JPH05307228A - Base for photographic printing paper - Google Patents

Abstract

PURPOSE:To obtain a substrate for the photographic printing paper excellent in cuttability and curl resistance and without any film nonunifomity in the resin coating layer on the rear. CONSTITUTION:A resin coating layer is formed on both sides of a paper base by an extruder to obtain a base for the photographic printing paper. In this case, a high-density PE and a low-density PE are melted and mixed, the mixture is pelleted, and the pellet is applied on the rear (not to be coated with an emulsion layer) by using the extruder. Consequently, a substrate for the photographic printing paper excellent in cuttability and curl resistance and without any film nonuniformity such as a V gel on the rear, so that a resin feed line is simplified, and the resin is measured and the mixer without any trouble.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a photographic paper support. More specifically, the present invention relates to a photographic paper support having improved cut characteristics and curl resistance and having no film unevenness such as V gel in the backside resin coating layer.

[0002]

2. Description of the Related Art In recent years, with the speeding up of development processing by photographic minilabs, etc., a water-resistant photographic printing paper support in which both sides of a base paper substrate are coated with a polyolefin resin is used in place of the conventionally used baryta paper. It is supposed to be done. The properties required for a photographic printing paper support are excellent in dimensional stability, moisture resistance, and adhesive hiding power,
Also, it may not adversely affect the photographic emulsion layer,
In addition, it is also necessary that the cutting characteristics of the blade and the curl resistance are excellent.

A photographic paper support is generally provided with a transparent polyolefin resin coating layer on one side and an opaque polyolefin resin coating layer containing a pigment such as titanium dioxide on the other side. The photographic emulsion paper is formed on the latter opaque polyolefin resin coating layer to form a photographic printing paper. A negative is printed on a photographic printing paper at a developing station, and then developed to obtain a print having a positive image. This print is then cut into a specified size with a guillotine cutter or the like. A support having a polyolefin resin coating layer, a photographic paper or a print made from this support are subjected to a shearing force between the upper and lower blades of a cutter during cutting. In many cases, the coating layer is cut into a stretched shape without showing a sharp cut surface. The photographic paper or print having such a cut surface naturally has a reduced commercial value due to its poor appearance. The phenomenon that causes such a cut surface defect is mainly caused by cutting from the emulsion surface side.
It remarkably occurs in the polyethylene resin coating layer on the surface side (back surface side) where the emulsion is not applied.

As a method of improving the cuttability of the polyolefin resin coating layer, especially the back side polyethylene resin coating layer, it is known to use a low molecular weight polyethylene resin (Japanese Patent Publication No. 58-41500). The resin coating layer made of low-molecular-weight polyethylene has a drawback that when the photographic paper runs in a printer or a developing processor, it is easily scratched if it comes into contact with a metal part or the like, and further, the curl resistance of the photographic paper is deteriorated. Have As a method of improving the above-mentioned drawbacks, a method of using high-density polyethylene having a specific molecular structure and physical properties as a polyethylene resin for coating a paper substrate (Japanese Patent Laid-Open No. 58-95731), or a high density having specific physical properties A method of using a polyethylene resin mixture prepared by mixing polyethylene and low density polyethylene having specific physical properties in specific ratios (JP-A-58)
-95732 and JP-A-60-15004.
No. 9) has been proposed, but these conventional improvement methods have satisfactory cutting characteristics and curl resistance at the same time, and the backside resin coating layer has a V-gel shape (high MI high density polyethylene and low It is still possible to obtain a support for photographic printing paper without film unevenness of a gel-like unmixed product which is generated when MI low-density polyethylene is simply mixed as pellets and melt-extruded by an extruder). Has not been done.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional support for photographic printing paper, has excellent cut characteristics and curl resistance, and has a V resin in the backside resin coating layer. It is an object of the present invention to provide a support for photographic printing paper without such film unevenness, and to eliminate troubles such as weighing of pellets by simplifying the resin supply line of the extruder in terms of operation.

[0006]

The photographic printing paper support of the present invention is a photographic printing paper support comprising a paper substrate and front and back polyolefin resin coating layers formed on both surfaces thereof. The resin used for the back surface coating layer is high density polyethylene (HDPE) and low density polyethylene (LD
A resin obtained by melt-kneading PE) in a mixing ratio of 90/10 to 60/40 and pelletizing again.
The density and melt index of HDPE used for the kneading are ρ = 0.955 g / cm ³ or more, MI = 20 g /
LDPE density and melt index ρ for 10 minutes or more
Is 0.910 g / cm ³ or more and MI is 4 g / 10 minutes or less, and is formed from a polyethylene resin composition containing a mixed polyethylene as a base material.

The present invention will be described in detail below. The present invention melt-mixes HDPE having a specific density and melt index and LDPE having a specific density and melt index in a specific ratio as a polyethylene resin matrix of a resin coating layer on the back side of a photographic paper support. The present invention improves the cutting property and curl resistance of a support and photographic paper obtained by extrusion coating a paper substrate with a pelletized polyethylene resin composition.

The melt index of the high density polyethylene component in the melt mixed polyethylene used in the present invention is 2
It is preferably 0 g / 10 minutes or more. If the melt index of the high-density polyethylene component is lower than 20 g / 10 minutes, the resulting substrate or photographic paper will have poor cutting properties. The melt index of the low-density polyethylene component in the melt-mixed polyethylene used in the present invention is preferably 4 g / 10 minutes or less. When the melt index of the low-density polyethylene component is higher than 4 g / 10 minutes, a film-like flow of the polyethylene resin composition melt extruded from the slit die during melt extrusion coating of the polyethylene resin composition arrives at the surface of the paper substrate. However, the melt film flow shrinks until it comes into contact, and thus the phenomenon that the width of the resin coating flow of the obtained polyolefin resin composition becomes narrower than a predetermined value, that is, the neck-in phenomenon becomes large, and therefore the support is increased. The operating efficiency and production efficiency of the body manufacturing process are significantly reduced.

The density and melt index of the resin mixture pelletized again after melt-mixing HDPE and LDPE used for the backside resin coating layer of the support for photographic printing paper of the present invention is ρ = 0.940 g / cm ³ or more. , MI = 20
It is preferably g / 10 minutes or less. If the density of the resin mixture is 0.940 g / cm ³ or less, the curl resistance of the resulting photographic printing paper support is deteriorated, and if the melt index is 20 g / 10 minutes or more, the neck-in phenomenon becomes large.

As a method for mixing the high density polyethylene and the low density polyethylene used for the backside resin coating layer of the support of the present invention, the melt mixing method of the present invention, that is, the HDPE pellets and the LDPE pellets are mixed with a Banbury mixer or the like. Melt kneading by using, and melt extrusion coating of the resin mixture re-pelletized by an extruder, as well as a simple dry mixing method, that is, simply mixing HDPE pellets and LDPE pellets in a pellet state and using an extruder. Although a method of melt extrusion coating is conceivable by this simple dry mixing method, at the time of melt extrusion coating of the polyethylene resin composition, a gel-like unmixed material is formed in the film-like flow of the polyethylene resin composition melt extruded from the slit die. Occurs, and even after the melt film is coated on the surface of the sheet-like substrate, gel-like film unevenness is generated. It is in many cases. A support having such a gel-like film unevenness or photographic paper naturally has a poor commercial value because of its poor appearance. However, the melt-mixing method of the present invention, in which HDPE pellets and LDPE pellets are once melt-mixed and the pelletized resin is coated with an extruder, does not cause gel-like film unevenness, thus improving the commercial value.

The density of the high-density polyethylene component in the melt-mixed polyethylene used for the backside resin coating layer of the support of the present invention is preferably 0.955 g / cm ³ or more. The melt index is 20g / 10
It is preferably at least minutes. Furthermore, the mixing ratio of the high density polyethylene component and the low density polyethylene component is 90/10.
It is preferably in the range of -60/40. When the density of the high-density polyethylene component is 0.955 g / cm ³ or less, or when the blending amount is 60 parts by weight or less, the density of the polyethylene resin composition obtained is low, and the obtained support is
Or, the curl resistance of the printing paper becomes poor. Further, if the melt index is lower than 20, the resulting support and photographic paper will have poor cut characteristics. Further, the pellet system supplied to the extruder requires two or more series in the simple dry mixing method. One line is enough. For this reason, it is possible to eliminate troubles in the resin measurement and the pellet mixer.

In general, a photographic printing paper support comprising a sheet-like substrate, front and back layers of a polyolefin resin composition coating layer, as described in JP-A-48-9963, has a polyolefin resin for the surface resin coating layer. Is lower than the density of the polyolefin resin in the backside resin coating layer to control the curl resistance of the resulting support and photographic paper. Therefore, it is preferable to increase the density of the polyolefin resin in the backside resin coating layer to some extent.

The blending amount of the high-density polyethylene component is 9
If the amount is more than 0 parts by weight, the amount of the low-density polyethylene component is naturally too small, so that the resulting support and the cutting property of the photographic paper are poor, and in the operation side, the coating layer is coated at the time of resin coating. It becomes difficult to adjust the profile, and the runnability is reduced. In the present invention, used as the backside resin coating layer as described above, as a mixing method of the polyolefin resin composition obtained by melt-mixing pellets of high-density polyethylene and pellets of low-density polyethylene and pelletizing again, one-step melting A method such as a mixing method, a multi-stage melt mixing method, or a combination thereof can be applied.
When kneading, a kneading machine such as a Banbury mixer, a kneader, and an extruder can be used. At this time, an antioxidant may be added to prevent resin deterioration.

The thickness and the weight of the polyolefin resin coating layer formed on the support of the present invention are not particularly limited, and are the same as the thickness of the polyolefin resin coating layer of the conventional photographic paper support. It may be. For example, its thickness is usually 10 to 100 microns, preferably 1
It is selected from the range of 5 to 80 microns. The polyolefin resin coating layer having the specific composition of the present invention may be formed on both the front and back surfaces of the sheet-like substrate, but at least on the back surface thereof (the surface opposite to the emulsion coating surface). I won't.

The polyolefin resin coating layer formed on the surface of the sheet substrate (the surface on which the emulsion is coated) may contain the specific polyolefin resin composition of the present invention, or may have any other desired composition. You may have one. Further, this polyolefin resin coating layer, a desired amount of additives, for example, white pigments such as titanium oxide, zinc oxide, talc, calcium carbonate, alumina, fibrous fillers such as glass fiber, asbestos, whiskers, carbon black, phthalocyanine. Pigments, yellow lead, titanium yellow,
Red iron oxide, color pigments such as ultramarine, stabilizers mixed with ordinary resins, antioxidants, antistatic agents, plasticizers, dispersants,
It may contain a lubricant, a fluorescent agent and the like. Regarding the kind, the amount, and the addition method of these additives, for example, U.S. Pat. Nos. 3,833,380 and 4,169,1
88, No. 3,501,298, No. 3,449,25
No. 7, and No. 3,499,762. Also, as described in U.S. Pat. No. 3,884,692, those additives can be applied thereon after forming the polyolefin resin coating layer.
Further, US Pat. Nos. 2,715,075 and 2,84
No. 6,727, No. 3,549,406, and No. 3,
As described in Japanese Patent No. 590,107, etc., the surface activation treatment of the polyolefin resin coating layer can be performed if necessary.

As the paper substrate used in the present invention, a base paper made of wood pulp such as hardwood pulp, softwood pulp, and hardwood mixed pulp is advantageously used, and kraft pulp, sulfite pulp, soda pulp and the like are usually used. Base papers made of known pulp can also be used. If necessary, synthetic pulp and pulp containing synthetic fibers can also be used. The type and thickness of the paper substrate is not particularly limited, but it is preferable that the paper substrate has improved surface smoothness by a treatment such as compression after applying a pressure to the paper substrate by papermaking. Generally, it is preferably 50 to 250 g / 〓.

The base paper used as the paper substrate in the present invention is
Various ordinary paper additives such as dry paper strength enhancer (cationized starch, cationized polyacrylamide and anionic polyacrylamide), sizing agent (fatty acid salt,
Rosin, maleated rosin cationic sizing agent, reactive sizing agent, etc.), filler (clay, kaolin, etc.), wet paper strengthening agent (melamine resin, epoxidized polyamide resin, etc.), fixing agent (aluminum sulfate, cationic starch) Etc.), a pH adjusting agent (caustic soda, sodium carbonate, etc.) and the like. The base paper is a water-soluble polymer additive, sizing agent, inorganic electrolyte, hygroscopic substance, pigment,
A tab size with a treatment liquid containing one or more kinds of pH adjusters,
Alternatively, it may be size-pressed.

The polyolefin resin coating layer formed on the photographic printing paper support of the present invention is formed by an extrusion coating method. Usually, the polyolefin resin coating layer is produced by a so-called extrusion coating method in which a heated melt of a resin is cast on a running paper substrate surface, and both surfaces of the paper substrate are coated with the resin. Further, the paper substrate may be subjected to activation treatment such as corona discharge treatment or flame treatment before being coated with the resin. Generally, the surface (emulsion surface) of a photographic printing paper support has a glossy surface, a matte surface, a matte surface, etc. depending on its application, and the back surface thereof is usually a matte surface, and the surface or if necessary. Both front and back surfaces may be subjected to activation treatment such as corona discharge treatment and flame treatment.

[0019]

The present invention will be described in detail with reference to the following examples.
The cutting characteristics of the printing papers prepared in Examples and Comparative Examples, that is, the state of the cut surface, and the curl resistance were evaluated as follows. (1) Characteristics to be cut The photographic paper was cut with a guillotine cutter, and the stretched and deformed state of the polyethylene resin coating layer was observed on the cut surface, and the results were evaluated in the following four stages. A: The cut surface was extremely smooth and no deformation was observed in the polyethylene coating layer. B: The polyethylene resin coating layer is partially stretched and deformed at the cut surface. C: The polyethylene resin coating layer is stretched and deformed over almost the entire cut surface. D: The polyethylene resin coating layer was greatly stretched over the entire cut surface and was greatly deformed. Among the above four grades, the grades A and B are acceptable and can be put to practical use.

(2) Curling resistance The photographic paper cut into 10 cm × 10 cm is 20 ° C., 65%
After being left in the atmosphere of RH for 16 hours, it was placed on a flat surface with the curved inner surface facing upward, the average distances between the four corners and the flat surface were measured, and the results were evaluated in the following four stages. A: The average distance from the plane of the four corners of the photographic paper is less than 1 mm. B: The average distance from the plane of the four corners of the printing paper is 1 mm or more and less than 2 mm. C: The average distance from the plane of the four corners of the photographic paper is 2 mm or more and less than 4 mm. D: The average distance from the plane of the four corners of the photographic paper is 4 mm or more. Of the above four grades, the grades A and B are acceptable and suitable for practical use. Examples 1 to 3 and Comparative Examples 1 to 6 A high-quality paper having a basis weight of 170 g / m ² was used as a sheet substrate, and after corona discharge treatment was applied to both surfaces of the sheet substrate, one surface of the sheet substrate was exposed by an extrusion coating method. A polyethylene having a thickness of 30 μm formed of a polyethylene composition having the composition shown in FIG. 1 and 10% by weight of anatase titanium dioxide was added to the other surface of the sheet-like substrate (density = Example 0.918 g / cm ³ , Melt index (MI) =
Mixture of 50 parts by weight of high-density polyethylene of 9 g / 10 minutes and 50 parts by weight of low-density polyethylene of density = 0.918 g / cm ³ , MI = 4 g / 10 minutes) Composition: thickness 30
A μm resin coating layer was formed.

Corona discharge was applied to the surface of the polyethylene resin coating layer on the front surface of each support containing titanium dioxide, and a normal photographic emulsion for black-and-white photography (trade name, manufactured by Rockland Colloid Co., Ltd. Liquid light) 15μ
A photographic paper was manufactured by applying the photographic paper to a thickness of m. The cut characteristics and curl resistance of this printing paper were evaluated. The results are shown in Table 1.

[0022]

[Table 1]

As is clear from Table 1, the cutting properties, curl resistance and V-gel film of the backside resin coating layer of the photographic paper obtained from the photographic paper support of the present invention in Examples 1 to 3 The unevenness and the neck-in resistance (operability) were all good, but the printing papers obtained from the photographic printing paper supports of Comparative Examples 1 to 8 had one of the above four characteristics.
One or two failed. That is, it was confirmed that the support for photographic printing paper of the present invention had excellent properties in practical use.

[0024]

The pellets of HDPE and LDPE are melt-kneaded and the pelletized resin mixture is melt-coated on a paper substrate with an extruder to have good cut characteristics and excellent curl resistance. It is possible to obtain a support for photographic printing paper without film unevenness such as V gel on the back surface, and to eliminate troubles of resin metering and resin mixing machines by simplifying the resin supply line to the extruder. ..

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Claims (3)

[Claims] 1. A photographic printing paper support comprising a paper substrate and resin coating layers provided on both sides of the paper substrate by means of an extruder. The back surface (the surface on which the emulsion layer is not provided) has a high density polyethylene and a low density. A support for photographic printing paper, comprising melt-kneading polyethylene pellets and coating the pelletized resin with an extruder. 2. A resin obtained by melt-kneading pellets of high-density polyethylene and low-density polyethylene and then pelletizing the pellet again has a density and a melt index of ρ = 0.94.
The support for photographic printing paper according to claim 1, wherein the support is 0 g / cm ³ or more and MI = 20 g / 10 minutes or less. 3. A high-density polyethylene pellet and a low-density polyethylene pellet are melt-kneaded, and then the pelletized resin is coated on the back surface (the surface on which the photographic emulsion is not coated) and the high-density polyethylene / low The mixing ratio of density polyethylene is 90/10 to 60/40, and the density and melt index of high density polyethylene are ρ = 0.955 g / cm ³ or more, MI = 20 g / 1.
At 0 minutes or more, the density and melt index of low-density polyethylene is ρ = 0.910 g / cm ³ or more, MI = 4 g /
The support for photographic printing paper according to claim 1 or 2, which is for 10 minutes or less.