EP0571000B1

EP0571000B1 - Packaging material for photosensitive materials

Info

Publication number: EP0571000B1
Application number: EP93113105A
Authority: EP
Inventors: Mutsuo Akao
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1988-01-29
Filing date: 1989-01-30
Publication date: 1998-12-30
Anticipated expiration: 2009-01-30
Also published as: DE68922001T2; EP0326181B1; EP0326181A2; DE68928890D1; DE68922001D1; EP0326181A3; DE68928890T2; EP0571000A1

Description

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to packaging materials for photosensitive materials.

Description of the Prior Art

Packaging bags capable of shielding completely from light are used for packaging the articles or the materials which lose commercial values by exposing to light, such as photosensitive materials. The packaging bags are necessary to have sufficient physical strength, such as tensile strength, tear strength and impact puncture strength, according to the size and weight of the materials to be packaged, as well as the above light-shielding ability. Moreover, since the opening portion of the packaging bags are usually heat-sealed, suitable heat sealing properties are necessary, and in order to prevent static electrification due to the friction between the photosensitive materials and the packaging bag, antistatic property is also necessary.

Heretofore, as the packaging materials used for such a packaging bag, there is a laminated film composed of a high pressure branched low density polyethylene (LDPE) resin film layer containing a light-shielding material, an aluminum foil layer and a bleached kraft paper layer laminated successively each through an LDPE resin extrusion adhesive layer. In general, single layer films are difficult to satisfy the various properties required as the packaging material for photographic photosensitive materials, and only a thick light-shielding LDPE resin single layer film containing carbon black was used for packaging light low photosensitivity photographic photosensitive materials placed in protective pad papers and for packaging light photographic printing papers.

As the packaging material, particularly the light-shielding heat seal bag, for packaging a roll of a photographic photosensitive material and sheets of a photosensitive material having a weight of heavier than 1 kg, the inventor has already disclosed the laminated film composed of a cross laminated film using uniaxially stretched high density polyethylene (HDPE) resin films having a great physical strength and a LDPE resin film containing at least either a light-shielding material or an antistatic agent (US-A-4,147,291). The inventor has also disclosed an inexpensive cross laminated film where heat sealing properties and light-shielding ability are improved (US-A-4,258,848).

Furthermore, the inventor has disclosed other packaging materials, composed of a laminated film containing a light-shielding film layer composed of linear low density polyethylene (L-LDPE) resin blended with carbon black, having a great physical strength, being excellent in heat sealing properties, and being inexpensive (US-A-4,701,359; Japanese Patent KOKAI No. 18547/1987). As a packaging material using a metallized film, the inventor has also disclosed a packaging material for photosensitive materials composed of a metallized film layer and two L-LDPE resin polymer layers containing more than 50 wt. % of L-LDPE resin laminated on both sides of the metallized film layer. One or both of the L-LDPE resin polymer layers contains 0.3 to 30 wt. % of a light-shielding material (US-A-4,663,218).

However, the aforementioned conventional laminated film composed of the LDPE resin film layer, the aluminum foil layer and the bleached kraft paper layer is thick and stiff, and therefore, packaging workability is inferior. Physical strength, such as tear strength, is small, and curling is great. Moreover, heat sealing properties are inferior, and it is expensive. As a result, the packaging material was difficult to secure light-shielding, moistureproofness and gas barrier because of the generation of dust, puncture, tear or separation of heat sealed portion during packaging work or transportation. In the case of the thick light-shielding LDPE resin single layer film, physical strengh is small, and heat sealing properties are inferior. Therefore, it is difficult to secure the quality of the photosensitive materials completely.

The packaging materials having a cross laminated film disclosed in US-A-4,147,291 and US-A-4,258,848 have a strong physical strength such as tear strength and tensile strength, and they were put to practical use for packaging weight materials up to recently. However, since an uniaxially stretched HDPE resin film is used as the heat seal layer, they are stiff, and inferior in packaging workability and heat sealing properties. Moreover, the physical strength and heat seal strength varies and curling occurs due to the uneven thickness of an adhesive layer, the uneven draw ratio of the uniaxially stretched HDPE resin films, or the like. Therefore, troubles occurred in processing or packaging process, and occasionally, they were punctured, or the heat sealed portion was separated during transportation. Moreover, the cross laminated film where a longitudinally uniaxially stretched film was laminated to a laterally uniaxially stretched film so that their orientation axes were crossed each other was expensive, because two kinds of film molding machines were necessary.

Since the packaging materials having a light-shielding L-LDPE resin single layer film disclosed in US-A-4,701,359 or Japanese Patent KOKAI No. 18547/1987 are inexpensive and excellent in heat sealing properties and physical strength such as tear strength and impact puncture strength, they are excellent as the packaging material for photosensitive materials. However, in the case of packaging a weight photosensitive material or a photosensitive material having sharp edges, the light-shielding L-LDPE resin films were occasionally elongated and made thin due to their low Young's modulus, though they were not punctured nor torn. In this case, light-shielding and moistureproofness cannot be secured sufficiently. In addition, in the case of using a L-LDPE resin having a density of less than 0.925 g/cm³, slipping character was insufficient, and blocking was liable to occur. In the packaging material disclosed in US-A-4,663,218, physical strength such as tear strength was improved. However, when a light-shielding material was incorporated into one side of the L-LDPE resin polymer layer alone, curling was great, and processibility was inferior. While, when the melting point of both L-LDPE resin polymer layers were almost indentical with each other, the outside layer was melted and broken, unless the heat sealer was modified. As a result, pinhole occurred, and strength was decreased. Appearance was also inferior. Therfore, this packaging material was put to practical use as a laminated film laminated with an aluminum vacuum deposited nylon film or polyester film having a large Young's modulus and heat resistance. However, the curling of the laminated film was great, and the aluminum vacuum deposited nylon film and polyester film were expensive.

The inventor has also developed a coextruded multilayer inflation film comprising an L-LDPE resin film layer and a polyolefin resin film layer, as a film improved in physical strength such as impact puncture strength (Japanese Patent KOKAI No. 62-18548). Such a coextruded multilayer inflation film is formed by using an inflation film molding machine, such as shown in Figure 1. The inflation film molding machine is composed of extruders 8 heating and kneading the resin, ring die 9 extruding the molten resin from the slit (not indicated) into tube-shaped, blast tube 10 blowing compressed air, air ring 11 cooling the molten resin extruded in tube-shaped, guide rollers 12 guiding the tube-shaped resin film 13, guide plates 14 guiding the tube-shaped resin film 13 into flat, a pair of squeeze roll 15 (nip roll) nipping to attract the tube-shaped resin film 13, and winder 16 winding the film. When the aforementioned coextruded multilayer inflation film composed of an L-LDPE resin film layer and a polyolefin resin film layer is molded by using the inflation film molding machine, L-LDPE resin and HDPE resin having prescribed compositions respectively 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 disposed on the inside, i.e. the HDPE resin film layer is disposed on the outside. At that time, compressed air is blown from the blast tube 10, and cooling air is blown from the air ring 11. The tube-shaped resin film 13 having a prescribed diameter thus formed ascends with the guide of the guide rollers 12,..., 12, and is led into flat by the guide plates 14. The film is made sheet shape by passing the squeeze roll 15, and wound with the winder 16.

However, in the above inflation film molding process wherein the L-LDPE resin film layer was disposed on the inside and the HDPE resin film layer was disposed on the outside, there was a problem that the L-LDPE resin film layer was contacted with each other to generate blocking at the time of winding it with the winder 16. Moreover, fatty acid or fatty acid compound such as fatty acid amide, paraffin wax or metal salt of fatty acid was added to the HDPE resin film layer in order to improve film moldability or to render halogen compounds harmless, the additive was exposed out of the HDPE resin film layer, and adhered to the guide rollers 12 resulting pressure mark and abrasion of the film 13. The adhered additive was detached from the guide rollers 12, adhered to the film in white lumps. When the film was wound, the white lumps rendered film rupture as well as pressure mark to the film. On the other hand, when the L-LDPE resin film layer was disposed on the outside and the HDPE resin film was disposed on the inside, wrinkling and furrows occurred, and the yield of the film decreased.

On the other hand, as the packaging bag for relatively heavy large photographic photosensitive materials, double-sheet bags were used. Such a double-sheet bag was, for example, composed of an outer sheet consisting of a Clupak paper, Duostress paper or unbleached kraft paper coated with polyethylene resin by extrusion laminating and an inner sheet consisting of an aluminum foil and two uniform polyethylene resin films containing carbon black laminated on both sides of the aluminum foil. The kind of the packaged product, instructions and the like were printed on the outer surface of the outer sheet during the packaging process or another process. The double-sheet bag is excellent in physical strength, and when the paper of the outer sheet contains a substance harmful for photographic photosensitive materials, its affect can be shielded by the inner sheet being in contact with the photographic photosensitive materials. However, the double-sheet bags have problems in inferior workability and in expensive packaging material cost. Therefore, various laminated films were developed for solving the inconvenience in bag-making process to make the bag double. An example of the laminated film shown in Figure 4 is composed 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 blended with a light-shielding material laminated on both sides of the aluminum foil layer 27 each through an adhesive layer 3. When a bag is made, the bleached kraft paper layer 26 is disposed on the outside, i.e. the LDPE resin film layer 28a is disposed on the inside. The physical strength of the laminated film is sufficient in the case of light photographic photosensitive materials, but it is insufficient for packaging heavy photographic photosensitive materials. Moreover, fibers occasionally adhered to the packaged photographic photosensitive materials, and caused developing troubles. Photographic photosensitive materials are liable to deteriorate because of utilizing oxidation-reduction reaction and containing a dye liable to degrade by pH, moisture, heat or the like. Therefore, even in the case that it was necessary to use an oxidizing or reducing substance for the surface of the packaging material to touch photographic photosensitive materials, the oxidizing or reducing substance was restricted in the kind and the blending amount. Moreover, unless the quality of the light-shielding material was limited in the particle size, pH, the content of impurities and the like, photographic troubles, such as fogging, spotting trouble and photosensitivity variation, occurred.

SUMMARY OF THE INVENTION

The object of the invention is to provide a packaging material for photosensitive materials which is a coextruded multilayer inflation film without the occurrence of blocking between the inner layers, pressure mark, abrasion, puncture, wrinkling nor furrowing.

Such an object has been achieved by a packaging material for photosensitive materials which is a coextruded multilayer inflation film of which the inner surface layer is a polyolefin resin film layer containing 0.5 to 70 wt. % of polyethylene resin having a density of more than 0.936 g/cm³.

Specific embodiments of the present invention are set forth in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic front view of an inflation molding machine.

Figure 2 is an enlarged sectional view of an inflation film at position A of Figure 1, and Figure 3 is an enlarged sectional view of the inflation film at position B of Figure 1.

Figure 4 is a partially sectional view of a conventional packaging material.

DETAILED DESCRIPTION OF THE INVENTION

The polyolefin resin film layer contains polyethylene resin having a density (ASTM D-1505) of more than 0.936 g/cm³, preferably 0.941 to 0.970 g/cm³. When the density is less than 0.936 g/cm³, it is difficult to obtain a high Young's modulus polyolefin resin film excellent in antiblocking properties. Moreover, the MI (ASTM D-1238) of the polyethylene resin is preferably more than 0.3 g/10 minutes, further preferably 0.5 to 10 g/10 minutes. When the MI is less than 0.3 g/10 minutes, film moldability is inferior. Moreover, molecular orientation is liable to occur greatly in longitudinal direction, and it is difficult to produce a film having a good balance between the physical strength in longitudinal direction and that in lateral direction. Lumps are liable to be generated, and damage the photosensitive materials to be packaged. The polyethylene resin content of the polyolefin resin film layer is 0.5 to 70 wt. %, preferably 2 to 40 wt. %, further preferably 5 to 30 wt. %. Wnen the content is less than 0.5 wt. %, blocking occurs. While, when the content is beyond 70 wt. %, physical strength decreases. The inner surface layer is too slippery, and wrinkling and furrowing occur. The polyolefin resin film layer may contain other resins, such as L-LDPE resin or LDPE resin.

In order to prevent blocking and static electrification, the polyolefin resin film layer may contain either or both of a light-shielding material and a fatty acid compound.

The light-shielding material is blendable or dispersible in the polyolefin resin film layer and capable of shielding visible and ultraviolet light. Examples of the light-shielding material are various carbon blacks, graphite, iron oxide, zinc white, titanium dioxide, clay, aluminum powder, aluminum paste, calcium carbonate, mica, barium sulfate, talc, cadmium pigments, red iron oxide, cobalt blue, copper-phthalocyanine pigments, monoazo and polyazo pigments and aniline blacks. Various carbon black, aluminum powder and aluminum paste from which volatile components are removed are preferred.

The carbon black used is blendable or dispersible in the polyolefin resin. It blocks the transmission of visible and ultraviolet rays, and impart light-shielding property to the polyolefin resin film. The carbon black not only improves the tear strength, impact puncture strength and heat sealing properties of the polyolefin resin film, but also functions to prevent the generation of lumps caused by the oxidation of the resin, to prevent blocking, to adsorp harmful substances such as oxidizing substance, reducing substance and metals. Carbon blacks are divided into gas black, lamp black, vegetable black and animal black according to their origin. Among these, oil furnace carbon black having a mean particle size of less than 200 mµ, particularly less than 50 mµ is preferred in terms of light-shielding character, cost, blendability and dispersibility. On the other hand, since acetylene black, Ketschen carbon black and graphite have antistatic characteristics, they are also preferred, though they are expensive. They may be blended with the oil furnace carbon black in order to improve its character. Suitable pH of carbon black is at 5 to 9, and suitable mean particle size is 10 to 200 mµ. The oil furnace carbon black having a pH 6 to 9 is preferred. By using the carbon black of such pH and particle size, a packaging material having the following merits is obtained. That is, the occurrence of fogging is rare, increase or decrease of photosensitivity rarely happens, light-shielding ability is great, the lumps of carbon black and pinholes such as fish eyes hardly occur, and the physical strength and heat sealing properties are improved. It is also preferred to improve conductivity by adding metal fiber, carbon fiber, metal powder or the like.

The blending method of carbon black into the resin may be carried out by a known method such as the compound coloring method (colored pellets), the liquid color method, the dry color method, the dye color granule method and the masterbatch method, and the dye color granule method and the masterbatch method are preferred in view of cost and the contamination of the working place.

As the preferable light-shielding material, metal powder is in second place. Metal powder is a light-reflective light-shielding material. It imparts a silver appearance, and it is excellent in moistureproofness, light-shielding, antistatic property, thermal shielding in the sunlight and gas barrier. As the metal powder, aluminum powder and its paste are preferable. The paste of aluminum powder is produced by adding mineral spirits and a small amount of a higher fatty acid such as stearic acid or oleic acid to form a paste at the production of aluminum powder according to a known method such as using a ball mill, a stamp mill or an atomizer. A polyolefin thermoplastic resin, such as various polypropylene resins, various polyethylene resins, EVA resin, EEA resin and EAA resin, is kneaded together with this aluminum paste while heating, and volatile components mainly mineral spirits are removed by a vacuum pump. This product is used as an aluminum paste compound resin or an aluminum paste masterbatch resin. The aluminum paste masterbatch resin is preferable because it eliminates the noxious smell and bad influences upon the photographic photosensitive materials. In order to eliminate the noxious smell and bad influences upon the photographic photosensitive materials, the content of mineral spirits should be less than 0.1 wt. %. When the aluminum paste content of coextruded double layer film is
made 2 wt. % by using a masterbatch resin containing 40 wt. % of aluminum paste and 1.0 wt. % of the mineral spirits, one part by weight of the masterbatch resin is blended with 19 parts by weight of the main resin. Since a part of the mineral spirits evaporates during molding, the final content of the mineral spirits is less than 0.05 wt. %. The aluminum powder includes microflakes produced from aluminum foil which is crushed by a ball mill or a stamp mill, in addition to usual aluminum powder manufactured by atomizaiton, dropping on a rotary disc or evaporation from melted aluminum. Since aluminum powder is unstable, it is stabilized by a known treatment, such as a surface treatment using a binder or a higher fatty acid.

The blending amount of the light-shielding material per an unit area of the inflation film is preferably 0.5 to 50 g/m². The blending method of the light-shielding material may be carried out by a known method, and the masterbatch method is preferable in view of cost and the contamination of the working place. Two or more light-shielding materials may be combined.

The fatty acid compound used for blending into the polyolefin resin film layer neutralizes the halide and the like added as the polymerization catalyst of the polyolefin resin which are harmful and adversely affected the photosensitive materials, and thereby makes them harmless. The fatty acid compound improves the dispersibility of carbon black, antiblocking properties, slipping character, and bag-making ability. It also prevents completely the degradation of heat sealing properties by the gradual bleed out of the additives in the polyethylene resin, together with the inhibition by more than 40 wt. % of the L-LDPE resin blended in the resin composition. The fatty acid compound suitable for the invention includes various saturated or unsaturated fatty acids such as oleic acid, stearic acid, lauric acid, ricinoleic acid, naphthenic acid, octylic acid, phthalic acid, adipic acid, sebacid acid, acetylricinoleic acid and maleic acid, fatty acid amides, such as oleic acid amide, erucic acid amide stearic acid amide and bisfatty acid amides, metal salts of fatty acids, such as magnesium stearate, calcium stearate, zinc stearate, aluminum stearate, barium stearate, calcium laurate, zinc octylate, and fatty acid esters, such as butyl oleate and bytyl stearate. Two or more fatty acid compounds may be combined.

The coextruded multilayer inflation film used in the invention is extruded so that the polyolefin resin film layer is disposed on the inside.

In the coextruded multilayer inflation film, the layer extruded as the outer surface layer is preferably an L-LDPE resin film layer. Preferable L-LDPE resins in view of physical strength and heat seal strength are those having the number of carbon atoms is 6 to 8, a MI (ASTM D-1238) of 0.8 to 30 g/10 minutes and a density (ASTM D-1505) of 0.870 to 0.940 g/cm³, produced by liquid phase process or vapor phase process. The L-LDPE resin content of the L-LDPE resin film layer is more than 30 wt. %, preferably 50 to 95 wt. %. One or more other resins, such as LDPE resin, HDPE resin, ethylene copolymer resin or polypropylene resin, may be blended into the L-LDPE resin film layer. One or more of a light-shielding material, a fatty acid compound and an antiblocking agent may be blended into the L-LDPE resin film layer in order to prevent blocking, oxidation, molding and static electrification. The light-shielding material and the fatty acid compound may be similar to mentioned previously.

Suitable antiblocking agents are silica, diatomaceous earth, calcium silicate, aluminum silicate, talc, magnesium silicate, calcium carbonate, higher fatty acid polyvinyl esters, n-octadecyl urea, dicarboxylic acid ester amides and the like.

The polyolefin resin film layer and the L-LDPE resin film layer may contain various additives listed below and lubricants including paraffin wax, fatty acids, fatty acid amides, silicones, esters, higher alcohols, various thermoplastic resins, deodorants, oxygen absorbers, absorber and rubbers.

Additives :

(1) Plasticizer;
phthalic acid esters, glycol ester, fatty acid ester, phosphoric acid ester, etc.

(2) Stabilizer;
lead compounds, cadmium compounds, zinc compounds, alkaline earth metal compounds, organic tin compounds, etc.

(3) Antistatic agent;
cationic surfactants, anionic surfactants, nonionic surfactans, ampholytic surfactans, various carbon blacks, metal powder, graphite, etc.

(4) Flame retardant;
phosphoric acid esters phosphoric acid ester halides, halides, inorganic materials, polyols containing phosphor, etc.

(5) Filler;
alumina, kaolin, clay, calcium carbonate, mica, talc, titanium dioxide, silica, etc.

(6) Reinforcing agent:
glass lobing, metallic fiber, glass fiber, glass milled fiber, carbon fiber, etc.

(7) Coloring agent;
inorganic pigments (Al, Fe₂O₃, TiO₂, ZnO, Cds, etc.), organic pigments, dyes, etc.

(8) Blowing agent;
inorganic blowing agents (ammonium carbonate, sodium hydrogen carbonate), organic blowing agents (nitroso compounds, azo compounds), etc.

(9) Deterioration preventing agent;
ultraviolet absorber, antioxidant, metal deactivator, peroxide decomposing agent, etc.

(10) Coupling agent;
silane compounds, titanium compounds, chromium compounds, aluminum compounds, etc.

One or more intermediate layers may be incorporated between the polyolefin resin film layer and the L-LDPE resin film layer.

The coextruded multilayer inflation film may be formed by using a known inflation film molding machine, such as a commercial machine.

The inflation film of the invention may be used for packaging photosensitive materials such as photographic photosensitive materials, foods, medicines or chemical substances.

In detail, the packaging material of the invention may be used for packaging photosensitive materials such as photographic photosensitive materials, foods, medicines or chemical substances, and it is particularly suitable for packaging silver halide phtographic photosensitive materials, diazo photographic photosensitive materials, photofixing-type thermosensitive photosensitive materials, photosensitive resin photosensitive materials, ultraviolet curing-type photosensitive materials, transfer-type heat developing photosensitive materials, direct positive type photographic photosensitive materials, self-developing type photographic photosensitive materials, photosensitive materials for lithographic printing and other photographic materials which is degraded by little amount of moisture, light or gas.

The package form may be conventional, and includes a single-sheet flat bag, a double-sheet flat bag, a self-standing bag, a single-sheet gusset bag, a double-sheet gusset bag, inner lining for a moisture proff box, inner lining for a light room-loading light-shielding box, wrapping paper and a leader paper. The bag-making form may also be conventional, and includes heat sealing, side welding (heat-cut sealing), impulse heat sealing, supersonic sealing and high frequency sealing. The methods of using an adhesive may also be utilized.

Since the coextruded multilayer inflation film of the invention is mold so that the polyolefin resin film layer is disposed as the inner surface layer, when the tubular film is wound by a winder, the polyolefin resin film layers touch each other to prevent blocking. When the L-LDPE resin film layer is the outer surface layer, adhesion of the additives to guide rollers and the like does not occur. Therefore, a coextruded multilayer inflation film obtained is excellent in quality.

The coextruded multilayer inflation film was formed by using the inflation film molding machine shown in Figure 1. The resin composition composing the polyolefin resin film layer 17 was put into one of the extruders 8, and the resin composition composing the L-LDPE resin film layer 18 was put into the other extruder 8. They were melted by heating. Subsequently, the resin composition of the pololefin resin film layer 17 was extruded from the inside slit of the ring die 9, and the resin composition of the L-LDPE resin film layer 18 was extruded from the outside slit of the ring die 9. Compressed air was blown from the blast tube 10, and cooling air was blown from the air ring 11. Thus, a tube-shaped resin film 13 was molded so that the polyolefin resin film layer 17 was disposed on the inside and the L-LDPE resin film layer 18 was disposed on the outside, as shown in Figure 2. The tube-shaped resin film 13 asended with the guide of the guide rollers 12,..., 12, and was led into flat by the guide plates 14. The film was deflated into sheet shap by passing the squeeze roll 15, and wound with the winder 16. In the above film-forming process, since the L-LDPE resin film layer 18 was contacted with the guide rollers 12,..., 12, the guide plates 14 and the squeeze roll 15, the additives of the film did not adhere to them. Since the inflation film was wound in the state that the polyolefin resin film layers 17 were contacted with each other, as shown in Figure 3, blocking did not occur between the inner surface layers.

By the above process, the following packaging materials were produced.

The packaging material of Example I:

The inner surface layer was a polyolefin resin film layer 35 µm in thickness composed of 20 wt. % of HDPE resin having a MI of 1.1 g/10 minutes and a density of 0.954 g/cm³, 76.9 wt. % of L-LDPE resin of a copolymer of ethylene and 4-methylpentene-1 having a MI of 2.0 g/10 minutes and a density of 0.920 g/cm³, 3 wt. % of oil furnace carbon black and 0.1 wt. % of oleic acid amide.

The outer surface layer was an L-LDPE resin film layer 35 µm in thickness composed of 96.75 wt. % of L-LDPE resin of a copolymer of ethylene and 4-methylpentene-1 having a MI of 2.1 g/10 minutes and a density of 0.920 g/cm³, 3 wt. % of oil furnace carbon black, 0.05 wt. % of oleic acid amide and 0.2 wt. % of synthetic silica as an antiblocking agent.

The packaging material of Example II:

The inner surface layer was a polyolefin resin film layer 35 µm in thickness composed of 2 wt. % of HDPE resin having a MI of 1.1 g/10 minutes and a density of 0.954 g/cm³, 93 wt. % of L-LDPE resin of a copolymer of ethylene and octene-1 having a MI of 2.0 g/10 minutes and a density of 0.920 g/cm³, 3 wt. % of oil furnace carbon black 2 wt. % of calcium stearate and 0.1 wt. % of oleic acid amide, and the rest was the same as Example II.

Comparative packaging material I:

The inner surface layer was an L-LDPE resin film layer 35 µm in thickness composed of 97 wt. % of L-LDPE resin of a copolymer of ethylene and octene-1 having a MI of 2.0 g/10 minutes and a density of 0.920 g/cm³ and 3 wt. % of oil furnace carbon black.

The outer furface layer was an L-LDPE resin film layer 35 µm in thickness composed of 96.75 wt. % of L-LDPE resin of a copolymer of ethylene and 4-methylpentene-1 having a MI of 2.1 g/10 minutes and a density of 0.920 g/cm³, 3 wt. % of oil furnace carbon black, 0.05 wt. % of oleic acid amide and 0.2 wt. % of synthetic silica.

Comparative packaging material II:

The inner surface layer was a HDPE resin film layer 25 µm in thickness composed of 95 wt. % of HDPE resin having a MI of 0.4 g/10 minutes and a density of 0.964 g/cm³, 3 wt. % of oil furnace carbon black and 2 wt. % of calcium stearate.

The outer surface layer was an L-LDPE resin film layer 45 µm in thickness composed of 96.95 wt. % of L-LDPE resin of a copolymer of ethylene and 4-methylpentene-1 having a MI of 2.1 g/10 minutes and a density of 0.920 g/cm³, 3 wt. % of oil furnace carbon black, 0.05 wt. % of oleic acid amide and 0.2 wt. % of synthetic silica as antiblocking agent.

Comparative packaging material III:

Having the same layer composition as Example II, except that the inner surface layer and the outer surface layer were turned inside out.

Conventional packaging material I:

A single layer inflation film 70 µm in thickness composed of 96.95 wt. % of LDPE resin having a MI of 2.4 g/10 minutes and a density of 0.923 g/cm³, 3 wt. % of oil furnace carbon black and 0.05 wt. % of oleic acid amide.

Various properties of the above films were measured, and the results are tabulated in Table 1.

Evaluations in Table 1 were carried out as follows:

A	very excellent	B	excellent
C	practical	D	having a problem
E	impractical

Antiblocking Property:

Each wound inflation film was cut in a size of 330 mm (lay-flat width) x 220 mm by a razor, and the antiblocking property was judged through opening of the cut portion.

Film Moldability:

Judged by motor load (electric current value), bubble stability, the position of frosting line, fish eye, lumps, wrinkling and the uniformity in film thickness collectively.

White Powder Generation:

Judged by the degree of the white powder and agglomerates thereof adhered to the guide rollers, guide plates and squeeze roll and wound film by visual observation, when each inflation film was molded using a die having a clearance of 1 mm at a blow-up ratio of 2.1.

Physical Strength:

Judged by tear strength (JIS P-8116), impact puncture strength, bursting strength (JIS P-8112) and heat seal strength collectively.

Wrinkling, Furrowing:

Judged by the generation degree of wrinkling and furrowing of each film by visual observation, when each film was molded using a die having a clearance of 1 mm at a blow-up ratio of 2.1.

Bag-Making Ability:

Judged by the difference of melting points between the inner surface layer and the outer surface layer, low temperature heat sealing properties, heat seal strength, hot tack properties, sealability with other materials, elapsed heat seal strength, curling, the generation of pinhole, bag rupture during transportation of products, collectively.

Claims

A packaging material for photosensitive materials which is a coextruded multilayer inflation film of which the inner surface layer is a polyolefin resin film layer containing 0.5 to 70 wt. % of polyethylene resin having a density of more than 0.936 g/cm³.
The packaging material of claim 1 wherein the polyethylene resin has a density of more than 0.941 g/cm³ and a melt index of more than 0.5 g/10 minutes.
The packaging material of claim 2 wherein the polyolefin resin film layer contains either or both of a light-shielding material and a fatty acid compound.
The packaging material of claim 1 wherein the outer surface layer of the coextruded multilayer inflation film is an L-LDPE resin film layer containing more than 30 wt. % of L-LDPE resin.
The packaging material of claim 4 wherein the L-LDPE resin film layer contains at least one of a light-shielding material, a fatty acid compound and an antiblocking agent.