HK1149037B - Method for producing microporous sheet - Google Patents

Description

Method for producing microporous sheet material

Technical Field

The present invention relates to a method of producing a microporous sheet material.

Background

Synthetic paper has been developed in recent years for use in the printing and labeling industry. Synthetic paper offers significant advantages over natural wood pulp paper, including, for example, improved print quality, water resistance, tear resistance, and tensile strength. These materials are typically composed of polymeric materials such as polyolefins or polyesters.

In the manufacture of certain microporous polyolefin sheets, polyolefin polymers are typically blended with finely divided water-insoluble fillers and organic plasticizers. The blend of materials is extruded through a sheeting die to form a continuous sheet composed of a polyolefin polymer matrix having finely divided water-insoluble filler distributed throughout the matrix. A network of interconnected pores is communicated throughout the microporous sheet material. Extracting an organic plasticizer from the sheet that facilitates the extrusion process by contacting the sheet with an extraction fluid (extraction fluid) composition. Conventional extraction fluid compositions include, for example, halogenated hydrocarbons such as 1, 1, 2-trichloroethylene, perchloroethylene, 1, 2-dichloroethane, 1, 1, 1-trichloroethane, 1, 1, 2-trichloroethane and dichloromethane; or alkanes such as hexane, heptane, and toluene.

For many end-use applications, it is important to remove some or a substantial portion of the organic plasticizer from the microporous sheet material. For example, in the case of microporous sheets used as printable sheets, residual plasticizer can negatively impact print quality. In addition, where the microporous sheet material is used as a layer in a multi-layer laminate structure, such as an identity card, high residual plasticizer content can negatively impact the laminate peel strength. Of course, for some end-uses, higher residual plasticizer content may be advantageous.

Also, it is desirable that minimal residual extraction fluid composition be present in the microporous sheet. For example, in the case of the microporous sheet material ultimately used as a label or packaging material for food or pharmaceutical products, residual extraction fluid should be minimized or completely removed from the microporous sheet material. In some manufacturing processes, the use of conventional extraction fluid compositions such as paraffins as described above has been avoided because these materials are flammable, requiring special handling and equipment. In addition, some conventional halogenated hydrocarbons have been identified as highly interesting materials in human health and environmental regulations, such as the recent chemical registration, evaluation and approval ("REACH") system adopted in the european union. For example, the class 2 carcinogen, chlorotrifluoroethylene, may be listed as a "carcinogenic, mutagenic, or reproductive toxic" ("CMR") substance in the REACH system.

In view of the foregoing, it would be desirable to manufacture microporous sheets using an extraction fluid composition that is easily removable from the final microporous sheet, is non-flammable, and is not a material of interest in human health and environmental regulations.

Summary of The Invention

The present invention relates to a method of producing a microporous sheet material comprising: a polymer matrix comprising a polyolefin, finely divided substantially water-insoluble filler distributed throughout the matrix, and a network of interconnecting pores communicating throughout the microporous material. The method comprises the following steps: (a) forming a mixture comprising a polyolefin, an inorganic filler and a processing plasticizer component; (b) extruding the mixture to form a continuous sheet; and (c) contacting the continuous sheet with a non-combustible extraction fluid composition to extract the processing plasticizer component from the continuous sheet. The extraction fluid composition has a boiling point of 75 ℃ or less and is substantially free of trichloroethylene. The microporous sheet so formed has performance characteristics such as tensile strength equal to or greater than 800 kPa. Also provided is a microporous sheet material produced by the method.

Detailed Description

It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless expressly and unequivocally limited to one referent.

For the purposes of this specification, unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and other parameters used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

All numerical ranges herein include all numbers and all numerical ranges within the listed numerical ranges. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

The various embodiments and examples of the invention provided herein are each to be construed as non-limiting with respect to the scope of the invention.

As previously mentioned, the present invention is directed to a process for producing a microporous sheet material comprising a polymeric matrix comprising a polyolefin, finely divided, substantially water-insoluble inorganic filler distributed throughout the matrix, and a network of interconnecting pores communicating throughout the microporous material.

The method of the invention comprises the following steps:

(a) forming a mixture comprising a polyolefin, a filler and a processing plasticizer component;

(b) extruding the mixture to form a continuous sheet; and

(c) the continuous sheet is contacted with a non-flammable extraction fluid composition to extract the processing plasticizer component from the continuous sheet, thereby forming a microporous sheet.

The extraction fluid composition has a boiling point of 75 ℃ or less and is substantially free of trichloroethylene. The microporous sheet has a tensile strength equal to or greater than 800 kPa.

As used herein, "microporous material" or "microporous sheet material" refers to a material having a network of interconnected pores, wherein the pores have a volume average diameter of 0.001 to 0.5 micrometers, on a coating-free, printing ink-free, impregnant-free, and pre-bonding (pre-bonding) basis, and constitute at least 5 volume percent of the material, as described herein below.

Polyolefins

The microporous materials of the present invention comprise a matrix of polyolefin (e.g., polyethylene and/or polypropylene), such as a matrix of high density and/or ultra-high molecular weight polyolefin.

Non-limiting examples of ultra-high molecular weight (UHMW) polyolefins may include substantially linear UHMW polyethylene or polypropylene. Because UHMW polyolefins are not thermosetting polymers with infinite molecular weight, they are technically classified as thermoplastic materials.

The ultra-high molecular weight polypropylene may comprise a substantially linear ultra-high molecular weight isotactic polypropylene. Often the polymer has an isotacticity of at least 95%, for example at least 98%.

While there is no particular limit on the upper limit of the intrinsic viscosity of the UHMW polyethylene, in one non-limiting example, the intrinsic viscosity can be from 18 to 39 deciliters/gram, such as from 18 to 32 deciliters/gram. Although there is no particular limit on the upper limit of the intrinsic viscosity of the UHMW polypropylene, in one non-limiting example, the intrinsic viscosity can be from 6 to 18 deciliters/gram, such as from 7 to 16 deciliters/gram.

For the purposes of the present invention, the intrinsic viscosity is determined by extrapolating to zero concentration the reduced or inherent viscosity of several dilute solutions of UHMW polyolefin in which the solvent is freshly distilled decalin to which 0.2% by weight of pentaerythritol 3, 5-di-tert-butyl-4-hydroxyhydrocinnamate [ CAS registry number 6683-19-8] is added. The reduced or inherent viscosity of UHMW polyolefins is determined from the relative viscosity obtained at 135 deg.C with a viscometer No. Ubbelohde1 following the general procedure of ASTM D4020-81, except that several dilute solutions of different concentrations are used.

The nominal molecular weight of UHMW polyethylene is empirically related to the intrinsic viscosity of the polymer according to the following equation:

wherein M is a nominal molecular weight,the intrinsic viscosity of UHMW polyethylene is expressed in deciliters/gram. Similarly, the nominal molecular weight of UHMW polypropylene is empirically related to the intrinsic viscosity of the polymer according to the following equation:

wherein M is a nominal molecular weight,is the intrinsic viscosity of UHMW polypropylene expressed in deciliters/gram.

A mixture of substantially linear ultra high molecular weight polyethylene and low molecular weight polyethylene may be used. In one non-limiting embodiment, the UHMW polyethylene has an intrinsic viscosity of at least 10 deciliters/gram, the low molecular weight polyethylene has an ASTM D1238-86 condition E melt index of less than 50 grams/10 minutes, such as less than 25 grams/10 minutes, such as less than 15 grams/10 minutes, and an ASTM D1238-86 condition F melt index of at least 0.1 grams/10 minutes, such as at least 0.5 grams/10 minutes, such as at least 1.0 grams/10 minutes. The amount (in wt%) of UHMW polyethylene used in this embodiment is described in U.S. patent 5,196,262, column 1, line 52-column 2, line 18, the disclosure of which is incorporated herein by reference. More specifically, fig. 6, relative to u.s.5,196,262, depicts the weight percent of UHMW polyethylene used; that is, reference is made to the polygon ABCDEF, GHCI, or JHCK of FIG. 6, which is incorporated herein by reference.

The nominal molecular weight of the Low Molecular Weight Polyethylene (LMWPE) is lower than the nominal molecular weight of the UHMW polyethylene. LMWPE is a thermoplastic material and many different types are known. One method of classification is by density, expressed in grams/cubic centimeter and rounded to the nearest decimal place according to ASTM D1248-84 (revalidation 1989). Non-limiting examples of densities of LMWPE are shown in table 1 below.

Any or all of the polyethylenes listed in table 1 above may be used as LMWPE in the matrix of the microporous material. HDPE may be used because it will be more linear than MDPE or LDPE. Processes for making various LMWPEs are well known and well described in the literature. They include high pressure processes, Phillips Petroleum Company processes, Standard Oil Company processes, and Ziegler processes. LMWPE has an ASTM D1238-86 Condition E (i.e., 190 ℃ and 2.16 kilogram load) melt index of less than about 50 grams/10 minutes. The condition E melt index tends to be less than about 25 g/10 min. The condition E melt index can be less than about 15 g/10 min. LMWPE has an ASTM D1238-86 condition F (i.e., 190 ℃ and 21.6 kilogram load) melt index of at least 0.1 g/10 min. In many cases this condition F has a melt index of at least 0.5 g/10 min, for example at least 1.0 g/10 min.

The UHMWPE and the LMWPE may together constitute at least 65 wt%, such as at least 85 wt%, of the polyolefin polymer in the microporous material. Additionally, the UHMWPE and LMWPE together may constitute substantially 100 wt% of the polyolefin polymer in the microporous material.

In one embodiment of the present invention, the microporous material may comprise a polyolefin comprising ultra-high molecular weight polyethylene, ultra-high molecular weight polypropylene, high density polyethylene, high density polypropylene, or mixtures thereof.

Other thermoplastic organic polymers may also be present in the matrix of the microporous material, if desired, provided their presence does not significantly affect the properties of the microporous material substrate in an adverse manner. The amount of other thermoplastic polymers that may be present depends on the nature of these polymers. In general, larger amounts of other thermoplastic organic polymers can be used if the molecular structure contains little branching, few long side chains and few bulky side groups than when there is a large amount of branching, many long side chains or many bulky side groups. Non-limiting examples of thermoplastic organic polymers that may optionally be present in the matrix of the microporous material include low density polyethylene, high density polyethylene, polytetrafluoroethylene, polypropylene, copolymers of ethylene and propylene, copolymers of ethylene and acrylic acid, and copolymers of ethylene and methacrylic acid. If necessary, all or a part of the carboxyl groups of the carboxyl group-containing copolymer may be neutralized with sodium, zinc or the like. Typically, the microporous material comprises at least 70 wt% UHMW polyolefin, based on the weight of the substrate. In one non-limiting embodiment, the other thermoplastic organic polymers described above are substantially absent from the matrix of the microporous material.

Filler material

As previously mentioned, the microporous material also comprises finely divided, substantially water-insoluble particulate filler. The filler may comprise an organic particulate material and/or an inorganic particulate material. The filler is typically not coloured, for example, the filler is a white or opalescent filler such as a siliceous (siliceous) or clay particulate material.

The finely divided substantially water-insoluble filler particles may constitute from 20 to 90 wt% of the microporous sheet material. For example, the filler particles may constitute 20 to 90 wt% of the microporous material, such as 30 to 90 wt% of the microporous material, or 40 to 90 wt% of the microporous material, or 50 to 90 wt% of the microporous material, or even 60 to 90 wt% of the microporous material.

The finely divided substantially water-insoluble filler may be in the form of primary particles (ultimatepraraticles), aggregates of primary particles, or a combination of both. At least about 90 wt% of the filler used to produce the microporous material substrate has a total particle size (gross particle size) of 0.5 to about 200 microns, for example 1 to 100 microns, as determined by using a laser diffraction particle sizer LS230 from Beckman Coulter capable of measuring particle sizes down to 0.04 microns. Typically, at least 90 wt% of the filler has a total particle size of 10-30 microns. The size of the filler aggregates can be reduced during processing of the composition used to produce the microporous material. Thus, the overall particle size distribution in the microporous material may be less than the raw filler itself.

Non-limiting examples of suitable organic and inorganic particulate materials are described in U.S. Pat. No. 6,387,519B1, column 9, line 4-column 13, line 62, the cited portions of which are incorporated herein by reference.

In a particular embodiment of the invention, the filler comprises a siliceous material. Non-limiting examples of siliceous fillers that may be used to produce the microporous material include silica, mica, montmorillonite, kaolinite, nanoclay such as cloisite montmorillonite from Southern Clay Products, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, calcium silicate, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gel, and glass particles. In addition to the siliceous filler, optionally other finely divided, substantially water-insoluble particulate fillers may also be employed. Non-limiting examples of such optional fillers may include carbon black, charcoal, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, antimony oxide, zirconium oxide, magnesium oxide, aluminum oxide, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, and magnesium carbonate. In one non-limiting embodiment, silica and any of the foregoing clays can constitute the siliceous filler. Non-limiting examples of silica include precipitated silica, silica gel, and fumed silica.

Silica gels are generally commercially produced by acidifying an aqueous solution of a soluble metal silicate, such as sodium silicate, with an acid at low pH. The acid employed is typically a strong inorganic acid such as sulfuric acid or hydrochloric acid, although carbon dioxide may be used. Since there is substantially no density difference between the gel phase and the surrounding liquid phase when the viscosity is low, the gel phase does not settle out, that is, it does not precipitate. Thus, silica gel can be described as a non-precipitated, cohesive, rigid, three-dimensional network of adjacent particles of colloidal amorphous silica. The state of the subparts can range from large solid blocks to submicroscopic particles, and the degree of hydration can range from nearly anhydrous silica to soft gelatinous materials containing about 100 parts water per part silica by weight.

Precipitated silicas are generally prepared commercially as follows: an aqueous solution of a soluble metal silicate, typically an alkali metal silicate such as sodium silicate, is combined with an acid such that colloidal particles of silica will grow in a weakly alkaline solution and be coagulated by alkali metal ions of the resulting soluble alkali metal salt. A variety of acids may be used including, but not limited to, mineral acids. Non-limiting examples of acids that can be used include hydrochloric acid and sulfuric acid, but carbon dioxide can also be used to prepare precipitated silica. In the absence of a coagulant, the silica does not precipitate from solution at any pH. In one non-limiting embodiment, the coagulant used to effect precipitation of the silica may be a soluble alkali metal salt produced during formation of the colloidal silica particles, or it may be an added electrolyte, such as a soluble inorganic or organic salt, or it may be a combination of both.

Precipitated silica may be described as precipitated aggregates of elementary particles of colloidal amorphous silica, which do not exist as macroscopic gels at any time during the preparation. The size and hydration of the aggregates can vary widely. Precipitated silica powders differ from silica gels in that they have been comminuted and generally have a more open structure, i.e. a higher specific pore volume. However, the specific surface area of precipitated silica, as measured by the Brunauer, Emmet, teller (bet) method using nitrogen as the adsorbate, tends to be lower than that of silica gel.

Many different precipitated silicas may be used as siliceous fillers for producing the microporous sheet. Precipitated silicas are well known commercial materials and their preparation processes are described in detail in a number of U.S. patents, including U.S. patent nos. 2,940,830, 2,940,830, and 4,681,750. The precipitated silicas used generally have an average primary particle size (whether or not the primary particles are aggregated) of less than 0.1 micron, for example less than 0.05 micron or less than 0.03 micron, as determined by transmission electron microscopy. Precipitated silicas are available in many grades and forms from PPG Industries, inc. These silicas are treated with Hi-The trade name is sold.

In one non-limiting embodiment, the finely divided substantially water-insoluble particulate siliceous filler constitutes at least 50 weight percent, such as at least 65 weight percent, at least 75 weight percent, or at least 90 weight percent of the substantially water-insoluble filler. The siliceous filler may constitute from 50 to 90 weight percent, for example from 60 to 80 weight percent, of the filler, or the siliceous filler may constitute substantially all of the substantially water-insoluble filler.

Fillers, such as siliceous fillers, typically have a high surface area that allows the filler to carry many of the processing plasticizer components used in the process of the present invention to produce microporous materials. High surface area fillers are materials of very small particle size, materials with high porosity, or materials that exhibit both properties. The surface area of at least the siliceous filler particles may be in the range of from 20 to 400 square meters per gram, for example from 25 to 350 square meters per gram, as determined by the Brunauer, Emmett, teller (bet) method according to ASTM D1993-91. By using Micromeritics TriStar 3000^TMBET surface area was determined by fitting 5 relative pressure points in nitrogen adsorption isotherm measurements performed by the instrument. FlowPrep-060^TMThe station may be used to provide heat and continuous gas flow during sample preparation. The silica samples were dried by heating to 160 ℃ for 1 hour in flowing nitrogen (PS) prior to nitrogen adsorption. Typically, but not necessarily, the surface area of any non-siliceous filler particles used is also within one of these ranges. The filler particles are substantially water insoluble and may also be substantially insoluble in any organic processing fluids used to produce the microporous material. This may facilitate retention of the filler in the microporous material.

Interconnecting pores

As noted above, the microporous sheet material produced by the method of the present invention comprises a network of interconnected pores communicating throughout the microporous material. The pores may constitute at least 15 volume percent, such as at least 20 to 95 volume percent, or at least 25 to 95 volume percent, or 35 to 70 volume percent of the microporous material, on an impregnant free basis. As used herein and in the claims, the porosity (also referred to as void volume) of a microporous material expressed as volume% is determined according to the following equation:

porosity of 100[1-d ]₁/d₂]

Wherein d is₁Is the density of the sample, which is determined from the weight of the sample and the volume of the sample determined from the measurement of the sample size, d₂Is the density of the solid portion of the sample, which is determined by the weight of the sample and the volume of the solid portion of the sample. The volume of the solid portion of the sample was measured manually with a Quantachrome manual densitometer (Quantachrome Corp.) according to the attached operating manual.

The volume mean diameter of the pores of the microporous material can be determined by mercury porosimetry using an Autopore III porosimeter (Micromeretics, Inc.) according to the attached operating manual. The volume average pore radius of a single scan is automatically determined by the porosimeter. At the operating porosity meter, scans were performed at high pressure ranges (138 kPa abs-227 MPa abs). If about 2% or less of the total mercury injection volume occurs at the lower end of the high pressure range (138-. Otherwise, another scan is performed at a low pressure range (7-165 kpa absolute) and the volume average pore diameter is calculated according to the following equation:

d＝2[v₁r₁/w₁+v₂r₂/w₂]/[v₁/w₁+v₂/w₂]

wherein d is the volume average pore diameter, v₁Is the total volume of mercury injected in the high pressure range, v₂Total volume of mercury injected in the low pressure range, r₁Is the volume average pore radius, r, determined by high pressure scanning₂Is the volume average pore radius, w, determined by low pressure scanning₁Weight of sample for high pressure scanning, and w₂The weight of the sample that was scanned for low pressure. The volume mean diameter of the pores may be 0.001 to 0.50 microns, for example 0.005 to 0.30 microns, or 0.01 to 0.25 microns.

In the determination of the volume average pore diameter of the above protocol, the maximum pore radius detected is sometimes recorded. Obtaining the maximum hole radius from the low pressure range scan, if performed; otherwise the maximum hole radius is obtained from the high pressure range scan. The maximum hole diameter is twice the maximum hole radius. Since some production or processing steps, such as coating processes, printing processes, impregnation processes and/or bonding processes, lead to a filling of at least some of the pores of the microporous material, and since some of these processes irreversibly compress the microporous material, the parameters of the microporous material with respect to porosity, volume average diameter of the pores and maximum pore diameter are determined before one or more of the above-mentioned production or processing steps are carried out.

Processing plasticizer component

As previously mentioned, the processing plasticizer component is used in the process of the present invention for producing microporous sheet material along with the polyolefin and inorganic filler. For the purposes of the present invention, the processing plasticizer component should have little solvating effect on the polyolefin at 60 ℃ and only a moderate solvating effect at elevated temperatures of about 100 ℃. The processing plasticizer component is generally liquid at room temperature. Non-limiting examples of processing plasticizer components include processing oils such as paraffinic, naphthenic, or aromatic oils. Examples of processing oils may include, but are not limited to, those that meet the requirements of ASTM D2226-82, types 103 and 104. Advantageously, the pour point of the process oil according to ASTM D97-66 (Reapproval 1978) is below 22 ℃, for example below 10 ℃. Non-limiting examples of processing oils that may be used may include412 oil, a,371 Oil (Shell Oil Co.), which is solvent refined and hydrotreated Oil derived from naphthenic crude Oil,400 oil(Atlantic Richfield Co.) andoils (Witco Corp.) they are paraffinic oils. Other non-limiting examples of processing plasticizers may include phthalate plasticizers such as dibutyl phthalate, bis (2-ethylhexyl) phthalate, diisodecyl phthalate, dicyclohexyl phthalate, butyl benzyl phthalate, and ditridecyl phthalate. Any mixture of the aforementioned processing plasticizers may be used in the process of the present invention.

Any of a number of optional ingredients may be included in addition to the polyolefin, inorganic filler, and processing plasticizer. For example, minor amounts, typically less than 10 wt%, of other materials used in processing, such as lubricants, surfactants, water, and the like, may also be present. Other materials introduced for specific purposes optionally may be present in the microporous material in small amounts, typically less than about 15 wt%. Examples of the above substances may include antioxidants, ultraviolet absorbers, reinforcing fibers such as chopped glass fiber bundles, dyes, pigments, security features (security features), and the like. The remainder of the microporous material is essentially an organic polymer, except for the filler and any coating, printing ink, or impregnant applied for one or more specific purposes.

Universal method for producing microporous sheet material

The inventive process for producing a microporous sheet material comprises mixing the polyolefin, inorganic filler, and processing plasticizer components (as well as any of the optional ingredients described herein below) until a substantially homogeneous mixture is obtained. This mixture, along with additional processing plasticizer components if desired, is then introduced into a heated barrel of an extruder (e.g., a screw extruder) connected to a sheet die. A continuous sheet formed by the sheet extrusion die is produced. Optionally, the sheet may be sent to a cooperating pair of heated calender rolls to form a continuous sheet having a thickness less than the continuous sheet exiting the die.

The continuous sheet is then passed to a first extraction zone where the processing plasticizer component is substantially removed by contacting the sheet with a non-flammable extraction fluid composition that is substantially free of trichloroethylene, typically an organic fluid, which is a good solvent for the processing plasticizer and a poor solvent for the polyolefin, and is more volatile than the processing plasticizer. Typically, but not necessarily, both the processing plasticizer and the extraction fluid composition are substantially immiscible with water. The continuous sheet may then be sent to a second extraction zone where the extraction fluid composition is substantially removed by steam and/or water. The continuous sheet may then be passed through a forced air dryer to substantially remove residual water and residual extraction fluid composition. The continuous sheet material, which is a microporous material, can be fed from the dryer to a take-up roll.

As used herein in the specification and claims, "non-flammable" means that the extraction fluid composition is not flammable and has a flash point above 55 ℃ as determined by the closed cup method.

As used herein in the specification and claims, "substantially free of trichloroethylene" means that the extraction fluid composition contains 0.5% or less, such as 0.1% or less, of trichloroethylene.

The resulting microporous sheet typically contains 70 wt% or less of the processing plasticizer component as residual processing plasticizer, for example 30 wt% or less, or 20 wt% or less, or 15 wt% or less, or 10 wt% or less, or 5 wt% or less, or 2 wt% or less, based on the weight of the microporous sheet. For purposes of the present invention, the level of residual processing plasticizer component present in the microporous sheet is determined by the Soxhlet extraction method described herein below in the examples.

Extraction fluid composition

As noted above, the extraction fluid compositions suitable for use in the process of the present invention are non-flammable and substantially free of trichloroethylene. Additionally the extraction fluid composition used in the process of the invention has a boiling point of 90 ℃ or less, for example 75 ℃ or less, or 60 ℃ or less, or 50 ℃ or less. For example, the extraction fluid composition may have a boiling point of 20 ℃ to 75 ℃, such as 20 ℃ to 65 ℃, or 20 ℃ to 45 ℃.

In addition, the extraction fluid compositions suitable for use in the methods of the present invention have a composition of 4 to 9 (J/cm)³)^1/2E.g. 4-6 (J/cm)³)^1/2Calculated solubility parameter coulomb term (delta. calculated soluble salt conjugate term) of (1)_clb). The calculated solubility parameter coulomb term (δ) can be determined using atomic simulations in the Amorphous Cell_clb) Amorphous Cell isThe product Material studio 4.2. Determining the calculated solubility parameter coulombic term (δ) is described in more detail in the examples below_clb) The method of (1). In the atomic simulation described above, cohesive energy is defined as the energy gain per mole of material if all intermolecular forces are eliminated. The cohesive energy density corresponds to the cohesive energy per unit volume. The solubility parameter (δ) is defined as the square root of the Cohesive Energy Density (CED). For the simulations used, the calculated solubility parameter has two terms: van der waals term (delta)_vdw) And coulomb term (δ)_clb) As shown in the following equation.

δ²-δ_vdw ²+δ_clb ²

The extraction fluid composition can comprise any of a variety of fluid compositions, provided that the extraction fluid composition is non-flammable and has a boiling point of 75 ℃ or less. The extraction fluid composition may comprise halogenated hydrocarbons, such as chlorinated hydrocarbons and/or fluorinated hydrocarbons. In one embodiment of the invention, the extraction fluid composition comprises a halogenated hydrocarbon and has a viscosity of 4 to 9 (J/cm)³)^1/2The calculated solubility parameter coulomb term (δ)_clb). Specific non-limiting examples of halogenated hydrocarbons suitable for use as extraction fluid compositions in the process of the present inventionIllustrative examples may include one or more azeotropes of halogenated hydrocarbons selected from trans-1, 2-dichloroethylene, 1, 1, 1, 2, 2, 3, 4, 5, 5, 5-decafluoropentane and/or 1, 1, 1, 3, 3-pentafluorobutane. The above substance can be used as VERTREL^TMMCA (binary azeotrope of 1, 1, 1, 2, 2, 3, 4, 5, 5, 5-dihydrodecafluoropentane and trans-1, 2-dichloroethylene: 62%/38%) and VERTREL^TMCCA (ternary azeotrope of 1, 1, 1, 2, 2, 3, 4, 5, 5, 5-dihydrodecafluoropentane, 1, 1, 1, 3, 3-pentafluorobutane and trans-1, 2-dichloroethylene: 33%/28%/39%), both available from MicroCare Corporation.

Microporous sheets produced by the present process typically contain 20ppm or less of residual extraction fluid composition, for example 10ppm or less, or 5ppm or less, or 1ppm or less, or 0.5ppm or less. For the purposes of this invention, the level of residual extracted fluid composition present in the microporous sheet is determined by the environmental protection agency EPA 8260B method (volatile organic compound determination by gas chromatography/mass spectrometry (GC/MS)). It should be noted that for purposes of the present invention, the term "residual extracted fluid composition" present in the microporous sheet material refers to the amount of extracted fluid composition (which has been used in the process of the present invention to extract the processing plasticizer from the microporous sheet material) remaining in the final microporous sheet material produced by the process.

For some end uses, the microporous sheet may be stretched to reduce the sheet thickness and increase the void volume of the sheet as well as to induce regions of molecular orientation in the polymer matrix. Suitable stretching apparatus, methods and parameters are described in detail in U.S. patent 4,877,679, column 9, line 19-column 11, line 32, the contents of which are incorporated herein by reference.

The microporous sheet produced by the process of the present invention in the form of an unstretched sheet or a stretched sheet may alternatively be further processed as desired. Examples of such further processing may include coiling (reelling), cutting, stacking, further treatment to remove residual processing additives, calendaring, pressing, embossing, impregnating (imbibing), coating, heating, annealing, molding, and making shapes for various end uses.

Microporous sheets produced by the process of the present invention using an extraction fluid composition substantially free of trichloroethylene have a tensile strength of equal to or greater than 800 kPa. For purposes of the present invention, "tensile strength" refers to the stress at 1% strain in the machine direction ("MD") as determined by ASTM D828-97 (Reapproved 2002) modified as follows: a sample crosshead speed of 5.08cm/min was used until a linear travel speed of 0.508cm was achieved, at which time the crosshead speed was accelerated to 50.8cm/s and where the sample width was about 1.2cm and the sample gauge length was 5.08 cm. It should be noted that in addition to tensile strength (i.e., stress at 1% strain), the tensile strength of the material can be further characterized by measuring the maximum tensile strength and maximum elongation by the methods just described above.

The microporous sheet material produced by the method of the present invention may be printed using any of a wide variety of printing media and printing processes known in the art. The term "printable" as used herein means that the object sheet is capable of being printed with some printing medium, such as printing ink, and one or more printing methods. Non-limiting examples of such printing methods include, but are not limited to, letterpress printing such as offset printing, letterpress printing, flexography, and offset-letterpress printing (also known as dry offset printing and indirect offset printing); gravure and gravure printing; lithography such as lithography, offset printing and xerography; stencil printing such as screen printing and copying; typing and dot matrix printing; ink jet printing and electrophotographic printing. Suitable printing inks may include, for example, water-based inks and toners, oil-based inks and toners. The ink and toner may be in liquid form or solid form.

The microporous sheet material produced by the method of the present invention is suitable for a wide variety of end uses, particularly those applications where a printable surface is desired. For example, the microporous sheet material is particularly suited for durable documents such as maps, menus, and cards. The microporous material exhibits stiffness or flex resistance and stability against printer influences such as elongation. In addition, the microporous sheet material is able to maintain its shape and support any subsequently applied layers. Thus, the microporous sheet material is suitable for use as one or more layers in a multilayer article, such as labels, e.g., pressure sensitive labels, in-mold labels, RFID inlays, as well as cards, identification cards, smart cards, loyalty cards, passports, driver's licenses, and the like.

The present invention is further described in conjunction with the following examples, which are intended to be illustrative rather than limiting and wherein all parts are parts by weight and all percentages are percentages by weight unless otherwise specified.

Examples

In section 1 of the following examples, materials and methods for preparing microporous materials for solvent extraction with examples 1 and 2 and comparative examples 1-3 are described. In section 2, a process for extruding, calendering, and extracting a sheet made from the mixture of section 1 is described. In section 3, methods for determining the physical properties reported in Table 3 are described. In section 4, a method for determining the calculated solubility parameters reported in Table 4 for examples 1 and 2 and comparative examples 1-8 is described. In section 5, the results of the analysis of volatile organic compounds according to EPA method 8260 on the microporous material made in section 2 are reported.

Part 1 mixture preparation

The dry ingredients were weighed into an FM-130D Littleford plow mixer with a high intensity chopper type mixing blade in the order and amounts (grams (g)) specified in Table 1. Dry ingredients were premixed with plough blades only for 15 seconds. The process oil is then pumped by hand pump through a nozzle at the top of the mixer with only the plough blades running. The pumping time for the examples varied between 45-60 seconds. Along with the plow blades, the high intensity chopper blades were turned on and the mixture was allowed to mix for 30 seconds. The mixer was stopped and the inside of the mixer was beaten to ensure that all ingredients were mixed uniformly. The mixer was turned around and the high intensity chopper and plow were both turned on and the mixture was allowed to mix for an additional 30 seconds. The mixer was closed and the mixture was poured into a storage container.

TABLE 1

Composition (I)	Microporous material, gram
		Silicon dioxide (a)	6,810
TiO2(b)	273
		UHMWPE(c)	1,893
HDPE(d)	1,893
		Antioxidant (e)	46
Lubricant (f)	68
		Processing oil (g)	11,441

(a) Use of HI-135 precipitated silica, commercially available from PPG Industries, inc.

(b)R-103 titanium dioxide, available from E.I.du Pont de Nemours and company.

(c)4130 Ultra High Molecular Weight Polyethylene (UHMWPE), available from Ticona corp.

(d)1288 High Density Polyethylene (HDPE), available from Total Petrochemicals.

(e)1790 antioxidant, Cytec Industries, Inc.

(f) Calcium stearate lubricant, technical grade, available from Fischer Scientific or ferro corporation.

(g)6056 Process oil, commercially available from PPC Lubricants.

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Part 2 extrusion, calendering and extraction

The mixture of microporous materials is extruded and calendered into the final sheet form using an extrusion system comprising a feed, extrusion and calendering system as described below. The weight loss in the gravimetric feed system (model K-tron K2MLT35D 5) was used to feed each mixture into a 27mm twin-screw extruder (model Leistritz Micro-27 gg). The extruder barrel contained 8 temperature zones and a heated joint connected to a sheeting die. The extrusion mixture feed port is located just before the first temperature zone. The vent is located in the third temperature zone. The vacuum exhaust is located in the seventh temperature zone.

The mixture was fed into the extruder at a rate of 90 g/min. Additional process oil is injected in the first temperature zone as needed to achieve the desired total oil content in the extruded sheet. The oil contained in the extruded sheet (extrudate) discharged from the extruder is referred to herein as "the oil weight percent of the extrudate".

The extrudate from the barrel was discharged into a 15 cm wide extruder having a 1.5 mm discharge orificeAnd (4) a tabletting die head. The extrusion melt temperature was 203-210 ℃ and the throughput was 7.5 kg/h.

The three-roller vertical calender set with one clamping point and one cooling roller is used to realize the calendering process. Each roll has a chrome surface. The roll size was about 41cm long and 14cm in diameter. The top roll temperature was maintained at 135 deg.C to 140 deg.C. The intermediate roll temperature was maintained at 140-145 ℃. The bottom roll was a chill roll, where the temperature was maintained at 10-21 ℃. The extrudate was calendered into sheet form and passed through a lower water cooled roll and wound.

Samples of sheet cut to widths up to 9 inches (22.9cm) and lengths of 6 feet (182.9cm) were taken up and placed in individual 2 litersIn a tank. The tank was filled with each solvent described in table 2. The extract obtained is subsequently used in part 31790 determination of antioxidant level. Each jar was gently shaken and left for 1 hour. Thereafter, each extracted sheet was air-dried and subjected to the followingTest methods.

TABLE 2

Part 3 test and results

The extracted and dried film was measured for physical properties, and the results are shown in Table 3. The thickness was measured using an OnoStokki thickness gauge EG-225. Two 4.5x5 inch (11.43cmx12.7cm) coupons were cut from each sample and the thickness of each coupon was measured at 9 locations (at least 3/4 inches (1.91cm) from either edge). The arithmetic mean of the readings is reported in mils to the last two decimal places and scaled to microns.

The weight percent residual oil was determined using a Soxhlet extractor. A sample of approximately 2.25X5 inches (5.72cmx12.7cm) was weighed and recorded four decimal places. Each sample was rolled into a cylinder and placed in a Soxhlet extraction apparatus and extracted with Trichloroethylene (TCE) as a solvent for about 30 minutes. The sample was then removed and dried. The extracted and dried sample is then weighed. The residual oil weight percent values were calculated as follows: oil Wt.% (initial weight-weight after extraction) x 100/initial weight.

Tensile strength and maximum elongation, as well as the total percent increase at maximum elongation, were determined according to ASTM D828-97 (Re-approval 2002) except that the sample crosshead speed was 5.08 centimeters per minute (cm/min) and the sample width was 1.27 cm. The property values indicated by MD (machine direction) were obtained from samples having their major axes oriented along the length of the sheet. CD (cross direction) performance was obtained from samples with the major axis oriented across the sheet. The above ASTM test methods are incorporated herein by reference.

The heat shrinkage was measured on samples at least 24 hours after extraction. The sample was cut from the center of the extracted sheet with a 13cm x11cm die traveling in the machine direction on the 13cm side. The sample was placed in an oven at 150 ℃ for 30 minutes. Thereafter, the sample was taken out and cooled at room temperature for 2 minutes. Each sample was measured 3 times in the Machine Direction (MD) at the top, middle and bottom of the sheet and in the same manner in the Cross Direction (CD). The arithmetic mean of the MD and CD results was determined and reported in table 3.

Measured in the extract prepared in part 21790 ppm level of antioxidant. 5mL of each extract was mixed with 5mL of tetrahydrofuran (THF-UV grade). With 4ppm to 100ppm of 50% by volume of trichloroethylene in 50% by volume of a THF-UV-grade mixed solvent1790 antioxidant preparation calibration standard. A gradient HPLC method with UV detection at 284nm was used. The detection limit of this method is 5 ppm.1790 the retention time of the antioxidant was 4.2 minutes. Using equipment with a temperature of 40 ℃GeminiC6-Ph, 5 mu, 150x4.6mm column1100 system. In Table 31790 results of antioxidant levels are reported as the arithmetic mean of replicate tests on the same extract tested in sample group B below. The injection volume was 10. mu.L, and the flow rate was 1.5 mL/min. The timetables for mobile phase a ═ distilled water and B ═ acetonitrile are as follows:

time (min)	Percentage A	Percentage B
			0	20	80
10	10	90
			12	0	100
30	0	100

The results of the testing of various fractions of the microporous material made in section 1 with the solvent extractions of examples and comparative examples in section 2 are shown in table 3. The replicates are identified in table 3 as example # a and example # B.

The results in table 3 show that the MD stress values at 1% strain for examples 1 and 2 are greater than the values for comparative example 2. The MD stress values at 1% strain for examples 1 and 2 are comparable to those for comparative examples 1 and 3, indicating that comparable strength microporous materials are made with examples 1 and 2. Examples 1 and 2 will be more energy efficient in use than comparative examples 1 and 3, as both have lower boiling points than comparative examples 1 and 3. MD stress values at 1% strain equal to or greater than 800kPa for embodiments of the present invention provide stiffness, i.e., resistance to bending, and stability against adverse printer effects such as elongation causing distortion of the printed image.

TABLE 3

Calculation of solubility parameter of part 4

The solubility parameter is defined as the square root of the Cohesive Energy Density (CED). The cohesive energy density corresponds to the cohesive energy per unit volume. In atomic simulation, cohesive energy is defined as the energy gain per mole of material if all intermolecular forces are eliminated.

Calculated solubility parameter (. delta.)_sp) Based on two calculation terms: van der waals term (delta)_vdw) And coulomb term (δ)_clb) As shown in the following equation.

δ_sp ²-δ_vdw ²+δ_clb ²Using computational tools executed in a Materials Studio4.2 software environmentThe amophorus Cell module measures the calculated solubility parameters of the solvent. Condensed-phase Optimized Molecular weights for atomic organization students (Compass force) were used to minimize energy in the Amorphous Cell. The construction and optimization of the molecular structure was performed for the following solvents: trichloroethylene, tetrachloroethylene, dichloromethane, trans-1, 2-dichloroethylene, 1, 1, 1, 2, 2, 3, 4, 5, 5, 5-decafluoropentane, 1, 1, 1, 3, 3-pentafluorobutane and cyclopentane. Solvent blend (i.e. VERTREL)^TMSolvent) was calculated using the solubility parameter and volume fraction (Φ) of the individual components as shown in the following equation:

δ_blends-Φ₁δ₁+Φ₂δ₂+....

For each solvent, 20 molecules were constructed at experimental densities within the 3-dimensional amophorus Cell. Molecular dynamics simulations were performed at 298 kelvin with the sum of atomic groups of van der waals and Ewald coulombic interactions. The Amorphous Cell was first equilibrated in an NVT (constant volume and temperature) ensemble for 50 picoseconds (ps). Data was collected every 5ps during a 100ps run. The solubility parameter for each structure (frame) was calculated based on cohesive energy density. The final solubility parameter for a single species is the arithmetic mean solubility parameter for the 20 structures listed in table 4.

TABLE 4

(h) Comparative example 4 is trans-1, 2-dichloroethylene.

(i) Comparative example 5 was 1, 1, 1, 2, 2, 3, 4, 5, 5, 5-decafluoropentane.

(j) Comparative example 6 was 1, 1, 1, 3, 3-pentafluorobutane.

(k) Comparative example 7 is cyclopentane.

(l) Comparative example 8 is VERTREL^TMMCA plus, which is reported as a mixture of trans-1, 2-dichloroethylene (45 wt%), 1, 1, 1, 2, 2, 3, 4, 5, 5, 5-decafluoropentane (50 wt%), and cyclopentane (5 wt%).

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Section 5 analysis of volatile organics according to EPA method 8260

EPA method 8260-determination of volatile organic compounds by gas chromatography/mass spectrometry (GC/MS) (revision 2, 12 months 1996) was used to determine the various volatile organic compounds (ppb levels) in microporous materials made with fractions 2 extracted in examples 1 and 2 and comparative examples 1-3. The levels of the compounds detected are listed in table 5.

TABLE 5

(m) method detection limits

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Although specific embodiments of the invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims (17)

1. A method of producing a microporous sheet material,

the microporous sheet material comprises:

a polymer matrix comprising a polyolefin,

a finely divided substantially water-insoluble filler distributed throughout the matrix, and

a network of interconnected pores communicating throughout the microporous sheet material,

the method comprises the following steps:

(a) forming a mixture comprising a polyolefin, an inorganic filler and a processing plasticizer component;

(b) extruding the mixture to form a continuous sheet; and

(c) contacting the continuous sheet with a non-flammable extraction fluid composition to extract the processing plasticizer component from the continuous sheet, thereby forming a microporous sheet;

wherein the extraction fluid composition has a boiling point of 75 ℃ or less and is substantially free of trichloroethylene; and

wherein the microporous sheet has a tensile strength equal to or greater than 800kPa, and

wherein the extraction fluid composition is selected from a plurality of azeotropes of halogenated hydrocarbons of trans-1, 2-dichloroethylene, 1, 1, 1, 2, 2, 3, 4, 5, 5, 5-decafluoropentane, and/or 1, 1, 1, 3, 3-pentafluorobutane.

2. The method of claim 1 wherein the microporous sheet material contains 70 wt% or less of the processing plasticizer component.

3. The method of claim 1 wherein the microporous sheet material contains 30 wt% or less of a processing plasticizer component.

4. The method of claim 1 wherein the microporous sheet material contains 20 wt% or less of the processing plasticizer component.

5. The method of claim 1, wherein the microporous sheet contains 20ppm or less of the extraction fluid composition.

6. The method of claim 5, wherein the microporous sheet contains 10ppm or less of the extraction fluid composition.

7. The method of claim 1, wherein the extraction fluid composition has a boiling point of 45 ℃ or less.

8. The method of claim 7, wherein the extraction fluid composition has a boiling point of 20 ℃ to 45 ℃.

9. The method of claim 1, wherein the extraction fluid composition has a pH of 4 to 9 (J/cm)³)^1/2The calculated solubility parameter coulomb term (δ)_clb)。

10. The method of claim 1, wherein the extraction fluid composition has a pH of 4 to 6 (J/cm)³)^1/2The calculated solubility parameter coulomb term (δ)_clb)。

11. The method of claim 1, wherein the processing plasticizer component comprises a processing oil selected from the group consisting of paraffinic, naphthenic, and/or aromatic oils.

12. The method of claim 1, wherein said extracting the fluid composition comprises a calculated solubility parameter coulombic term (δ)_clb) Is 4-9 (J/cm)³)^1/2An azeotrope of halogenated hydrocarbons of (a).

13. The process of claim 1, wherein the olefin comprises ultra-high molecular weight polyethylene, ultra-high molecular weight polypropylene, high density polyethylene, and/or high density polypropylene.

14. The method of claim 1, wherein the filler comprises an inorganic filler comprising a siliceous filler.

15. The method of claim 14, wherein the siliceous filler comprises silica.

16. The method of claim 1, wherein the filler is present in the microporous sheet material in an amount of 50 to 90 weight percent.

17. The method of claim 1 wherein the interconnected pores comprise 35 to 70 volume percent of the microporous sheet material.