The use of neutral paper as a package material for a photosensitive material

Abstract: A neutral paper comprises 20 to 100 % of partially chemically processed pulp produced in a 65 to 95 % yield using a cooking agent consisting essentially of NaOH, Na₂CO₃, NaHCO₃, Na₂SO₃, NaHSO₃ or a combination thereof and has a pH of 6 to 9. A paper tube made of the above paper joined by emulsion adhesive or water-soluble adhesive of pH 6 to 9 is also provided.

Description: This invention relates to the use of a neutral paper as a package material for a photosensitive material or a tube being in contact with or close to a photosensitive material. Papers used as materials for photosensitive materials such as a protecting sheet or a paper tube are made from chemical pulp (JP-A-58-43730) and therefore, the yield of the pulp from wood is low resulting in high costs. On the other hand, papers made from high yield pulp are used in a wide range for various packaging materials such as a paperboard because of their low price and high rigidity. The high yield pulp includes mechanical pulp produced by a mechanical process such as groundwood pulp, refiner groundwood pulp and thermomechanical pulp and partially chemically processed pulp produced by a partial chemical process such as chemigroundwood pulp and chemithermomechanical pulp. The mechanical pulp is not preferred for packaging materials for photosensitive materials because it contains lignin and resin extracts of wood in addition to cellulose. The partially chemically processed pulp is also not preferred for a packaging material for a photosensitive material because it contains a high amount of lignin. Therefore, the partially chemically processed pulp has not been used for packaging materials for photosensitive materials. If a conventional paper made from partially chemically processed pulp is used as a packaging material for photosensitive materials, it adversely affects the photosensitive material such as by fogging. It is the object of the present invention to provide a neutral paper which is cheep and does not adversely affect the photosensitive material. Said object is achieved by use of a neutral paper which comprises 20 to 100% of partially chemically processed pulp produced in a 65 to 95% yield by using a cooking agent consisting essentially of NaOH, Na₂CO₃, NaHCO₃, Na₂SO₃, NaHSO₃ or a combination thereof and which has a pH of 6 to 9, as a package material for a photosensitive material, and the use of said neutral paper as a tube being in contact with or close to a photosensitive material. The use of Na₂S as a cooking agent adversely affects photosensitive materials. When Na₂SO₃ and Na₂CO₃ are used in combination as the cooking agent in the monosulfite process, the sensitivity of a color photographic paper is increased which is caused by the acidity of the paper. When the pH is not less than 6, the increase of the sensitivity is, however, within a tolerance limit, particularly, when the pH is not less than 7, an increase of the sensitivity does not occur. When NaOH and Na₂CO₃ are used in combination as the cooking agent in the soda process, the sensitivity of a color photographic paper is decreased which is caused by the alkali in the paper. When the pH is not more than 9, the decrease of the sensitivity is within a tolerance limit; particularly, when the pH is not more than 8,5, a decrease of the sensitivity does not occur. The partially chemically processed pulp includes semichemical pulp, chemiground pulp and chemithermo-mechanical pulp produced in a yield of 65 to 95% , preferably 80 to 90%. The yield is indicated as yield from wood chips to paper, corresponding to the cooling yield. The neutral paper may be composed of the above partially chemically processed pulp only, and unbleached kraft pulp may be added to the partially chemically processed pulp in order to prohibit breaking during paper making and to improve the weakness due to lignin. The partially chemically processed pulp is produced in the partially chemically processed process and contains a high amount of lignin. To increase the quantity of the partially chemically processed pulp is preferred for products which need light-shielding because of a high opacity. The pH of the neutral paper is adjusted to 6 to 9, preferably 6.5 to 8.5 according to JIS P 8113 § 4,2. If the pH of the neutral paper needs to be raised to 6 to 9, an addition of NaOH, KOH or other alkalies is suitable. The use of NaOH is most preferred. If the pH needs to be lowered, various acids such as H₂SO₄, HCl and CH₃COOH and salts which are acidic in an aqueous solution such as aluminum sulfate can be used. Aluminum sulfate is most preferred. Some photosensitive materials are not strongly affected by acids and alkalis. In this case the neutral paper can be blended with corrugated board old papers, unbleached kraft old papers, or deinked pulp in order to save costs and resources. The above blending materials are restricted to those which hardly adversely affect the photosensitive materials. Alternatively they are removed by washing during the breaking process. The content of the partially chemically processed pulp is from 20 to 100%, preferably from 50 to 100%, more preferably from 80 to 100%. The neutral paper usually has an area weight in the range of 100 to 800 g/m², desirably in the range of 200 to 600 g/m². The method for making the neutral paper is not restricted. When a thick board is made, a modified starch, or a corn starch is preferably blended in order to improve the ply bond strength during making a multi-ply paper using a cylinder machine. The neutral paper is preferably located to touch the photosensitive material. The paper tube is formed by joining the above neutral paper with an emulsion adhesive or a water-soluble adhesive having a pH of 6 to 9. When the pH of the adhesive is less than 6 or beyond 9, an increase or decrease of the sensitivity which is out of the tolerance limit occurs. The paper tube is usually a laminate of the neutral paper. The emulsion adhesive includes polyvinyl acetate, polyacryl, ethylene-vinyl acetate (EVA), and styrene-butadiene rubber (SBR). The water-soluble adhesive includes natural polymers such as starch, sea wead, and protein, modified substances of cellulose, and starch, and synthetic polymers such as polyvinyl alcohol (PVA) sodium polyacrylate. The paper tube may be utilized as the core for winding a paper, a foil or a web in addition to a photosensitive strip material. The neutral paper may be utilized for packaging materials of various products such as protection sheets and boxes for protecting photosensitive materials. The neutral paper is inexpensive by using a partially chemically processed pulp of high yield, and does not adversely affect photosensitive materials. Moreover, the rigidity of the neutral paper is improved by a high content of lignin. The paper tube is inexpensive as well and has a high compressive strength, and moreover, it does not adversely affect photosensitive materials by use of an adhesive having a pH of 6 to 9. The following examples illustrate the invention. Example 1 Pulp: Material: hardwood (L material) Cooking Agent: Na₂SO₃ and Na₂CO₃ Yield: 83 % pH: 7.5 (adjusted with NaOH) Neutral Paper: area weight : 380 g/m². Example 2 Pulp: Material: hardwood (L material) Cooking Agent: NaOH and Na₂CO₃ Yield: 90 % pH: 8.5 (adjusted with Al₂(SO₄)₃) Neutral Paper: area weight : 380 g/m². Example 3 Pulp: The same pulp as Example 2: 80 % Soft wood unbleached kraft pulp: 20 % (NUKP) pH: 8.0 (adjusted with Al₂(SO₄)₃) Neutral Paper: area weight : 380 g/m². Comparative Example 1 Comparative Example 1 is the same as Example 1 except of using unadjusted pulp of pH 5. Comparative Example 2 Comparative Example 2 is the same as Example 2 except of using unadjusted pulp of pH 9.5. Conventional Example 1 Pulp: Soft wood bleached sulphite pulp: 100 % (NBSP) Material: soft wood (N material) Cooking Agent: H₂SO₃, NaHSO₃ and Na₂SO₃ Yield: 46 % pH: 5.0 Paper: area weight: 400 g/m². The above papers were placed in an atmosphere of 20°C and 65 % RH for two days to adjust the moisture, and were cut into sizes of 4 cm x 15 cm. The papers were packaged together with color photographic papers in seal by moistureproof bags, kept at 50°C for five days and then taken out. The color photographic papers were exposed and developed, and the exposure index according as 0,5 of reflection density was measured. The moistureproof bags have a water vapor transmission of less than 0,5 g/m² in 24 hours and an aluminum foil with a thickness of 7 um. A package bag with photographic papers alone was provided as a blank. The exposure index of the blank was subtracted from the exposure index of the above samples and the results are indicated as variation of exposure index in Table 1. Samples Variation of Exposure Index Example 1 0 Example 2 -0.01 Example 3 +0.01 Comparative Example 1 +0.07 Comparative Example 2 -0.05 Conventional Example 1 +0.01 Example 4 Paper tubes were made of the paper of Examples 1, 2 or 3 or Conventional Example 1 using a polyvinyl acetate adhesive with a pH of 6.5. The paper tubes had an inner diameter of 76,2 mm, a length of 100 mm and were 10 ply. The paper tubes were kept at 40°C for one day to dry and then at 20°C and 65 % RH for three days to adjust the moisture. A color photographic paper was wound on the paper tube one time and the paper tube was placed in the above moistureproof bag in a seal. The above treatments were conducted and the results were compared. Moreover, other paper tubes adjusted in moisture were provided, the paper tube was pressed in the diameter direction at 10 mm per minute by two parallel plates, and the maximum load was measured. The results are shown in Table 2. Samples Variation of Exposure Index Strength against Pressure (kg) Example 1 +0.02 105 Example 2 +0.01 97 Example 3 +0.02 98 Conventional Example 1 +0.02 60

Claims: Use of a neutral paper which comprises 20 to 100% of partially chemically processed pulp produced in a 65 to 95% yield by using a cooking agent consisting essentially of NaOH, Na₂CO₃, NaHCO₃, Na₂SO₃, NaHSO₃ or a combination thereof and which has a pH of 6 to 9, as a package material for a photosensitive material. The use of claim 1 wherein the partially chemically processed pulp is produced by using Na₂SO₃ and Na₂CO₃ as the cooking agent and wherein the pH is adjusted by adding NaOH. The use of claim 1 wherein the partially chemically processed pulp is produced by using NaOH and Na₂CO₃ as the cooking agent and wherein the pH is adjusted by adding aluminum sulfate. The use of claim 1 wherein the neutral paper is located to touch the photosensitive material. Use of a neutral paper which comprises 20 to 100% of partially chemically processed pulp produced in a 65 to 95 % yield by using a cooking agent consisting essentially of NaOH, Na₂CO₃, NaHCO₃, Na₂SO₃, NaHSO₃ or a combination thereof and which has a pH of 6 to 9, as a tube being in contact with or close to a photosensitive material. The use of claim 5 wherein the neutral paper is joined using an emulsion adhesive or a water-soluble adhesive having a pH of 6 to 9.

Inventors: NISHIYAMA YOSHIHIRO C O FUJI P, SETO YOSHIHIRO C O FUJI PHOTO, NISHIYAMA, YOSHIHIRO, C/O FUJI PHOTO FILM CO. LTD., SETO, YOSHIHIRO, C/O FUJI PHOTO FILM CO. LTD.
Applicants: FUJI PHOTO FILM CO LTD, FUJI PHOTO FILM CO., LTD.
Application year: 1990
Main classification: D21H27
IPC codes: D21B1, D21C3, G03C1, D21H11, B65H75