JPH0377978B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a synthetic resin laminated film for packaging photographic materials with excellent heat sealability. A laminated film (cross-laminated film), which has improved physical strength by laminating two uniaxially stretched films such that their stretching axes intersect, is conventionally known. In order to use this as a packaging material for photographic materials, it is desirable to laminate a film with good heat-sealability on one side, which is important in completely sealing the opening and ensuring light-shielding and moisture-proof properties. . Therefore, attempts have been made in the past to laminate another layer with good heat sealability on top of the cross-laminated film layer. For example, Jikko 56-
No. 19087 discloses a cross-laminated layer of high-density polyethylene stretched film laminated with low-density polyethylene (LDPE) containing a light-shielding material as a heat-sealing layer. This laminated film is
Although it can be used for normal purposes as a packaging material superior to previous packaging materials of the same type, it has the following problems when used as a light-shielding film for packaging a wider range of photographic materials. (a) Heat seal strength is still insufficient for heavy goods packaging. (b) Since carbon black is added to low-density polyethylene, which has low surface strength, black powder may be generated due to friction and may adhere to the product in spots. (c) When products are packaged using automatic packaging machines, the seal stretches, causing pinholes and poor light shielding. (d) It has a large coefficient of friction with photosensitive materials, making it less suitable for automatic packaging machines and may cause blocking. (e) Increasing the thickness of the LDPE layer to improve light-shielding properties not only increases cost but also increases rigidity, which is disadvantageous for automatic packaging. The basic purpose of the present invention is to solve these problems. More specifically, we need a packaging material that can directly seal and package photographic materials with a thickness of 3 cm or more, a volume of 500 cm ³ or more, and a weight of 2 kg or more using a direct heat sealing method to ensure complete light-shielding properties and seal strength. It is about providing. More specifically, we have created a packaging material that does not generate pinholes during heat sealing, is highly suitable for automatic packaging machines, and has a superior coefficient of friction than conventional products in terms of adhesion to photosensitive materials and a coefficient of friction that can cause malfunctions such as scratches. The purpose is to provide. According to the present invention, in a light-shielding film including a cross-laminated film layer in which two uniaxially stretched films are laminated at an angle of 45 to 90 degrees to each other in the stretching direction, one surface of the cross-laminated film layer is Furthermore, L-LDPE, which is made of 60% by weight or more of linear low-density polyethylene (L-LDPE) and other polyolefin resins, has a melting point of 5°C or more lower than the uniaxially stretched film and a sliding angle of 7 to 15 degrees.
- The above object can be achieved by a light-shielding packaging material for photographic materials characterized by laminating LDPE resin layers. That is, the present invention provides a light-shielding packaging material for photographic materials, in which the specific linear low-density polyethylene (L-LDPE) resin layer is further laminated as a heat-sealing layer on the cross-laminated film layer. Here, L-LDPE is a copolymer of ethylene and α-olefin, and is a copolymer of ethylene and 3 to 13 carbon atoms, preferably 4 to 10 carbon atoms.
It is a copolymer of α-olefins, and is a polyethylene polymer having a linear straight chain structure with short branches, and an ethylene content of 80 to 99.5 mol% is suitable for the present invention. This linear low-density polyethylene L-LDPE is generally produced by a low-pressure method, and the density is generally considered to be low to medium, but the one that can be used in the present invention is within the range of 0.91 to 0.95 g/cm ³ It is preferably 0.91 to 0.94 g/cm ³ .
Melt index (MI, 190℃) is 0.2 to 40
(preferably 0.4 to 15) can be used. Examples of α-olefins include butene-1, octene-1, hexene-1, 4-methylpentene-1, etc., and 4-methylpentene-1 and hexene-1 are preferably used. Specific examples of L-LDPE that can be used in the present invention include Unipol (UCC), Dowlex (Dow Chemical),
Examples include Skrea (Dupont Canada), Marex (Philips), and Urtoex (Mitsui Petrochemical). Particularly preferred among these L-LDPEs are those having an ethylene content of 90 to 99.5 mol%, an MI of 0.4 to 15, a density of 0.91 to 0.94 g/cm ³ , and α-
Hexene-1 or 4-methylpentene-1 is used as the olefin. The L-LDPE resin mainly contains 60% by weight or more of this L-LDPE or L-LDPE,
A resin having a melting point 5° C. or more lower than that of uniaxially oriented HDPE is used, and a blend resin of L-LDPE and other polyethylene (excluding HDPE) (LDPE, etc.) or other polyolefin resin is used. From this L-
If the amount of LDPE is small, the characteristics of L-LDPE will not be fully exhibited. As the polyolefin resin, ethylene vinyl acetate (EVA), propylene-ethylene, ethylene-acrylic acid, copolymers with ethylene, ethylene-ethyl acrylate, ionomers, vinyl chloride-propylene, polypropylene, etc. can be used. can. This L-LDPE layer may be laminated directly onto the cross-laminate layer, or it may be laminated with a separately manufactured L-LDPE layer.
-LDPE films may be laminated via an adhesive layer. In the former case, the appropriate thickness is 13 to 70 μm (more preferably 20 to 50 μm), and in the latter case, 13 to 90 μm (more preferably 35 to 70 μm). In the case of L-LDPE, it has excellent heat-sealing strength, so it is possible to create a stronger seal with the same thickness compared to conventional high-pressure low-density polyethylene (LDPE). An even more significant feature is that it is necessary to provide the heat-sealing layer with light-shielding properties in order to ensure that the packaging is light-shielded. (Especially if the heat sealability becomes thicker, it becomes essential) However, in L-LDPE, even if carbon black is added, the strength does not decrease like in LDPE, and when the content is 1 to 15% by weight, there is no decrease in strength. There are characteristics that improve with time. Therefore, the present invention is particularly useful as a packaging material for photographic materials that require complete light-shielding properties. Furthermore, the ability to obtain sufficient light-shielding properties with a thin layer is not only advantageous in terms of cost, but also makes it possible to suppress stiffness, resulting in improved suitability for automatic packaging machines. The light-shielding substance is contained in the laminate in an amount of 0.5 to 35 g/m ² . The addition of carbon black is applied to the heat seal layer (L-
It is particularly preferable to add it in an amount of 1 to 15% by weight based on LDPE) from the viewpoint of improving the strength, but it can also be added in an amount of 15 to 20% by weight if particularly desired to improve the light-shielding property. In addition to or in place of carbon black, known organic/inorganic pigments, colorants, etc. can be used as light-shielding substances. In terms of heat sealability, L-LDPE is advantageous in that it has a melting point that is 5° C. or more lower than that of the uniaxially stretched film. Therefore, heat sealing can be performed at a lower temperature or in a shorter time at the same temperature, which is advantageous for automatic packaging of photographic materials that are at risk of deterioration due to temperature (thermal fog). In addition, in the case of the present invention, the heat sealing temperature is determined by the total thickness.
A 100 μm film can be heated at 140 to 180 degrees, but a uniaxially stretched film requires about 180 to 210 degrees. Second, it has the advantage of high sealing strength immediately after heat sealing. In the case of L-LDPE, the sealing surface hardens quickly. Therefore, there is little risk that the sealing portion will be stretched and thinned, resulting in deterioration in light-shielding properties, a decrease in strength, or the occurrence of pinholes. Another advantage of the heat seal layer of the present invention is that it has a high surface strength and is free from scratches. This is related to the strength properties when carbon black is added, and has the effect of eliminating the problem of black powder generation in the case of low density polyethylene. Furthermore, one of the advantages of the L-LDPE heat seal layer is its sliding properties. When inserting a product into a packaging material, the smaller the coefficient of friction, the easier it is to insert the product, and the less likely the product will be scratched or the packaging material will be damaged. This ease of insertion is particularly important when automatic packaging is performed by a machine. This sliding property is even more required when the product is large and heavy. Since the sliding angle of the L-LDPE layer surface is 7 to 15 degrees, the LDPE (18 to 25
It is also superior in this respect compared to The uniaxially stretched films cross each other in the adhesive layer (45~
90 degrees), and the stretching ratio is 2.2 to 15 times.
Thickness 13-70μm (no light-blocking substance added), or stretching ratio 2-10 times, thickness 13-90μm (light-blocking substance 0.5-9
% by weight) is preferred. As the uniaxially stretched thermoplastic resin films 1 and 2, films made of all thermoplastic resins that can be uniaxially stretched are used, but availability, versatility,
From the viewpoint of manufacturing suitability and cost, films made of polyethylene, polypropylene, polystyrene, polyvinylidene chloride, polyvinyl chloride compounds, polycarbonate, polyethylene terephthalate, polyamide, etc. with various densities are preferred, and among these, films with a density of 0.94 g/cm ³ or more are particularly preferred. A uniaxially stretched high-density polyethylene film is desirable in terms of the above-mentioned suitability. Note that the stretching direction of the uniaxially stretched thermoplastic resin films 1 and 2 may be vertical, horizontal, or diagonal, and in any case, when the two are bonded together, the stretching directions make an angle of 45 to 90 degrees to each other. It is necessary to cross them like this. Note that the above uniaxially stretched thermoplastic resin films 1 and 2
It is also possible to use molecularly oriented polymer films. It is preferable from the viewpoint of physical strength (tear strength, tensile strength, bursting strength, etc.) that the cross-angle of the stretching axes of the uniaxially stretched film of the cross-laminate layer is 45 to 90 degrees. As mentioned above, the packaging material of the present invention requires at least three layers: two stretched films and an L-LDPE layer, but in actual use, various other layers may be added depending on the purpose. Good too. For example, an adhesive layer may be provided between each layer, or a layer of metal foil or paper containing a light-blocking substance may be added as a light-blocking layer. In addition, flexible sheets such as paper, cellophane, nonwoven fabric, and other plastic films can be added and laminated according to each purpose. When packaging materials for photosensitive materials particularly require light-shielding properties, it is not limited to L-LDPE layers or stretched film layers.
A light-blocking substance may be added to any layer of the laminate, and methods such as printing may be used in combination. Addition of carbon black or metal powder also has an antistatic effect, and can prevent the adverse effects of static electricity on photographic light-sensitive materials. As the light-shielding substance, carbon black, metal powder, metal foil such as aluminum foil, and other dispersible powders, pastes, or foils commonly used in packaging materials for photosensitive materials are selected. use As an example of a particularly preferred embodiment of the packaging material of the present invention, a bag for packaging heavy photographic materials will be described below. A cross-laminated film (total 100 μm) in which the molecular orientation axes of HDPE containing 4.5% carbon black are orthogonal is coated with an L-LDPE layer (20 μm in total) with a friction coefficient of 0.35.
~35μm) as a heat seal layer, L-LDPE is placed on the outside of the molecularly oriented HDPE layer.
Through a 9-50 μm thick adhesive layer of LDPE, EEA, ionomer, EVA, and blends thereof,
Laminate 50-100g/ ^m2 of kraft paper. This packaging material has particularly excellent rigidity, sliding properties, surface strength, tear strength, etc. when mechanically packaging photographic materials weighing 2 kg or more, and also has good heat sealing properties, eliminating the problems encountered with conventional packaging materials. It can be sealed without any problems. [Example] Thickness containing 4.5% by weight of carbon black
Two 40μm HDPE uniaxially stretched films 10μm thick
(1) A combination of 15 μm LDPE, 25 μm L-LDPE containing 6% by weight of LDPE, and 5% by weight of carbon black (4th layer) (2) L-LDPE 40 μm single layer (layer structure similar to that in Figure 5), (3) L-LDPE containing 3% by weight of carbon black
Three types of products of the present invention were manufactured in which a single layer of 40 μm LDPE (layer structure similar to that shown in FIG. 6) was laminated, respectively. As a conventional product, HDPE uniaxially stretched film (thickness 40μm)
The two sheets are cross-laminated and a heat-sealing layer containing 5% carbon black is used.
A comparison was made with a stack of 50 μm LDPE layers (the same layer configuration as in Figure 1). The thickness of all laminates is 130 μm. All of the products of the present invention were excellent in sealing properties, heat seal strength, sliding properties, abrasion resistance, hot tack properties, impact puncture strength, and tear strength.

[Table] 〓Evaluation: ◎ Very good, ○ Excellent, ●
Within practical limits, ▲ Problems, × Not practical〓
Measurement method: 1. Detection and evaluation based on the degree of fog on ASA100 photographic film with light shielding of 80,000 lux 3. Sealing conditions: Pressure: 1 kg, 1 second Measurement conditions: Pulling speed: 30 mm/min Chuck spacing: 10 cm 4. Sliding angle: Sheet to be tested Cut out a part of the
Attach to the bottom of a 75mm/width 35mm block with a load of 200g. On the other hand, cut out a part of the sheet to be tested in the same way, stick it on an inclined surface, place the sheet surface of the block on the inclined surface, change the inclination angle of this inclined surface, and see if the block starts to slide. Read the angle when the 5. Abrasion resistance A bag is made using the two types of laminated sheets mentioned above, an article weighing approximately 5 kg is stored in the bag, and the bag is sealed and then subjected to a vibration test according to the JIS level to examine the degree of damage to the surface of the laminated sheet. 6 Hot-tack property: Tighten the open end of two packaging materials (width 15 mm) immediately after heat-sealing at 160°C to 45 mm on one side.
Measured by the hot peel distance (cm) when pulled at a peel angle of 22.5 degrees with a load of 1.5 g. 7 JIS P8134 8 JIS P8116 To further facilitate understanding, Figs. 1 to 3 show examples of layer structures of conventional products, and Figs. 4 to 8 show examples of layer structures of products of the present invention. Each layer is as follows. 1, 2; Uniaxially stretched film (including uniaxially oriented film) 3; Adhesive layer 4 L-LDPE heat seal layer (layer laminated directly on the uniaxially stretched film) 5; L-LDPE heat seal layer (separately formed film) Layer) 6; Flexible sheet layer with melting point 10°C higher than that of uniaxially stretched film 7 Heat seal layer with inner paper B laminated to outer paper A of the double bag 7'; Layer 7 containing light-shielding substance 8; Photographic photosensitive layer Material 10; Tape or label for sealing or sealing, etc. (Note) The layer with the dash is a light-shielding substance or a layer containing it. In addition, the B layer in Figure 8 is temporarily attached to the A layer with a point seal, etc. only at the edges. FIG. 9 is a sectional view of a package in which the photographic material 8 is completely sealed with the product of the present invention. In addition, uniaxially stretched films 1 and 2
are bonded together by an adhesive layer 3 existing therebetween, and include a uniaxially stretched film 2 and a light-shielding substance.
- The LDPE heat seal layer 5 is adhered by the adhesive layer 3 existing therebetween. Further, as shown in FIG. 10, layer A may be used as an outer packaging material to form a double bag. In this case, the strength is greater than that of laminating A and B with an adhesive layer, and the weight is medium,
Suitable for packaging large-sized items.

[Brief explanation of drawings]

1 to 3 are cross-sectional views of conventional packaging materials. 4 to 8 are several cross-sectional views showing embodiments of the present invention, FIG. 9 is a cross-sectional view of a completely sealed photographic light-sensitive material, and FIG. 10 is a black-and-white or color roll-shaped light-sensitive material. FIG. 2 is a cross-sectional conceptual diagram showing the packaging form of (photographic paper, movie film, printing film, indirect X-ray film, micro film, etc.). 1, 2... Uniaxially stretched film (1', 2': containing light-shielding substance), 4, 5... L-LDPE heat seal layer.

Claims (1)

[Claims] 1. Two uniaxially stretched films whose stretching directions are mutually
In a light-shielding film including cross-laminated film layers laminated at an angle of 45 to 90 degrees, linear low-density polyethylene (L-LDPE) is further added to one surface of the cross-laminated film layer.
A photograph characterized in that an L-LDPE resin layer is laminated, comprising 60% by weight or more of L-LDPE resin and other polyolefin resin, and has a melting point 5°C or more lower than the uniaxially stretched film and a sliding angle of 7 to 15 degrees. Light-shielding packaging material for photosensitive materials. 2 Other polyolefin resins included in the L-LDPE resin include high-pressure low density polyethylene (LDPE), ethylene-vinyl acetate (EVA) copolymer, propylene-ethylene copolymer, and ethylene-vinyl acetate (EVA) copolymer.
2. The light-shielding packaging material according to claim 1, which is an acrylic acid copolymer, an ethylene-ethyl acrylate copolymer, an ionomer, a vinyl chloride-propylene copolymer, polypropylene, or a mixture thereof. 3. The L-LDPE resin layer contains 1 to 15% by weight of carbon black.
Light-shielding packaging material as described in Section 1.