JPH0336412B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL FIELD OF APPLICATION The present invention relates to base paper for photographic printing, particularly to base paper for photographic printing coated with resin. BACKGROUND OF THE INVENTION A typical base paper for photographic printing consists of a high quality paper support with a coating on one or both sides thereof. This coating serves to form the basic physical structure of a layer suitable for carrying an image, usually a layer or layers of gelatin-based photographic emulsion. Conventional photographic base paper had a coating of barite (barium sulfate) on its surface, but in recent years, both the front and back sides have been coated with a layer of synthetic resin material, particularly a layer of polyolefin resin. Resin coatings of this type protect the base paper from the relatively aggressive substances and conditions used, among other things, in advanced color printing processes. This base paper is known as "photographic base paper" and is often abbreviated as "photobase."
On the other hand, resin-coated base paper is called "resin-coated photographic base paper."
It is also known as ``resin-coated photobase.'' Uncoated base paper is called "raw photobase." The side of the sheet photobase coated with photographic emulsion is known as the ``printing side,'' and the other side is known as the ``wire side'' (because this is the side that comes into contact with the wire of the Fourdrinier machine during papermaking). In resin-coated photobases, the resin coatings on the printing surface and the wire surface are known as the "printing surface resin coating" and the "wire surface resin coating," respectively. To prevent (or at least reduce) the loss of optical sharpness that occurs in color developer prints due to internal reflection of incident light, the print surface coating is pigmented. The commonly used pigments are white pigments such as titanium dioxide (TiO ₂ ). Problems to be Solved by the Invention Focusing on the point that photographic print products must not be stiff, one of the important physical properties required of a photobase is its rigidity. The importance of these physical properties is particularly noticeable when large-sized prints such as enlarged prints are manually processed. Another advantage of good stiffness is that it reduces the occurrence of curling phenomena in photosensitive printing papers carrying gelatin-based photographic emulsion layers. Considering that the typical resin used to coat raw photobases, low density polyethylene (LDPE), exhibits relatively low stiffness, the stiffness of currently available resin-coated photobases is much lower than that of resin coatings. It mainly comes from the base paper itself. It is considered that it is practically impossible to use a highly rigid polymer for the resin coating on the printing surface and/or the wire surface for the reasons described below. Resins that have adequate rigidity and are acceptable for photographic use often suffer from fatal drawbacks, such as being too expensive, difficult to color properly, or unable to adhere properly to base paper. This is because it accompanies. High-density polyethylene (HDPE) can be added to increase the stiffness of LDPE, but the maximum amount of HDPE used is relatively small due to its tendency to form a "gel" in the print surface resin coating. It is. Gels are small-scale resin regions that are harder than surrounding resin regions. The gel tends to protrude from the resin surface, resulting in damage to the photographic emulsion layer coated on top of the resin. Therefore, in terms of printing surface resin coating, HDPE and
It is reasonable to use blends of LDPE to improve stiffness. Other types of rigid resins such as polypropylene (PP) and polycarbonate (PC)
Because it cannot be blended satisfactorily with LDPE, it does not produce a homogeneous coating that will properly adhere to the base paper. On the other hand, the resin coating on the wire surface of the photo base may contain a relatively large amount of HDPE. The presence of gel in the wire surface resin coating is unlikely to cause any inconvenience, and since coloring is not required, almost no gel will form in the absence or presence of a low concentration of pigments such as TiO ₂ . In this way, a highly rigid resin coating on the wire surface can be formed, and the curling phenomenon caused by the photographic emulsion coating on the gelatin base supported on the photobase can be suppressed. Means for Solving the Problems It has now been discovered that the stiffness of the photo base can be significantly improved by coating the top surface of the colored resin layer in the printed surface resin coating with a thin layer of a relatively stiff polymer. I've reached it. According to the invention, from 10 to 50 g of a low density polyethylene or a low density polyethylene blend comprising at least 50 weight percent low density polyethylene, having a paper support carrying a composite coating on the printing side, the composite coating comprising a low density polyethylene or at least 50 weight percent low density polyethylene.・consisting of a first extruded coating layer of m ^-2 ;
The first coating layer comprises at least 5 weight percent opaque pigment and further comprises a second coating layer of 0.1 to 18 gm ^-2 of polycarbonate having a stiffness modulus of at least 0.5 GPa; A photographic base paper is provided which is encapsulated and fixed onto one coating layer. It has been found that the use of a polycarbonate resin layer as the second coating layer in the base paper of the present invention is extremely advantageous, as detailed below. According to the present invention, a paper support carrying a composite coating layer on the printed surface, the composite coating layer being made of low density polyethylene or a low density polyethylene blend comprising at least 50 weight percent low density polyethylene. 50 g m ^-2 of a first extruded coating comprising at least 5 weight percent of an opaque pigment and further comprising 0.1 of a polycarbonate resin.
There is also provided a resin-coated photographic base paper comprising a second extruded coating of 18 g.m ^-2 , the second coating being encapsulated and fixed onto the first coating. If the second coating layer as described above is coated on the printed surface resin coating, it is possible to significantly improve the rigidity without coating the wire surface of the paper support with resin. is a paper support with a polyolefin resin coating formed on the wire surface. By applying this type of wire surface resin coating, the developing solution used when processing photographic prints,
It is possible to improve the resistance of the photobase against the intrusion of fixing fluids and other chemicals. The wire surface resin coating may be a single layer or multiple layers,
It can include an outer layer of a rigid polymer.
According to the invention, a paper support carrying a composite coating on the printed surface, the composite coating comprising a low density polyethylene or a low density polyethylene blend comprising at least 50 weight percent low density polyethylene.
0.1 to 18 g.m −2 of a polymer comprising a first extruded coating layer of 10 to 50 g.m ⁻² , said first coating layer comprising at least 5 weight percent opaque pigment, and further having a stiffness modulus of at least 0.5 GPa ^{. 2}
The second extruded coating layer is encapsulated and fixed onto the first coating layer, and especially when the second coating layer is made of polycarbonate resin, the wire surface is coated with polyolefin resin. 10 to 50
g m ^-2 of the first layer of extruded polyolefin resin if a coating on the wire side is required.
from 0.1 to 50 g m ^-2 and a second layer of extruded polymer having a stiffness modulus of at least 0.5 GPa
There is also provided a resin-coated photographic base paper comprising 18 g.m ^-2 , wherein said first layer is encapsulated and bonded to said second layer. The second layer of the printed surface resin coating according to the invention is formed of a polymer having a stiffness modulus of at least 0.5 GPa. This polymer usually has at least
High modulus polymers having a modulus of 1 GPa, for example 2 GPa or more, are particularly preferred. In a broad sense, the modulus of LDPE is approximately 0.23GPa, and that of HDPE is approximately
1.2GPa, PP about 1.4GPa, and PC about 2.5GPa.
The stiffness modulus used herein is based on the American Standard Test Method (ASTM).
Modulus measured based on D790-80. Polycarbonate is a material particularly suitable for the second layer because it has high rigidity, and the application of this polycarbonate to the second layer constitutes one of the important features of the present invention. In addition to stiffness, the required properties of the polymer for the second layer are that it be virtually colorless and that it can be extruded at temperatures up to 300°C;
It should be substantially inert to light and resistant to discoloration upon exposure, it should not interfere with photographic emulsions, and it should be substantially inert to substances used for developing and fixing photographic images. Examples of polymers that can be used as the second layer are HDPE, PP, PC, linear low density polyethylene (LLDPE), nylon 11, nylon 6,
These are polyamides such as nylon 66, and polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). A particularly preferred polymer is PC, as mentioned above. Polymers such as polystyrene and polyvinyl chloride do not have sufficient thermal stability and/or light stability;
Also, the stabilizers currently in use are either not tolerated by photobases or significantly reduce the stiffness of the polymer, rendering it unsuitable. The second layer of rigid polymer is formed from a homopolymer as described above, but may also be formed from a copolymer or a blend of polymeric materials having the desired stiffness. In the case where the second layer is a single layer, multiple layers of the rigid polymer can be used, and typically layers of different compositions are superimposed. Suitable examples of multiple layers within the second layer are a combination of a transparent rigid outer layer and a colored rigid inner layer, or a combination of a rigid outer layer and an inner layer of an outer phase polymer-first layer polymer blend. In this way, for example, a PC/PC+
Form an LDPE/LDPE structure. The reason for including a single layer (or multiple layers) of the polymer blend is to improve the adhesion between the "first layer" and the "second layer." A method for enhancing adhesion will be described later. The rigid second layer is a thin layer with a coverage of 0.1 to 18 g·m ⁻² approximately corresponding to a thickness of 0.1 to 15 my·m (micrometers) depending on the density of the polymer used. Among the rigid polymers listed above,
The density of HDPE is 0.95, PP is 0.9, and PC is 1.2g cm ^-3
It is. In general, the thicker the second layer (thickening), the greater the degree of improvement in rigidity. However, since rigid polymers, including polycarbonate, are more expensive than conventional polyethylene, it is desirable to use a second layer containing less than 15 g.m ^-2 of rigid polymer for cost savings. Given that no improvement in effectiveness was observed using more than about 10 g.m ^-2 of polymer, this value is a suitable maximum for increasing stiffness in most cases. The inventors have a thickness of approx.
Although we prepared thin layer samples for a stiff second layer at 0.1 my·m (by coextrusion), we were unable to consistently form a second layer of approximately 1 my·m or less even using coextrusion. In practice, it is difficult to do so. The practical thickness range of the second layer is 3 to 10 mym,
Especially from 4 to 8 my m. Since polycarbonate has a higher density than the other rigid polymers mentioned above, the density of the second layer must be taken into account when converting thickness to g.m ^-2 quantities. In maximizing the increase in stiffness, the emphasis is on whether the second layer of rigid polymer adheres properly to the first layer. One approach to improving adhesion is to use a blend in the intermediate layer, as described above, which can be achieved by incorporating the respective polymers to form a suitable homogeneous and stable blend. Typically, the blend has physical properties intermediate to those of the individual polymer components, depending on the proportions. Another approach is to sandwich between the first and second layers an intermediate layer of polymer that provides strong adhesion between the first and second layers. Examples of strong adhesive polymers are ethylene/vinyl acetate copolymer (EVA), ethylene/acrylic acid copolymer (EAA), ethylene/methacrylic acid copolymer (EMA), and ethylene/vinyl acetate terpolymer. Union,
Ethylene terpolymer and C.X.
A” [CXA, Dupont], “Modesk”
(MODIC, Mitsubishi), “PLEXAR” [PLEXAR,
Chemically modified polyolefin resins such as those sold under the trade name Chemplex. The amount of coverage of the intermediate layer is 1 to 10 g・m
^-2 , usually 4 to 9 g·m ^-2 . The stiffness of the highly adhesive polymers mentioned above is relatively low, somewhat lower than that of LDPE. Surprisingly, sandwiching an intermediate layer of this type of polymer does not appear to have an adverse effect on the overall stiffness of the photobase. The intermediate layer may be formed from a blend of a strong adhesive polymer and, for example, polyethylene, which blend can contain up to 75% of the other polymer if it has the appropriate physical properties. Since pigments are commonly used as masterbatches, for example in low-density polyethylene, it is important to use the blends described above, especially when coloring interlayers. Sandwiching the strongly adhesive interlayer is considered to be another important feature of the invention. According to the invention, from 10 to 50 g of a low density polyethylene or a low density polyethylene blend comprising at least 50 weight percent low density polyethylene, having a paper support carrying a composite coating on the printing side, the composite coating comprising a low density polyethylene or at least 50 weight percent low density polyethylene.・consisting of a first extruded coating layer of m ^-2 ;
The first coating layer includes at least 5 weight percent opaque pigment and further comprises a polycarbonate resin.
a second coating layer of 0.1 to 18 g.m ^-2 , the second coating layer encapsulating the first coating layer, the photobase comprising a wire face resin coating and a second layer of rigid polymer; If it may include an interlayer of a strongly adhesive polymer, it may also contain from 1 to 10 g·m ⁻² of an interlayer of a polymer sandwiched between said first coating layer and said second coating layer.
There is also provided a resin-coated photographic base paper comprising: the intermediate layer having strong adhesive properties to both the first coating layer and the second coating layer and fixing the two layers. A traditional problem in producing resin-coated photobases is how to achieve good adhesion between the resin coating and raw paper. Although various methods are known to overcome this problem, in the present invention, a layer of polymer is carefully coextruded between the pigmented LDPE first coating layer and the green base paper using coextrusion techniques. This polymer layer exhibits good adhesion. The amount of coverage in this case is approximately the same as that for the intermediate layer described above, 1 to 10 g m ^-2 , especially 4 to 9
g・m ^-2 . Polymers that can be used in the polymer layer are the above-mentioned polymers that are suitable for being sandwiched as a strong adhesive layer between the first coating layer and the second coating layer. The use of this type of adhesive layer between the colored LDPE and the raw base paper is a further feature of the invention. It is also possible to sandwich a layer of this highly adhesive polymer between the polyolefin resin coating on the wire side and the raw base paper. According to the present invention, the paper support carries a composite coating on the printed surface, the composite coating comprising a low density polyethylene or a blend of low and high density polyethylene comprising at least 50 weight percent low density polyethylene. comprising a first extruded coating layer of 50 g.m ^-2 , said first coating layer comprising at least 5 weight percent opaque pigment, and further comprising a second coating layer of 0.1 to 18 g.m ^-2 of polycarbonate resin;
The second coating layer encapsulates the first coating layer and further comprises an intermediate layer of 1 to 10 gm ^-2 of polymer sandwiched between the base paper and the first coating layer, the intermediate layer comprising: A resin coated photographic base paper is also provided in which a layer has strong adhesive properties to both the base paper and the first coating layer to secure them both. The effect of forming a second thin layer of rigid polymer encapsulating the colored first layer in the printed surface resin coating is to increase the stiffness of the photobase. It is difficult to accurately assess the expected increase in stiffness when considering the photobase of the present invention as a combined beam. Such evaluations depend on assumptions about the behavior of the various photo-based sites and interactions at the polymer-polymer and polymer-paper interfaces. It goes without saying that the increase in rigidity actually measured from the standard physical properties is generally higher than expected. Although we do not have a satisfactory explanation for this, it is possible that the thin second layer undergoes some degree of orientation during extrusion and/or cooling, and that this orientation could make the second layer more stiff than the polymer itself. (Based on published stiffness data for "plaque" tests several mm thick). It is also conceivable that the photobase could otherwise be made more rigid due to its composite structure. However, what has just been suggested does not satisfactorily explain the physical properties actually measured for the photobase of the present invention. 3 second coating layer
The case of polycarbonate with a coverage of from 4 to 18 g.m ^-2 , especially from 4 to 10 g.m ^-2 is particularly difficult to explain. Although stiffness increases in the longitudinal direction (MD), it has been found that the increase in the transverse direction (CD) is proportionally higher. Since the measured CD stiffness also depends on the bending direction, the measured stiffness when the polycarbonate is in tension is considerably higher than when it is in compression. Similar comparisons also show no significant difference in MD stiffness. Effects based on this phenomenon include that the photographic base paper of the present invention is "strong" and less likely to curl. It is extremely difficult to explain the above considerations. When multiple layers of wire face coating and polycarbonate second layer are used, the overall stiffness is significantly improved. This is because each polycarbonate coating mutually compensates for the increase in CD stiffness, resulting in a reduction or elimination of stiffness anisotropy. The second layer may be uncolored or colored with conventional opaque pigments. However, if the polymer used in the second layer contains a high amount of pigment, for example about 5% or more, it may be relatively difficult to coextrude the polymer onto the paper. Therefore, the amount of opaque pigment is approximately the same as the amount used in the first layer. The pigments used are white pigments, especially titanium dioxide.
If the amount of pigment used in the second layer is reduced, there is an advantage that the amount of pigment used in the first layer can be increased. Details will be described later. The first layer of the photographic base paper according to the invention consists of LDPE or at least 50%, in particular at least 70%
Made from a blend of LDPE and HDPE and contains opaque pigments. Opaque pigments are so-called "instant"
Although it may be black, such as the carbon black used in the manufacture of photobases for printing, the color of the present invention is usually white, in which case it is almost exclusively titanium dioxide, especially rutile titanium dioxide. The total amount of pigment is such that the desired opacity is achieved and is at least 5% as discussed above. If rutile titanium dioxide is used, the amount is at least 8%, in particular 12 to 15%, based on the layer weight.
In the present invention, it has been discovered that it is possible to coextrude a significantly larger amount of pigment into the first layer without making the second layer too heavily colored. Although the benefits derived from increasing the pigment concentration in the first layer are unpredictable,
It becomes possible to use anatase titanium dioxide in high concentrations as an opaque pigment, making it advantageous for application to photobases. Anatase type titanium dioxide is rutile type titanium dioxide (for example, an ultramarine blue pigment is sometimes used in combination with rutile type titanium dioxide to increase the blueness of the printing surface resin).
The former is superior to the latter as an opaque pigment in a resin-coated photobase, as it produces a product with a stronger blue tone and higher brightness. but,
Despite the advantages mentioned above, the addition of anatase has often been avoided, as it is extremely difficult to use it in concentrations that would allow it to function as a good opacifying pigment. According to the manufacturing method of the present invention, excellent opacity and color tone can be achieved using high concentrations of antase without incurring the severe manufacturing problems of conventional methods. In this way, when a large amount of pigment is used, the pigment concentration is 25%, and if it is higher than that, for example 35%.
It may be %. If a strongly adhesive intermediate layer is used, the intermediate layer may be colored, as described above, in which case the amount of pigment is approximately the same as the amount in the LDPE layer (first layer). The pigment content range mentioned above (12 to 15%) is from 20 to
This is the range used for conventional resin-coated photobases with a printed surface resin coating thickness of 40 my·m.
Since the manufacturing method of the present invention allows the use of pigments in high concentrations, somewhat thinner colored layers than previously considered appropriate can be applied while retaining the opaque pigments. Other conventional additives can be added to the first layer. Examples of additives are long-term stabilizers such as phosphonates described in British Patent Specification No. 2048278;
Hindered polymeric amine [Kimasusorb 944] described in European Patent Specification No. 85523
(Chimassorb 944)], optical brighteners and blue pigments such as ultramarine pigments that are added to increase the visible brightness of the photobase. The wire surface polyolefin resin coating of the present invention can be formed with conventional coatings for photobases, typically LDPE or 50% to 75%
Formed from a blend of LDPE and HDPE, including LDPE. The amount of resin coating on the wire surface is 5 to 50.
g.m ^-2 , in particular from 15 to 35 g.m ^-2 . Pigments can be added to the wire surface coating, but this is not necessary and does not provide any particular effect. If an enveloping layer of a rigid polymer and optionally an intermediate layer of a highly adhesive polymer is used, the thickness of these layers is approximately the same as the thickness of the printed surface resin coating. The surfaces of both the wire side and the printed side of the resin coating can be finished with a gloss finish, a silk finish, a stipple finish, or any other desired finish. The maximum gloss of the printing surface resin coating in the photographic base paper product obtained by the manufacturing method of the present invention is higher than the gloss of currently commercially available photographic base papers. This improvement in maximum gloss is not only particularly remarkable when the second layer is formed of polycarbonate, but also allows a higher linear velocity to be maintained than when forming a glossy surface on an LDPE film. This advantage is of practical importance. The outer surface of the wire-faced resin can also be additionally treated with conventional paints to enhance writability. Another unexpected benefit of using a second layer of a rigid polymer, particularly polycarbonate, in the printed surface resin coating is a lower incidence of pitting compared to a single layer of LDPE pigmentation. Although the reason for this is not clear, it is an important effect in that the second layer can be formed with a low coating amount. The various advantages achieved using a second layer of a rigid polymer, particularly a layer in which the polymer is polycarbonate, include the industrial advantage that a relatively thin layer of such a polymer can be applied as a second layer. It means something. Although this does not result in a significant improvement in rigidity, it is possible to improve other physical properties. The reason behind this compromise is the fact that rigid polymers, such as polycarbonate, are relatively expensive, about four times as expensive as LDPE. The photographic base paper of this invention is made by extrusion coating multiple layers of various polymers onto the paper. At least some of these multiple layers are formed sufficiently thin. With existing technology, it is not possible to industrially produce such unsupported thin layers by extrusion. The above problems can be overcome by employing a coextrusion process in which two or more coating layers are extruded through a single extrusion die and coated simultaneously onto the paper support. In actual extrusion operations, it is believed that all layers (two or more layers) in a multilayer coating can be extruded simultaneously via a single coating operation. According to the invention, the method comprises co-extruding a composite coating onto the printing side of a paper support, the composite coating comprising 10 to 50
g m ^-2 low density polyethylene or at least
consisting of a first layer of a low-density polyethylene blend containing 50 weight percent low-density polyethylene;
said first layer comprising at least 5 weight percent opaque pigment and further comprising a second layer of polycarbonate having a stiffness modulus of at least 0.5 GPa from 0.1 to 18 g.m ^-2 , said second layer comprising at least 5 weight percent opaque pigment; A method of making a resin coated photographic base paper is provided which is spaced apart from the surface of the first layer. As is clear from the above description, it is particularly preferred that the second layer is made of polycarbonate. The co-extruded structure has strong adhesive properties to the "first layer" and "second layer" and has a polymer intermediate layer sandwiched between the first and second layers. It may also include. According to the present invention, the method comprises coextruding a composite coating of a first layer and a second layer as described above onto the printing surface of a paper support, and further comprising: before and after coextruding the composite coating onto the paper support. There is also provided a method for making resin-coated photographic base paper comprising extrusion coating the wire side of the paper support with a coating of 10 to 50 g.m ^-2 of polyolefin resin. The coating on the wire side of the paper support may be a multilayer coating as described above, and this type of coating can be formed by coextrusion in the same manner as in the case of the printing surface resin. The relative amounts of layers in the printed surface coating are controlled by adjusting the throughput of the extruder. Conventional coextrusion equipment can be used, provided that it can be extruded at temperatures of 280 to 320°C, which are higher than those required for forming resin-coated photobases, i.e., in other applications. No. The wire surface resin coating can be formed by extrusion or coextrusion prior to or subsequent to coextrusion coating of the printed surface.
This coating can be carried out in-line using a tandem coating device or off-line at a separate drug stage. Adhesion between gelatin-based photographic emulsions and polymers of the type used in photobases is generally not very good. In order to increase the adhesion of the emulsion, the printing surface resin is surface treated, for example by corona discharge.
This surface treatment technique is applicable to the resin-coated photobase of the present invention and its manufacturing method. The adhesion between the photobase and the emulsion, which has been improved by the corona discharge treatment, deteriorates over time, but in that case, an adhesive deterioration inhibitor can be applied. The inhibitor is a gelatin solution that forms a very thin gelatin film of less than 1 g·m ⁻² . This gelatin film adheres to the photobase and forms a good bond with the photographic emulsion. The manufacturing method of the present invention also includes treating the corona-treated photobase with an adhesive anti-fading agent, particularly a gelatin solution, to form a very thin film on the photobase. The invention comprises a photobase according to the invention or a photobase formed according to the invention,
A photographic printing paper carrying a photographic emulsion on top of the second layer of the photobase is included. When a layer of adhesive anti-attenuation agent is used, it is sandwiched between the second layer and the photographic emulsion layer. Examples Hereinafter, the present invention will be explained based on examples. Parts or percentages are by weight unless otherwise specified. The test method was as follows. Rigidity (hardness): Kenley tester and Lorentzen
Two types of testers were used: Wettre's tester. The test method is as follows. 1 Kenrei Hardness A piece of paper 1.5 inches (38.1 mm) wide is sandwiched so that it projects 2.25 inches (57.2 mm) vertically upward from the horizontal lamp. The probe carrying the gas sensor is placed so as to move within a line perpendicular to the midline of the test piece, 4 cm above the clamping surface. Move the probe and deflect the specimen to a position where the line connecting the probe tip and the clamp is tilted 15° from vertical for 2.5 to 30 seconds. The force measured at this position is the stiffness. The force measured by the Kenrei tester is given in grams, but here it is expressed as millinewtons (mN) (the properly obtained value is force x length ^{- 1} , but the effective length is defined by the width of the specimen, so the measured force is directly quoted as the Kenley hardness). 2 Lorentzen-Wetztre Stiffness This test is performed using a rectangular paper sample measuring 70 mm x 38.1 mm. A paper sample is held in a vertical gripper with the long side of the sample horizontal and the short side vertical.
The gripper is rotatably attached to the vertical shaft as a fulcrum. Position the paper sample so that it is in contact with the vertical cutting edge fixed to the gas sensor and at a distance of 25 mm from the clamping locus on the plane of the paper surface. Operate the device to rotate the gripper by the set angle (15°).
The maximum force detected by the force sensor is the hardness of the paper sample. The device displays the number of millinewtons (mN) (as with the Kenrei tester,
The result obtained is the force x length ^{- 1} dimension, but the read value is directly quoted as the hardness). Example 1 40% on the printing surface of 178g・m ^-2 white raw paper for photography
g.m ^-2 various polymer coatings were extrusion coated. As a control, one coating made of only colored LDPE was prepared. Another coating consisted of a first layer of colored LDPE containing 12.5% rutile titanium dioxide and a second layer of uncolored rigid polymer according to the invention. The coating uses a glossy chilled roll, and the length is 50m.
It was carried out in a Pilot two-layer coextrusion coater at a linear speed of min ^-1 . The relative coverage and total coverage were controlled by adjusting the throughput of both extruders. The substances used were as follows. LDPE: [Dow Chemicals] HDPE: Same as above PP: Tenite 4G7DP, Eastman Chemicals] PC: Lexan 1972-2 [Lexan 1972- 2. General Electric Plastics] TiO ₂ : Amperset A.D. 11485
−S [(Ampacet AW11485−S, HDPE
Master batch containing 50% TiO ₂ )] Table 1 shows the coating amount of the above substance and the stiffness test results.

[Table] As is clear from the results in Table 1, the rigidity can be significantly increased simply by encapsulating only a thin layer of rigid polymer as a second layer in the printed surface resin coating. This effect is particularly remarkable when the thin second layer is made of polycarbonate. Example 2 170 gm ^-2 of raw photographic base paper was coated with resin using a pilot two-layer coextrusion coater using a chilled roll. Various coating structures shown in Table 2a were prepared. A control structure was prepared by coextruding colored LDPE onto green base paper from both extrusion paths of a coextruder to efficiently form a monolayer. The three-layer structure is made by first coloring the raw base paper to a predetermined coverage amount.
A monolayer of LDPE was extrusion coated, and then a given EVA/PC layer was coextrusion coated on top of the monolayer. Next, on the wire side of the photo base.
Consisting of a blend (1:1) of LDPE and HDPE27
A single extrusion coating of an unpigmented coating of g·m ^-2 was applied. Table 2b shows the stiffness test results (Lorenzen-Wetztor)
Shown below. The polymers used for the printing surface were as follows. LDPE: Escorene LD 252 [Escorene
LD252, Esso Chemicals Ltd. TiO ₂ : Amperset AW11485-2 EVA: Escolen U.L. 00909
[(Escorene UL00909, EVA copolymer containing 9 weight percent VA) PC: Lexan 1972-2 A blend of Escorene EVA (71.1%) and Ampaset Masterbatch (28.9%) was used as the colored EVA.

【table】

[Table] (Note) +: Printing surface resin under tension
-: Printing surface resin under compression
Difference: Percentage difference between sample average value and control average value Example 3 165 g·m ^-2 raw photographic base paper was coated with resin by coextrusion using a gloss chilled roll. table
Coverage shown in 3a (measured amount based on base paper product)
Various coating structures having the following properties were prepared as follows. The substances used were as follows. LDPE: Escoren LD252 TiO ₂ : Amperset AW11485-S HDPE: [Dutch State Mines
EVA: Escolene VL00909 PC: Lexan 1972-2 The colored resin layer was formed using appropriate amounts of uncolored resin and TiO ₂ masterbatch. The printed surface coating of base paper products formed according to the present invention is a pigmented blend of LDPE and HDPE (57.8%
An inner layer of LDPE + 13.3% HDPE + 28.9% _TiO2 ),
Consisting of an intermediate layer of pigmented EVA (71.1% EVA + 28.9% TiO ₂ masterbatch in LDPE) and an outer layer of PC, the wire face coating consists of an inner layer of a blend of 50% LDPE and 50% HDPE and an intermediate layer of unpigmented EVA. , PC
It consisted of an outer layer of It is difficult to distinguish the inner and middle layers on both sides of the photobase in the product. "Target" coverage of each intermediate layer and outer layer, inner -
The "actual" coverage (calculated from thickness measurements) of the intermediate combined layer and the outer layer is shown in Table 3a. Actual coverage can be determined by microscopic examination.

【table】

[Table] The stiffness and gloss test results are shown in Table 3b. Since both coatings on the printed surface and the wire surface contained polycarbonate layers, no significant anisotropy in stiffness as occurred in Example 2 was observed. Gloss measurements are comparative in nature rather than absolute measurements. Although a glossy chilled roll was used as the chilled roll, some variation in the surface finish occurred, and this variation was visually observed during coating, and the surface quality of the chilled roll was not suitable for use in extrusion coaters on a photo-based production scale. This is because it was inferior to the standard glossy chilled roll. Nevertheless, the photobase product obtained by coextruding a polycarbonate layer on the outside of the printed surface showed superior gloss than the control. The incidence of pitting was investigated for the obtained photobase product. The number and size of pits in the resin coating of photobase products formed according to the present invention were significantly fewer and smaller than the control. None of the products of the invention produced gels. Two control samples were used in this example. The control sample for stiffness comparison is a standard commercially available resin-coated photobase for color printing, consisting of a colored blend of LDPE and HDPE on the printing surface of 165 g m ^-2 raw base paper.
A film of 30g・m ^-2 is applied individually to the wire surface.
30g of uncolored blend of %LDPE and 50% HDPE.
It was coated with a single film of m ^-2 . The control sample for comparison of glossiness and pitting rate was 165g.
LDPE and HDPE on the printing surface of m ^-2 raw photo base
Colored blend (57.8% LDPE + 13.3% HDPE +
30g of 28.9% TiO ( ₂ masterbatch) in LDPE.
A film of m ^-2 was coated singly using a coextruder. Gloss was measured using an MK2 glossmeter [MK2] equipped with a 75° photometric head.
Glossmeter, Sheen Instruments Ltd.]. The reading of this gloss meter is 0%, that is, 100% of the faded black surface (the zero level adjustment is based on the faded standard product). The scale is set using a gloss standard (in this case the standard is a black glass plate with a 97.8% gloss with a 75° photometric head).

Claims (1)

Claims: 1. A paper support carrying a composite coating on the printed surface, the composite coating comprising low density polyethylene or a blend of low and high density polyethylene comprising at least 50 weight percent of low density polyethylene. 50
g.m ^-2 of polycarbonate, the first coating layer comprising at least 5 weight percent opaque pigment and further having a stiffness modulus of at least 0.5 GPa.
^-2 second coating layer, the second coating layer being encapsulated and fixed onto the first coating layer. 2. The photographic base paper of claim 1, wherein the second coating layer is formed of polycarbonate having a stiffness modulus of at least 2.0 GPa. 3. The photographic base paper according to claim 1 or 2, wherein the second coating layer has a coating amount of 1 to 15 g·m ^-2 . 4. The photographic base paper according to claim 3, wherein the second coating layer has a coating weight of 3 to 10 g·m ^-2 . 5 An intermediate layer of 1 to 10 g m ^-2 of a polymer sandwiched between the first coating layer and the second coating layer, the intermediate layer being sandwiched between the first and second coating layers. The photographic base paper according to any one of claims 1 to 4, which has strong adhesive properties to fix both layers. 6 The intermediate layer is an ethylene/vinyl acetate copolymer,
Polymers selected from the group consisting of ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, ethylene/vinyl acetate terpolymers, ethylene terpolymers, and chemically modified polyolefin resins. A photographic base paper according to claim 5, which is formed of: 7 An intermediate layer of 1 to 10 g m ^-2 of a polymer sandwiched between the base paper and the first coating layer, the intermediate layer being strong to both the base paper and the first coating layer. The photographic base paper according to any one of claims 1 to 6, which has an adhesive property and is fixed to both the base paper and the base paper. 8. The photographic base paper according to any one of claims 1 to 7, wherein the wire surface of the base paper is coated with a polyolefin resin film of 10 to 50 g·m ^-2 . 9. The photographic base paper according to claim 8, wherein the polyolefin resin of the first coating layer is low density polyethylene or a blend of low and high density polyethylene. 10 The coating on the wire face comprises a first extruded coating layer of 10 to 50 g.m ^-2 of polyolefin resin and a second coating layer of 0.1 to 18 g.m ^-2 of polycarbonate having a stiffness modulus of at least 0.5 GPa. 10. The photographic base paper according to claim 8 or 9, wherein the second coating layer is encapsulated and fixed onto the first coating layer. 11 The second coating layer on the wire surface is 3 to 10
11. The photographic base paper according to claim 10, which is made of polycarbonate of g·m ^-2 . 12 An intermediate layer of 1 to 10 g m ^-2 of a polymer sandwiched between the base paper and the first coating layer, the intermediate layer being resistant to both the base paper and the first coating layer. The photographic base paper according to any one of claims 8 to 11, which has adhesive properties to fix both. 13 A method for producing resin-coated photographic base paper, comprising simultaneously extruding a composite coating of a first layer and a second layer onto the printing surface of a paper support, the first coating layer weighing from 10 to 50 g. m ⁻² of low density polyethylene or a low and high density polyethylene blend comprising at least 50 weight percent low density polyethylene, said first coating layer comprising at least 5 weight percent opaque pigment, and said second coating layer comprising at least 5 weight percent opaque pigment; layer
A method of manufacturing a polycarbonate having a stiffness modulus of at least 0.5 GPa of 0.1 to 18 gm ^-2 , wherein the second coating layer is encapsulated and secured over the first coating layer. 14. The manufacturing method according to claim 13, wherein the wire side of the base paper is extrusion coated with 10 to 50 g.m ^-2 of low density polyethylene or a blend of low density polyethylene and high density polyethylene. 15 A composite coating of a first coating layer and a second coating layer is formed on the wire surface, and the first coating layer has a thickness of 10 to 50%.
g.m ^-2 of polyethylene, and the second coating layer is made of 3 to 10 g.m ^-2 polycarbonate, and the second coating layer is encapsulated over the first coating layer. The manufacturing method according to item 14.