JPH0361936B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a photographic paper support having a smooth surface on which a light-sensitive emulsion is coated. More specifically, the present invention relates to a photographic paper support in which the paper layer coated with a thermoplastic resin is smoothed to thereby smooth the coated resin surface on which a photosensitive emulsion is applied. Photographic paper manufactured by coating with thermoplastic resin differs from conventional photographic paper using baryta paper.
Print finishing is performed without ferrotyping due to poor heat resistance and lack of water vapor permeability of the support. For this reason, the smoothness of the finished photographic paper surface is largely controlled by the smoothness of the paper layer. Therefore, in order to obtain photographic paper with good smoothness, it is necessary to form a smooth paper layer. The smoothness of the resin-coated photographic paper support (hereinafter referred to as base paper) is defined in JIS P-8119.
It is not measured by the "Smoothness test method using a paper and paperboard tester," but refers to regular ripple-like irregularities parallel to the longitudinal direction of the base paper (paper machine flow direction). The visual smoothness of photographic paper is controlled by the degree of regular ripple-like unevenness and does not directly depend on the degree of irregular unevenness measured with a Beck tester. The smoothness of base paper varies depending on the type of pulp used as a raw material, pulp treatment, added chemicals, papermaking method, papermaking conditions, post-treatment, etc. Among these, the properties of the raw material pulp are particularly important. Although the base paper is smoothed in the calendering step of the post-processing process, depending on the nature of the raw material pulp, even if the calendering treatment is strengthened to some extent, smoothing may not proceed. According to the present invention, by forming a paper layer in which the amount of voids with a pore size of 0.4 μm or less measured by mercury porosimetry is 0.04 ml/g or more, a smooth base paper with few ripple-like irregularities can be obtained. I can do it. The porosity is measured by the mercury porosimetry described in the present invention by the procedure described below. The sample is buried in a mercury reservoir, and pressure is applied to the mercury using ethanol, etc. as a medium, and the applied pressure and sample (porous) are
The amount of mercury that has entered the sample (corresponds to the amount of voids in the sample)
It is a measurement method that records the relationship between Here, assuming that the void in the sample is cylindrical, the radius of the cylinder (rμ
The following relational expression (Kelvin's equation) is established between m) and the pressure applied to mercury (Ppa), and the pore diameter can be determined from the applied pressure from this equation. r (μm) = 735.5/P (Kpa) The measurement was performed using a Carlo Erba Model 1500 mercury porosimeter. The detailed measurement method is based on the method described in the Journal of the Paper and Pulp Technology Association (Vol. 33, No. 5, page 39). The pores with a pore diameter of 0.4 μm or less mentioned in the claims correspond to the tail on the small pore diameter side from the peak position of the pore distribution. This point can be easily understood by looking at Figure 1. In Fig. 1, the curve marked with symbol A represents the pore distribution of base paper made from LBKP, and the curve marked with symbol B represents the pore distribution of base paper made from LBSP. This peak in the void volume distribution curve is caused by fiber gaps in the sheet, but this is a problem in the present invention.
The voids with a pore diameter of 0.4 μm or less correspond to irregularities on the fiber surface, particularly voids near the bonding points between fibers, and voids between thin layers within the fiber cells (not within the lumen). In order to obtain smoothness of the base paper, it is necessary for the layered structure within the fiber cell wall to be peeled between layers during calendering, causing slips, and that microscopic voids must exist within the fiber cell wall. The present inventors have discovered that the ripple-like regular unevenness that particularly affects the visual smoothness is caused by the thickness of 0.4μ of the paper layer.
It was revealed that the pore size is controlled by the amount of pores with a diameter of m or less. According to the present invention, if the amount of voids with a pore size of 0.4 μm or less is 0.04 ml/g or more, the interlayers in the fiber walls are loose and the interfiber bonds do not develop.
The fibers are also crushed well and good smoothness can be obtained. By calendering, the amount of large voids between fibers corresponding to the main peak of the void amount distribution curve is greatly reduced, but the amount of voids is not significantly reduced in the void region of 0.4 μm or less, which is the target of the present invention. This is because voids of 0.4 μm or less contribute to increasing the flexibility of the fibers, and are not directly related to the apparent density of the paper layer (which is controlled by the amount of voids in the entire paper layer). That's what it means. This effect becomes greater as the amount of voids of 0.4 μm or less increases, but as shown in FIG. 2, satisfactory smoothness can be obtained in a region exceeding 0.04 ml/g. The scale on the vertical axis in Figure 2 is the smoothness determined visually.
The grading was determined as follows. Grade A Only extremely fine irregularities B Fine irregularities and extremely small ripples C Slightly noticeable ripples D Large ripples A grade of B or higher is a satisfactory level. The photographic paper support of the present invention contains additives commonly used in paper making, such as antifoggants, fillers, dyes, sizing agents, paper strength enhancers, fixing agents, and retention improvers, as required. It is also possible to perform surface treatment with starch, polyvinyl alcohol, gelatin, etc., and antistatic treatment with sodium sulfate, sodium chloride, aluminum chloride, etc. on the base paper, if necessary. The polyolefin resin may be a homopolymer of α-olefin such as ethylene or propylene or a homopolymer of α-olefin such as ethylene or propylene.
Preference is given to copolymers consisting of .alpha.-olefins or copolymers of .alpha.-olefins as a main component with other monomers copolymerizable therewith, and mixtures thereof. In addition, white pigments such as titanium oxide and alumina, colored pigments, stabilizers that are usually mixed with resins,
Antioxidants, dispersants, lubricants, etc. may be added. The polyolefin resin-coated photographic paper support of the present invention is produced by a so-called extrusion coating method in which heated and molten resin is cast onto a running base paper, and both sides of the support are coated with the resin. The polyolefin resin-coated photographic paper support of the present invention includes color photographic paper paper, black and white photographic paper paper,
Used for typesetting photographic paper, photographic photographic paper, etc. To form the paper layer with the void of the present invention,
As the raw material pulp, voids with a pore size of 0.4 μm or less are used.
Use a large amount of hardwood bleached sulfite pulp (LBSP). Even in the same LBSP, the amount of voids changes depending on the degree of sulfite cooking, and the more advanced the degree of cooking, the greater the amount of voids. However, if the degree of digestion is too high, the paper layer will have insufficient strength as a photographic paper support, which is not preferable. As a result of studies conducted by the present inventors, the amount of voids with pores of 0.4 μm or less in the paper layer after calendering was 0.04 ml/g.
As described above, it has become clear that by adjusting the blending ratio of LBSP, it is possible to provide a support for photographic paper with the desired visual smoothness. The blending ratio of LBSP depends on the amount of vacancy in the LBSP, but it must be at least 30%. Method for Forming Paper Layer The photographic paper support of the present invention is one in which the surface of the paper layer (at least one side) is coated with a thermoplastic resin, and the paper layer of this support is formed by the following procedure. . Bleached pulp is beaten with a refiner or beater, a fine fiber retention improver, filler, and sizing agent are added, and the pulp is fed to a paper machine, formed into a sheet, dried, and then calendered. As the bleached pulp, hardwood bleached kraft pulp (LBKP) and hardwood bleached sulfite pulp (LBSP) are used alone or in combination. The degree of beating is adjusted according to the Canadian standard water filtration rate. In calendering, the linear pressure is adjusted so that the paper web obtained has appropriate density and smoothness. The above formulation and manufacturing conditions vary depending on the paper machine used and cannot be generally provided. The type of pulp, mixing ratio, degree of beating, and calender linear pressure are adjusted so that the formed paper layer exhibits the characteristics described in the claims. The present invention will be described in detail below with reference to Examples, but the present invention is not limited to the Examples. Example 1 Domestic hardwood chips were cooked under the following conditions (1) and (2).
LBSP was adjusted by bleaching. Then condition LBSP
A paper layer was formed by beating under (3) and paper-making under condition (4), and then both sides of the paper layer were coated with resin under condition (5) to produce a photographic paper support. (1) Cooking chemical solution: PH1.5 Total acid 6% Maximum temperature: 140℃ Liquid ratio: 5 Total cooking time: 6 hours Maximum temperature holding time: 2 hours 20 minutes (2) Bleaching Chlorine (abbreviation C) → Sodium hydroxide Bleach in the order of (abbreviation E) → sodium hypochlorite (abbreviation H) → chlorine dioxide (abbreviation D). The temperature, time, pulp concentration, and chemical addition rate of each stage are shown in Table 1.

[Table] (3) Beating: Beat with a refiner to Canadian standard water level (JISP-8121-76) 350ml. (4) Paper making: Fourdrinier paper machine with a paper width of 500 mm at a paper speed of 15 m/
The paper was made into paper in 1 minute, and wet pressing was carried out by passing it twice through a roll press with a linear pressure of 20 kg/cm. The calendering process was performed once through a super calender with a linear pressure of 60 kg/cm. (5) Resin coating: After corona treatment of calendered paper, low-density polyethylene containing 10% titanium oxide is coated on the surface and low-density polyethylene is coated on the back with a coating of 30 μm using an extrusion coating machine at a resin temperature of 330°C. A photographic paper support was obtained by coating to a certain thickness. This sample is designated as sample number 1. Example 2 The maximum temperature holding time during cooking was 2 hours,
The chemical addition rate was increased to 3 in the sodium hydroxide treatment stage of bleaching.
A photographic paper support was obtained in the same manner as in Example 1 except that the percentage was changed. This sample will be designated as sample number 2. Comparative Example 1 A photographic paper support was obtained in the same manner as in Example 1, except that the maximum temperature holding time during cooking was 1 hour and 40 minutes, and the chemical addition rate was 3% in the sodium hydroxide treatment stage of bleaching. Ta. This sample will be designated as sample number 3. Comparative Example 2 A photographic paper support was obtained in the same manner as in Example 1, except that commercially available LBKP (manufactured from domestic hardwood) was used as the pulp. This sample is designated as sample number 4. The above results are summarized in Table 2.

[Table] As is clear from Table 2, photographic paper supports made of base paper with voids of 0.4 μm or less and 0.04 ml/g or more have good smoothness (visual grade).

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the pore diameter (logarithmic scale) of the pores in the base paper and the pore frequency. FIG. 2 is a graph showing the relationship between the amount of voids of 0.4 μm or less in the base paper and the visual smoothness grade of the photographic paper support. B...Void distribution of base paper used as raw material for LBKP, RO...
...Void distribution of base paper used as raw material for LBSP.

Claims (1)

[Claims] 1. A photographic paper support coated with a thermoplastic resin on the surface of the paper layer, in which the paper layer is made of bleached hardwood manufactured by the sulfite method with a maximum cooking temperature of 140°C or higher and a holding time of 1 hour and 50 minutes or more. 1. A photographic paper support comprising pulp and having a void content of 0.04 ml/g or more with a pore diameter of 0.4 μm or less as measured by mercury porosimetry after calender treatment.