EP0298188A1 - Base for photographic coatings - Google Patents

Abstract

The base material for photographic layers consists of a paper or film material coated on one or both sides with a polyolefin resin which contains a fluorinated polymer.

Description

The invention relates to a waterproof support material coated with polyolefin resin for photographic layers.

Polyolefin-coated photographic support materials usually consist of a sized base paper with waterproof polyolefin resin layers preferably applied on both sides. In a widespread embodiment, the polyolefin resin layers consist of polyethylene and are applied to the paper by means of extrusion coating (J. Appl. Photographic Engineering 5th (1979) pp. 110-117).

One or more photographic layers are then applied to one of the polyolefin resin layers (front side layer) after a pretreatment of the layer surface which is necessary for promoting adhesion. These photographic layers can be those for black / white as well as for color photography with associated auxiliary layers.

The front layer usually contains light-reflecting white pigment, preferably a titanium dioxide and, if appropriate, color pigments, optical brighteners and other additives, such as dispersing agents for the pigments, release agents, lubricants, antioxidants, antistatic agents or the like.

The synthetic resin layer (back layer) arranged on the paper side opposite the light-sensitive layers is preferably not pigmented. However, it can also contain pigment and other additives which result from the use of the coated paper as a photographic support material and which can in principle correspond to those of the front layer.

Additional functional layers can be located between the front layer and the actual photographic layers, which, for example, improve the adhesion of the photographic layers or perform another function due to the use of the material.

The back layer can also be covered with further functional layers which improve, for example, the writeability, the conductivity, the adhesiveness, the flatness or other properties of the carrier material.

In order to ensure that a photographic paper support coated on both sides with polyolefin does not have an undesirably strong curvature to the front after one-sided application of photographic layers, the procedure for polyolefin coating is usually such that the front layer consists predominantly of a lower density polyolefin (e.g. LDPE), while the back layer mainly consists of a higher density polyolefin (e.g. HDPE). (J. Appl. Photographic Engineering 7. (1981) p. 71).

The coating of photographic base papers with polyolefin is generally done as a melt coating with the aid of extrusion coating systems with a slot die. This process is known both as a single coating process and as a multiple coating process. Auxiliary layers and additional functional layers can be applied with the aid of all known coating methods both in separate coating systems and "in line" with the extrusion coating (EP 21749).

It is generally known that the design of photographic support materials is determined in various ways by taste considerations. This applies, for example, to tinting both the base paper and the front layer with small amounts of dyes or color pigments. This also applies in a special way to the design of the surface of the front layer. There are Both glossy and matt and structured surfaces are known. The degree of roughness or the surface structure can be determined very precisely with the help of differently designed cooling rollers and can be tailored to different customer requirements.

Each coating process, as well as each coating material, has specific advantages and disadvantages which are well known to the person skilled in the art and which lead him to decide on a case-by-case basis which process and which material is used in which combination for a specific photographic support material. The person skilled in the art is also aware that he has to avoid certain additives which are customary in the plastics or paper industry because they can react with constituents of the photographic layers and are therefore troublesome in photographic support materials and can even lead to the uselessness of the support material , while others are indispensable for the production of polyolefin resin coated substrates for photographic layers. The latter group includes, for example, white pigments such as preferably titanium oxides, colored pigments, dispersants for pigments, antioxidants, optical brighteners or some processing aids.

Certain processing aids, which are also known as lubricants or release agents, are added to most polyolefin coating compositions for photographic supports and are indispensable, in particular, for those coating compositions which are processed with the aid of a glossy cooling roller to form layers with a glossy surface. These release agents include stearic acid, glycerol stearates, metal salts of higher fatty acids or amides of higher fatty acids. Additions of magnesium stearate, zinc stearate, aluminum stearate or erucic acid amide are very common for polyolefin coated papers for photographic purposes. It is also known to use polyethylene glycol as a release agent in polyolefin coating compositions.

An important function of these release agents is to ensure that the extruded polyolefin film is separated easily and evenly from the chill roll. In the absence of such release agents, the detachment of the polyolefin film from the chill roll does not always occur uniformly but at short rhythmic intervals, and fine elevations are formed which run transversely to the web direction. These hair-fine surveys cannot be detected by conventional tactile methods for measuring the surface profile, but are clearly visible as fine lines on shiny surfaces with oblique light incidence, which run parallel to one another and are at a distance of about 1 mm from one another. That is why they are also called "staff lines". The "staff lines" generally occur at coating speeds that are greater than 70-80 m / min and increase with increasing speed.

Only by adding one or more of the release agents mentioned to the coating composition is it possible to produce high-gloss surfaces in the extrusion coating process. The release agent additive is roughly proportional to the coating speed, i.e. higher coating speeds require higher amounts of release agent. Amounts between 0.5 and 1 wt .-% based on the coating composition are quite common.

Any addition of lubricants or release agents is associated with disadvantages. Release agents not only facilitate the detachment of the polyolefin film from the chill roll, but also weaken the adhesion of the polyolefin film to the base paper. The release agents also sweat due to the high extrusion temperatures. The vapors partially condense on machine parts and the condensate can drip onto the web. In the worst case, greasy deposits form on the chill roll and are transferred from there to the polyolefin surface, where they are not only visible as gloss defects but also impair the formation and adhesion of photographic layers applied later.

While the so-called "note lines" are naturally only observed on glossy polyolefin surfaces, exudation with unpleasant deposits on the cooling roller is disadvantageous both on glossy and on structured or matt surfaces. There is therefore a strong interest in finding a way to reduce the release agent additives. In particular, there is a need to completely eliminate the fatty acid amides and fatty acid esters, which are very susceptible to deposits, and yet to be able to produce defect-free, high-gloss surfaces at economical operating speeds. It is particularly desirable to be able to produce matt or glossy surfaces with the same coating mixture, in order not to have to change the coating mixture unnecessarily when changing the surface structure (cooling roller change).

The object of the invention is therefore to provide a polyolefin-coated support material for photographic layers which does not have the disadvantages described. In particular, it is an object of the invention to produce a polyolefin-coated substrate without so-called "note lines", which contains significantly less release agent in the outer polyolefin layer, and to provide a polyolefin coating composition which can be used without restriction both for matt surfaces and for production of flawless high-gloss surfaces.

It is a further object of the invention to propose a process for the production of polyolefin-coated substrates for photographic purposes in which there is no disruptive exudation of release agents and which enables the production of defect-free high-gloss surfaces under economically acceptable production conditions. A coating speed of more than 100 m / min is considered to be an economically acceptable production condition.

This object is achieved according to the invention in that a fluorine-containing polymer is admixed with the polyolefin coating composition used to produce a polyolefin coating and a photographic base material, e.g. a photographic base paper, is coated with this coating material. In a preferred embodiment, the admixed fluorine-containing polymer is a polymer or copolymer of vinyl fluoride, vinylidene fluoride, trifluorochlorethylene or hexafluoropropylene, which contains 30-76% by weight of fluorine and is added in an amount of 40 to 1500 ppm to the polyolefin coating composition.

The invention accordingly relates to a material coated on at least one side with polyolefin, for example paper, the polyolefin coating of which contains a fluorine-containing polymer, a polymer which contains 30-76% by weight of fluorine and the polyolefin coating composition in an amount of 40 to 1500 ppm being preferred was added.

The invention relates in particular to a polyolefin-coated backing paper for photographic layers, in which the polyolefin layer (front layer) initially located in the photographic layer is a polymer or copolymer of vinyl fluoride, vinylidene fluoride, trifluorochloroethylene or hexafluoropropylene in one Contains an amount of 40 - 1500 ppm.

The invention further relates to a method for producing a polyolefin-coated support material for photographic layers by means of extrusion coating, which is characterized in that a fluorine-containing polymer is mixed in the form of a premix at least into the polyolefin coating composition used for coating the front side. The blended amount of fluorine-containing polymer is preferably 40-1500 ppm based on the polyolefin coating composition and is a polymer or copolymer with a fluorine content of 30 to 76% by weight.

The base material coated with polyolefin according to the invention is preferably a photographic base paper which is internally sized in a known manner and has been given a surface size. The base material can also be a paper made of synthetic fiber material or film material.

The polyolefin coating is carried out in a known manner by means of extrusion coating. One side of the material can have several polyolefin layers on top of one another. There may also be another layer under a polyolefin layer, for example a conventional barite layer, an electron beam hardened layer, an adhesion promoting layer or a barrier layer, and further known layers may be applied to the polyolefin layer before a photographic layer is placed over it.

The fluorine-containing polymer is advantageously first kneaded into a premix containing 1-5% by weight of fluoropolymer with polyolefin, granulated and mixed in this form with the rest of the coating mixture before extrusion. The preferred polyolefin for the preparation of the premix is polyethylene, in particular a lower polyethylene Dense, so-called LDPE.

The fluorine-containing polymer admixed according to the invention with the polyolefin mixture is preferably a polymer or copolymer of fluorine-containing monomers such as vinyl fluoride, vinylidene fluoride, trifluorochloroethylene or hexafluoropropylene. Other fluorine-containing monomers may also have been used in a minor amount to produce the polymer, for example a copolymer of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene is also suitable as an additive for layers according to the invention. In addition, the fluorine-containing polymer can also contain non-fluorine-containing monomers, for example ethylene, vinyl chloride, acrylic acid or others, in minor amounts.

The molecular weight of the fluorine-containing polymer is variable in a wide range. Polymers with a molecular weight of 5,000 were used with good results as well as those with an average molecular weight of 500,000.

In a particularly preferred embodiment of the invention, the polyolefin resin layer which contains the fluorine-containing polymer is a white pigment-containing polyolefin layer. Therein, the white pigment is usually a rutile or anatase type titanium dioxide pigment or a mixture containing titanium dioxide with other white pigments. The white pigments used in extrusion coating compositions are generally those which have received an inorganic or organic or inorganic and organic surface treatment. In addition to white pigment, the layer may contain small amounts of colored pigments, dispersing aids, optical brighteners, antioxidants or other additives known in connection with photographic supports.

In a further embodiment of the invention, the polyolefin layer contains a release agent combination consisting of the fluorine-containing polymer and a polyether glycol. The polyether glycol is a polyethylene glycol with a molecular weight between 200 and 35,000 or a polypropylene glycol with a molecular weight between 400 and 10,000 or an ethylene oxide / propylene oxide copolymer with a molecular weight between 400 and 30,000. The amount of used Polyether glycol is between 10 and 500 ppm based on the complete coating mixture.

Polyolefin coating compositions according to the invention with an addition of fluorine-containing polymer show clear processing advantages in comparison with all previously known mixtures. Fatty acid derivatives as release agents are unnecessary and, if desired, a matt and glossy surface can be produced without quality-reducing exudation and without the dreaded "score lines". The adhesion to the paper or film base is unexpectedly not deteriorated, but is even slightly improved, and in spite of the incompatibility of the fluorinated polymer with the polyolefin resin, no inhomogeneities are observed in the extruded film. Small admixtures of salts of higher fatty acids, e.g. Magnesium stearate, which is occasionally present in polyolefin mixtures as a dispersant for pigment or as a neutralizing component for catalyst residues, is tolerated without disadvantages, especially since it is present in amounts which remain below 0.3% by weight. The undesired fatty acid amides and fatty acid esters can be completely dispensed with, and fatty acid salts are also superfluous for reasons of separation.

The result is particularly surprising because the separation of the polyolefin mixture from the chill roll is easy and without residue formation, but the adhesion between Substrate and coating is even improved. The adhesion of the photographic layers to a polyolefin layer containing fluorinated polymer according to the invention is also not impaired.

There are no particular restrictions on the polyolefin resin used for the extrusion coating. All polyolefin resins already described for extrusion coating with a slot die can be used, provided their melt index is between 1 and 35 g / 10 min. This can be polyethylene (HDPE, LDPE, LLDPE), polypropylene, ionomer resin or another olefin copolymer resin. It is crucial that the resin is suitable for the melt coating process and that the layer produced is no longer adhesive after cooling.

The invention is illustrated by the following examples.

Meaning of the abbreviations used:

LDPE = low density polyethylene
LLDPE = linear low density polyethylene
HDPE = high density polyethylene
d = density (g / cm³)
MFI = melt index (g / 10 min.)
MG = average molecular weight

Description of the examples

The following fluoropolymer, auxiliary and white pigment premixes were used to compile the mixtures listed in the examples: Fluoropolymer premixes Fluoropolymer Composition: copolymer of ... Fluorine content average Molecular weight MG LDPE weight% F1 Vinylidene fluoride hexafluoropropylene 65 150,000 2nd F2 Tetrafluoroethylene vinylidene fluoride 69 70,000 3rd F3 Tetrafluoroethylene vinylidene fluoride hexafluoropropylene 73 300,000 3rd F4 Tetrafluoroethylene propylene 38 120,000 4th F5 Trifluorochloroethylene-ethylene 45 10,000 5 F6 Vinyl fluoride-hexafluoropropylene-tetrafluoroethylene 70 220,000 3rd F7 Vinylidene fluoride hydropentafluoropropylene hexafluoroethylene 67 20,000 3rd

Aid premixes

H 1:
98.65 wt% LDPE; d = 0.915 g / cm³, MFI = 15g / 10 min.
1.3% by weight of ultramarine blue
0.05% by weight polypropylene glycol; MG ∼ 6000
H 2:
98.3% by weight of LDPE, as in H 1
1.3% by weight of ultramarine blue
0.4% by weight polyethylene glycol; MG ∼ 10,000
H 3:
98.2% by weight of LDPE, as in H 1
1.3% by weight of ultramarine blue
0.5% by weight erucic acid amide

White pigment premixes

W 1:
49.9 wt% LDPE, d = 0.915 g / cm³, MFI = 8g / 10 min.
49.9% by weight of titanium dioxide, rutile type, surface-treated with Al₂O₃
0.2% by weight magnesium stearate
W 2:
49.0% by weight of LDPE, as in W 1
49.0% by weight of titanium dioxide, as in W 1
2.0% by weight magnesium stearate
W 3:
50.0% by weight of LDPE, as in W 1
50.0% by weight of titanium dioxide, as in W 1
W 4:
50.0 wt% LDPE. as in W 1
50.0 wt .-% titanium dioxide, anatase type, with Al₂O₃ and organic surface treatment
W 5:
50.0% by weight LLDPE; d = 0.920 g / cm³, MFI = 4.4 g / 10 min. (Copolymer with 3.2 mol% octene)
50.0% by weight of titanium dioxide, as in W 1

example 1

A base paper for photographic supports with a mass per unit area of 170 g / m² was coated on the back after corona pretreatment with 30 g / m² of the following mixtures, a matt surface being given to these coatings by means of a matted cooling roller:
70% by weight HDPE; d = 0.950 g / cm³, MFI = 10 g / 10 min.
30 wt% LDPE; d = 0.924 g / cm³, MFI = 4 g / 10 min.
Immediately afterwards, after corona pretreatment, the front was coated with 30 g / m² of the following mixtures, a glossy surface being given to these coatings by means of a high-gloss cooling roller: Additions in% by weight example 1 LDPE d = 0.923 g / cm³ MFI = 4g / 10min. HDPE d = 0.950 g / cm³ MFI = 10g / 10min. White pigment premix Fluoropolymer premix Fluoropolymer content Type Type ppm a 38.5 38.5 20.0 W 3 3.0 F 1 600 b 39.0 39.0 20.0 W 3 2.0 F 2 600 c 39.0 39.0 20.0 W 3 2.0 F 3 600 d 39.25 39.25 20.0 W 3 1.5 F 4 600 e 39.4 39.4 20.0 W 3 1.2 F 5 600 f 39.0 39.0 20.0 W 3 2.0 F 6 600 G 39.0 39.0 20.0 W 3 2.0 F 7 600 Compare: h 40.0 40.0 20.0 W 3 - - All coatings were applied using a tandem extrusion coating system at a melting temperature of 310 ° C. and 110 or 160 m / min. Machine speed performed.

Example 2

The photo base paper from Example 1 was coated on the back as in Example 1.

Immediately afterwards, after corona pretreatment, the front was coated with 30 g / m² of the following mixtures, a glossy surface being given to these coatings by means of a high-gloss cooling roller: Additions in% by weight Ex .: 2 LDPE d = 0.923 g / cm³ MFI = 4g / 10min. HDPE d = 0.950 g / cm³ MFI = 10g / 10min. Aid premix White pigment premix Fluoropolymer premix Fluoropolymer content Type Type Type ppm a 22.7 56.8 - 20.0 W 3 0.5 F 1 100 b 22.6 56.4 - 20.0 W 3 1.0 F 1 200 c 21.7 54.3 - 20.0 W 3 4.0 F 1 800 d 20.9 52.1 - 20.0 W 3 7.0 F 1 1400 e 21.7 54.3 - 20.0 W 1 4.0 F 1 800 f 21.7 54.3 - 20.0 W 2 4.0 F 1 800 G 21.7 54.3 - 20.0 W 4 4.0 F 1 800 H 18.9 47.1 10.0 H 1 20.0 W 3 4.0 F 3 1200 i 18.9 47.1 10.0 H 2 20.0 W 3 4.0 F 3 1200 k 18.9 47.1 10.0 H 3 20.0 W 3 4.0 F 3 1200 Compare: l 22.9 57.1 - 20.0 W 3 - - Compare: m 20.0 50.0 10.0 H 1 20.0 W 3 - - Compare: n 20.0 50.0 10.0 H 2 20.0 W 3 - - Compare: o 20.0 50.0 10.0 H 3 20.0 W 3 - All coatings were applied using a tandem extrusion coating system at a melting temperature of 310 ° C. and 110 or 160 m / min. Machine speed performed.

Example 3

A base paper for photographic supports with a mass per unit area of 110 g / m² was coated on the back with 22 g / m² of the following mixtures after corona pretreatment, a matt surface being given to these coatings by means of a matted cooling roller:
69.9% by weight HDPE; d = 0.950 g / cm³, MFI = 10 g / 10 min.
27.1% by weight LDPE; d = 0.924 g / cm³, MFI = 4 g / 10 min.
3.0 wt% fluoropolymer premix F1
Immediately afterwards, after corona pretreatment, the front was coated with 25 g / m² of the following mixtures, with matt or glossy surfaces being given to these coatings by means of a matt or high-gloss cooling roller: Additions in% by weight Ex .: 3 surface LDPE d = 0.934g / cm³ MFI = 3g / 10min. LDPE d = 0.915g / cm³ MFI = 8g / 10min. HDPE d = 0.963g / cm³ MFI = 11g / 10min. White pigment premix Fluoropolymer premix Fluoropolym content Type Type ppm a frosted - 19.1 47.9 30.0 W 5 3.0 F 2 900 b glittering - 19.1 47.9 30.0 W 5 3.0 F 2 900 c glittering 20.1 13.4 33.5 30.0 W 5 3.0 F 7 900 d glittering 23.1 15.4 38.5 20.0 W 2 3.0 F 7 900 Compare: e glittering - 20.0 50.0 30.0 W 5 - - Comp .: f glittering 24.0 16.0 40.0 20.0 W 2 - - All coatings were applied using a tandem extrusion coating system at a melting temperature of 310 ° C. and 110 or 160 m / min. Machine speed performed.

Description of the test methods

Film liability:
The adhesion of the polyolefin resin film to the base paper is assessed by peeling off a 10 mm wide strip at an angle of 180 ° in the running direction of the coating. Grades from 1 to 5 are awarded, where grade 1 means very good liability and grade 5 means no liability.
Staff lines:
They run transversely to the web direction at intervals of about 1 mm and are visible on the glossy surface when the light falls at an angle. The assessments are clear, weak and none.
Disorders: (due to volatile components)
The length of the web is indicated, which could be coated without problems, before cleaning measures have to be taken due to the formation of condensate, cooling rollers or matt spots on the glossy surface of the coated base pair. In all examples, the cooling water temperature of the cooling roll was + 10 ° C.
Exam results: Examples Film liability on paper Staves at Faults after approx. (Km) 110m / min. 160m / min. 1a 2nd no no > 150 b 2nd no no > 150 c 2nd no no > 150 d 3rd no no > 150 e 2-3 no no > 150 f 2nd no no > 150 G 2nd no no > 150 Comparison h 3-4 weak clear > 150 2a 3rd no weak > 150 b 2-3 no no > 150 c 1-2 no no > 150 d 1-2 no no > 150 e 2nd no no 40 f 3rd no no 4th G 1-2 no no > 150 H 2nd no no 80 i 2nd no no 55 k 4th no no > 150 Comparison l 3-4 weak clear > 150 Comparison m 3rd weak clear 75 Comparison n 3rd no weak 55 Comparison o 4-5 no no > 150 3a 1-2 no no > 150 b 1-2 no no > 150 c 1-2 no no > 150 d 3rd no no 5 Comparison e 3rd weak clear > 150 Comparison f 3-4 weak clear 5

The results show that by adding fluoropolymers to the mixtures, the proportion of low molecular weight release agents can be significantly reduced or even avoided without the surface of the coatings having lines of marks.

By reducing or dispensing with low-molecular release agents, there are almost no exudations even at the high melting temperatures, so that extensive cleaning work during production is largely unnecessary.

Despite the easier separation of the polyolefin layers from chill rolls by the addition of fluoropolymers, the adhesion of these layers to the base paper is improved.

Claims (17)

1. Support material for photographic layers, consisting of a paper or film material coated on one or both sides with polyolefin resin, characterized in that at least one of the outer polyolefin layers contains a fluorine-containing polymer. 2. Support material according to claim 1, characterized in that the fluorine-containing polymer is contained in an amount of 40 to 1500 ppm. 3. Support material according to claim 1, characterized in that the fluorine-containing polymer is a polymer or copolymer with a fluorine content of 30-76% by weight. 4. Support material according to claim 1, characterized in that the fluorine-containing polymer is a polymer or copolymer of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, trifluorochloroethylene or hexafluoropropylene. 5. Support material according to claim 1, characterized in that the polyolefin layer also contains at least one further function-related additive. 6. Support material according to claim 5, characterized in that a further additive is a polyether glycol. 7. Support material for photographic layers made of paper or film material coated on one or both sides with polyolefin resin, in which at least one of the polyolefin layers contains a white pigment, characterized in that the polyolefin layer containing the white pigment is a fluorine-containing polymer with a fluorine content of 30- Contains 76 wt .-%. 8. Support material according to claim 7, characterized in that the amount of the fluorine-containing polymer makes up 40 - 1500 ppm of the pigment-containing polyolefin layer. 9. Support material according to claim 7, characterized in that the fluorine-containing polymer is a polymer or copolymer of vinyl fluoride, vinylidene fluoride, trifluorochloroethylene or hexafluoropropylene. 10. A carrier material according to claim 7, characterized in that the polyolefin layer containing the white pigment additionally contains at least one colored pigment of the blue, red or violet type. 11. Support material according to claim 8, characterized in that the resin layer additionally contains 10 - 1000 ppm of a polyether glycol. 12. Support material according to one of claims 7 and 10, characterized in that the resin layer additionally contains at least one dispersant caused by the pigment addition. 13. A carrier material according to claim 7, characterized in that the resin layer contains at least one further function-related additive. 14. A method for producing a polyolefin resin-coated support material for photographic layers, in which at least one polyolefin layer containing a white pigment is formed on a substrate by means of extrusion coating, characterized in that the polyolefin coating mixture is admixed with a fluorine-containing polymer in the form of a premix with polyethylene before the extrusion becomes. 15. The method according to claim 14, characterized in that the premix is made of 1-5 wt .-% fluorine-containing polymer and 95 to 99 wt .-% polyethylene. 16. The method according to claim 14, characterized in that the polyolefin coating mixture is admixed with the premix of the fluorine-containing polymer to such an extent that the resin layer on the substrate contains 40-1500 ppm of fluorinated polymer. 17. The method according to claim 14, characterized in that a polymer with a fluorine content of 30-76 wt .-% is used as the fluorine-containing polymer.