DE68922001T2 - Packaging material for photosensitive goods. - Google Patents

Description

This invention relates to packaging materials for photosensitive materials.

For packaging articles or materials that lose their commercial value under the effect of light, such as photosensitive materials, packaging bags (containers) that can completely shield light are used. The packaging bags must have sufficient physical strength, such as tensile strength, tear resistance and puncture resistance, depending on the size and weight of the materials to be packaged, as well as the above-mentioned light-shielding ability. In addition, since the opening portion of the packaging bags is usually heat-sealed, suitable heat-sealing properties are required, and in order to prevent electrostatic charge as a result of friction between the photosensitive materials and the packaging bag, antistatic properties are also required.

So far, as packaging materials used for such a packaging bag, there is a laminate film consisting of a high-pressure resin film layer of branched low-density polyethylene (LDPE) containing a light-shielding material, an aluminum foil layer and a bleached kraft paper layer, which are each laminated by means of an LDPE resin extrusion adhesive layer. In general, it is difficult to impart to single layer films the various properties required as packaging materials for light-sensitive photographic materials, and therefore, only a thick light-shielding LDPE resin single layer film containing carbon black has been used for packaging light-weight light-sensitive photographic materials having a low photosensitivity contained in protective sleeve papers and for packaging light-weight photographic copy papers.

As a packaging material, particularly as a light-shielding heat-sealing bag for packaging a roll of a photographic light-sensitive material and sheets of a light-sensitive material weighing more than 1 kg, the inventor has already described a laminate film consisting of a cross-laminated film using uniaxially stretched high-density polyethylene (HDPE) resin films having high physical strength and an LDPE resin film containing at least either a light-shielding material or an antistatic agent (US-A-4,147,291). The inventor has also described an inexpensive cross-laminated film having improved heat-sealing properties and light-shielding properties (US-A-4,258,848).

In addition, the inventor has described other packaging materials consisting of a laminate film containing a light-shielding film layer made of a linear low-density polyethylene resin (L-LDPE) mixed with carbon black, which have high physical strength, excellent heat-sealing properties and are inexpensive (US-A-4 701 359, Japanese Patent KOKAI No. 18547/1987). As a packaging material in which a metallized film is used, the inventor has also described a packaging material for photosensitive materials consisting of a metallized film layer and two L-LDPE resin polymer layers containing more than 50% by weight of L-LDPE resin laminated to both sides of the metallized film layer. One or both L-LDPE resin polymer layers contain(s) 0.3 to 30% by weight of a light-shielding material (US-A-4 663 218).

However, the above-mentioned conventional laminate film consisting of the LDPE resin film layer, the aluminum foil layer and the bleached kraft paper layer is thick and rigid, and therefore the handling in packaging is poor. The physical strength, such as tear resistance, is low and the tendency to curl is large. In addition, the heat sealing properties are poor and it is expensive. As a result, it has been difficult to ensure good light-shielding, moisture-proofing and good gas barrier properties with this packaging material due to the occurrence of dust, punctures, cracks or opening of the heat-sealed portion during packaging or during transportation. In the case of the thick light-shielding LDPE resin single-layer film, the physical strength is low and the heat sealing properties are poor. Therefore, it is difficult to fully guarantee the quality of the photosensitive materials.

The packaging materials having a cross-laminated film as described in US-A-4 147 291 and US-A-4 258 848 have high physical strength such as tear strength and tensile strength and are used in practice to this day for packaging heavy materials. However, since a uniaxially stretched HDPE resin film is used as a heat sealing layer used, they are stiff and their handling in packaging and heat sealing properties are poor. In addition, the physical strength and heat sealing strength vary and curling tends to occur due to the uneven thickness of an adhesive layer, the uneven stretch ratio of the uniaxially stretched HDPE resin films or the like. Therefore, troubles occur in the processing or packaging process and occasionally they are punctured or the heat-sealed portion comes off during transportation. In addition, the cross-laminated film in which a longitudinally uniaxially stretched film is laminated on a transversely uniaxially stretched film so that their respective orientation axes cross each other is expensive because two kinds of film forming devices are required.

Since the packaging materials using a light-shielding L-LDPE resin single-layer film as described in U.S. Patent No. 4,701,359 or Japanese Patent KOKAI No. 18547/1987 are inexpensive and have excellent heat sealing properties and physical strength such as tear resistance and puncture resistance, they are excellent as packaging materials for photosensitive materials. However, in the case of packaging a heavy photosensitive material or a photosensitive material having sharp edges, the light-shielding L-LDPE resin films are occasionally stretched and thinned due to their low Young's modulus, although they are neither punctured nor torn. In this case, sufficient light-shielding and moisture-proofing cannot be ensured. In addition, in the case of using an L-LDPE resin having a density of less than 0.925 g/cm3, the sliding properties are insufficient and blocking easily occurs. In the case of US-A-4 663 218 described, the physical strength such as tear resistance is improved. However, when a light-shielding material was incorporated into only one side of the L-LDPE resin polymer layer, the tendency to curl was strong and the processability was poor. In addition, when the melting point of both L-LDPE resin polymer layers was almost the same, melting and cracking of the outer layer occurred if the heat sealer was not modified. As a result, pinholes occurred and the strength was reduced. Also, the appearance was poor. Therefore, this packaging material has been used in practice as a laminate film laminated on a nylon film or vacuum-deposited aluminum polyester film having a high Young's modulus and high heat resistance. However, the tendency to curl of the laminate film was strong and the nylon film and vacuum-deposited aluminum polyester film were expensive.

The inventor has also developed a co-extruded multilayer inflatable film of an L-LDPE resin film layer and a polyolefin resin film layer as a film having improved physical strength such as puncture resistance (Japanese Patent KOKAI No. 62-18548). Such a co-extruded multilayer inflatable film is manufactured by using an inflatable film forming apparatus such as that shown in Fig. 7. The inflatable film forming apparatus consists of extruders 8 which heat and knead the resin, a ring die 9 which extrudes the molten resin from the slot (not shown) into a tubular shape, a blowing hose 10 for blowing compressed air, an air ring 11 for cooling the molten resin extruded into a tubular shape, guide rollers 12 which guide the tubular resin film 13, guide plates 14 which make the tubular resin film 13 flat (even), a pair of nip rollers 15 for receiving the tubular resin film 13 and a reel 16 for winding the film. When the above-mentioned co-extruded multilayer inflatable film consisting of an L-LDPE resin film layer and a polyolefin resin film layer is molded using the inflatable film molding apparatus, an L-LDPE resin and an HDPE resin each having the prescribed compositions are melted and kneaded by the extruders 8 and extruded from the circular slit of the ring die 9 so that the L-LDPE resin film layer is arranged inside, that is, the HDPE resin film layer is arranged outside. At this time, compressed air is blown in through the blowing hose 10 and cooling air is blown out from the air ring 11. The tubular resin film 13 having the prescribed diameter thus formed rises due to the guidance of the guide rollers 12...12 and is flattened by the guide plates 14. The film is formed into a sheet by passing through the squeezing roller 15 and wound onto the reel 16.

However, in the above-described inflatable film molding method in which the L-LDPE resin film layer is disposed inside and the HDPE resin film layer is disposed outside, there is a problem that the L-LDPE resin film layers come into contact with each other so that blockage occurs when the same is wound onto the reel 16. Moreover, a fatty acid or fatty acid compound such as fatty acid amide, paraffin wax or fatty acid metal salt was added to the HDPE resin film layer in order to improve the film moldability or to render halogen compounds harmless, and the additive migrated outward from the HDPE resin film layer and adhered to the guide rollers 12, causing a pressure mark and abrasion on the film 13. The adhered additive came off from the guide rollers 12 and adhered to the film in the form of white lumps. When the film was wound up, the white lumps caused a film break as well as a pressure mark on the film. On the other hand, when the L-LDPE resin film layer was arranged outside and the HDPE resin film layer was arranged inside, wrinkles and furrows occurred and the film yield decreased.

On the other hand, double-layer bags have been used as packaging bags for relatively heavy and large photographic photosensitive materials. Such a double-layer bag, for example, consisted of an outer film consisting of a Clupak paper, Duostress paper or unbleached kraft paper coated with polyethylene resin by extrusion lamination, and an inner film consisting of an aluminum foil and two uniform polyethylene resin films containing carbon black laminated on both sides of the aluminum foil. The type of product packaged therewith, instructions and the like were printed on the outer surface of the outer film during the packaging process or other process. The double-layer bag has excellent physical strength, and when the paper of the outer film contains a substance harmful to photographic photosensitive materials, its influence can be shielded by the inner film which comes into contact with the photographic photosensitive materials. However, the double-layer bags have problems such as poor processability and high cost of the packaging material. Therefore, various laminate films have been developed to eliminate the disadvantage of the bag manufacturing process to make the bag double-layered. An example of a laminate film as shown in Fig. 6 consists of an aluminum foil layer 27, a bleached kraft paper layer 26 mainly composed of bleached kraft pulp, and an LDPE resin film layer 28a mixed with a light-shielding material, which are bonded to the film using an adhesive layer 3. both sides of the aluminum foil layer 27. When a bag is made therefrom, the bleached kraft paper layer 26 is arranged on the outside, that is, the LDPE resin film layer 28a is arranged on the inside. The physical strength of the laminate film is sufficient for the packaging of light-weight photographic photosensitive materials, but it is not sufficient for the packaging of heavy-weight photographic photosensitive materials. In addition, fibers occasionally adhered to the packaged photographic photosensitive materials, resulting in development failure. Photographic photosensitive materials tend to be degraded (deteriorated) because an oxidation-reduction reaction is used and they contain a dye which tends to be degraded by pH, moisture, heat or the like. Therefore, even when it was necessary to use an oxidizing or reducing substance for the surface of the packaging material which comes into contact with the photographic photosensitive materials, the type and blending amount of the oxidizing or reducing substance were limited. In addition, when the quality of the light-shielding material was not restricted in terms of particle size, pH value, impurity content, etc., photographic troubles such as fogging, staining and variation in photosensitivity occurred.

An object of the invention is to provide a packaging material for light-sensitive photographic materials which has sufficient physical strength for the packaging of heavy light-sensitive photographic materials and which has few problems with respect to development disturbances.

Another object of the invention is to provide a packaging material for light-sensitive photographic materials which does not adversely affect the light-sensitive photographic materials packaged therewith and is inexpensive.

These objects have been achieved by a packaging material for photographic light-sensitive materials comprising a vacuum-metallized, biaxially stretched thermoplastic resin film layer, a long fiber paper layer in which more than 50% of the fibers have a fiber length longer than 3 mm, containing a paper reinforcing agent and having a pH of 4 to 9 as determined by the cold water extraction method (JIS P-8133), laminated to one side of the above thermoplastic resin film layer, and a polyolefin resin film layer containing 0.1 to 15% by weight of carbon black having a pH of 4 to 9 and an average particle size of 15 to 80 mµm and more than 5% by weight of an ethylene copolymer resin, laminated to the other side.

Figures 1 to 4 show partial sectional views of a preferred embodiment of the invention.

Fig. 5 shows a partial sectional view of a comparative packaging material.

Fig. 6 shows a partial sectional view of a conventional packaging material.

Fig. 7 shows a schematic partial view of an inflation molding device.

Vacuum aluminum metallized biaxially stretched thermoplastic resin film is a biaxially stretched thermoplastic resin film treated using the vacuum deposition process to form an aluminum vacuum vapor deposition layer. The film improves the tensile strength and burst strength of the packaging material and prevents the formation of pinholes, bag tearing and thinning. by stretching the packaging material even when a heavy product is placed on it. It also improves moisture-proofing, gas barrier properties, antistatic properties and light-shielding properties. By biaxially stretching the thermoplastic resin film, the stretched film has a high Young's modulus and excellent moisture-proofing and gas barrier properties even though it is thin. Since the stretched film is heat-resistant, crazing (formation of surface cracks) hardly occurs when the aluminum vacuum evaporation layer is formed. The formation of crazing (surface cracks) in the aluminum vacuum evaporation layer is also prevented by the increased Young's modulus and resistance to stretching. Examples of the resin suitable for the film include a polyester resin, polyamide (nylon) resin, polyethylene resin, polystyrene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, vinylon resin, copolymer resins of the above resins and other resins, e.g., binary, ternary or higher copolymers polymerized by random copolymerization or block copolymerization, modified or crosslinked resins, and resin mixtures of the above resins and other resins. The stretching can be carried out using a known biaxial stretching method, for example, simultaneous biaxial stretching or sequential biaxial stretching, wherein both stretching ratios in the longitudinal direction (MD) and in the transverse direction (CD) are 1.5 to 20 times, preferably 3 to 15 times. The stretching device may be a known device such as a T-die film forming device or an inflatable film forming device. A preferable thickness of the biaxially stretched thermoplastic resin film is 7 to 60 µm. If the thickness is less than 7 µm, wrinkling and cracking occur in the laminating process. (notching) occurs. If the thickness is more than 60 µm, the rigidity is too large. As a result, the bag-making ability and handling are inferior and the film is expensive. The biaxially stretched thermoplastic resin film may be a single-layer film or a co-extruded multi-layer film. In addition, another resin such as a polyvinylidene chloride resin, silicone resin or Teflon resin is coated or printed on the stretched film in the form of a layer or a metal membrane is provided thereon. The metal membrane may be deposited by vacuum deposition, sputtering, ion plating, electron beam deposition or the like.

A preferable thickness of the aluminum vacuum deposition layer is 55 to 1200 Å, particularly 100 to 600 Å, in view of ensuring physical strength, light-shielding, antistatic properties, moisture-proofing and gas-barrier properties, cost and quality. If the thickness is less than 55 Å, the electrostatic charges generated around the aluminum vacuum deposition layer cannot be reduced. It is difficult to ensure moisture-proofing, gas-barrier properties and light-shielding properties. When the thickness is more than 1200 Å, problems arise in respect to the degradation of the stretched film, wrinkling due to shrinkage, formation of hairline cracks (surface cracks) in the vacuum deposition layer caused by the heat of vacuum deposition, and decrease in the physical strength of the packaging bag, although the antistatic properties, moisture-proofing, gas barrier properties and light-shielding properties are still ensured.

If necessary, a protective layer can be provided on the aluminum vacuum deposition layer. Examples The resin usable for the protective layer includes an acrylic resin, cellulose resins such as cellulose acetate resin, a urethane resin, epoxy resin, polyester resin, ionomer resin, polyethylene resin, ethylene copolymer resin and polypropylene resin. Besides, wax, gelatin, polyvinyl alcohol or the like is also usable. The thickness of the protective layer is made extremely thin, for example, thinner than 50 µm, preferably thinner than 5 µm, in order to effectively eliminate static electricity. Such a protective layer can be formed by known extrusion coating, solution coating or spray coating.

More than 50%, preferably more than 70%, of the fibers constituting the long fiber paper layer have a fiber length of more than 3 mm, usually 3 to 7 mm. If the fiber length is less than 3 mm, the formation of paper dust and roughening cannot be effectively prevented. If the fibers having a fiber length of more than 33 mm are less than 50% of the total fibers, the formation of paper dust and roughening cannot be effectively prevented. The paper reinforcing agent is incorporated into the long fiber paper to effectively prevent the formation of paper dust and roughening. Examples of the paper reinforcing agent usable in the present invention include a cation-induced styrene/acrylic copolymer, an aminoamide-epichlorohydrin condensate, carboxymethylcellulose, various polyacrylamides and copolymers thereof, carboxyl-modified polyacrylamide, polyethyleneimine, gum oil resin, sodium silicate, synthetic rubber latex, a non-acetylated PVA fiber, various starches including modified starches, a sulfomethylated resin, urea resin, alkylstyrene resin, alkylketene dimer, gelatin, PVA, casein, methacylamide, polyamideamine-epichlorohydrin, sodium polyacrylate, carboxyl-modified polyvinyl alcohol, hydroxyethylcellulose and the like. A suitable content of the paper strengthening agent is 0.05 to 8 wt%, preferably 0.3 to 5 wt%. A cold water extraction pH (JIS P-8133) of the long fiber paper is in the range of 4 to 9, preferably 5 to 9. If the cold water extraction pH is less than 4 or more than 9, substances harmful to the light-sensitive photographic material are formed. Long fiber neutral papers are particularly preferred. The total content of substances harmful to light-sensitive photographic materials should be less than 1000 ppm. The harmful substances are radioactive substances and the materials obtained by using a radioactive substance, such as the paper produced by using river water, pulps, shredded or waste paper exposed to rain after a nuclear test, mercury, alloys thereof, mercury compounds and agents containing mercury such as mercury, organic mercury agents, a broken fluorescent tube and sludge control agents used for papermaking, secondary treatment products of silicone such as silicone oil and silicone grease, sulfur compounds such as Na₂S, H₂S and Na₂S₂O₃, lead compounds such as PbS and PbSO₄, iron and iron compounds such as iron powder, Fe₂O₃, FeO and FeCl₃, copper and copper compounds such as copper powder, CuO, CuSO₄. and CuCl₂, and aldehydes such as formaldehyde and acetaldehyde. If the content of any of the above substances is more than 1000 ppm, it seriously adversely affects the light-sensitive photographic properties. The adverse effect of the substance can be reduced by neutralization, adsorption or the like. In this case, the content of the above harmful substance can also be more than 1000 ppm. For example, the adverse influence of iron, iron compounds and other metal compounds can be eliminated by adding a chelating agent, and the adverse influence of formaldehyde can be by adding urea, thiourea, a hydrazine compound, dicyandiamide or an acid salt thereof, hydroxylamine or an acid salt thereof such as hydroxylamine hydrochloride or hydroxylamine sulfate, or formamide. The adverse influence of the harmful substances can also be eliminated by selecting the equipment and materials so that the amounts of contamination are minimized, by using clean water such as spring water, and by prohibiting the use of pulp, shredded and waste paper which has been exposed to rain. In order to reduce the formation of paper dust, the surface of the long fiber paper is preferably treated by Yankee calendering or super calendering and the surface strength is preferably more than 6. In order to increase the surface strength of the paper, refining is required. Refining must be carried out so that more than 50% of the fibers have a fiber length of more than 3 mm. The long fiber paper may be a combination paper and it may be white or colored.

The polyolefin resin film layer contains 0.1 to 15 wt% of carbon black having a pH of 4 to 9 and an average particle size of 15 to 80 mm. The carbon black absorbs the substances harmful to photosensitive photographic materials when the long fiber paper is contaminated, and prevents deterioration of photographic properties such as fogging, fluctuation in photosensitivity and decrease in concentration when a photosensitive photographic material is stored for a long period of time in a packaging material according to the invention, in addition to light-shielding. When the pH of the carbon black is less than 4 or more than 9, deterioration of photographic properties such as fogging, fluctuation in photosensitivity and decrease in concentration occurs. concentration. If the average particle size is less than 15 mµm, the carbon black particles aggregate into lumps and a fisheye problem occurs. If the average particle size is more than 80 µm, the light-shielding ability decreases. In addition, it is preferable that the content of free sulfur is less than 1000 ppm because deterioration of photographic properties such as fogging, variation in photosensitivity and decrease in concentration occur when its content is more than 1000 ppm. The carbon black content is 0.1 to 15 wt%. If the content is less than 0.1 wt%, the effect of the carbon black such as ensuring light-shielding, preventing electric charge and preventing oxidation is insufficient; if the content is more than 15 wt%, the physical strength of the film, particularly tear resistance and puncture resistance, become lower and the heat sealing properties become worse. In addition, the surface strength decreases and there is a risk of dust formation. The dust adheres to the light-sensitive photographic materials and causes development problems and contamination.

The polyolefin resin film layer contains more than 5 wt% of an ethylene copolymer resin. The ethylene copolymer resin improves heat sealing properties such as hot tack properties, sealability with other materials, long-term heat sealing strength, heat sealing strength and heat sealing tolerance, and the formation of pinholes in the heat-sealed portion is prevented. The dispersibility of carbon black is also improved. Examples of the ethylene copolymer resin include an EVA resin, EEA resin, EMA resin, EAA resin and L-LDPE resin. The L-LDPE resin is on improving the physical strength, heat sealing properties and dispersibility of the carbon black. The L-LDPE resin is similar to that described earlier except that the preferred MI is 0.4 to 20 g/lO min and the preferred density is 0.87 to 0.95 g/cm³. The content of the ethylene copolymer resin is more than 5 wt%, preferably 15 to 95 wt%. If the content is less than 5 wt%, unless the heat sealing width is increased, the heat sealing properties, particularly the long-term heat sealing strength and the sealability with other materials, are inferior and there is a risk that pinholes are formed. In addition, there is a risk that the heat-sealed portion is opened. When the ethylene copolymer resin is an L-LDPE resin, its suitable content is 5 to 99.9 wt%, preferably 10 to 97 wt%. The polyolefin resin film layer may be oriented or stretched.

The above-mentioned flexible film layers can be laminated by a known method such as heat sealing (hot bar sealing), impulse heat sealing, ultrasonic welding and the like, or by a method using an adhesive (wet lamination, dry lamination, hot melt lamination, extrusion lamination and the like).

The adhesive is selected from the viewpoint that both layers are to be combined with each other, and includes thermoplastic resin hot melt adhesives such as a polyolefin adhesive, hot melt type rubber adhesives and solution type adhesives. Examples of the polyolefin adhesives include a homopolymer and a copolymer of an olefin such as various polyethylenes, polypropylenes, polybutenes and ethylene/propylene copolymers. and L-LDPE, a copolymer of an olefin and another monomer such as ethylene/vinyl acetate copolymer, ethylene/acrylate ester copolymer, various ionomers ("SURLYN" of Dupont, "HIMIRAN" of Mitsui Polychemicals Co., Ltd., etc.) and a graft copolymer. The solution type adhesives are classified into wet lamination adhesives and dry lamination adhesives. The wet lamination adhesives are emulsion type or latex type. Examples of the emulsion type adhesives are polyvinyl acetate emulsion, vinyl acetate/ethylene copolymer emulsion, vinyl acetate/acrylate ester copolymer emulsion, vinyl acetate/maleate ester copolymer emulsion, acrylic copolymer emulsion and ethylene/acrylic acid copolymer emulsion. Examples of the latex type adhesives are natural rubber latex, styrene/butadiene rubber latex, acrylonitrile/butadiene rubber latex and chloroprene rubber latex. An example of the dry lamination adhesives is a polyurethane adhesive. In addition, there may also be used adhesives for melt lamination containing paraffin wax, microcrystalline wax, ethylene/vinyl acetate copolymer and ethylene/ethyl acrylate copolymer, pressure-sensitive adhesives and temperature-sensitive adhesives. The melting point of the adhesive used is preferably more than 5ºC lower than the melting point of the flexible film in order to achieve lamination without adverse effects on the flexible film due to thermal melt adhesion.

The thickness of the adhesive layer formed by extrusion lamination using a thermoplastic resin is usually 6 to 50 µm, preferably 10 to 20 µm. However, the thickness is determined based on the cost, the application speed, the thickness of the total layers and the like, and therefore the thickness is not limited to the above range.

The adhesive strength of the adhesive layer can be improved by applying an anchor coating layer, by physical surface treatment, by treatment with a chemical agent or the like.

An anchor coating agent is a general name for an adhesion promoter and a cross-linking agent used in the field of lamination, and it is also called a primer. Representative examples of the anchor coating agent are as follows:

an organic titanate anchoring coating agent:

Tetrapropyl titanate or tetraisobutyl titanate is used as the main ingredient and tetrastearyl titanate is added as a hydrolysis adjusting agent.

a polyethyleneimine anchoring coating agent:

A relatively high polymer ethyleneimine (-CH₂-CH₂-NH-)n is used. This agent is particularly preferred because it is easy to handle and its pot life (service life) is long.

a polyisocyanate anchoring coating agent:

One-component type: a polymer containing only one isocyanate group,

2-component type: a combination of a polymer having an isocyanate group and a polyester having an OH group.

A chemical reaction, such as a cross-linking reaction, occurs in both types and an adhesion effect is obtained. The pot life (service life) is short and this coating agent is expensive.

a polyester and urethane anchor coating agent:

A saturated polyester resin or a urethane resin is dissolved in a solvent, such as ethyl acetate or toluene.

a polyolefin anchor coating agent; a polybutadiene anchoring coating agent

The anchor coating layer is preferably made extremely thin. The coating method may be a gravure roll coating, a pad roll coating, a curtain coating, a bar coating, a reverse roll coating, a direct roll coating, an air knife coating or the like.

Representative examples of the physical surface treatment are described below. Two or more types of physical surface treatment may be combined, or the physical surface treatment may be combined with coating with an anchor coating agent.

Flame treatment: the running costs are high and there is a risk of fire.

Plasma treatment: Argon gas is converted into plasma and the surface to be bonded is treated with the plasma. The treatment strength is several times that of corona discharge treatment, but the equipment costs for plasma treatment are several tens of times higher than for corona discharge treatment.

Corona discharge treatment: treatable materials are various polymer films and foils, aluminum foil, vacuum-metallized aluminum film, etc. This cheap treatment is widely used and the treatment effect is high.

Sandblasting treatment: Sand such as silica sand is blown under high pressure onto the surface to be bonded and the surface is roughened.

Representative examples of other treatments are the following:

Treatment with a chemical agent: treatment is carried out with a dichromate solution or similar.

Ozone treatment: treatment takes place in a container filled with ozone gas. Even if the resin temperature is reduced during extrusion lamination, the bonding strength is still improved.

Preheating treatment: the flexible film to be subjected to extrusion lamination is preheated using a heating drum, hot air or the like.

Ultraviolet irradiation,

High frequency heating,

dielectric heating,

Microwave heating etc.

The packaging material according to the invention can be used for packaging light-sensitive materials, e.g. light-sensitive photographic materials, foodstuffs, medicines or chemical substances, and it is particularly suitable for packaging light-sensitive silver halide photographic materials, diazo photographic light-sensitive materials, photofixing type light-sensitive and heat-sensitive materials, resin type light-sensitive materials, ultraviolet curing type light-sensitive materials, transfer type heat-developable light-sensitive materials, direct positive type light-sensitive photographic materials, self-developing type light-sensitive photographic materials, light-sensitive materials for a lithographic printing plate and other light-sensitive materials which are degraded (affected) by a small amount of moisture, light or gas.

The packaging form may be conventional and includes a flat single layer bag, a flat double layer bag, a self-standing bag, a single layer folding bag, a double layer folding bag, an inner liner for a moisture-proof container, an inner liner for a room light-fillable light-shielding container, a wrapping paper and a leader paper. The bag-making form may also be conventional and includes heat sealing, side sealing (heat cut sealing), impulse heat sealing, ultrasonic sealing and high frequency sealing. Methods using an adhesive may also be adopted. In the packaging material for photographic light-sensitive materials described above, no release of fibers and no roughening of paper occur in the long fiber paper and they do not adhere to the photographic light-sensitive materials as foreign matter. The long fiber paper improves Young's modulus, heat resistance and writing ability with writing tools. The biaxially stretched thermoplastic resin film layer, metallized with aluminum in vacuum, provides antistatic properties, Moisture-proofing, gas barrier properties and light-shielding properties and prevents the penetration of harmful substances. The polyolefin resin film layer ensures sealing and the carbon black contained therein does not adversely affect the photosensitive photographic materials. The packaging bag made from the packaging material can be a single-layer bag and it has excellent bag-making ability and packaging processability.

Representative embodiments of the packaging material, which include a vacuum aluminum metallized, biaxially stretched thermoplastic resin film layer, a long fiber layer and a polyolefin resin film layer, are illustrated in Figs. 1 to 4.

The packaging material of Fig. 1 consists of a vacuum aluminum-metallized biaxially stretched thermoplastic resin film layer 21 consisting of a biaxially stretched thermoplastic resin film layer 19 and an aluminum vacuum deposition layer 20, a long fiber paper layer 22 laminated as an outer layer on the aluminum vacuum deposition layer 20, and a light-shielding polyolefin resin film layer 23a as an inner layer on the biaxially stretched thermoplastic resin film layer 19, each of which is laminated using an adhesive layer 3.

The packaging material of Fig. 2 is similar to the packaging material of Fig. 1, except that the light-shielding polyolefin resin film layer 23a is replaced by a coextruded multilayer film layer 25a consisting of a light-shielding thermoplastic resin film layer 24a and a light-shielding polyolefin resin film layer 23a.

The packaging material of Fig. 3 is similar to the packaging material of Fig. 2, except that the aluminum vacuum metallized, biaxially stretched thermoplastic resin film layer 21 is turned from the inside out.

The packaging material of Fig. 4 is similar to the packaging material of Fig. 1, except that the light-shielding polyolefin resin film layer 23a is directly laminated using the extrusion lamination method.

Fig. 5 shows a comparative packaging material I similar to the packaging material of Fig. 2, but in which the long fiber paper layer 22 is replaced by a conventional bleached kraft paper layer 26.

Examples

Examples I and II are examples of the packaging material comprising a vacuum aluminum-metallized biaxially stretched thermoplastic resin film layer, a long fiber paper layer and a polyolefin resin film layer.

The packaging material of Example I corresponds to that shown in Fig. 2.

The long fiber paper layer 22 consisted of a bleached kraft paper consisting of fibers with a fiber length of about 4 mm, which contained 2.5 wt.% polyacrylamide resin ("Polystlon" from Arakawa Rinsan Kagaku KK) as a paper reinforcing agent and less than 500 ppm each of substances harmful to light-sensitive photographic materials and had a cold water extraction pH of 4.8, a surface strength of 9 and a basis weight of 35 g/m² as well as a glossy surface by treatment with a Yankee calender, prepared using aluminium sulfate as a fixing agent.

The biaxially stretched thermoplastic resin film 19 of the vacuum aluminum-metallized biaxially stretched thermoplastic resin film layer 21 was a biaxially stretched nylon resin film having a thickness of 15 µm. The thickness of the aluminum vacuum deposition layer 20 was 400 Å.

The light-shielding polyolefin resin film layer 23a of the coextruded multilayer film layer 25a consisted of 91.75 wt% of ethylene/4-methylpentene-1 copolymer resin, 5 wt% of LDPE resin, 3 wt% of oil furnace carbon black having a pH of 8.0, an average particle size of 21 mµm and a free sulfur content of 450 ppm and 0.2 wt% of antioxidant, and 0.05 wt% of oleic acid amide and had a thickness of 40 µm.

The light-shielding thermoplastic resin film layer 24a consisted of 71.75 wt% of ethylene/4-methylpentene-1 copolymer resin, 20 wt% of HDPE resin having a density of 0.954 g/cm3, 5 wt% of LDPE resin, 3 wt% of the same oil furnace carbon black as used in the light-shielding polyolefin resin film layer 23a, 0.2 wt% of antioxidant, and 0.05 wt% of oleic acid amide, and had a thickness of 40 µm.

The adhesive layers 3 were LDPE resin extrusion lamination adhesive layers with a thickness of 13 µm.

The laminations of the laminate film were carried out using the same procedure that uses the tandem laminator.

The packaging material of Example II corresponds to that shown in Fig. 2.

The long fiber paper layer 22 consisted of an unbleached kraft neutral paper consisting of fibers with a fiber length of about 3.5 mm, containing 0.2 wt. % alkyl ketene dimer ("Aquapell" from Dick Hercules) and 0.5 wt. % modified starch as paper strengthening agents and less than 1000 ppm each of substances harmful to light-sensitive photographic materials and having a cold water extraction pH of 6.8, a surface strength of 8 and a basis weight of 50 g/m², produced using aluminum sulfate as a fixing agent.

The other layers were the same as in example

The comparison packaging material I corresponds to that shown in Fig.5.

The bleached kraft paper layer 26 consisted of a semi-bleached kraft paper consisting of fiber having a fiber length of 2.5 mm, containing 2.0 wt% melamine-formaldehyde resin as a paper strengthening agent and 1870 ppm formaldehyde which adversely affects light-sensitive photographic materials, and having a cold water extraction pH of 4.3, a surface strength of 6 and a basis weight of 50 g/m2, made using aluminum sulfate as a fixing agent.

The other layers were the same as in Example I.

The conventional packaging material I corresponds to that shown in Fig. 6.

The bleached kraft paper layer 26 consisted of a bleached kraft paper consisting of fibers with a fiber length of 2.5 mm, having a cold water extraction pH of 4.5, a surface strength of 5 and a basis weight of 30 g/m2, prepared using aluminum sulfate as a fixing agent.

The metal foil layer 27 was an aluminum foil with a thickness of 7 µm.

The thermoplastic resin film layer 28a was an LDPE resin film having a thickness of 80 µm containing 3 wt% of the same carbon black as in Example I.

The adhesive layers 3 were LDPE resin extrusion lamination adhesive layers with a thickness of 40 µm.

The laminated film was prepared by laminating them together using double extrusion lamination techniques.

Various properties of the above films were determined and the results are summarized in Table 1. Table 1 Packaging material of the invention Comparative packaging material Conventional packaging material Layer composition Light-shielding performance after dripping test Hot tack properties Sealability with other materials Long-term heat sealing strength Bag breaking strength Paper dust formation Surface strength Photographic properties Tear strength (MD) (g) The evaluations in Table 1 were made as follows: A excellent B excellent C practicable D no problem E not practicable

In the following tests, the packaging bag used was a single-layer gusseted bag and four rolls of color printing paper measuring 8.9 cm wide and 180 m long were arranged in two layers with a corrugated cardboard pad in between in a corrugated cardboard container.

Light shielding after the drop test

After the drip test according to JIS Z-0202 Section I, each packaging bag was exposed to light of 80,000 lux for 1 hour. The color copy paper was developed and the light shielding was evaluated.

Hot tack properties (heat sealability)

Two sheets of each exemplary film with a width of 15 mm were heat sealed at 170ºC and immediately thereafter, the open ends were pulled with a weight of 45 g at a peel angle of 22.5º. This property was evaluated by the peel length (cm).

Sealability with other materials

Each exemplary film was cut to a width of 15 mm and a cigarette end after smoking was pressed onto the heat sealing surface using a finger. Two sheets of the films were then placed over it and heat sealing was performed at any temperature for 1 s at a sealing pressure of 1 kg/m2. This property was evaluated by the load required to open (peel off) the sealed portion at an angle of 180º.

Long-term heat seal strength

Two sheets of each example film with a width of 15 mm were heat-sealed at the respective optimum temperature for 1 s under a sealing pressure of 1 kg/m². This property was evaluated by the load required to open (peel off) the sealed portion at an angle of 180º one month after heat-sealing.

Bag breaking strength

It was evaluated based on the bag breakage state after the drop test according to JIS Z-0202, Section I.

Paper dust formation

It was evaluated based on the amount of paper dust generated after the shaking test according to JIS Z-0232, Section I.

Surface strength

It was determined according to the wax method according to JIS P-8129 and is expressed as the wax number.

Photographic properties

It was determined after a contact test with the top layer.

Tear resistance

Determined in accordance with JIS P-8116.

Claims (3)

1. A packaging material for photographic light-sensitive materials comprising an aluminum vacuum-deposited, biaxially stretched thermoplastic resin film layer, a long fiber paper layer, more than 50% of the fibers having a fiber length of more than 3 mm, containing a paper reinforcing agent and having a pH of 4 to 9 as measured by the cold water extraction method (JIS P-8133), laminated on one side of the above-mentioned thermoplastic resin film layer, and a polyolefin resin film layer containing 0.1 to 15% by weight of carbon black having a pH of 4 to 9 and an average particle size of 15 to 80 µm and more than 5% by weight of an ethylene copolymer resin, laminated on the other side. 2. A packaging material according to claim 1, wherein the long fiber paper has a surface strength of more than 6 in terms of wax number (according to JIS P-8129). 3. Packaging material according to claim 1, wherein the ethylene copolymer resin is an L-LDPE resin.