Packing material for photosensitive materials

Abstract: A packaging material for photosensitive materials comprising a combination of a linear very low density polyethylene resin and a high density polyethylene resin as the resin components. The linear very low density polyethylene resin improves flexibility, low temperature resistance, heat sealing properties and physical strength such as impact puncture strength and tear strength. The polyethylene resin exhibits anitblocking property. The packaging material of the invention is excellent in flexibility, low temperature resistance and impact puncture strength, and blocking does no occur. Since the dispersibility of carbon black is excellent, lump generation trouble and fish eye trouble are rare. Moreover, low temperature heat sealability is excellent.

Description: This invention ralates to a packaging material for photosensitive materials, suitable for packaging relatively heavy products among various photographic photosensitive materials, other photosensitive materials and electronic parts, such as a roll film for movie. In general, packaging materials for the products of high technology, such as photographic photosensitive materials, are required to satisfy various properties, such as gas barrier, moistureproofness, physical strength such as breaking strength, tear strength, impact puncture strength, Gelbo test strength and wear resistance, heat sealing properties such as heat seal strength, side welding properties, hot tack properties and sealability with other materials, antistatic properties, slip properties, low dusting, and flatness, in addition to the light-shielding ability capable of shielding light completely. Heretofore, various proposals have been made for satisfying the above properties. The inventor has investigated for improving the packaging materials for photosensitive materials, and for example, I disclosed a packaging material of which the physical strength is improved by combining two uniaxially stretched films (USP 4,331,725). I also disclosed a laminated film, composed of a foamed sheet having a thickness of 0.3 to 2 mm and a blow-up ratio of 5 to 50 times and two uniaxially molecular oriented thermoplastic resin films adhered on the both sides of the foamed sheet by melt adhesion directly or through an extrusion laminating adhesive layer so that respective molecular orientation axes crosses each other at an angle of more than 30 degrees, of which the thickness is reduced to 40 to 85 % of the total thickness by pressing (USP 4,565,733). The laminated film has a great impact puncture strength and Gelbo test strength, and it is excellent as a packaging material for heavy products. However, the above packaging materials were inferior in the dispersibility of carbon black, and lumps and fish eyes frequently occurred. They were also inferior in heat sealing properties and bag-making ability, nevertheless expensive. EP-A-100689 discloses a composition containing (A) 60 to 90 wt% of an ethylene-α-olefin copolymer (L-LDPE) resin having a density of 0.905 to 0.925 g/cm³ and a melt index of 0.5 to 2.5 g/10 min and (B) 10 to 30 wt% polyethylene having a density of 0.95 to 0.97 g/cm³ and a melt index of 0.05 to 1 g/10 min. The composition is used in the manufacture of films for packaging materials, but not for light shielding materials. The object of the invention is to provide a packaging material for photosensitive materials not occuring lump generation trouble, fish eye trouble nor blocking, having a great physical strength and being excellent in bag-making ability and inexpensive. The present invention provides a packaging material for photosensitive materials, which comprises a light-shielding linear low density polyethylene resin film layer comprising 40 to 97 wt.% of a linear very low density polyethylene resin having a density (ASTM D-1505) of 0.870 to 0.918 g/cm³, a melt flow rate (ASTM D-1238) of 0.3 to 5 g/10 minutes and a Vicat softening point (ASTM D-1525) of lower than 99°C, 3 to 50 wt.% of a polyethylene resin having a density of 0.930 to 0.965 g/cm³, a melt flow rate of 0.4 to 5 g/10 minutes and a Vicat softening point of higher than 110°C, 0.1 to 15 wt.% of carbon black and 0.01 to 2 wt.% of an antioxidant. Figures 1 to 8 are partially sectional views of preferred embodiments of the invention. In the following the invention is described in more detail. The linear very low density polyethylene resin is the linear low density polyethylene (L-LDPE) resin having a density (ASTM D-1505) of 0.870 to 0.918 g/cm³. When the density is less than 0.870 g/cm³, resin productivity is inferior, and blocking is liable to occur. While, when the density is beyond 0.918 g/cm³, the light-shielding L-LDPE resin film layer cannot exhibit the characteristics because the superiorities of this resin e.g. in flexibility, impact puncture strength, film moldability, low temperature resistance and filler-filing ability decrease. A density (ASTM D-1505) in the range of 0.890 to 0.910 is particularly preferred. The melt flow rate (MFR, ASTM D-1238) is 0.3 to 5 g/10 minutes, preferably 0.8 to 3 g/10 minutes. When the MFR is less than 0.3 g/10 minutes, film moldability is inferior. Melt fracture occurs, and discharge sharply decreases. While, when the MFR is beyond 5 g/10 minutes, film moldability is inferior. Draw down occurs, and bubble is unstable. Moreover, blocking greatly occurs. The Vicat softening point (ASTM D-1525) is lower than 99°C, preferably 55 to 97°C. When the Vicat softening point is beyond 99°C, motor load at the time of molding is great. Melt fracture is liable to occur, and film moldability is inferior. The superiorities in flexibility, low temperature resistance, low temperature heat sealability are lost. The molecular weight distribution (weight average molecular weight/number average molecular weight) of such a L-LDPE resin is necessary to be more than 2.5, preferably 3.5 to 9, more preferably 4 to 8, measured by gel permeation chromatography. Examples of commercial linear very low density polyethylene resins are "NUC-FLX" (tradename) being a copolymer of ethylene and butene-1, "ULTZEX" (tradename) being a copolymer of ethylene and 4-methylpentene-1, "TUFLIN" (tradename) and "TUFTHENE" ( tradename) being copolymers of ethylene and hexene-1, and "STAMILEX" (tradename), "DOWLEX" (tradename) and "MORETEC" (tradename) being copolymers of ethylene and octene-1 (tradename). The content of the linear very low density polyethylene resin is 40 to 97 wt. %. The density (ASTM D-1505) of the polyethylene resin is 0.930 to 0.965 g/cm³, and high density polyethylene resin having a density of 0.940 to 0.960 g/cm³ is particularly preferred. When the density is less than 0.930 g/cm³, antiblocking property is insufficient in the resin content of the invention. While, when the density is beyond 0.965 g/cm³, film moldability is inferior, as well as lump generation trouble and fish eye trouble increase. Moreover, tear strength in longitudinal direction decreases. The MFR (ASTM D-1238) is 0.4 to 5 g/10 minutes, preferably 1 to 3 g/10 minutes. When the MFR is less than 0.4 g/10 minutes, the polyethylene resin is inferior in the blending ability with the principal component of the linear very low density polyethylene resin. As a result, lump generation trouble and fish eye trouble occur, and film moldability is inferior. Moreover, molecular orientation is liable to ocur in longitudinal direction, and the difference between the tear strength in longitudinal direction and that in lateral direction is great. While, when the MFR is beyond 5 g/10 minutes, draw down is liable to occur. Physical strength decreases, and antiblocking effect reduces. The Vicat softening point (ASTM D-1525) is higher than 110°C, preferably 120 to 135°C. When the Vicat softening point is lower than 110°C, antiblocking effect is insufficient in the resin content of the invention. The content of the polyethylene resin is 3 to 50 wt. %, preferably 5 to 30 wt. %. When the content is less than 3 wt. %, antiblocking effect is insufficient. While, when the content is beyond 50 wt. %, the superiorities of the linear very low density polyethylene resin, such as flexibility, tear strength, impact puncture strength, low temperature resistance, low temperature heat sealability, are lost. Carbon blacks are divided into gas black, oil furnace black, anthracene black, acethylene black, lamp black, vegetable black and animal black according to their origin. Among these, oil furnace carbon black is preferable in terms of light-shielding characteristics, costs and improvement of properties. On the other hand, since acetylene black and Ketschen carbon black have antistatic characteristics, they are also preferable, though they are expensive. They may be blended to the oil furnace black in order to improve its characteristics. A suitable pH of carbon black is at 5 to 9, particularly at 6 to 8, and a suitable mean particle size is 10 to 80 nm (mµ). Particularly, the oil furnace carbon black and the acetylene black having pH 6 to 9 and mean particle size of 15 to 50 nm (mµ) are preferable. By using the carbon black of such pH and particle size, the packaging material having the following merits is obtained. That is, the occurrence of fogging is rare, increase or decrease of photosensitivity scarcely happens, light-shielding ability is large, and the lump of carbon black and pinhole such as fish eye hardly generate. The content of carbon black is 0.1 to 15 wt. %, preferably 0.5 to 7 wt. %. When the content is less than 0.1 wt. %, light-shielding ability is insufficient, and antiblocking effect, antistatic effect, antioxidizing effect and the improvement in physical strength decrease. While, when the content is beyond 15 wt. %, carbon black releases by the friction with the packaged products during transportation, and adheres to the surface of the products. Moreover, e.g. heat sealing properties and moistureproofness are degraded. Suitable antioxidants are for example phenol antioxidants, sulfur-containing antioxidants and phosphorus-containing antioxidants. The phenol antioxidants include n-octadecyl-3-(3',5'-di-t-butyl-6'-hydroxyphenyl)propionate, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-p-cresol (BHT), 2,2'-methylenebis(4-methyl-6-t-butylphenol), 4,4'-thiobis(3-methyl-6-t-butylphenol), 4,4'-butylidenebis(3-methyl-6-t-butylphenol), stearyl-β-(3,5-di-4-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl) benzene, octadecyl-3-(3,5-di-t-buyl-4-hydroxyphenyl) propionate and tetrakis methylene-3(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate methane. The sulfur-containing oxidation inhibitors include dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, laurylstearylthiodipropionate, distearyl-3,3'-thiodipropionate and ditridecyl-3,3'-thiodipropionate. The phosphorus-containing antioxidants include trinonylphenylphosphite and triphenylphosphite. Particularly effective antioxidants are e.g. BHT, low volatile high molecular weight phenol antioxidants (e.g. "Irganox 1010", "Irganox 1076", trade names; "Topanol CA", trade name), dilaurylthiodipropionate, distearylthiodipropionate and dialkylphospate. Particularly preferable antioxidants are phenol antioxidants. Two or more antioxidants may be combined. The content of the antioxidant is in the range of 0.01 to 2 wt. %, preferably 0.02 to 0.5 wt. %. When the content is less than 0.01 wt. %, the antioxidizing effect hardly appears. While, when the content is beyond 2 wt. %, fogging of the packaged photographic photosensitive materials and variation of photosensitibity occur. Moreover, weighting effect of the antioxidant is little. A lubricant is preferably added to the light-shielding L-LDPE resin film layer. Preferable lubricants are fatty acid amide lubricant, and include: Oleic acid amide lubricants; such as "ARMOSLIP-CP" (tradename), "NEWTRON" and "NEWTRON E-18" ( tradename), "AMIDE-O" ( tradename), "DIAMID 0-200" and "DIAMID G-200" ( tradename), "ALFLOW E-10" (tradename); Erucic acid amide lubricants, such as "ALFLOW P-10" (tradename), "NEWTRON S" ( tradename); Stearic acid amide lubricants, such as "ALFLOW S-10" (tradename), "NEWTRON 2" ( tradename), "DIAMID 200" (tradename); Bis fattty acid amide lubricants, such as "BISAMIDE" (tradename), "DIAMID-200 BIS" (tradename), "ARMOWAX-EBS" (tradename). A suitable content of the fatty acid amide lubricant is 0.01 to 1 wt. %. The packaging material of the invention may for example be a single layer film, a coextruded multilayer film containing the light-shielding L-LDPE resin film layer or a laminated film laminated with flexible sheet(s). 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 photographic photosensitive materials, diazo photographic photosensitive materials, photosensitive resins, self-developing type photographic photosensitive materials, heat-developing type photosensitive materials, direct positive color photosensitive materials, diffusion transfer type photographic photosensitive materials and other photographic materials which is degraded by little amount of light or moisture or gas. Package form may be conventional, and includes e.g. 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 moistureproof box, inner lining for a light room-loading light-shielding box and a leader paper. The sealing form may also be conventional, and includes e.g. heat sealing, side welding, impulse heat sealing, ultrasonic sealing, and high frequency sealing. The methods of using an adhesive may also be utilized. In the packaging material of the invention, the linear very low density polyethylene resin improves flexibility, low temperature resistance, heat sealing properties and physical strength such as impact puncture strength and tear strength. The polyethylene resin exhibits antiblocking property. Carbon black imparts light-shielding and antistatic property, and improves antiblocking property and physical strength. Antioxidant prevents yellowing and coloring, when the resin is heated at a high temperature. The packaging material of the invention is excellent in flexibility, low temperature resistance and impact puncture strength, and blocking does not occur. Since the dispersibility of carbon black is excellent, lump generation trouble and fish eye trouble are rare. Moreover, low temperature heat sealability is excellent. Representative embodiments of the packaging material of the invention are illustrated in Figures 1 to 8. The packaging material of Figure 1 is a single layer film composed of the light-shielding L-LDPE resin film layer 1a. The pacaging material of Figure 2 is a coextruded multilayer light-shielding film composed of the light-shielding L-LDPE resin film layer 1a and a thermoplastic resin film layer 2a containing a light-shielding material. The packaging material of Figure 3 is a coextruded multilayer light-shielding film composed of two light-shielding L-LDPE resin film layers la,la and an intermediate layer 3 interposed therebetween. The packaging material of Figure 4 is a coextruded multilayer light-shielding film composed of the light-shielding L-LDPE resin film layer la, a thermoplastic resin film layer 2a containing a light-shielding material and an intermediate layer 3 not containing a light-shielding material interposed therebetween. The packaging material of Figure 5 is composed of the light-shielding L-LDPE resin film layer la and a flexible sheet layer 5 laminated through an adhesive layer 4. The packaging material of Figure 6 is composed of the light-shielding L-LDPE resin film layer la and a heat seal layer 7 directly laminated thereto. The packaging material of Figure 7 is composed of the coextruded multilayer film shown in Figure 2 and a flexible sheet layer 5 laminated on the thermoplastic resin film layer 2a side through an adhesive layer 4. The packaging material of Figure 8 is composed of the coextruded multilayer film shown in Figure 2, a metal foil 6 laminated on the thermoplastic resin film layer 2a side through an adhesive layer 4 and a flexible sheet layer 5 laminated on the metal foil 6 through an adhesive layer 4. EXAMPLES The packaging material of Example I consisted of the light-shielding L-LDPE resin film layer 70 µm in thickness composed of 76.8 wt. % of linear extremely low density polyethylene resin being a copolymer of ethylene and 4-methylpentene-1 having a density of 0.910 g/cm³, a MFR of 2.0 g/10 minutes and a Vicat softening point of 93°C, 20 wt. % of HDPE resin having a density of 0.954 g/cm³, a MFR of 1.1 g/10 minutes and a Vicat softening point of 126°C, 3 wt. % of furnace carbon black and 0.2 wt. % of antioxidant. The packaging material of Example II consisted of the light-shielding L-LDPE resin film layer 70 µm in thickness composed of 81.8 wt. % of linear extremely low density polyethylene resin being a copolymer of ethylene and 4-methylpentene-1 having a density of 0.915 g/cm³, a MFR of 2.3 g/10 minutes and a Vicat softening point 97°C, 15 wt. % of the same HDPE resin as employed in Example I, 3 wt. % of furnace carbon black and 0.2 wt. % of antioxidant. Comparative packaging material I consisted of a single layer film 70 µm in thickness composed of 97 wt. % of L-LDPE resin being a copolymer of ethylene and octene-1 having a density of 0.930 g/cm³, a MFR of 2.0 g/10 minutes and a Vicat softening point of 112°C and 3 wt. % of furnace carbon black. Comparative packaging material II consisted of a single layer film 70 µm in thickness composed of 94.5 wt. % of the same linear extremely low density polyethylene resin as employed in Example I, 3 wt. % of furnace carbon black and 2.5 wt. % of antioxidant. Conventional packaging material I consisted of a single layer film 70 µm in thickness composed of 96.7 wt. % of LDPE resin having a density of 0.923 g/cm³ and a MFR of 2.4 g/10 minutes, 3 wt. % of furnace carbon black and 0.3 wt. % of antioxidant. Various properties of the above packaging materials were measured, and the results are shown in Table 1. Invention Comparative Conventional I II I II I L-LDPE Resin Density g/cm³ 0.910 0.915 0.930 0.910 - MFR g/10 min. 2.0 2.3 2.0 2.0 - Vicat Softening Point °C 93 97 112 93 - Content wt. % 76.8 81.8 97 94.5 - Polyolefin Resin - HDPE HDPE - - LDPE Density g/cm³ 0.954 0.954 - - 0.923 MFR g/10 min. 1.1 1.1 - - 2.4 Vicat Softening Point °C 126 126 - - 93 Content wt. % 20 15 - - 96.7 Carbon Black Content wt. % 3 3 3 3 3 Antioxidant Content wt. % 0.2 0.2 - 2.5 0.3 Photographic Properties - B B B E B Film Moldability - B B C D B Antiblocking Properties - A A B E B-C Bag-Making Ability - A A C A D Physical Strength - A A D B E Dispersibility of Carbon Black - B B D A C Flexibility - A A D A B Evaluations in Table 1 were carried out as follows: A very excellent B excellent C practical D having a problem E impractical Density: ASTM D-1505 MFR: ASTM D-1238 Vicat Softening Point: ASTM D-1525 Photographic Properties: A photographic sheet film of ASA 100 was placed in a flat bag made of each exemplified film, and completely sealed. Respective flat bags were exposed to the light of 80,000 ℓx for one hour, and the light-shielding ability was estimated by the fogging degree of each photographic film after development. On the other hand, the above sealed bag was allowed to stand in a room at 50°C in 80 % RH for 3 days, and the photographic sheet film was developed. Then, the variations in photosensitivity, gradation, concentration and fogging were also evaluated in comparison with the same photographic sheet film not placed in the room. Film Moldability: Judged by total inflation film moldability including motor load (electric current value), bubble stability, the position of frosting line, fish eye, lumps, wrinkling and the uniformity in film thickness, when each exemplified film was molded by using an inflation film molding machine. Antiblocking Properties: An open end of two sheets of each packaging material having a width of 15 mm was separated by pulling one end with a load of 45 g at an angle of 180 degrees immediately after molded through inflation process, and the antiblocking properties was judged by the resistance. Smaller resistance was judged better. 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 track properties, sealability with other materials, elapsed heat seal strength, curling, the generation of pinhole, bag rupture during transportation of products, collectively. Physical Strength: Judged by tear strength (JIS P-8116), impact puncture strength (JIS P-8134), bursting strength (JIS P-8112) and heat seal strength, collectively. Dispersibility of Carbon Black: Judged by the light-shielding ability, the generation degrees of fish eye and lumps of each exemplified packaging material, when each exemplified film was molded by using an inflation film moulding machine. The evaluation of the light-shielding ability was carried out in the same manner as in the above photographic properties. Flexibility: Judged by the rigidity (JIS P-8125) and the hand feeling, when the opening (for the insertion of product) of two-sided fin seal flat bag was turned.

Claims: A packaging material for photosensitive materials, which comprises a light-shielding linear low density polyethylene resin film layer comprising 40 to 97 wt.% of a linear very low density polyethylene resin having a density (ASTM D-1505) of 0.870 to 0.918 g/cm³, a melt flow rate (ASTM D-1238) of 0.3 to 5 g/10 minutes and a Vicat softening point (ASTM D-1525) of lower than 99°C, 3 to 50 wt.% of a polyethylene resin having a density of 0.930 to 0.965 g/cm³, a melt flow rate of 0.4 to 5 g/10 minutes and a Vicat softening point of higher than 110°C, 0.1 to 15 wt.% of carbon black and 0.01 to 2 wt.% of an antioxidant. The packaging material of claim 1, wherein the linear very low density polyethylene resin has a density of 0.890 to 0.910 g/cm³, a melt flow rate of 0.8 to 3 g/10 minutes and a Vicat softening point of 55 to 97°C. The packaging material of claim 1 or 2, wherein the molecular weight distribution of the linear very low density polyethylene resin is more than 2.5 measured by gel permeation chromatography. The packaging material of any of claims 1 to 3 which further comprises 0.01 to 1 wt.% of a fatty acid amide lubricant. Use of the packaging material of any of claims 1 to 4 for packaging photosensitive materials. Use of the packaging material of any of claims 1 to 4 for packaging photographic photosensitive materials.

Inventors: AKAO MUTSUO, AKAO, MUTSUO, AKAO, MUTSUO FUJI PHOTO FILM CO., LTD.
Applicants: FUJI PHOTO FILM CO LTD, FUJI PHOTO FILM CO., LTD.
Application year: 1989
Main classification: C08L23
IPC codes: C08L23, C08K3, B32B27, G03C3