METHOD FOR PRODUCING A BREATHABLE FILM

Description

[0001] The invention relates to a process for producing a breathable film based on polyvinyl chloride (PVC).

[0002] PVC-based films are used, for example, in the production of artificial leather, which typically consists of a composite of textile, glass, or carbon fiber fabrics, knitted fabrics, polymer foams, or nonwovens coated with such a PVC film. Depending on the application, these coatings can be either compact or foamed and, for example, can have a grained surface through embossing, thus mimicking a leather texture.

[0003] If the PVC-based film is to have breathable properties, which is advantageous, for example, when used in seat covers or shoe uppers, as well as in wall and ceiling coverings to allow the passage of water vapor, the film must have a sufficient number of pores through which the water vapor can pass.

[0004] For the purposes of this invention, breathable properties are considered synonymous with combined air and moisture permeability. However, numerous prior art proposals describe breathability only in terms of existing water vapor permeability, not the additional ability to allow air exchange. These include, for example, ultra-thin coatings made of polyurethane, polyester, polyethylene glycol films, or similar materials.

[0005] It is known from the prior art to make non-breathable PVC-based films breathable, for example, by means of needle punching, i.e., the pores are subsequently introduced mechanically. However, this entails undesirable additional processing steps and, moreover, creates relatively large pores that have an unsightly appearance on the surface.

[0006] EP 2 918 629 B1 describes a generic method for producing a breathable film based on a hybrid of PVC and polyurethane, which can be used for the construction of artificial leather structures.

[0007] The problem with the breathable films known to date is that, even if they are sufficiently breathable, they cannot meet the high demands on flame retardancy, such as electric burners M1, M2 and M3 (NF P 92-503), (PDF-P-89 M 1, M2 and M3), edge flame exposure according to DIN 534838-2 and Grib 5 (BS 5852 No. 5). Previous designs are classified in terms of flame resistance for the automotive specification FMVSS 302 and the interior specifications BS-5852 IS-0 and IS1 as well as DIN EN 1021 Parts 1 and Part 2, which describe exposure to cigarette and gas flames for periods of 15 seconds and 20 seconds on the surface. However, to meet higher fire protection standards such as Grib 5 and M1, M2, B1 and B2, fundamental formulation and design changes must be made.Among other things, non-breathable PVC and / or PUR constructions achieve these higher fire protection standards (flame retardancy) through the use of flame retardants and / or in combination with halogen- and / or phosphate-containing plasticizers or compounds. However, the possibility of breathability—i.e., air and moisture permeability—in combination with flame retardancy and practical high abrasion resistance is not available in the current state of the art.

[0008] The object of the invention is to provide a method for producing a breathable film which is highly flame-retardant, sufficiently breathable and highly abrasion-resistant, so that it is suitable, for example, for use in the commercial sector, residential areas, public areas, hospitals as well as in the nautical and transport sectors.

[0009] To achieve the stated object, the invention proposes the design of a method according to the features of patent claim 1.

[0010] Advantageous embodiments and further developments of the invention are the subject of the dependent claims.

[0011] The proposal according to the invention is based on providing a pasty mass for the production of the breathable film based on polyvinyl chloride (PVC), which comprises at least a first fraction of PVC and a second fraction, which are mixed together to form the pasty mass, the pasty mass is then applied to a substrate and then, with the addition of heat, is formed into the film by drying and gelling, whereby pores with an average pore diameter of 1 µm to 1 mm (in situ) are formed running from one surface of the film to the other, which pores impart breathability to the film with a gas permeability of 0.1 to 200 l dm -2< min -1< and a water vapor permeability of 0.1 to 200 mg cm -2< h -1< in order to achieve the desired air and water vapor permeability.

[0012] In order to achieve the desired high flame retardancy and abrasion resistance, the invention proposes to form the first fraction from a paste PVC and flame-retardant additives and / or plasticizers and to form the second fraction from an aqueous PVC dispersion which does not contain any additional solvents other than water.

[0013] Within the scope of the invention, it was found that a breathable film produced from such a pasty mass based on paste PVC with flame-retardant additives and / or plasticizers as well as an aqueous PVC dispersion, despite the desired continuous pore formation for good air and water vapor permeability, meets the highest requirements for flame retardancy and abrasion resistance, so that it is ideally suited for use in automobile and other vehicle interiors, in the commercial sector and the like.

[0014] According to a proposal of the invention, emulsion PVC or microsuspension PVC with a K value of 63 to 90 or mixtures thereof are used as the first fraction, which can be based on PVC homopolymers, PVC copolymers, PVC vinyl acetates and / or PVC acrylates.

[0015] According to one proposal of the invention, flame-retardant plasticizers suitable for use in the first fraction are those belonging to the classes of phosphorus-containing, nitrogen-containing, halogen-containing and / or sulfate-containing plasticizers. Blends with polymer, phthalate, adipate or trimellitate plasticizers as well as sustainable plasticizers based on soybean oils, sebacates, castor oils or glycols are also possible within the scope of the invention. The proportion of flame-retardant plasticizers within the first fraction is preferably in the range from 40 to 160 phr (parts per hundred) and is based on 100 parts of paste PVC in the first fraction. Due to the variable proportion of plasticizers in the range from 40 to 160 phr, the softness, strength and extensibility, flexibility and cold stability of the resulting breathable film as a single layer orwithin a composite in which the breathable film is used as at least one layer, can be adjusted within wide limits.

[0016] According to the invention, the first fraction, based on a paste PVC, also contains flame-retardant additives, which according to the invention include, for example, phosphorus- and / or nitrogen-containing solids, e.g., ammonium polyphosphates, melamine cyanorates, and melamines, as well as fillers based on aluminum and magnesium compounds, ammonium salts, polymeric phosphates, borates, zinc salts, molybdenum and antimony compounds, and / or tin compounds. Furthermore, these compounds also include zeolites, clays, and thermally conductive compounds such as nitrides, carbides, for example, boron nitrides, silicon carbides, etc. Intumescent flame retardants, such as expandable graphite, can also be used individually or in combination, with the invention providing for the solids content to be adjusted to approximately 0 to 70 phr, preferably 0 to 45 phr, in each case based on 100 parts of paste PVC in the first fraction.

[0017] Furthermore, according to the invention, the first fraction can also comprise stabilizers based on uracil, perchlorate, barium, calcium, zinc, tin, epoxy, and / or beta-diketone in the liquid or solid state as flame-retardant additives. Blocked phenolic compounds or mixtures thereof can also be used. These stabilizers are preferably used in a total amount of approximately 0.5 to 20 phr, based on 100 parts of paste PVC of the first fraction.

[0018] A preferred mixing ratio of the pasty mass of first and second fraction according to this invention comprises about 5 to 50 wt.% of the first fraction and correspondingly 95 to 50 wt.% of the second fraction, so that a total of the first and second fractions of 100 wt.% is achieved.

[0019] Within the scope of the invention, it is particularly proposed to form the second fraction from an aqueous PVC dispersion having a K value of 58 to 80, wherein the particle sizes of the PVC particles used in the aqueous PVC dispersion are in a range from 20 nm to 60 µm, preferably 50 to 1000 nm.

[0020] The aqueous PVC dispersion of the second fraction further preferably has a solids content of the PVC particles used of about 5 to 65%, preferably 30 to 60%, and contains no other solvents apart from water and contributes significantly to the flame-retardant material properties of the breathable film obtained.

[0021] In addition, the soaps and ionic groups contained in the aqueous PVC dispersion form incompatible interfaces with the paste PVC of the first fraction, which, when the water contained evaporates as a result of heat input, form the desired pores in the breathable film to achieve the specified gas and water vapor permeability.

[0022] According to a further proposal of the invention, the formulation of the pasty mass for producing the breathable film can contain, in addition to the first and second fractions explained above and at least contained therein, a third fraction which is based on polyether, polyester or polycarbonate polyurethane or mixtures thereof and can be added to the pasty mass in an amount of up to 50% by weight, based on the total amount of the first and second fractions.

[0023] According to a proposal of the invention, the solids content of the third fraction amounts to approximately 5 to 65%, preferably 30 to 60%.

[0024] The third fraction may alternatively or additionally comprise thermoplastic polyurethane (TPU), which is used as a powder with an average grain size (fineness) of 50 nm to 120 µm, preferably 50 nm to 60 µm. This TPU polymer can be in the form of a polyether, polyester, or polycarbonate.

[0025] Additionally, the third fraction may also contain corresponding crosslinkers, which can be used in weight proportions ranging from 0 to 20 phr, preferably 0 to 8 phr, based in each case on 100 parts of polyurethane in the third fraction. These crosslinkers can be selected, for example, from isocyanates, carbodiimides, melamines, epoxides, and / or aceridines.

[0026] In addition to or as an alternative to the third fraction, the formulation of the pasty mass according to the invention for producing the breathable film can comprise, in addition to the at least contained first and second fractions, a fourth fraction containing coloring substances, such as cool-color pigments, inorganic and organic pigments, carbon blacks, quantum dots, and / or effect pigments, in an amount of approximately 0 to 40 phr, in particular 2 to 30 phr, based on 100 parts of PVC of the first fraction. According to the invention, the amount of the fourth fraction used based on coloring substances can comprise up to 30% by weight, based on the total amount of the first and second and, if appropriate, third fractions.

[0027] The production of the pasty mass provided within the scope of the invention comprises the homogenization of all fractions by mixing and dispersing in a suitable vessel, whereby a spreadable paste is obtained, the viscosity of which is determined by fillers, PVC types used, plasticizer content, dispersion contents and the particle sizes and is preferably adjusted to a viscosity of about 5 to 500 poise (0 to 10 4< mPas).

[0028] The pasty mass produced in this way is spreadable and can be applied to a provided substrate, for example by means of a reverse or roll coater, by doctoring, spraying or printing, preferably with a basis weight of about 10 to 800 g / m 2< .

[0029] A so-called release liner, for example made of silicone, olefin, PET etc. or based on a paper with a silicone, chromium stearate, polyolefin or acrylate finish as well as a metal foil or similar, is suitable as a base.

[0030] By subsequently heating and drying or gelling the pasty mass applied to the substrate together with the substrate under heat supply at temperatures between 70 and 250 °C, preferably 80 to 200 °C, for example in a drying oven through which the pasty mass applied to the substrate passes, the desired breathable film with the desired pore size and number is formed.

[0031] The backing can either be peeled off after the film has formed or is formed by a substrate which remains on the film after it has formed.

[0032] With the method according to the invention, it is possible to produce at least one layer from a breathable film produced in this way, which can be used, for example, for the production of artificial leather, in which a cover layer made of a breathable film according to the invention is applied to a textile carrier.

[0033] However, it is also possible to provide the breathable film according to the invention in a multi-layer composite system in a single layer or multiple layers.

[0034] A multilayer composite system of this type can comprise a textile carrier made of a woven, knitted, or warp-knitted fabric, onto which the breathable film according to the invention and / or additional layers are laminated, for example, by flame or adhesive lamination. Additional layers can include reticulated foams, spacer fabrics, spacer fleeces, glass fibers, or carbon fibers. The textile carriers can be based on polymers such as polyurethane, polyester, nitrides, polyamide, cellulose, viscose, wool, or silicones.

[0035] For the production of abrasion-resistant surface layers, various systems based on PVC, fluorinated components, acrylates, polyurethanes including UV-curable varnishes and digital printing layers can be used, which can be applied to the breathable film according to the invention.

[0036] Through various surface coating layers, including UV-curable layers, the environmental resistance to light, abrasion, heat, etc. as well as the feel and appearance can be adjusted and other properties such as skin care and UV protection, insecticides and insect repellents can be incorporated or imparted.

[0037] By applying suitable processes, such as steel and ceramic embossing, vacuum embossing, silicone cloth roller embossing and the like, the breathable film according to the invention or a multilayer composite formed using this breathable film can be superficially structured in the region of its visible side, for example in order to introduce a leather grain structure.

[0038] The breathable film according to the invention explained above is therefore particularly suitable for the formation of artificial leather, but also opens up possible applications in the object sector, for example to form wall and ceiling coverings and the like (Living Solutions), which not only have excellent breathability with regard to air and simultaneous water vapor permeability, but are also highly abrasion-resistant and particularly flame-retardant.

[0039] In one exemplary embodiment, a breathable film was obtained which had a breathability to air of at least 10 l / min / dm 2< and a water vapor permeability of 5 mg / h / cm 2< at a Martindale abrasion (Cotton Duck) 10 of 400k revolutions and a flexibility of 200 kT at RT and easily met the flammability criteria M1-3, Grib 5, edge and surface flame exposure.

[0040] In particular, it has been shown within the scope of the invention that when a cover material is made of the breathable film according to the invention, an outstanding insensitivity and resistance to ignition by cigarettes is achieved, which is particularly predestined for use in public transport, waiting areas and the like.

Claims

1. Process for producing a breathable film based on polyvinyl chloride (PVC) comprising the steps of: - providing a pasty mass at least comprising a first fraction of PVC and a second fraction, which are mixed with one another to afford the pasty mass; - applying the pasty mass to a support; - drying and gelling the pasty mass applied to the support, with supply of heat to the film, forming pores of an average pore diameter of 1 µm to 1 mm from one surface of the film to the other, which give the film breathability with a gas permeability of 0.1 to 200 l dm-2 min-1 and a water vapour permeability of 0.1 to 200 mg cm-2 h-1; characterized in that the first fraction is formed of a paste PVC and low-flammability additives and / or plasticizers and the second fraction comprises an aqueous PVC dispersion.

2. Process according to Claim 1, characterized in that the first fraction comprises emulsion PVC or microsuspension PVC having a K value of 63 to 90 or blends thereof based on PVC homopolymers, PVC copolymers, PVC vinyl acetates and / or PVC acrylates.

3. Process according to any of Claims 1 or 2, characterized in that the first fraction comprises, as low-flammability plasticizers, phosphorus-, nitrogen-, halogen- and / or sulfate-containing plasticizers with or without addition of polymer, phthalate, adipate or trimellitate plasticizers or plasticizers based on soyabean oil, sebacates, castor oil or glycols in a total amount of 40 to 160 phr (parts per hundred), based on 100 parts of paste PVC of the first fraction.

4. Process according to any of Claims 1 to 3, characterized in that the first fraction comprises, as low-flammability additives, phosphorus- and / or nitrogen-containing solids and fillers based on aluminium and magnesium compounds, ammonium salts, polymeric phosphates, borates, zinc salts, molybdenum and antimony compounds and / or tin compounds, zeolites, clays, electrically conductive compounds and / or intumescent flame retardants individually or in combination thereof, having a solids content of 0 to 70 phr, based on 100 parts of paste PVC of the first fraction.

5. Process according to any of Claims 1 to 4, characterized in that the first fraction comprises, as low-flammability additives, stabilizers based on uracil, perchlorate, barium, calcium, zinc, tin, epoxide and / or beta-diketone in solid or liquid form and / or blocked phenol compounds or blends thereof in a total amount of 0.5 to 20 phr, based on 100 parts of paste PVC of the first fraction.

6. Process according to any of Claims 1 to 5, characterized in that the pasty mass comprises 5% to 50% by weight of the first fraction and 95% to 50% by weight of the second fraction, where the sum of the first and second fractions is 100% by weight.

7. Process according to any of Claims 1 to 6, characterized in that the second fraction has a K value of 58 to 80 and / or a solids content of the PVC particles used in the dispersion of 5% to 65%.

8. Process according to any of Claims 1 to 7, characterized in that the pasty mass comprises a third fraction based on polyether, polyester or polycarbonate polyurethanes or blends thereof in an amount of up to 50% by weight based on the total amount of the first and second fractions.

9. Process according to Claim 8, characterized in that the third fraction comprises a polyurethane dispersion having a solids content of 5% to 65%, preferably 30% to 60%.

10. Process according to any of Claims 8 to 9, characterized in that the third fraction comprises crosslinkers selected from isocyanates, carbodiimides, melamines, epoxides and / or azeridines in an amount of up to 20 phr, based on 100 parts of the third fraction.

11. Process according to any of Claims 1 to 10, characterized in that the pasty mass comprises a fourth fraction based on colouring substances in an amount of up to 30% by weight, based on the total amount of the first and second fractions and also, where present, the third fraction.

12. Process according to any of Claims 1 to 11, characterized in that the drying and gelling of the pasty mass to afford the pore-containing film takes place with supply of heat at temperatures between 70°C and 250°C.

13. Process according to any of Claims 1 to 12, characterized in that the support is removed from the film after the formation of the film or is formed from a substrate which remains on the film after formation of the film.