Polyurethane film comprising graphene and method for preparing same
阅读说明：本技术 包含石墨烯的聚氨酯膜及其制备方法 (Polyurethane film comprising graphene and method for preparing same ) 是由 劳拉·焦尔吉亚·里齐 阿尔多·恰莱利奥 朱利奥·朱塞佩·塞萨雷奥 安布罗焦·唐吉 于 2018-05-03 设计创作，主要内容包括：一种包含聚氨酯树脂和石墨烯的聚氨酯膜及其制备方法,其中所述石墨烯基于膜的总重量以1重量％至30重量％的量存在并且由石墨烯纳米片状体组成,其中至少90％具有50nm至50000nm的横向尺寸(x,y)和0.34nm至50nm的厚度(z),其中所述横向尺寸始终大于所述厚度(x、y>z),其中C/O比率≥100:1。(polyurethane film comprising a polyurethane resin and graphene and a process for its preparation, wherein the graphene is present in an amount of 1 to 30 wt% based on the total weight of the film and consists of graphene nanoplatelets, wherein at least 90% has a lateral dimension (x, y) of 50 to 50000nm and a thickness (z) of 0.34 to 50nm, wherein the lateral dimension is always greater than the thickness (x, y > z), wherein the C/O ratio ≧ 100: 1.)
1, polyurethane film comprising a polyurethane resin and graphene, characterized in that the graphene is present in an amount of 1 to 30 wt. -%, based on the total weight of the film, and that the graphene consists of graphene nanoplatelets, wherein at least 90% have a lateral dimension (x, y) of 50 to 50000nm and a thickness (z) of 0.34 to 50nm, wherein the lateral dimension is always greater than the thickness (x, y > z), and wherein the C/O ratio ≧ 100: 1.
2. The polyurethane film of claim 1, comprising from 0.1 to 5 weight percent of an antiblock additive based on the total weight of the film.
3. Polyurethane film according to claim 1 or 2, characterised in that it comprises at least two bonded layers, of which are graphene-free films.
4. The polyurethane film of claim 1, wherein the graphene nanoplatelets have a ratio C/O ≧ 200: 1.
5. Polyurethane film according to claim 1, characterized in that at least 90% of the graphene nanoplatelets have a lateral dimension (x, y) of 100 to 25000nm, preferably 500 to 15000nm, and a thickness (z) of 0.34 to 20nm, preferably 0.34 to 8 nm.
6. Polyurethane film according to claim 1, characterised in that the graphene is present in an amount of 2 to 25 wt. -%, based on the total weight of the film, preferably in an amount of 3 to 15 wt. -%, based on the total weight of the film.
7. The polyurethane film of claim 1, comprising from 0.1 to 5 weight percent of an antiblock additive based on the total weight of the film.
8. The polyurethane film of claim 7, wherein the antiblock additive is selected from the group consisting of silica, silicone, and kaolin.
9, A method for preparing a polyurethane film comprising graphene, comprising the steps of:
(A) preparing a composition comprising:
a1) a polyurethane resin or a precursor thereof,
a2)0.1 to 5% by weight of an antiblocking additive,
a3)1 to 30% by weight of graphene consisting of graphene nanoplatelets, wherein at least 90% have a lateral dimension (x, y) of 50 to 50000nm and a thickness (z) of 0.34 to 50nm, wherein the lateral dimension (x, y) is always greater than the thickness (x, y > z), and wherein the C/O ratio ≧ 100: 1;
(B) adjusting the viscosity of the composition of step (a) by adding a solvent until the viscosity reaches the range of 4000cP to 15000 cP;
(C) applying the composition having the viscosity of step (B) to a flat support until a layer having a thickness of 10 to 100 μ ι η is formed;
(D) heating the layer at an elevated temperature of 30 ℃ to 180 ℃ to form a polyurethane film;
(E) separating the membrane from the support.
10. Method according to claim 9, characterized in that it comprises a step (D) subsequent to said step (D)1) And step (D)2) In step (D)1) Combining the polyurethane film prepared according to steps (a) to (D) with a further graphene-free film via calendering; in step (D)2) Heating the two bonded films at an elevated temperature of from 30 ℃ to 180 ℃ to form a multilayer film, the method comprising the step (E) of separating the films from the support.
11. The method according to claim 9, characterized in that the antiblock additive is chosen from silica, silicones and kaolin.
12. The method according to claim 10, characterized in that the non-graphene containing membrane is selected from Polytetrafluoroethylene (PTFE), Thermoplastic Polyurethane (TPU), polyolefins, polyamides, polyesters.
13. The method according to claim 9, characterized in that the flat support used in step (C) consists of a non-stick paper, optionally provided with a surface finish on the side on which the composition is applied.
14, shaped articles comprising the polyurethane film of or more of claims 1-8.
Technical Field
The present invention relates to a polyurethane film comprising graphene and a method for preparing the same.
Background
Films (films) or polymer films (membranes) comprising graphene are known in the production of articles, which are also combined with additional films or textile substrates if desired, the properties and performance of the articles can be improved by the presence of suitable amounts of graphene. Indeed, graphene can improve, for example, the thermal and electrical conductivity of the film, and thus make the use of the film advantageous for the production of articles in various product industries, such as the apparel, furniture industry, and industrial industry.
From the patent literature, polymer compositions comprising graphene for the production of films and articles comprising said films are known.
CN 105504773(a) describes conductive polyurethane films comprising 1 to 10 parts by weight of graphene, obtained by a process requiring pre-mixing of graphene with parts of polyurethane and subsequent mixing with the remaining polyurethane, the mixing being carried out at high rotational speeds (800r.p.m to 8000 r.p.m.) in a machine suitable for generating high shear stresses, the conductivity of the obtained films being 103Omega to 105Ω。
WO 2017/037642 a1 describes methods of producing multilayer polyurethane films comprising graphene, more specifically the films are formed from a polyurethane layer that is free of graphene (referred to as "neutral") and a polyurethane layer comprising graphene, thus becoming conductive, in preferred embodiments the conductive layer is provided with terminals for electrical connection with a cell adapted to apply a low voltage to the conductive layer and thus heat the film.
WO 2014/198752 a1 describes heatable mouldings made from electrically conductive thermoplastic polyurethane which contain conductivity-imparting additives selected from the group consisting of nanotubes, graphene and conductive-grade carbon black. Carbon nanotubes are preferred. With respect to graphene, C/O ratios that are reported to be highly variable are suitable, e.g., 3:1 to 500:1, and no limitation on lateral dimensions is mentioned.
Thus, there is a need for such graphene-containing polyurethane films: which has better properties than the known films and can therefore advantageously be used to produce articles having better properties than the known articles.
There remains a need to provide such improved graphene-containing polyurethane films by a simple and efficient production process.
Disclosure of Invention
Therefore, objects of the present invention are to provide a graphene-containing polyurethane film having improved properties with respect to known graphene-containing films and which can therefore be advantageously used for producing articles having better properties than known articles, such as articles in the textile and clothing industries.
It is another objects of the present invention to provide a simple and efficient method of preparing a polyurethane film comprising graphene.
Thus, aspects of the invention relate to a polyurethane film comprising a polyurethane resin and graphene, characterized in that the graphene is present in an amount of 1 to 30 wt% based on the total weight of the film, and that the graphene consists of graphene nanoplatelets, wherein at least 90% has a lateral dimension (x, y) of 50 to 50000nm and a thickness (z) of 0.34 to 50nm, wherein the lateral dimension is always greater than the thickness (x, y > z), and wherein the ratio C/O ≧ 100: 1.
According to preferred aspects, the polyurethane film further comprises 0.1 to 5 weight percent of an antiblock additive, based on the total weight of the film.
In embodiments, the polyurethane film is a multilayer film including at least two bonded layers, of which at least consists of the graphene-containing polyurethane film as defined above.
Another aspect of the invention relates to a method for preparing a polyurethane film comprising graphene, the method comprising the steps of:
(A) preparing a composition comprising:
a1) a polyurethane resin or a precursor thereof,
a2)0.1 to 5% by weight of an antiblocking additive,
a3)1 to 30% by weight of graphene consisting of graphene nanoplatelets, wherein at least 90% have a lateral dimension (x, y) of 50 to 50000nm and a thickness (z) of 0.34 to 50nm, wherein the lateral dimension is always greater than the thickness (x, y > z), and wherein the C/O ratio is ≥ 100: 1;
(B) adjusting the viscosity of the composition of step (a) by adding a solvent until a viscosity in the range of 4000cP to 15000cP is obtained;
(C) applying the composition having the viscosity of step (B) on a flat support until a layer having a thickness of 10 μm to 100 μm is formed.
(D) Heating the layer to an elevated temperature of 30 ℃ to 180 ℃ to form a polyurethane film;
(E) separating the polyurethane film from the support.
In embodiments, the process according to the invention comprises combining the polyurethane film prepared according to steps (a) to (D) with at least additional resin layers or resin films (D)1) And heating (D)2) Obtaining a multilayer film; and a subsequent step (E) of separating the multilayer film from the support.
Detailed Description
The polyurethane film according to the present invention includes a polyurethane resin and graphene in an amount of 1 to 30% by weight based on the total weight of the film.
Preferably, the graphene is present in an amount of 2 to 25 wt%, more preferably 3 to 15%, based on the total weight of the film.
Graphene consists of graphene nanoplatelets, wherein at least 90% have a lateral dimension (x, y) of 50nm to 50000nm and a thickness (z) of 0.34nm to 50nm, wherein the lateral dimension is always greater than the thickness (x, y > z), and wherein the C/O ratio is ≥ 100: 1;
in the polyurethane film according to the present invention, at least 90% of the graphene nanoplatelets preferably have a lateral dimension (x, y) of 100nm to 25000nm, more preferably 500nm to 15000nm, even more preferably 800nm to 10000 nm.
In the polyurethane film according to the present invention, at least 90% of the graphene nanoplatelets preferably have a thickness (z) of 0.34 to 20nm, more preferably 0.34 to 8 nm.
The graphene is formed by sp2A material consisting of a monoatomic layer of formal hybridized carbon atoms. Thus, the carbon atoms are arranged in a hexagonal close packing heightA crystalline regular honeycomb structure.
From the scientific and patent literature, various methods are known for the preparation of graphene, such as chemical vapour deposition, epitaxial growth, chemical exfoliation and chemical reduction of oxidized forms of Graphene Oxide (GO).
The most common chemical method for preparing graphene involves the formation of graphene oxide under highly oxidative conditions, which even after reduction, lacks the electronic properties of the original graphene.
According to aspects of the invention, the graphene nanoplatelets defined above are nanoplatelets of pristine graphene, i.e. graphene obtained not by reduction of graphene oxide but by intercalation (intercalation) and expansion/exfoliation of graphite and subsequent size reduction.
The applicant's direc Plus s.p.a. is the holder of european patent EP 2038209B 1, which describes among others methods for producing structures comprising layers of graphene obtained by intercalation and subsequent expansion/exfoliation of graphite.
The applicant's Directa Plus S.p.A is also the holder of International patent applications WO 2015/193267A 1 and WO 2015/193268A 1, which describe processes for the production of aqueous dispersions of highly pure graphene, from which graphene nanoplatelets having C/O ratios of ≥ 100:1 and ≥ 200:1 can be obtained. This ratio is important because it defines the maximum amount of oxygen bound to the carbon constituting the graphene. In fact, the best characteristics of graphene are obtained when the amount of oxygen is minimal, which results from its highly crystalline nature.
Highly pure graphene (i.e., ratio C/O ≧ 100) in which there are no or minimal lattice defects (which can be verified by Raman spectroscopy), minimal or no foreign substances (including surfactants or graphene functionalizing or coupling agents) constitutes an essential component for improving the properties of the polyurethane film according to the present invention.
The C/O ratio in the graphene used in the polyurethane film according to the present invention is determined by elemental analysis by means of an element analyzer (CHNS O) that provides the weight percentages of the respective elements by normalizing the values obtained with respect to the atomic weights of the substances C and O and finding the ratio, the C/O ratio is obtained.
It has been found that graphene in an oxidized form, such as that obtained by reduction of Graphene Oxide (GO), has characteristics and characteristics that are different from pure graphene (pristine graphene). For example, the electrical conductivity, thermal conductivity, and mechanical strength of pristine graphene are all superior to those of GO and the reduction products obtained from GO, also because there are a large number of lattice defects and crystal structure defects caused by the reduction reaction.
Analysis at 1350cm was performed by Raman spectroscopy-1The strength and shape of the D band at (a) was used to evaluate the nanoplatelets for lattice defects.
According to an embodiment described in the above-mentioned patent document by the applicant's Directa Plus s.p.a., the process for producing pristine graphene is carried out in a continuous mode, graphite flakes are continuously fed to an expansion step at high temperature, the expanded graphite thus obtained is discharged into an aqueous medium in a continuous manner and the expanded graphite dispersed in the aqueous medium is continuously subjected to exfoliation treatment and size reduction by ultrasound and/or homogenization at high pressure.
The method for producing pristine graphene includes a plurality of steps.
The th step of the process consists in preparing expanded and/or exfoliated graphite from the intercalated graphite.
The expansion step of the intercalated Graphite is carried out by subjecting a Graphite Intercalation Compound (GIC) having a transverse dimension of 500 μm or less to a temperature of between 1300 ℃ and 12000 ℃ for less than 2 seconds, the treatment being carried out as described in patent EP 2038209B 1, i.e. by generating heat in the GIC, preferably by means of an electric arc, microwave oven or high-frequency induction oven or plasma-forming oven, the latter treatment is particularly preferred, since the desired temperatures associated with high turbulence can be reached.
The second step of the process comprises collecting and dispersing the expanded graphite obtained in step in an aqueous medium immediately after the expanded graphite is formed.
Preferably, the expanded graphite is dropped by gravity into a container containing an aqueous medium in the absence of a surfactant or in the presence of a surfactant in an amount of less than 1% by weight relative to the weight of the graphite.
The introduction of the expanded graphite as it is formed into an aqueous medium allows to obtain an optimal dispersion thereof without the need to use surfactants.
Obtaining an optimal aqueous dispersion of expanded graphite without the aid of surfactants has important advantages, both in terms of lower costs due to surfactant savings and in terms of improved properties of the final product, as will be described further in the specification, however, small amounts of surfactants of less than 1 wt% can be used without unduly compromising the quality of the final product.
If the dispersion of the expanded graphite is carried out in the presence of a surfactant, the surfactant is preferably an anionic surfactant, more preferably an anionic surfactant: wherein the anion constituting the hydrophilic polar group is selected from sulfonates, sulfates and carboxylates, and the hydrophobic non-polar moiety is selected from structures comprising aromatic rings (e.g. benzene, naphthalene, pyrene) or cyclic aliphatic structures (e.g. derivatives of cholic acid). The preferred surfactant is sodium benzenesulfonate.
The dispersion was obtained by gentle stirring.
The expanded graphite is dispersed in water at a concentration of 0.5 to 5 wt%, preferably 1 to 4 wt%, more preferably 2 to 3 wt%.
The aim of the third step of the process is to obtain exfoliation of the expanded graphite and its size reduction until obtaining nanoplatelets of pristine graphene, at least 90% of which have a lateral dimension (x, y) of 50nm to 50000nm and a thickness (z) of 0.34nm to 50nm, the lateral dimension being greater than the thickness (x, y > z).
Such exfoliation and size reduction is obtained by subjecting a dispersion of graphite in water (with no surfactant or less than 1% by weight of surfactant) to sonication or to homogenization under high pressure which causes collisions between the expanded graphite particles.
The ultrasonication treatment is carried out at an energy level of from 10 to 200Wh per gram of the expanded graphite obtained in the preceding step.
Preferably, the ultrasonication of the aqueous dispersion of expanded graphite is carried out at an energy level of from 10Wh/g to 100 Wh/g. The ultrasonic treatment is carried out using equipment such as a commercial ultrasonic instrument for treating liquids, in which acoustic energy is transmitted to the system by cavitation (formation and implosion of bubbles) using an ultrasonic generator immersed in the liquid at a wave frequency of about 24kHz and with a power as defined above.
The combination of the expansion treatment at high temperature of the intercalated graphite and the subsequent ultrasound treatment in an aqueous medium achieves both exfoliation of the graphite and its size reduction, obtaining graphene nanoplatelets directly dispersed in water in a relatively short time.
The high pressure homogenization process is carried out with a homogenizer in which a dispersion of expanded graphite is pumped at a pressure above 35MPa through or more microchannels or constrictions where the particles in the dispersion experience extremely high shear stresses resulting from the sudden drop in pressure and undergo collisions between them and with the surfaces of the microchannels or constrictions.
The term "constriction" means that the cross-section of the pipe through which the dispersion is forced to flow is significantly reduced at point , while the term "microchannel" means a constriction extending in the direction of flow of the particle dispersion.
The treatment allows obtaining a significant reduction in the dimensions of the expanded graphite until values according to the aforementioned x, y and z axes are reached. The constriction may be of a static type, for example a flow channel with a maximum dimension of 500 μm, or of a dynamic type, for example a valve with an adjustable cross-section so as to define a constriction with a maximum dimension of 500 μm.
High pressure homogenization equipment using a static type neck was manufactured by Microfluidics International corporation (Newton, Mass.) under the trade name MicrofluidicsAnd (5) selling. In the apparatus, a swelling stone is put inThe dispersion of ink is pumped at a pressure above 35MPa through a plurality of flow channels having a maximum dimension of 500 μm, wherein the particles of expanded graphite are collided. Preferably, the maximum pressure is 500 MPa. The structure and operation of the device is also described in patent US 8,367,004B 2.
A high pressure homogenizing apparatus using a dynamic type neck was sold by GEA NIRO-Soavi (Palma, Italy). The structure and operation of the device is also described in patent US 4,773,833.
The aqueous dispersion of expanded graphite may be treated several times in a homogenizer depending on the entity of which size reduction is desired. This may be done in a continuous manner through the homogenizer a plurality of times.
Preferably, the high pressure homogenization process is one in which a dispersion of expanded graphite is pumped through or more microchannels or necked homogenizers at pressures above 100 MPa.
As previously mentioned, the final dispersion of graphene nanoplatelets obtained after exfoliation treatment and size reduction with or more of the methods defined above may be concentrated or dried, depending on the desired final form of graphene.
Concentration of the dispersion can be carried out using techniques known to those skilled in the art (e.g., removal of water by evaporation, filtration, or centrifugation). The absence or presence of a minimum amount (less than 1%) of surfactant means that in addition to ensuring the feasibility of liquid-solid separation, the problem of possible polymerization of the surfactant can be avoided and higher operating temperatures can be used.
The concentration of the dispersion can be increased up to 30% by weight by the techniques indicated above. The obtained product in a concentration range of 6 to 30 wt.% has a high viscosity and consistency of a paste and can be advantageously used as a master batch (masterbatch) for water-based formulations.
The advantage of using a dispersion concentrated to a concentration in the range of 6 to 30 wt% is: 1) formulation freedom, i.e. the product can be diluted to the desired concentration and the optimum surfactant can be selected for the specific application; 2) high dispersibility due to the presence of residual water interposed between the graphene nanoplatelets weakening van der waals type bonds established between the graphene nanoplatelets; 3) the product may be used directly by application to a desired substrate; 4) the graphene nanoplatelets are confined in a matrix and are therefore easy to handle and transport.
A particularly advantageous method of concentrating the dispersion is filtration, where the water is removed until a dispersion having a concentration in the desired range is obtained on a filter
In the case of liquids which are undesirable or cannot be handled at the process level, or in the case of water which cannot be used at the chemical compatibility level, the aim of drying the dispersion is to obtain such a dry powder: it can be easily re-dispersed in different matrices (both solvent and polymer).
Furthermore, low oxygen content and absence of lattice defects ensure high chemico-physical properties at , and no re-agglomeration of nanoplatelets in a stable manner due to covalent type chemical interactions at another .
In practice, the absence of a surfactant has been shown to allow the conductivity of the graphene obtained to be significantly better than that of graphene obtained by methods using surfactants.
The pristine graphene nanoplatelets have a high electrical conductivity, at least 90% of the pristine graphene nanoplatelets having a lateral dimension (x, y) of 50nm to 50000nm and a thickness (z) of 0.34nm to 50nm, the lateral dimension being greater than the thickness (x, y > z), the C: O ratio being ≧ 100: 1. The conductivity was determined on a film obtained by depositing an aqueous dispersion of the nanoplatelets on a glass substrate to form a 1cm x 1cm film and drying to 100 ℃ with a hot plate for 15 minutes and was measured in van der Waals configuration. The conductivity of the membrane is more than or equal to 1500S/m, preferably more than or equal to 2000S/m.
It was also demonstrated that when a dispersion of graphene nanoplatelets is formed in the presence of a surfactant, the surfactant deposits on the surface of the sheet and tends to promote agglomeration of the graphene nanoplatelets.
In the present description, graphene nanoplatelets are dimensionally referenced to a system of cartesian axes x, y, z, it being understood that the particles are substantially flat sheets, but may also have irregular shapes. In any case, the lateral dimensions and thicknesses provided in relation to the directions x, y and z are to be understood as the largest dimensions in the above-mentioned directions.
The lateral dimensions (x, y) of the graphene nanoplatelets are determined as follows: in the case of the production method described above, the measurement was directly performed under a Scanning Electron Microscope (SEM) after diluting the final dispersion in deionized water at a ratio of 1:1000 and dropping it on a silicon oxide substrate arranged on a plate heated to 100 ℃.
Alternatively, SEM analysis was performed directly on the powder deposited on the carbon ribbon with the nanosheets in a dry state. In both cases, at least 100 nanoplatelets are measured.
The thickness (z) of graphene nanoplatelets is determined with an Atomic Force Microscope (AFM), which is essentially a profilometer with sub-nanometer resolution, is widely used to characterize (primarily topographical) surfaces and nanomaterials analysis of this type is commonly used to evaluate the thickness of graphene platelets produced in any way, and thus to determine the number of layers making up the platelets (monolayer ═ 0.34 nm).
The final dispersion of nanoplatelets was diluted in isopropanol at a ratio of 1:1000, then 20ml was collected and sonicated in an ultrasonic bath (Elmasonic S40) for 5 minutes. Nanoplatelets are then deposited as described for SEM analysis and scanned directly with an AFM tip, where measurements provide a topographical image of the graphene sheets and their profile relative to the substrate, allowing for accurate thickness measurements. Measurements were performed on at least 50 nanoplatelets.
Alternatively, in the case where the nanosheet-like body is in a dry state, the powder is dispersed in isopropanol at a concentration of 2 mg/L. 20ml were collected and sonicated in an ultrasonic bath (Elmasonic S40) for 30 minutes. Nanoplatelets were then deposited as described for SEM analysis and scanned by AFM.
In the concentrated final dispersion or in the dried form obtained after drying, at least 90% of the lateral dimensions (x, y) in the graphene nanoplatelets are preferably from 100nm to 25000nm, more preferably from 500nm to 15000nm, and the thickness (z) is preferably from 0.34nm to 20nm, more preferably from 0.34nm to 8 nm.
Graphene having the characteristics defined above is produced by the applicant's Directa Plus SpA and sold under the trade name G +.
Graphene nanoplatelets having the above-mentioned size and purity characteristics, thus having a very low oxygen level (as defined by the above-mentioned C: O ratio) and not functionalized with other molecules, have proved to be particularly suitable for use as components of polyurethane films, where the desired properties can be obtained, for example: i) high air permeability; ii) high impermeability; iii) high abrasion resistance; iv) increased thermal conductivity, useful for heat dissipation; v) increased electrical conductivity, useful for dissipating electrostatic energy, useful for electrical heating and useful for data transmission; vi) antibacterial activity, useful for applications in the clothing and medical industries; vii) infrared absorption, which can be used to increase the insulating power of the membrane.
Regarding the composition and the production method of the polyurethane film according to the present invention, in step (a), component a1) is composed of a polyurethane resin or a precursor thereof. By this definition we mean a polyurethane resin: it may be of the one-component type or have multiple components that must be mixed to form the polyurethane resin. When component a1) is of a multiple component type, it may comprise a catalyst and/or the prepolymer itself or a functionalized prepolymer, as is known in the art. The polyurethane may be aliphatic or aromatic.
According to preferred aspects, the polyurethane film further comprises as component a2) from 0.1 to 5 weight percent, preferably from 0.2 to 1.5 weight percent, more preferably from 0.3 to 3 weight percent of an antiblock additive, based on the total weight of the film.
In addition to the components a1), a2), a3) and the solvent of step B, the composition for producing the polyurethane film according to the invention may also comprise further components, for example additives, processing agents, antioxidants, plasticizers, flow additives, as is known to the experienced person in the field of polyurethane films.
In embodiments, the polyurethane film is a multilayer film comprising at least two bonded layers of polyurethane resin, at least of which consist of films comprising graphene as defined above Another films may also be polyurethane films with or without graphene, or may be films without graphene consisting of a polymer or mixture of polymers other than polyurethane.
In the embodiment in which the film is of the multilayer type, the preparation method comprises combining the film produced by the above-described method with another film produced or obtained separately.
The invention will now also be described with reference to fig. 1, fig. 1 schematically showing a method according to the invention.
The method for preparing a polyurethane film according to the present invention comprises the steps of:
(A) preparing a composition comprising:
a1) a polyurethane resin or a precursor thereof,
a2)0.1 to 5% by weight of an antiblocking additive,
a3)1 to 30% by weight of graphene consisting of graphene nanoplatelets, wherein at least 90% have a lateral dimension (x, y) of 50 to 50000nm and a thickness (z) of 0.34 to 50nm, wherein the lateral dimension is always greater than the thickness (x, y > z), and wherein the C/O ratio is ≥ 100: 1;
(B) adjusting the viscosity of the composition of step (a) by adding a solvent until a viscosity in the range of 4000cP to 15000cP is obtained;
(C) applying the composition having the viscosity of step (B) on a flat support until a layer having a thickness of 10 μm to 100 μm is formed.
(D) Heating the layer to an elevated temperature of 30 ℃ to 180 ℃ to form a polyurethane film;
(E) separating the polyurethane film from the support.
In step (a), the components a1), a2) and a3) were put into a container provided with a stirring system and mixed. Preferably, a mechanical stirrer is used at a rotational speed of 100r.p.m to 2000r.p.m, more preferably 150r.p.m to 100r.p.m.
Preferably, the composition of step (a) further comprises a flow additive (component a 4).
Antiblocking additive a2) is as defined above.
In step (B), the viscosity of the mixture of a1), a2) and a3) is adjusted in the range of 4000 to 15000cP, preferably 6000 to 12000cP, by adding an organic solvent. An example of such a solvent is Dow Chemical under the trade name Dow Chemical
Steps (C) to (E) are described with reference to fig. 1.
In fig. 1, numeral 10 indicates a paper roll suitable for constituting a support belt on which the compositions prepared in steps (a) and (B) are applied, which is known in the art as release paper or cast & release paper. The paper has non-stick properties, on which a polyurethane film is formed and then the polyurethane film can be peeled and separated therefrom due to the non-stick properties of the paper and a specific surface finish.
In step (C), the release roll 10 is unwound at a suitable speed (e.g. 3 to 30 m/min) in the direction of arrow a and a controlled amount of the composition prepared in steps (a) and (B) is deposited on the paper in a continuous mode. The thickness of the layer thus formed is defined by adjusting the distance between the paper strip and the blade 14 positioned above its top. Typical thicknesses are for example 10 μm to 100 μm.
In step (D), the paper tape on which the polyurethane composition layer having the desired thickness has been deposited is introduced into an oven 16 and heated to an elevated temperature of 30 ℃ to 180 ℃, thereby forming a polyurethane film.
In a subsequent step (E), the film is separated from the release paper tape and wound on a roll in a manner not shown in fig. 1 but known to the person skilled in the art.
In the preparation of the multilayer film, the process comprises, after the heating step (D), bonding the polyurethane film prepared according to steps (a) to (D) with at least additional resin layers or resin films 18, thereby providing an intermediate bonding step (D)1) And a heating step (D)2) Obtaining a multilayer film; and a subsequent step (E) of separating the multilayer film from the support. The film 18 is composed of a second polyurethane film without graphene or a film composed of a different resin without graphene. Suitable resins include, for example, Polytetrafluoroethylene (PTFE), Thermoplastic Polyurethane (TPU), polyolefins (polypropylene, polyethylene), polyamides, and polyesters.
The thickness of the film 18 combined with the polyurethane film containing graphene is generally 10 μm to 100 μm.
According to step (D)1) The film 18 wound on the roll is unwound and laid on the polyurethane film exiting from the oven 16 and combined with the polyurethane film via a passing calender 20.
According to step (D)2) The combination of release paper, polyurethane film containing graphene, and second film is sent to a
At the outlet of the
The single-or multilayer polyurethane films comprising graphene according to the invention exhibit superior properties to known films and can therefore be advantageously used for the production of articles of various technical fields, such as the clothing industry (in particular garments and sports equipment, footwear, work clothes and wearable electronics), the furniture industry and the industrial industry.
In embodiments, the film according to the invention was a three-layer film, in which the layer consisted of a polyurethane film comprising graphene, another layer consisted of a film without graphene, and the third layer consisted of a heat-adhesive material also without graphene.
In another embodiments, the film according to the invention is a two-layer film, wherein layers consist of the graphene-containing polyurethane film and another layers consist of the graphene-free film, and the release paper used to prepare the graphene-containing polyurethane film has a specific surface finish that can transfer a specific aesthetic appearance (e.g., opaque black, defined as the carbon appearance) to the graphene-containing film.
The following examples illustrate embodiments of the present invention and are provided by way of non-limiting examples.
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