classification is performed by passing through a standard screen).
A titanium dioxide slurry, hereinafter referred to as fines, which is substantially free of coarse-grained titanium dioxide, is prepared. For fines that are still in slurry form with coarse particles removed, aluminum hydroxide, silicon hydroxide,
The surface of the titanium dioxide particles is surface-treated with an inorganic surface treating agent such as hydrous titanium oxide, particularly preferably aluminum hydrous oxide, in a reaction treatment tank equipped with a stirrer. After the reaction treatment,
It is produced by filtering with a filter press, drying with a band drier, and usually finish crushing with an impact crusher or fluid energy crusher. In the case of a titanium dioxide pigment, the state of secondary agglomeration varies greatly depending on such a surface treatment method, a drying and crushing method, and a storage state after the bag is packed as a product.

In the present invention, as a method for evaluating the degree of secondary agglomeration of titanium dioxide pigment, particle size distribution measurement by impactor method is used for evaluation, and d ₅₀ is 1.5 μm or less and d
_An excellent photographic thermoplastic resin composition can be produced by using a titanium dioxide pigment having ₉₀ of 6 μm or less.

The resin used in the present invention is a homopolymer or copolymer of polyolefin, polystyrene, polyvinyl chloride, polyacrylic acid ester, linear polyethylene such as polyethylene terephthalate, polycarbonate, polyamide such as nylon, polyacrylonitrile and the like. , Ethylene-vinyl acetate copolymer and any of them as long as it is possible to coat a resin film on a base paper such as a mixture thereof, particularly, a thermoplastic resin such as polyolefin, polystyrene, polyethylene terephthalate, or polyvinyl chloride is preferable, and among them, Polyolefin resin is particularly advantageous in terms of extrusion coating property, good adhesion to base paper, cost and the like. The polyolefin resin in the present invention means a homopolymer such as low density polyethylene, high density polyethylene, polypropylene, polybutene, polypentene or ethylene-
A copolymer comprising two or more olefins such as a propylene copolymer and a mixture thereof, each having various densities and melt viscosity indexes (melt indexes: simply abbreviated as MI hereinafter) alone or by mixing them. Can be used.

If the amount of the titanium dioxide pigment in the photographic thermoplastic resin composition of the present invention is less than 5% by weight as the content of the titanium dioxide pigment contained in the resin layer of the photographic resin-coated paper, the photographic support is supported. As a body, the hiding power is insufficient. On the other hand, when it exceeds 40% by weight, the fluidity is deteriorated, which is not preferable. Therefore, it is preferably 5 to 40% by weight, particularly preferably 7.5 to 25% by weight. . A fatty acid metal salt may be included in the photographic thermoplastic resin composition of the present invention. Examples of these fatty acid metal salts include zinc stearate, calcium stearate, aluminum stearate, magnesium stearate, zirconium octylate, sodium palmitate, calcium palmitate, sodium laurate and the like. Further, the addition amount thereof is 0.01 wt% to 5 wt% with respect to the resin composition containing titanium dioxide.
The range of is desirable.

In addition to the titanium dioxide pigment and, if necessary, a fatty acid metal salt, a white pigment such as zinc oxide, talc and calcium carbonate, stearic acid amide, Fatty acid amides such as alkyd acid amides, tetrakis (methylene-3-
Antioxidants such as (3,5-di-tert-butyl-4-hydroxy-phenyl) propionate) methane, 2,6-di-tert-butyl-4-methylphenol, cobalt blue, dark blue, ultramarine blue, cobalt violet You may add coloring pigments, such as, and a fluorescent whitening agent.

The photographic resin coated paper coated with the photographic thermoplastic resin composition of the present invention comprises a heat-melted titanium dioxide pigment on a normally running paper or synthetic paper substrate (hereinafter simply referred to as base paper). The resin composition is produced by melt extrusion coating on a film from a slit die. If the resin is a polyolefin resin, the melt extrusion temperature is 200 ° C
It is preferably from to 350 ° C. In addition, before applying the resin composition to the base paper, it is preferable to subject the base paper to activation treatment such as corona discharge treatment or flame treatment. The thickness of the treated layer of the resin-coated paper is not particularly limited, but it is generally advantageous to use extrusion coating to a thickness of about 5 to 50 microns. Further, in a normal resin-coated paper in which the surface of the base paper is coated with a resin, the resin surface containing the titanium dioxide pigment has a glossy surface, a matte surface, a silky surface, etc. depending on the application, and the opposite side. The back surface of is usually a matte surface, and the front surface or both of the front and back surfaces can be subjected to activation treatment such as corona discharge treatment if necessary.

The base paper used in the practice of the present invention may be ordinary natural pulp paper, synthetic fibers, or so-called synthetic paper obtained by quasi-synthesizing synthetic resin film, but softwood pulp, hardwood pulp, softwood hardwood. Natural pulp paper based on wood pulp of mixed pulp is advantageously used. The thickness of the base paper is not particularly limited, but base paper having a good surface smoothness is preferable, and the basis weight is 50 g /
m ² is preferred. The base paper containing natural pulp as a main component advantageously used in the practice of the present invention includes various polymer compounds,
Additives can be included. For example, as a dry paper strengthening agent, cationized starch, cationized polyacrylamide, anionized polyacrylamide, carboxy-modified polyvinyl alcohol, gelatin and the like, and as a sizing agent, fatty acid salt, rosin derivative, dialkylketene dimer emulsion, petroleum resin emulsion Ammonium salts of styrene-maleic anhydride copolymer alkyl ester,
As a pigment, clay, kaolin, calcium carbonate, barium sulfate, titanium oxide, etc., as a wet paper strength enhancer, melamine resin, urea resin, epoxidized polyamide resin, as a fixing agent, a polyvalent metal salt such as aluminum sulfate, aluminum chloride, etc. , Cation-modified polymers such as cationized starch, pH adjusting agents such as caustic soda, sodium carbonate, hydrochloric acid, etc., inorganic electrolytes such as salt, sodium sulfate, etc., other dyes,
An optical brightener, a latex and the like can be contained in an appropriate combination.

Various silver halide emulsion layers can be provided in the photographic resin-coated paper in which the photographic thermoplastic resin composition of the present invention is used. Further, the silver halide emulsion layer may contain a color coupler to provide a multilayer silver halide emulsion layer. As the binder for these emulsion layers, in addition to ordinary gelatin, hydrophilic polymer substances such as polyvinyl hydridone, polyvinyl alcohol, and sulfate ester compounds of polysaccharides can be used. Further, the silver halide emulsion layer may contain various additives. For example, as sensitizing dyes, cyanine dyes, merocyanine dyes, etc., as chemical sensitizers, water-soluble gold compounds, sulfur compounds, etc., hydroxy-triazolopyrimidine compounds as antifoggants or stabilizers, mercapto-heterocyclic compounds, etc., As a hardener, formalin, vinyl sulfone compound, aziridine compound, etc., coating aid, benzene sulfonate, sulfosuccinate salt, etc., antifouling agent, dialkylhydroquinone compound, etc., development accelerator, hydroquinone, phenidone, etc. , As a UV absorber, a benzotriazole compound or the like, other fluorescent whitening agent, a sharpness improving dye, an antistatic agent, a pH adjusting agent, and a water-soluble iridium compound, a water-soluble rhodium compound, etc. when the silver halide is produced and dispersed Can be included in combination That. Further, on the back surface of the photographic resin-coated paper using the photographic thermoplastic resin composition of the present invention, that is, on the side of the support opposite to the side on which the photographic constituent layer, mostly a silver halide photographic constituent layer, is applied. A coating layer composed of a hydrophilic colloid layer called a pack coat layer can be provided on the top for the purpose of preventing curling, preventing electrification, preventing sticking, preventing slipping and the like. The pack coat layer may contain a binder or protective colloid, a curing agent, an antistatic agent, a surfactant, a matting agent, latex and the like.

[0028]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. Examples 1 to 3 and Comparative Examples 1 to 5 Titanium dioxide (rutile titanium dioxide “Super Titania G” manufactured by Showa Titanium Co., Ltd. (average particle size 0.2 μm)
m)) was added to a titanium dioxide aqueous slurry containing 10% by weight, and 0.8% of alumina was added to the titanium dioxide.
An aqueous solution of sodium aluminate (concentration of 20% by weight in terms of alumina) corresponding to weight% was added. Since this slurry exhibits alkalinity, 5% by weight dilute sulfuric acid was added to adjust the pH to 7.0, and it was aged for 3 hours to coat the titanium dioxide surface with hydrous aluminum oxide. The slurry after the surface treatment was filtered with a filter press, and subsequently the titanium dioxide cake in the filter press was washed with pure water. Next, with respect to the cake after the washing, a vacuum stirring dryer (AV-10 manufactured by Nippon Dryer Co., Ltd.), a vibration fluidized dryer (VU-30 manufactured by Chuo Kakoki Co., Ltd.), an indirect heating stirring dryer. (Nara Machinery PD-3W), spray dryer (SDR-3 manufactured by Tokyo Rika Co., Ltd.), tray dryer (SHKS-2 manufactured by Peng Seisakusho Co., Ltd.), CD dryer (CD-901 manufactured by Nishimura Steel Co., Ltd.), The cake was dried at a cake temperature of 110 ° C. using an instantaneous vacuum dryer (Cracks system manufactured by Hosokawa Micron Co., Ltd.) and a medium fluidized dryer (MSD manufactured by Nara Machine Co., Ltd.).

Each dry powder was heated to 250 with a steam mill.
After crushing at ℃, the particle size was evaluated by the above-mentioned impactor, and d ₅₀ and d ₉₀ were calculated. The values of the respective samples are shown in Table 1. Next, 50 parts by weight of the titanium dioxide powder thus obtained and 50 parts by weight of low-density polyethylene (“SHOREX L-170” manufactured by Showa Denko KK),
In addition, 2 parts by weight of zinc stearate were dry mixed in a Henschel mixer for 5 minutes. This dry mixture is quantitatively supplied to a continuous kneading extruder with a screw type quantitative feeder,
A masterbatch was produced at a kneading temperature of 150 ° C. The screw diameter of the feed section of the continuous kneading extruder used is 80 m.
mφ, screw diameter of metering part is 35 mmφ, number of kneading parts is 6 sets (6 rotating disks), rotating disk diameter is 98.5 mm
φ, kneading section cylinder inner diameter 101.5 mmφ was used. Further, the rotary disc of the kneading section is fan-shaped, fan-shaped, chrysanthemum-shaped, chrysanthemum-milled, millet-milled, from the feed section.
A mortar-vent screw rotating disc was attached. The fixed disk facing the rotating disk was a fixed disk having the same pattern as the rotating disk.

Using the masterbatch thus obtained, the resin pressure as defined in the present invention was measured.
The resin pressure A of the resin containing no titanium dioxide is 1
It was 3.5 kg / cm ² . Table 1 shows the resin pressure B-A of the thermoplastic resin composition defined in the present invention.

Next, a hardwood bleached kraft pulp 50 is further added.
50 parts by weight of softwood bleached sulfite pulp with 50 parts by weight of Canadian Standard Freeness 31
The mixture was beaten to 0 ml, and further, with respect to 100 parts by weight of pulp, 3 parts by weight of cationized starch, 0.2 part by weight of anionized polyacrylamide, 0.4 part by weight of emulsion of alkyl ketene dimer (as ketene dimer content), polyaminopolyamide epichlorohydrin. 0.4 part by weight of resin was added to produce paper having a basis weight of 160 g / cm ² . The obtained wet paper is 11
After drying at 0 ° C., an impregnating liquid consisting of 3 parts by weight of carboxy-modified polyvinyl alcohol, 0.05 part by weight of optical brightener, 0.002 part by weight of blue dye, 0.2 part by weight of citric acid and 97 parts by weight of water was added. Impregnated with 25g / m ² and 110 ℃
Was dried with hot air and further subjected to supercalendering at a linear pressure of 90 kg / cm to produce a base paper of photographic resin-coated paper.

Next, after corona discharge treatment was applied to the back surface of the base paper, high density polyethylene (density 0.96 g / cm ³ , M
I = 5) and low density polyethylene (density 0.92 g / cm
³ , 1: 1 mixture of MI = 5) was coated at a resin temperature of 320 ° C. to a thickness of 30 μm using a melt extrusion coating machine. Then, after corona discharge treatment on the surface of the base paper, a mixture comprising 30 parts by weight of the titanium dioxide pigment master batch, 30 parts by weight of high density polyethylene (MI = 5) and 40 parts by weight of low density polyethylene (MI = 5). The above resin composition was coated at a resin temperature of 320 ° C. to a thickness of 30 μm to produce polyethylene resin compositions containing titanium dioxide pigment. At that time, the surface of polyethylene containing the titanium dioxide pigment was processed into a completely flat glossy surface, and the image quality of the back polyethylene was processed into a matte surface such as paper.
The number of microgrit appearing on the surface of the polyethylene resin-coated paper containing the thermoplastic resin composition for photography thus obtained was counted with the naked eye. Table 1 shows the number of microgrits in each case.

[0033]

[Table 1]

As can be seen from the results in Table 1, d ₅₀ is 1.5.
As long as it is less than μm and d ₉₀ is less than 6 μm, B−A
The value of resin pressure defined in is less than 20 kg / cm ² ,
As a result, the number of microgrits is extremely reduced. However, since the optimum conditions for each type of dryer have not been thoroughly investigated, it cannot be generally said that the number of microgrits will decrease or increase depending on the type of dryer.

Example 4 and Comparative Examples 6 to 7 The same photographic thermoplastic resin as in Example 1 was prepared by drying the titanium dioxide cake in a medium fluidized dryer and then changing the mill used for crushing. A composition was produced. As the type of mill, a jet mill (AFG200 manufactured by Alpine), a centrifugal flow mill (CF400 manufactured by Ube Industries, Ltd.), and an impact mill (atomizer manufactured by Fuji Paudal Co., Ltd.) were used. Table 2 shows the results of particle size measurement with an impactor after crushing and the resin pressure and the number of microgrit of the thermoplastic resin composition for photography.
Note.

[0036]

[Table 2]

[0037]

INDUSTRIAL APPLICABILITY By using a titanium dioxide pigment whose d ₅₀ and d ₉₀ measured by an impactor method are not more than the specified ranges as in the present invention, a thermoplastic thermoplastic photographic resin composition having a very small amount of microgrit Can be built.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for particle size distribution measurement by an impactor method.

[Explanation of symbols]

 1 bronze paper 2 cylindrical container in disperser 3 introduction pipe 4 lower port for air introduction 5 upper part of cascade impactor 6 conical introduction part of cascade impactor 7 plate with nozzle outlet 8 collision plate 9 nozzle outlet 10 blower (or Compressor) 11 Exciter 12 Flow meter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaru Kubota, 3-4-2 Marunouchi, Chiyoda-ku, Tokyo Sanryo Paper Co., Ltd. (72) Tohru Noda 3-4-2, 3-4 Marunouchi, Chiyoda-ku, Tokyo Ryo Paper Co., Ltd.

Claims (1)

[Claims] 1. A method for producing a photographic thermoplastic resin composition comprising at least a thermoplastic resin and a titanium dioxide pigment, wherein 5 in particle size distribution measurement by an impactor method is used.
A process for producing a photographic thermoplastic resin composition, which comprises using a titanium dioxide powder having a 0% weight cumulative diameter of 1.5 μm or less and a 90% weight cumulative diameter of 6 μm or less.