JPH0816773B2 - Support for photographic paper - Google Patents

Description

The present invention relates to a support for photographic printing paper, and more specifically, it is a photographic printing suitable for producing photographic printing paper excellent in photographic sharpness. The present invention relates to a paper support.

[Conventional technology]

In recent years, with the speeding up of photographic development processing, a water-resistant photographic printing paper support in which both sides of a base paper are coated with a polyolefin resin has come to be used instead of the conventionally used baryta paper.

The properties required for a photographic paper support are excellent in dimensional stability, moisture resistance, adhesiveness, hiding power, etc.,
Also, it may not adversely affect the photographic emulsion layer.

In particular, the hiding power (light scattering property) of the surface side coating layer (hereinafter referred to as the surface coating layer) of the sheet-like substrate has a great influence on the photographic sharpness of the photographic paper obtained from the photographic paper support. . In general, a resin composition used for forming a surface coating layer contains titanium dioxide as a high refractive index pigment in order to enhance the hiding power. However, in the conventional technology,
Since the titanium dioxide pigment was not evenly dispersed in the polyolefin resin, sufficient hiding power could not be obtained, or pigment aggregates (grit) were generated and a satisfactory surface coating layer could not be obtained. . Further, if the content of the titanium dioxide pigment is increased in order to obtain sufficient hiding power, the cost becomes high, or such a polyolefin resin composition is melt extruded from a slit die into a film to form a coating layer. In this case, needle-like or icicle-like deposits or stains (hereinafter referred to as die lip stains) tend to occur on the tips of the die lip after a short time extrusion. Tends to grow big.

When this die lip stain occurs during melt extrusion coating of the polyolefin resin composition, a photographic printing paper support produced without removing it has vertical stripes on its surface, or At times, the dirt adheres to the film, resulting in the inclusion of foreign matter. The photographic printing paper support manufactured in such a state has a significantly impaired image quality, and thus has no commercial value as a photographic printing paper support requiring excellent image quality. There was a point.

[Problems to be Solved by the Invention]

The present invention improves the above problems of the prior art, namely, the poor dispersion of the titanium dioxide pigment contained in the polyolefin resin composition used for the surface coating layer, and provides a photographic printing paper excellent in photographic sharpness. It is intended to provide a photographic paper support suitable for manufacturing.

[Means and actions for solving the problems]

The support for photographic printing paper of the present invention comprises a sheet-like substrate, a front surface (a surface on which a photographic emulsion is applied) side and a back surface (a surface opposite to a photographic emulsion-coated surface) side of the substrate, and a polyolefin resin as a main component And a coating layer comprising a resin composition as a component, the resin composition of the surface side coating layer of the substrate, a polyolefin resin masterbatch containing at least a titanium dioxide pigment, a temperature of 140 ℃, and 5000 1 / A polyolefin resin composition containing a titanium dioxide pigment prepared by diluting and kneading with a polyolefin resin having a melt viscosity of 1.0 × 10 ³ poise or more at a shear rate of 2 seconds.

Here, the melt viscosity at a temperature of 140 ° C. and a shear rate of 5000 1 / sec is a commercially available capillary viscometer (capillary graph manufactured by Toyo Seiki Seisakusho Co., Ltd.), and the length (L) of the capillary is 10 mm and the diameter is (D) is 1 mm
Is the melt viscosity value when measured with

Generally, when producing a polyolefin resin composition for a surface coating layer containing titanium dioxide, a masterbatch having a titanium dioxide content higher than the titanium dioxide content of the composition is prepared, and the masterbatch is used to prepare a titanium dioxide-free polyolefin. It is customary to dilute with resin to a given titanium dioxide content. As a result of earnest research on the dispersibility of the titanium dioxide pigment in the polyolefin resin composition produced by this method, the present inventors have found the following. That is, the dispersibility of the titanium dioxide pigment is greatly affected by the melt viscosity of the diluting resin that dilutes the masterbatch, especially at a temperature of 140 ° C and at low temperatures such as 5000 1 / sec and high shear rates. The larger the value, the better the dispersibility of the titanium dioxide pigment.

The reason for this phenomenon is not fully clear yet, but the following may be considered. Generally, a single-screw or twin-screw extruder is used for diluting a polyolefin resin masterbatch containing a titanium dioxide pigment to a predetermined titanium dioxide content with a diluting resin. In this case, the dilution efficiency is highest in the compression part of the machine, that is, in the low temperature, high shear rate part.
Therefore, it is considered that the polyolefin resin having a high melt viscosity at a low temperature and a high shear rate gives a high stress to the masterbatch and makes the dispersion of the titanium dioxide pigment good. In the prior art, it has been proposed to specify the diluted resin by the melt index (Japanese Patent Laid-Open No. 62-15024).
8) This melt index is a value of 190 ℃, which is remarkably high temperature and low shear rate compared with the compression part of a practical dilution machine, so it does not necessarily match the dilution efficiency of a practical dilution machine.

The support for photographic printing paper of the present invention comprises a sheet-like substrate and front and back side coating layers.

As the sheet-like substrate used in the present invention, base paper made of commonly used pulp such as kraft pulp, sulfite pulp, soda pulp, such as hardwood pulp, softwood pulp, and hardwood mixed softwood pulp can be used. Further, if necessary, base paper produced from synthetic pulp or pulp containing synthetic fibers can also be used.

There is no particular limitation on the type and thickness of the sheet-shaped substrate, but it is preferable that after the sheet-shaped substrate is manufactured, pressure is applied to the sheet-shaped substrate to compress it to improve the surface smoothness, and the basis weight is 50 to 250 g / m ^3, its thickness is 40
It is preferably ˜270 μm.

The base paper used as the sheet-like substrate in the present invention includes various ordinary paper additives such as a dry paper strength enhancer (cationized starch, cationized polyacrylamide, anionic polyacrylamide, etc.), sizing agent (fatty acid salt, rosin). , Maleated rosin, cationized sizing agent, reactive sizing agent, etc.), filler (clay, kaolin, etc.), wet paper strengthening agent (melamine resin, epoxidized polyamide resin, etc.), fixing agent (aluminum sulfate, cationized starch) Etc.), a pH adjusting agent (eg, soda, sodium carbonate, etc.) and the like. Further, the base paper may be tab-sized or size-pressed with a treatment liquid containing one or more kinds of water-soluble polymer additives, sizing agents, inorganic electrolytes, hygroscopic substances, pigments, pH adjusting agents and the like.

The polyolefin resin used as the masterbatch resin and the diluting resin in the present invention is a low-density polyethylene, a medium-density polyethylene, a high-density polyethylene or a linear low-density polyethylene which is a copolymer of ethylene and an α-olefin, and It is a mixture.

The diluting resin used in the present invention has a melt viscosity of 1.0 × 10 at a temperature of 140 ° C. and a shear rate of 5000 1 / sec.
It is a polyolefin resin with ³ or more poise. However, when the melt viscosity is excessively high, melt extrusion coverage is deteriorated, so the melt viscosity under the above conditions is 1.0 × 10 ³ poises or more,
It is preferably 2.0 × 10 ³ poise or less.

The melt viscosity of the polyolefin resin for masterbatch used in the present invention under the above conditions is preferably equal to or less than the melt viscosity of the diluted resin in consideration of the dilution efficiency.

In the present invention, the diluting polyolefin resin satisfying the above requirements may be used in a proportion of 40% by weight or more based on the weight of the polyolefin resin component of the target titanium dioxide pigment-containing resin composition upon dilution. Preferably
This makes the effect particularly remarkable.

In the present invention, the content of the titanium dioxide pigment in the surface coating layer is not particularly limited, but is preferably 5 to 30% by weight. The content of the titanium dioxide pigment in the masterbatch is not particularly limited, but is preferably 40 to 70% by weight. The titanium dioxide pigment may be either of the sulfuric acid method or the chlorine method, and may be of the rutile type or the anatase type, but the anatase type is advantageous in terms of whiteness. It is also possible to use a titanium dioxide pigment which has not been surface-treated, or a titanium dioxide whose surface is treated with an inorganic surface-treating agent such as hydrous aluminum oxide, or an organic surface-treating agent such as organopolysiloxane. It is also possible to use those coated with an agent, further, those coated with a combination of an inorganic surface treatment agent and an organic surface treatment agent as appropriate, but at least 0.2 as Al ₂ O ₃ min.
It is desirable that the aluminum oxide is treated with aluminum hydroxide up to 2.0%.

The resin composition of the surface coating layer used in the present invention may contain a metal salt of fatty acid.

Examples of such metal salts of fatty acids include zinc stearate, calcium stearate, aluminum stearate, magnesium stearate, zirconyl octylate, sodium palmitate, calcium palmitate, sodium laurate and the like.

The amount added is 0.01 to the total amount of the resin composition.
It is preferably in the range of 5% by weight.

Further, in the resin composition of the surface coating layer used in the present invention, in addition to the fatty acid metal salt, further zinc oxide, talc, calcium carbonate, aluminum hydroxide, white pigments such as barium sulfate, stearic acid amide, Fatty acid amides such as arachidic acid amide, tetrakis [methylene-3
(3,5-ditert-butyl-4-hydroxy-phenyl) propionate] methane, antioxidants such as 2,6-di-tert-butyl-4-methylphenol, ultramarine blue, red iron oxide, carbon black, titanium yellow, etc. Color pigments, fibrous substances such as glass, asbestos, whiskers, and fluorescent whitening agents may be contained.

In the present invention, the kneading machine used for the production of the masterbatch may be any of the commonly used melt kneading machines, for example, Banbury mixer, kneader, two rolls, three rolls and single-screw or double-screw. The kneading extruder, etc. are used, but it is particularly advantageous to use a Banbury mixer or a twin-screw kneading extruder.

The polyolefin resin used for the resin coating layer on the back surface side of the support of the present invention is not particularly limited, but generally selected appropriately from high-density polyethylene, medium-density polyethylene, low-density polyethylene, polypropylene and blended products thereof. You can

In the production of the support of the present invention, the sheet-shaped substrate is coated with the polyolefin resin composition by a melt extrusion method, and the melt extrusion temperature at that time is appropriately 200 to 350 ° C., and the slit die used at that time is used. It is preferable to use a flat die such as a T-type die or an L-type die.

Further, it is preferable that the substrate is subjected to activation treatment such as corona discharge treatment or flame treatment before the substrate is coated with the resin composition. The thickness of the resin layer of the resin-coated paper is not particularly limited, but it is generally preferable that the resin layer is extrusion-coated to a thickness of about 5 to 50 microns. In addition, in a usual resin-coated support in which both sides of the substrate are coated with resin,
The surface of the resin layer containing the titanium dioxide pigment has a glossy surface, a matte surface, a silky surface, etc. depending on its application, and the opposite side surface (back surface) is usually a matte surface, and the surface or if necessary. Both front and back sides may be subjected to activation treatment such as corona discharge treatment and flame treatment. In addition, if necessary, a sub-coat for improving the adhesiveness with the photographic emulsion on the surface resin coating layer, or a back coat for improving the printability and antistatic property on the back resin coating layer is applied. You may.

〔Example〕

The present invention is described in detail below with reference to examples. Incidentally, the deterioration of the surface quality of the support due to the photographic sharpness of the photographic printing paper prepared from the support for photographic printing paper prepared in each of the Examples and Comparative Examples, and the occurrence of die lip stains was as follows. evaluated.

1. Photo sharpness of photographic paper The photographic sharpness of photographic paper is as follows:
That is, it is affected by the hiding power of the surface side coating layer of the support for photographic printing paper, and the hiding power depends on the light scattering coefficient when the same coating amount of the surface coating layer is compared. Therefore, the higher the light scattering coefficient of the surface coating layer of the support, the higher the photographic sharpness of the photographic printing paper obtained therefrom. In order to evaluate the photo sharpness of photographic printing paper, the coating amount 30
The light scattering coefficient of the surface side coating layer at g / m ² was calculated.

The resin coating layer was peeled from the support produced by the resin melt extrusion coating method, and the obtained resin film was subjected to the following light scattering test.

Equipment: Hunter whiteness index needle (using blue filter) Measurement method: (i) A white plate having a reflectance Rg was applied to the back of the resin film under test to measure the light reflectance R of the film under test.

(Ii) A black plate having a reflectance of O was applied to the back surface of the test film to measure the reflectance R ₀ of the test film.

(Iii) The weight (g / m ² ) W of the test resin film was measured.

[Note: Rg value is usually 0.8 to 0.85] Calculation: The light scattering coefficient S (cm ² / g) of the sample film is kubel
It was calculated from the following modified equation of the ka-Munk equation.

[However, in the above formula In order for the photographic printing paper to have good photographic sharpness, the light scattering coefficient of the surface coating layer of the photographic printing paper support is preferably 750 or more.

2. Evaluation of die lip stain Commercially available melt extruder with T die (Toyo Seiki Seisakusho Labo Plastomill, extrusion diameter 20 mm, L / D = 25)
Screw extruder, having a 150 mm wide T-die. ) Is used to coat the polyolefin composition at a coating speed of 14 m / mi
n, Melt temperature 320 ℃, melt extruded to a film thickness of 30 g / m ² to cover the sheet-like substrate, and 1 hour after the start of melt extrusion, stains due to die lip stain in the full width sample The number of lines was measured (number / 150mm
Width).

Examples 1 to 5 and Comparative Examples 1 to 4 In each of Examples 1 to 5 and Comparative Examples 1 to 4, first, a master batch having the following composition was prepared as a master batch for the surface coating layer. Density 0.951g / cm ³ , melt index 9g / 10
20 parts by weight of high-density polyethylene, and a density of 0.918 g / cm ³ ,
20 parts by weight of low-density polyethylene having a melt index of 4 g / 10 minutes, 60 parts by weight of anatase-type titanium dioxide (trade name: A-220 manufactured by Ishihara Sangyo Co., Ltd.) treated with alumina, and 2 parts by weight of zinc stearate. Was kneaded using a Banbury mixer under conditions of 160 ° C., 150 rpm and 10 minutes to prepare a polyethylene resin masterbatch containing 60% by weight of titanium dioxide, which was designated as masterbatch A.

Further, using a Banbury mixer, 40 parts by weight of linear low-density polyethylene having a density of 0.925 g / cm ³ and a melt index of 15 g / 10 min, 60 parts by weight of titanium dioxide, and 2 parts by weight of zinc stearate were used in a Banbury mixer. The mixture was kneaded at 150 ° C. for 10 minutes to prepare a masterbatch containing 60% by weight of titanium dioxide, which was designated as masterbatch B.

Next, the master batch shown in Table 1 and the diluted resin were diluted with the compounding amounts shown in Table 1 by a uniaxial extruder to prepare a resin composition for the surface coating layer. Separately, a corona discharge treatment was applied to the surface side of a sheet-like substrate made of high-quality paper having a basis weight of 170 g / m ² . On the corona discharge treated surface of the sheet-shaped substrate, by extrusion coating method of the resin composition at a resin temperature of 320 ℃, the thickness of the surface coating layer obtained is 30 g /
It was coated so that it would be m ² .

Also, on the back surface of the sheet-like substrate, 50 parts by weight of high density polyethylene having a density of 0.958 g / cm ³ and a melt index of 20 g / 10 min, and low density polyethylene 50 having a density of 0.924 g / cm ³ and a melt index of 4 g / 10 min. Polyethylene resin consisting of 1 part by weight was melt extrusion coated at a resin temperature of 330 ° C.

With respect to the surface coating layer of the obtained support sample, the light scattering coefficient was measured by the above-described method, and the occurrence of die lip stain during the formation of the surface coating layer was evaluated. The results are shown in Table 1.

As is clear from Table 1, Examples 1 to 1 according to the present invention
The light scattering coefficient of the surface coating layer of the support for photographic printing paper obtained in No. 5 is sufficiently high, and therefore the photographic sharpness of the photographic printing paper obtained therefrom is sufficiently high. On the other hand, Comparative Example 1
The light-scattering coefficient of the surface coating layer of the photographic printing paper support obtained in any of 3 to 3 is low and insufficient, and the photographic sharpness of the photographic printing paper is low and unsatisfactory.

Further, as shown in Comparative Example 4, when the content of the titanium dioxide pigment was increased by using a large amount of the masterbatch, the light scattering coefficient of the obtained surface coating layer was improved, but streaks due to stains on the die lip occurred. The quality has deteriorated significantly.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The photographic printing paper support of the present invention is suitable for producing a photographic printing paper having good photographic sharpness while preventing deterioration of surface quality due to stains on the die lip.

Claims (1)

[Claims] 1. A sheet-like substrate, and a resin composition containing a polyolefin resin as a main component, which is formed on the front surface (the surface on which the photographic emulsion is coated) side and the back surface (the surface opposite to the photographic emulsion coated surface) of the substrate. And a resin composition of the surface side coating layer of the substrate, a polyolefin resin masterbatch containing at least a titanium dioxide pigment,
1.0 at a temperature of 0 ° C and a shear rate of 5000 1 / s
A support for photographic paper, comprising a titanium dioxide pigment-containing polyolefin resin composition prepared by diluting and kneading with a polyolefin resin having a melt viscosity of × 10 ³ poise or more.