JPS5893049A - Substrate for photographic printing paper - Google Patents

Abstract

PURPOSE:To improve smoothness and curling properties by coating PE of specific density and melt index on the side to be coated with an emulsion layer. CONSTITUTION:Coating of PE of which the density is in a 0.910-0.930g/cc and the melt index is in a 20-40g/10min range is formed on the emulsion layer side of photographic paper which is coated with PE on both sides of base paper. If the density is larger than said range, the paper is vulnerable to curling with the emulsion layer side inward. If the melt index is smaller than said range, the smoothness of the surface of the coating layer is not enough and if said index is larger than said range, neck-in is large and stability is poor. The coating of density in excess of 0.930g/cc is used on the side where no emulsion layer is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a support for photographic paper. More specifically, the present invention relates to an improvement in a support for photographic paper, which is formed by providing a polyolefin resin coating layer on both sides of a base paper. Development has been underway for some time,
A support for photographic paper that is made waterproof by providing a polyolefin resin coating layer on both sides of a base paper has already been put into practical use. Among the polyolefin coating layers of such a polyolefin-coated support for photographic paper, the surface of the coating layer on the side where the photographic emulsion layer is provided is generally required to have high smoothness.

That is, the image-side surface of photographic paper is generally required to have a high gloss and high smoothness.

Of course, photographic paper with a patterned surface, called matte or grain, is also used, but the most common photographic paper is one that has a surface with excellent gloss and high smoothness. The surface condition and pattern of such photographic paper are directly influenced by the surface condition of the polyolefin coating layer of the support, which serves as the base layer of the photographic emulsion layer on which the image is formed. Therefore, for example, in order to obtain a photographic paper surface with excellent gloss and high smoothness, such as a mirror surface, it is desirable to provide the surface of the polyolefin coating layer of the photographic paper support with as much smoothness as possible.

Another important characteristic of photographic paper that similarly requires consideration is curling, which is a phenomenon in which the side of the photographic paper where the emulsion layer is present is bent inward or outward. In other words, if curls occur in the photographic paper during the manufacturing process of photographic paper, or during the enlarging and printing of photographs, the efficiency of these processes will decrease, and it will also be difficult to stack the photographic papers or paste them into albums. Even when attaching
There are also problems such as a decrease in work efficiency due to the occurrence of curls. Therefore, it is necessary to suppress curling of photographic paper as much as possible. Of these curls, curls that bend the emulsion layer side of the photographic paper inward are particularly likely to occur, which poses a practical problem. Therefore, in the case of a normal polyolefin-coated support for photographic paper (hereinafter referred to as polyolefin-coated paper), the paper is curled in advance so that the side on which the emulsion layer is to be provided is placed on the outside. Measures have been taken to compensate for curls that occur during the processing process, such as turning the emulsion layer side inward. Such intentional curling of polyolefin-coated paper is achieved, for example, by utilizing and adjusting the crystallinity of polyethylene, which is the most commonly used polyolefin. That is, the side (front side) of the base paper of the photographic paper support on which the emulsion layer is provided usually has a density of 0.930 g/cc or less and a melt index of 1.5-10 g/10 min. The resin coating layer is made of polyethylene with a density of 0.930 on the back side.
By forming resin coating layers each made of polyethylene with a particle size exceeding g/cc, the polyethylene-coated paper is curled so that one front side, that is, the side on which the photographic emulsion layer is provided, is the outside.

The method for producing the above-mentioned polyolefin-coated paper is as follows. Extrusion coating method.

In other words, polyolefin melted at high temperature,
The most common method is to coat the surface of a running base paper by casting.

Conventional supports for photographic paper are manufactured using the materials and methods described above, but in these conventional methods, the surface smoothness of polyolefin-coated paper is mainly determined by the surface condition of the base paper of the support. Since the surface of the polyolefin-coated paper is greatly affected by this, smoothness is imparted to the surface of the polyolefin-coated paper by methods such as using base paper with a highly smooth surface.

However, there is a limit to the smoothing of the surface of the base paper, and therefore there is also a limit to the smoothing of the polyolefin resin-coated surface.

Another known method for imparting high smoothness to the surface of polyolefin-coated paper is to thicken the resin coating layer. However, when this method is used, not only does it have a negative effect on the curling properties of polyolefin-coated paper, but it also causes undesirable problems such as an increase in manufacturing costs, so although it is not an advantageous method in practical use, do not have.

As a result of repeated research in search of a method for improving the surface smoothness of polyolefin-coated paper used as a support for photographic paper, the present inventor has determined that the polyolefin coating layer on the side where the photographic emulsion layer is provided has a specific range of surface smoothness. Sparrow degree and melt index in a different range than before.

It has been found that a support for photographic paper with high surface smoothness, which does not have the problems of conventional methods, or at least has improved them, can be obtained by forming the support from polyethylene having a high surface smoothness. We have arrived at the present invention. .

The present invention provides a support for photographic paper in which polyolefin resin coating layers are provided on both sides of a base paper, in which the coating layer on the side on which the photographic emulsion layer is provided has a density of 0.910-0.
．． 830g/cc (preferably 0.920-0.9
30 g/CC) and has a melt index of 20-40 g/10 min (preferably 25
-40 g/10 minutes) is provided.

Next, the present invention will be explained in detail.

The photographic paper support of the present invention has a basic structure consisting of a base paper and a polyolefin resin coating layer provided on both sides of the base paper.

The base paper is selected from materials commonly used for photographic paper. Examples of such materials include natural pulp paper, synthetic pulp paper, mixed paper of natural pulp and synthetic pulp, and various laminated papers. Base paper is typically used in thicknesses of 30-500 microns.

In the present invention, the polyolefin resin coating layer on the side (front side) on which the photographic emulsion layer is provided has a density of 0.91O-0.9
30g/cc (preferably 0.920-0.11
30g/cc) and has a melt index of 20-40g/10min (preferably 25-40g/cc).
g/10 min). Here, polyethylene includes both an ethylene homopolymer and a copolymer consisting of ethylene and one or more copolymerizable organic compounds of 10% by weight or less with respect to ethylene.

Examples of such copolymerizable organic compounds include α-olefins such as propylene and butene-1, styrene,
Vinyl compounds such as vinyl stearate, vinyl acetate, acrylic acid, methacrylic acid, acrylamide, esters of vinyl carboxylic acid compounds such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, metals of acrylic acid and methacrylate Mention may be made of diene compounds such as salts, butadiene and isoprene.

As mentioned above, these polyethylenes used for forming the coating layer on the side where the emulsion is provided in the present invention have a density in the range of 0.810-0.830 g/cc and a melt index (MI) of 20- It is necessary to be in the range of 40g/10 minutes. The density of polyethylene is 0.
If the value exceeds 930 g/cc, curling with the emulsion layer side facing inward tends to occur, making it unsuitable as a support for photographic paper. Also, the melt index is 20g.
If it is less than /10 minutes, the surface smoothness of the polyethylene coating layer formed will be insufficient, and it will be difficult to achieve the two objectives of the present invention. On the other hand, when the melt index exceeds 40 g and 710 minutes, neck-in (a phenomenon in which the side surfaces of the polyethylene coating layer curve inward) increases, and the stability of the neck-in also becomes poor. Therefore,
The polyethylene used in the present invention must simultaneously satisfy both the above-mentioned density limitations and melt index limitations. In addition, the bo-reethylene density is, for example,
It can be measured according to ASTM-D t505-88, and the melt index JtJjSK 8?1iO
-1988 can be measured by 0 In the present invention,
The values obtained by these measurement methods are used as the standard.

There is no particular restriction on the molecular weight of these polyethylenes as long as extrusion coating is possible, but polyethylenes having a molecular weight in the range of 20,000 to 200,000 are usually used. The polyethylene of the present invention may be low density polyethylene alone, or may be a mixture prepared by mixing low density polyethylene and medium density and/or high richness polyethylene to have a density and melt index within the above specific range. Any form is acceptable.

It is desirable to use extrusion coating techniques, such as those utilized in the prior art, to apply the polyethylene of the present invention to the base paper for a photographic paper support to form a resin coating layer. Examples of equipment for carrying out this extrusion coating method include known polyethylene extruders and laminators.

There is no particular restriction on the thickness of the resin coating layer made of polyethylene of the present invention, which is formed on the side where the photographic emulsion layer is provided. It can be determined according to the thickness. Its thickness is typically 10-100 microns,
and especially in the range of 15-30 microns.

In the present invention, the polyolefin resin coating layer on the side (back side) on which the photographic emulsion layer is not provided is formed from a polyolefin resin such as polyethylene, which is conventionally used for forming the back side and has a density exceeding 0.930 g/cc. Further, conditions such as the molecular weight of the polyolefin resin and the thickness of the resin coating layer are determined according to the conditions commonly used in the production of conventional polyolefin-coated paper.

It is already known that various additives such as white pigments, colored pigments, optical brighteners, and antioxidants are added to the polyolefin resin used to form the resin coating layer of polyolefin resin-coated paper for photographic paper. Therefore, it is naturally possible to add such various additives to the polyethylene having a density and melt index within a specific range used in the present invention, and it may be preferable depending on the purpose. Examples include UV absorbers such as 2-hydroxybenzophenone, and distearylpentaerythritol.
Various stabilizers such as antioxidants such as diphosphites;
Fillers such as titanium oxide, zinc oxide, talc, clay, calcium carbonate, white pigments such as lithopone, and inorganic pigments such as ultramarine; dyes such as phthalocyanine; surfactants such as zinc stearate; l,4-di( Examples include the addition of optical brighteners such as benzoxacylyl-2) naphthalene.

Regarding the types, amounts, and methods of adding such various additives, see, for example, U.S. Patent No. 3:833.380;
No. 4.1139.188, No. 3,501,298,
No. 3,449. No. 257, No. 3, 4! 3! It, 78
It is described in detail in publications such as No. 2. or,
These additives can also be applied onto the coating layer after it is formed, as described in US Pat. No. 3,884,892.

Further, the surface of the polyethylene coating layer on the side where the emulsion layer of the support for photographic paper of the present invention is provided may be subjected to surface activation treatments such as corona discharge treatment and flame treatment. No. 2,715,07 for
No. 5, $2,848,727, No. 3゜5411.40
No. 6, No. 3,590, 10? These treatments can also be performed in the present invention. Furthermore, if necessary, an undercoat layer made of gelatin or the like may be provided on the surface of the polyethylene coating layer to improve adhesion to the photographic emulsion layer. ′”j In order to coat the support for photographic paper of the present invention with a photographic emulsion to produce photographic paper, methods conventionally used for manufacturing photographic paper can be used. For processing such as development and fixing of photographic paper manufactured by ) , C, E, ni, Me
ss rTHE THEORY 0FTHE P)
IOTOGRAPHIC PROCESS J 3rd,
It is described in detail in books such as , ed.

As described in detail above, the support for photographic paper of the present invention can be manufactured by selecting polyethylene having physical properties within a specific range as the material for the resin coating layer on the side where the photographic emulsion layer is provided. This makes it possible to improve the smoothness of the resin coating layer without increasing the curling property or the manufacturing cost, and therefore, it is of high practical value.

Next, Examples and Comparative Examples of the present invention will be described.

[Example 1-3 and Comparative Example 1-3] Basis weight 180g/
m' on one side (front surface) of the base paper for water-resistant photographic paper support,
An extrusion coating method using a laminator with a mirror-finished cooling roll surface to coat polyethylene (homopolymer, containing 10% by weight of rutile titanium oxide) having the density and melt index (MI) listed in Table 1. A coating layer having a thickness of 30 microns was formed by extrusion at a temperature of 310°C. On the other side (back side),
Density is 0.960g/cc, melt index is 2
5g/10min high enrichment polyethylene extruded, thickness 25
A polyolefin coated paper having a resin coating layer on both sides was produced by forming a micron coating layer.

The polyolefin-coated paper obtained as described above was evaluated for surface smoothness and curling property on the front side.

Regarding smoothness, since the method of visually determining smoothness through mutual comparison is the most accurate and practical, this visual determination based on mutual comparison was used as the standard. That is, each sample of the obtained polyolefin-coated paper was compared with each other, and based on the difference in smoothness, the smoothness of each sample was graded into five grades (A, B, C, D) from good to poor. , E
). Here, A means the best smoothness,
On the other hand, E means the state with the lowest smoothness.

Regarding the curling property, a circular sample with a diameter of 10 cm was cut from polyolefin-coated paper, and this circular sample was
℃ and 60% RH for 24 hours, and in the 0 judgment using the method of judging curls that have occurred, curls appeared with the front side, that is, the side on which the photographic emulsion layer is provided, facing outward. The sample was judged as (+). This phenomenon is preferable as a support for photographic paper.
On the other hand, the sample with curls with the front side facing inward (-)
It was determined that This phenomenon is undesirable as a support for photographic paper and is unsuitable for practical use. In addition, a value was calculated by subtracting the length of the chord connecting both ends along the curl after curling from the diameter (10 cm) of the circular sample before curling, and this was used as an evaluation of the degree of curling. The larger the value, the more severe the curl.

The results obtained are shown in Table 1.

Table 1 Polyethylene physical properties Smoothness Curl density (g/cc
) MI (g/10 min) Evaluation Evaluation Example 1 0.92630 B (+)0.
3cm2 0, a22 38A
(+)0.5cm3 0.930 25
B (+)0.1cm Comparative Example 1 0.1128 2 E
(+)0.3cm2 0.915 15
0 (+)O, 7cm3 0.960
30 B (-)0.1cm':

Claims (1)

[Scope of Claims] 1. In a photographic paper support comprising polyolein resin coating layers provided on both sides of a base paper, the coating layer on the side on which the photographic emulsion layer is provided has a density of 0:81O-0,930g.
/cc and melt index is 20-
1. A support for photographic paper, characterized in that it is formed from polyethylene in a range of 40 g/10 min. 2. The density of polyethylene is 0.820-0. l130g
/CC and melt index is 25-
The support for photographic paper according to claim 1, characterized in that the support is in the range of 40 g/10 minutes.