JPH01280751A - Base for photographic printing paper - Google Patents

Abstract

PURPOSE:To obtain the base which has high resistance to water and scratching and has excellent curling resistant and hole punching properties by forming the front side coating layer of the base into a two-layered structure consisting of both half layers on the inner and outer layers by using a polyolefin resin. CONSTITUTION:The base 1 consists of a sheet-like substrate 2, the front side coating layer 3 and the rear side coating layer 4. The layer 3 consists of the outer half layer 3a and inner half layer 3b consisting of the resin compsn. different from each other. The average density of the polyolefin resin used in the half layers 3a, 3b of the layer 3 is confined to <=0.940 and is set lower than the density of the polyolefin resin contained in the layer 4. The density of the half layer 3a is set higher than the density of the half layer 3b. The curl balance of the base 1 is hardly obtainable and the hole punching property is degraded if the density of the half layer 3a exceeds 0.945. Flaws are likely to be generated in the layer 3 surface when the density is below 0.930. The resistance to scratching and water is thereby enhanced and the curling resistant and hole punching properties are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a photographic paper support.More specifically, the present invention relates to a substrate having a titanium dioxide-containing polyolefin resin composition on the surface side. This is a resin-coated photographic print that has a two-layer structure and a polyolefin resin coating on the back side, which has excellent water resistance and scratch resistance, excellent hole punching properties, and a good curl balance. This invention relates to paper supports.

[Prior art]

Conventionally, baryta paper has been used as a support for photographic printing paper, but in recent years, water-resistant supports having coating layers made of polyolefin resin on both sides of a sheet-like substrate have come to be used. This water-resistant support shortens washing and drying times during development of photographic papers produced from it, eliminates the need for ferrotypes, reduces chemical consumption, maintains high levels of stiffness and strength, It also has many advantages, such as reducing stains caused by chemical penetration.

A support for photographic paper generally has a transparent polyolefin resin coating layer on one side (back side) and a highly white, highly opaque pigment such as titanium dioxide on the other side (front side). A photographic paper is formed by providing a photographic emulsion layer on the opaque polyolefin resin composition coating layer on the surface side of the support.

The polyolefin resin generally used for the support provides water resistance to the entire support, and the surface of the support (emulsion coated side)
It has the role of maintaining the smoothness of the substrate, increasing the adhesion between the substrate and the coating layer, balancing the curling properties of the entire support, and improving hole punching properties. As the polyolefin resin, a low-density resin is used, and as the polyolefin resin for the back side, a resin with a higher density than that for the front side is used, and both are used properly (Japanese Patent Laid-Open No. 58-93049). However, with this type of support that uses low-density polyethylene for the surface resin coating layer, the support or photographic paper may be damaged by the feed roll during support manufacturing, emulsion coating, and photographic paper development. It may shift and scratches may occur on its surface. If the surface of the support is scratched, the gloss and smoothness of the surface will be reduced, resulting in a serious problem of degrading the quality of photographic paper produced from this support. Furthermore, if low-density polyethylene is used as the resin for the surface layer, the unevenness of the mantle-treated surface on the back side will be transferred to the soft resin surface on the front side during the manufacturing and winding of the support. This results in a reduction in the smoothness and gloss of the coating layer, which also reduces the quality obtained from the support.

Therefore, in order to improve the scratch resistance of the surface of the support, a method of using low density polyethylene with specific physical properties (Japanese Patent Laid-Open No. 58-93
0.1.9), a method has been proposed that uses high-density polyethylene with specific physical properties to improve both scratch resistance and cut resistance (Japanese Patent Application Laid-open No. 58-95731), but none of these methods The layer is coated with a single resin, and the former has insufficient scratch resistance, and the latter has disadvantages such as poor adhesion to a sheet-like substrate. In addition, the surface layer has a two-layer structure, the inner half layer is composed of low density polyethylene, or a blend containing low density polyethylene of at least 50% by weight, and the outer single layer is composed of at least Q, 5% by weight.
There is a technique for improving the rigidity of a support by forming it from a polymer having a stiffness modulus of GPa, such as polycarbonate 1. However, there was a problem with the pole punching ability, and there remained a problem in this respect because no consideration was given to the balance of the curl.

[Problem to be solved by the invention]

An object of the present invention is to significantly improve the scratch resistance of a photographic paper support in which both sides of a sheet-like substrate are coated with polyolefin resin without deteriorating its curling properties and hole punching properties. An object of the present invention is to provide a support for photographic paper having a surface side coating layer.

[Means to solve the problem]

The support for photographic paper of the present invention comprises a sheet-like substrate, a coating layer which covers the front side (photographic emulsion coated side) and the back side of this substrate, and whose main component is a polyolefin resin. The surface-side coating layer is composed of an inner half layer (substrate side) made of a titanium dioxide-containing polyolefin resin composition having different compositions, and an outer single layer, and the outer single layer contains a polyolefin. The density of the resin is higher than the density of the polyolefin resin contained in the inner half layer, and the average density of the polyolefin resin in both the outer and inner half layers is 0.940 or less, and the back side It is characterized by a density lower than that of the polyolefin resin contained in the coating layer.

Preferably, the outer single layer of the surface-side coating layer has a thickness of 2 to 10 μm.

Further, it is preferable that the inner and outer bilayers of the surface-side coating layer are simultaneously formed on the surface side of the sheet-like substrate by a melt-extrusion coating method.

As mentioned in the prior art section, resins for photographic paper supports have properties related to photographic suitability, such as smoothness of the surface resin layer, physical properties of the laminate, such as curl resistance, and adhesion to the substrate. The front and back sides are selected separately, taking into account the following. However, it is extremely difficult to achieve a delicate balance of these properties by using a single type of resin for each of the front and back side layers. In particular, in recent years, the quality of photographic paper has become higher, and as a result, there is a tendency for supports to have higher titanium content in the surface resin coating layer and a higher coating amount. Unless the density of the resin is lowered, the balance of curl resistance will be lost unless the resin of the back side layer is made to have a higher density and a higher coverage. In response to the above requirements, the present invention has developed a resin that has good scratch resistance and a good curl balance while maintaining the surface side resin at a low density as a whole (average value of both the inner and outer layers). The purpose is to obtain a support, and for this purpose, the surface side coating layer is not a single resin layer, but has a two-layer structure, an inner layer and an outer layer, made of two types of polyolefin resins with different densities.

The support of the present invention has surface side coatings having different compositions.
It has a two-layer structure consisting of an outer single layer, and the density of the polyolefin resin contained in the outer half layer is higher than the density of the polyolefin resin contained in the inner half layer, and the polyolefin resin contained in both the inner and outer single layers. Average density of resin is 0.9
It is characterized in that it is 40 or less and lower than the density of the polyolefin resin contained in the back side coating layer. In FIG. 1, a support 1 includes a sheet-like base 2, a front side coating layer 3 formed on the front side thereof, and a back side coating layer 4 formed on the back side thereof, and the front side The coating layer 3 includes an outer half layer 3a and an inner half layer 3b made of different resin compositions.
It consists of.

There is a correlation between the polyolefin resin density of the coating layer of the support and its scratch resistance; when the resin density is high, the scratch resistance is excellent, and when the surface coating layer of the present invention has a two-layer structure, it is naturally scratch resistant. There is no problem at all. however,
If a single surface coating layer is formed using such a high-density polyolefin resin, then the back coating layer must be made of a higher-density polyolefin resin, or if the coating amount is increased, the balance of curling properties may need to be balanced. I can't take it, and
If such a structure is adopted, the resin density of the entire coating layer becomes excessively high, and therefore the hole punching of the support or the photographic paper obtained from the support becomes very poor. Therefore, in the support of the present invention, it is necessary that the average density of the polyolefin resin used in the surface layer and the outer single layer is 0.940 or less. If this average density is higher than 0.940, the resulting support will have poor curl resistance and hole punching properties.

The scratch resistance of the surface layer is controlled by the average density of the polyolefin resin contained therein, but when it has a two-layer structure as described above, the scratch resistance is almost controlled by the density of the resin in the outer half layer. The present inventors have discovered that. Although there is no particular limitation on the amount of coverage of each of the inner and outer single layers, it is important that the density of at least the outer half layer is higher than the density of the inner half layer. The total coverage can be freely selected within the range of 10 to 50 μm generally used for conventional supports, and the ratio of coverage of both the inner and outer monolayers can also be freely selected.

Furthermore, the content of titanium dioxide in the amphiboid layer can be freely selected for each monolayer. Generally, the average titanium dioxide content of both monolayers is preferably in the range of 5 to 30%.

When the thickness of the outer half layer of the surface-side coating layer is set to 2 to 10 μm, the curl resistance and hole punching properties can be further improved without substantially affecting the scratch resistance of the surface-side coating layer. .

In FIG. 2, the surface-side coating layer 3 included in the support 1 is
It consists of an extremely thin outer half layer 3a and an inner half layer 3b formed inside the outer half layer 3a. The curling property of a laminate in which both sides of a sheet-like substrate are coated with resin is determined by the difference in shrinkage of the resins on both sides, that is, the difference in consistency. When the resin density (average density) of the front side layer and the resin density of the back side layer are fixed to constant values, and the front side layer has a two-layer structure with different resin compositions, the inner half layer is Even if the density of the outer half layer is higher than that of the outer half layer, or vice versa, the curling property is hardly affected. However, by making the outer half layer higher in density than the inner single layer and reducing the coating layer thickness, the average density of the resin in the surface side coating layer can be lowered, and the curl that occurs is reduced by this amount. In other words, by reducing the thickness of the resin coating on the outer half layer, while maintaining the scratch resistance at the required level, the average density of the resin on the entire surface layer can be reduced, and the curl balance of the entire support can be improved accordingly. This makes it easier to remove the material and provides economical effects such as reducing the amount of polyolefin resin coated on the back side coating layer.Furthermore, it avoids increasing the density of the resin on the back side coating layer, thereby preventing deterioration in punching properties. You can. However, it is an essential requirement of the present invention that the resin density of the back side coating layer be higher than the average resin density of the two front side layers.

If the thickness of the outer half layer is less than 2 μm, film cracking, uneven coating, etc. may occur. Also, its thickness is 1
Even if the thickness is larger than 0 μm, the effect of improving scratch resistance reaches a ceiling and there is little particular effect.

The content of titanium dioxide contained in the surface side coating of the present invention is preferably 5 to 30% on average for both monolayers.

Furthermore, the titanium dioxide content of each monolayer is preferably within the range of 0 to 35%. In the support of the present invention, the titanium dioxide content of the outer half layer can be made greater or less than that of the inner single layer to improve the optical properties of the coating layer on the surface side of the support. .

In the support of the present invention, in order to form the inner and outer half layers on the surface side, each soil layer may be coated separately in two stages, or both single layers may be coated by a conix trusion (co-extrusion coating) method. A simultaneous extrusion coating method may also be used, but a simultaneous extrusion coating method is preferred in terms of efficiency. For example, any of the methods described in "New Laminating Processing Handbook" (Processing Technology Publication), pages 84 to 92, can be used as the coniki trusion method.

The water-resistant, thermoplastic resin used to coat the surface of the sheet-like substrate is a polyolefin resin. The polyolefin resin can be selected from homopolymers of ethylene, α-olefins such as propylene, copolymers of at least two of the above-mentioned olefins, and mixtures of at least two of these various polymers, particularly according to the present invention. Preferred polyolefin resins are low density, medium density, high density polyethylene and mixtures thereof. There is no particular restriction on the molecular weight of these polyolefin resins, but usually 20
,000 to 200,000.

Practically speaking, the polyolefin resin contained in the inner single layer is polyethylene resin, and its density is 0.915 to 0.9.
40, and its melt index (Ml) is 1 to 2.
5, and its swelling ratio (SR) is 0.
It is preferably selected from those in the range of 8 to 2.0. In addition, the outer half layer contains polyolefin resin or polyethylene resin, and its density is 0.930 to 0.9.
45, its MI is 1 to 25, and its SR
is preferably in the range of 0.8 to 2.0.

If the polyolefin resin density of the outer half layer exceeds 0.945, it will be difficult to maintain the curl balance of the support as a whole.
Not only this, but also the hole punching performance may be deteriorated. Furthermore, if the resin density of the outer half layer is less than 0.930, scratches are likely to occur on the surface of the front side coating layer.

The density of polyolefin resins can be measured according to ASTM D-1505. Since the measured density and the calculated density of the mixture almost match, the use of the calculated density allows sufficient control in implementing the present invention.

When coating the resin composition, it is preferable to subject the sheet-like substrate to a corona discharge treatment in advance, and after coating, the resin surface can be mirror-finished or molded using a cooling roll. Further, in order to improve the adhesion between the surface-side coating layer and the photographic emulsion layer, corona discharge or subcoating may be applied thereon. The resin for the coating layer used in the support of the present invention may contain a desired amount of additives, such as white pigments such as titanium oxide, zinc oxide, talc, calcium carbonate, and alumina, and fibrous materials such as glass fiber, asbestos, and voice car. Fillers, carbon blanks, phthalocyanine pigments, coloring pigments such as yellow lead, titanium yellow, hengara, ultramarine, stabilizers mixed with ordinary resins, antioxidants, antistatic agents, plasticizers, dispersants, lubricants, fluorescence It may also contain agents. Regarding the types, amounts, and methods of addition of these additives, see, for example, U.S. Pat.
No. 3,501.298, No. 3.449,257, and No. 3.499,762. The additives can also be applied to the polyolefin resin coating after it is formed, as described in U.S. Pat. No. 3,884,692. Additionally, U.S. Patent No. 2,715,075;
, No. 727, No. 3,549,406, and No. 3.5.
As described in No. 90.107, the surface activation treatment of the polyolefin resin coating layer can be performed as necessary.

The sheet-like substrate used in the present invention includes wood pulp such as hardwood pulp, softwood pulp, hardwood mixed pulp, kraft pulp, sulfite I pulp,
Base paper made of commonly used pulp such as soda pulp can be used. Furthermore, synthetic pulp, synthetic fibers, and natural fibers can also be used if necessary.

There are no particular restrictions on the type and thickness of the base paper, but it is preferable to improve the surface smoothness by compressing the base paper by applying pressure in a calender after making the base paper. 250 g/n (preferably.

The base paper used as a sheet-like substrate in the present invention contains various conventional paper additives, such as dry paper strength enhancers (cationized starch, cationized polyacrylamide, etc.), sizing agents (fatty acid salts, rosin, maleated rosin, Cationized chair agents, reactive sizing agents, etc.) fillers (clay, kaolin, titanium, etc.), wet paper strength agents (melamine resins, epoxidized polyamide resins, etc.), fixing agents, (aluminum sulfate, cationized starch, etc.), It may contain one or more of Pl+regulators (caustic soda, soda carbonate, etc.). Furthermore, the base paper may be tab-sized or size-pressed with a treatment solution containing one or more of water-soluble polymer additives, sizing agents, inorganic electrolytes, hygroscopic substances, pigments, dyes, circle I regulators, etc. good.

〔Example〕

The present invention will be explained in detail below with reference to Examples. The glossiness (substitute property for scratch resistance), curling degree, and hole punching property of the supports prepared in each of the Examples and Comparative Examples were tested and evaluated as follows.

1. Glossiness The ease with which the surface side coating layer is damaged by rubbing or pressing is expressed as the value of the reduction in glossiness by pressing. i.e. 150 x 1
A support sample cut into 50 mm squares was heated at 30°C x 65% R.
The temperature was controlled in the test chamber of H, and 5 test pieces were stacked on top of each other.
A pressure of 11 kg/cI was applied for 60 minutes, and the reduction in surface gloss due to the matte finish on the back side of the support was measured at 75° gloss for the three intermediate sheets.

2. Cut the curl support sample into a 5 mm W x 50 n + L rectangle crosswise to the flow of the base paper, and cut this test piece into a 25゛c x 80
%RH for 24 hours, and the degree of curl of this test piece was evaluated by comparing it with a curl grade diagram classified into 10 levels prepared separately. If the support is curled on the front side, it is a plus (+), and if it is curled on the back side, it is a minus (
-) was displayed. The smaller the absolute value of the numerical value, the smaller the curl, that is, the higher the curl resistance. It is desirable that the support is such that the curl of photographic paper after emulsion coating is 0 to - (minus), so it is desirable that the degree of curl is at least negative at the stage of the support. .

3. Cut the hole-punched support sample using a one-hole banding machine (manufactured by Plus Co., Ltd.), observe the stretched and deformed state of the polyethylene resin coating layer on the cut surface, and compare the results with the following: 10, ranging from "extremely smooth with no fuzz and no deformation of the polyolefin layer" (Grade 1) to "polyethylene resin coating layer is greatly stretched over the entire cut surface and has significant deformation" (Grade 10) Rated in stages. Grade 1 has the best hole punching properties, and Grade 10 has the worst ball punching properties.

-11-5, and Konoso 1m-7- Kanazoian Standard Freeness (JIS P-8
121-76) 20% softwood intersulfite pulp (NBSP) beaten to 250 ME and freeness 280
Hardwood intersulfate pulp (1, [P
) to form a paper substrate having a basis weight of 17 h/rrf, a tensity of 1.0 g/cnt, and a moisture content of 8%. At this time, the following paper-making additives were added in the following amounts based on the bone dry weight of the bulb.

Cationized starch 2.0% Argyl ketene dimer resin 0.4% Onionic polyacrylamide resin 0.1% Caustic soda
The pH was adjusted to 7.5. Also, as a size press chemical, carboxyl-modified PVA and I-lium chloride were added to
:1 weight ratio, and a 5% size solution prepared by dissolving this in water was applied to both sides of the paper at a rate of 25 g/rd. A paper substrate was thus obtained.

First, the back side of the paper base was subjected to corona discharge treatment, and on the treated side, resin C as noted in Table 1 was melt-extruded and laminated at 330°C, and a mantle mold was applied to this using a cooling roll. This was then cooled to form a back side coating layer with a thickness of 30 μm.

Next, the surface side of the paper base was subjected to corona discharge treatment, and on this treated surface, the resin of the type listed in Table 1 was melt-extruded at a resin temperature of 320° C. for the outer half layer having the structure listed in Table 1. A surface side coating layer having a total thickness of 30 #m was formed by laminating the layers by a method. A shiny resin-coated support was obtained. The glossiness, curling degree, and hole punching properties of the obtained support were as shown in Table 1.

Table 1 compares a first block consisting of Examples 1-2 and Comparative Examples 1-4 and a second block consisting of Examples 3-4 and Comparative Examples 5-7. In Example 1 of the first block I, the surface side coating layer was made of a low-density resin with a thickness of 9 μm for the inner half layer, and the outer half layer was made of a higher-density resin B to a thickness of 21 μm. Coextrusion coating was performed. Example 2
In this case, the thickness of the inner and outer measurement single layers is 21 μm and 9.0 μm, respectively. u
m, and was coated in the opposite manner to Example 1. In Comparative Example 1, the inner half layer was coated with medium density resin B to a thickness of 21 μm, and the outer half layer was coated with low density resin A to a thickness of 9 μm (the average density was 0 as in Example 1). .928). In Comparative Examples 2 to 4, resin A alone, a mixed resin of A/B=3/7, and resin B alone were each coated by extrusion in a single layer to a thickness of 30 μm.

In addition, Examples 3 and 4 of the second block to Comparative Examples 5 to 7
The same experiments as in Examples 1 to 2 and Comparative Examples 1 to 4 were conducted in each case. However, the medium-density resin B was replaced with a high-density resin, and in the surface-side coating layer, an inner half layer was first formed, and then an outer layer was formed on top of it.

The supports of Examples 1 to 2 and 3 to 4, in which a relatively high density resin was used for the outer half layer in each block, were compared to Comparative Examples 1 and 5, in which the outer half layer was formed of a low density resin, respectively. It also has significantly better gloss and curl,
There was almost no difference in ball punching properties, and it was actually better. In addition, in each block, the supports obtained in Examples 1 and 3 were used in Comparative Examples 1 and 3, and 5 and 6.
When compared with the support obtained in Example 1, the average density of the corresponding surface layer is the same, but the gloss is lower than that of Example 1.
The supports in cases 3 and 3 are more slanted. The surface layer formed in Comparative Example 2 has too low density and the surface gloss is greatly reduced, and in Comparative Example 4, the surface layer formed has good gloss but is insufficient in curling and hole punching properties.

The surface side layer of the support of Comparative Example 7 shows excellent gloss, but the resin density is 0.940 or more, and the ball punching property and curling property are poor. Increasing the density and coating amount of the resin in the layer may result in poor ball punching properties.

Blank space below [Effects of the Invention] In the support of the present invention, the surface side coating layer is made of a polyolefin resin having a specific density and has a two-layer structure of an inner and outer inspection single layer, thereby increasing scratch resistance. , curling properties and hole-punching properties can be moderately controlled. Such supports are suitable for producing high quality photographic papers.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are respectively sectional explanatory views of one embodiment of the support of the present invention. ■, 1a...Support, 2...Sheet-like substrate,
3... Surface side coating layer, 3a... Outer half layer, 3
b... Inner half layer, 4... Back side coating layer. Hatake 1 Diagram 2 Figure 3・11 Front side coating layer 4, ・ Back side coating layer

Claims (1)

[Claims] 1. A sheet-like substrate, and a coating layer that covers the front side (photographic emulsion coated side) and the back side of this substrate and whose main component is a polyolefin resin. , the surface side coating layer is composed of an inner half layer (substrate side) and an outer half layer made of titanium dioxide-containing polyolefin resin compositions having different compositions, and the outer half layer has a polyolefin resin composition contained in the outer half layer. density is higher than the density of the polyolefin resin contained in the inner half layer, and the average density of the polyolefin resin in both the outer and inner half layers is 0.940 or less, and the back side coating layer A support for photographic paper, characterized in that it has a density lower than that of a polyolefin resin contained in.