FIELD

This application is directed to laminate materials, particularly laminate materials that include a polyolefin dry-process membrane as one layer of the laminate. The laminate materials may be used to form desiccant bags or other items were the properties of the laminate materials would be favorable.

BACKGROUND

Desiccant packets or bags are used to absorb moisture. They can be used in items ranging from packaged food to shipping containers.

Typical desiccants are hygroscopic, meaning they absorb water and the volume of the material may increase. One typical desiccant that operates this way is silica. Another type of desiccant is a deliquescent desiccant. This type of desiccant is a solid that absorbs water and becomes a liquid or brine. One typical deliquescent desiccant is CaCI ₂ .

Currently, some desiccant bags or packets may be formed from materials including Kraft paper with a coating, particle stretched polyethylene, Tyvek ^® , Gore-Tex ^® (including fluorinated polymers such as e-PTFE). See U.S Patent No.7, 857896 and EP0832686. Some issues with current materials include, but are not limited to, the following: lower dimensional stability (higher shrinkage), which makes them less desirable for applications where desiccant bags or packets are reactivated (involving oven drying at temperatures around 120°C), being environmentally unfriendly (e.g., containing fluoropolymers); being expensive; and having insufficient water resistance, which makes the material less desirable for applications where the desiccant is a deliquescent desiccant that forms water or brine that exerts pressure on the desiccant bag or packet.

Thus, there is a need for improved materials for use in the formation of desiccant bags or packets.

SUMMARY

In one aspect, disclosed herein is a laminate material for a desiccant bag or packet that addresses some of the issues of prior materials as described hereinabove. In some embodiments, the laminate material for a desiccant bag or packet comprises a dry-stretch porous polyolefin membrane. The laminate comprising the dry-stretch porous polyolefin membrane exhibits one or more, two or more, three or more, four or more, five or more, six or more, seven or more, or all eight of the following properties: is non dusting; is mold resistant; is mildew resistant; has higher dimensional stability as indicated by a MD shrinkage less than 30%, less than 10%, less than 7%, less than 5%, or less than 3% at 120°C and/or a transverse direction (TD) shrinkage less than 15%, less than 10%, less than 7%, less than 5%, less than 3%, or less than 1% at 120°C; is chemically inert; has a high moisture vapor transmission rate (MVTR) as indicated by a value greater than or equal to 500 g/(m ² *day), greater than or equal to 550 g/(m ² *day), greater than or equal to 600 g/(m ² *day), greater than or equal to 650 g/(m ² *day), greater than or equal to 700 g/(m ² *day), equal to or greater than 710 g/(m ² *day), equal to or greater than 720 g/(m ² *day), equal to or greater than 730 g/(m ² *day), equal to or greater than 740 g/(m ² *day), equal to or greater than 750 g/(m ² *day), equal to or greater than 760 g/(m ² *day), equal to or greater than 770 g/(m ² *day), equal to or greater than 780 g/(m ² *day) , equal to or greater than 790 g/(m ² *day), equal to or greater than 800 g/(m ² *day) when measured according to ASTM-E96A; has higher water resistance as indicated by a value above 3,000 mml-hO, above 5,000 mml- O, above 7,000 mml-hO, or above 9,000 mml-hO when measured according to AATC 127; and has heat sealability, meaning a sufficient strength seal can be formed in the bag or packet formation process with minimal effects on the properties of the laminate material.

In some embodiments, the laminate may include at least one other layer in addition to the dry-stretch porous polyolefin membrane. The other layer may be a polyolefin membrane, a polyolefin mesh or net , or a polyolefin non-woven. In the laminate, the dry-stretch porous polyolefin membrane may be an exterior layer or an interior layer.

In another aspect, a desiccant bag or packet comprising a deliquescent desiccant in the bag or packet is disclosed. The desiccant bag or packet may be formed using a laminate material comprising a dry-stretch porous polyolefin membrane as one layer of the laminate. Some properties of the laminate material include, but are not limited to a water resistance above 3,000, above 5,000, above 7,000, or above 9,000 mml- O when measured according to AATC 127. The laminate may also have an MD shrinkage less than 30%, less than 10%, less than 5%, or less than 3% at 120°C and/or a transverse direction (TD) shrinkage less than 15%, less than 10%, less than 7%, less than 5%, less than 3%, or less than 1% at 120°C may be preferred. In some embodiments, another layer of the laminate is a polyolefin membrane, polyolefin mesh or net, or polyolefin non-woven. In some embodiments, the dry-stretch porous polyolefin membrane is an exterior layer of the laminate. In some embodiments, the dry-stretch porous polyolefin membrane is an interior layer of the laminate

In another aspect, a desiccant bag or packet that satisfies the requirements of MIL-D-3464E (MIL-SPEC) for Type I, Type II, or Type III bags is disclosed. The desiccant bag or packet is formed from a laminate material comprising a dry-stretch porous polyolefin membrane as one layer of the laminate. The laminate used to form the desiccant bag or packet satisfying MIL-SPEC may have at least one of an MD shrinkage less than 30%, less than 10%, less than 5%, or less than 3% at 120°C and a transverse direction (TD) shrinkage less than 15%, less than 10%, less than 7%, less than 5%, less than 3%, or less than 1% at 120°C.

In some embodiments, a desiccant in the bag or packet comprises CaO, silica gel, clay, molecular sieves, CaO, CaS04, or combinations thereof.

In some embodiments, another layer of the laminate is a polyolefin membrane, polyolefin mesh or net, or polyolefin non-woven. In some embodiments, the dry-stretch porous polyolefin membrane is an exterior layer of the laminate. In some embodiments, the dry-stretch porous polyolefin membrane is an interior layer of the laminate.

In another aspect, a rechargeable desiccant bag or packet, which includes a desiccant capable of being recharged, is disclosed. The desiccant bag or packet is formed using a laminate comprising a dry-stretch porous polyolefin membrane as one layer of the laminate. The laminate used to form the desiccant bag or packet may have at least one of an MD shrinkage less than 30%, less than 10%, less than 5%, or less than 3% at 120°C and a transverse direction (TD) shrinkage less than 15%, less than 10%, less than 7%, less than 5%, less than 3%, or less than 1% at 120°C.

In some embodiments, the laminate may comprise another layer that is a polyolefin membrane, a polyolefin mesh or net, or a polyolefin non-woven. In some embodiments, the dry-stretch porous polyolefin membrane is an exterior layer of the laminate. In some embodiments, the dry-stretch porous polyolefin membrane is an interior layer of the laminate. DESCRIPTION OF THE FIGURES

Fig. 1 shows laminate materials according to some embodiments described herein.

Fig. 2 is a table including data for comparative and inventive embodiments described herein.

Fig. 3 is a scanning electron microscope (SEM) image of a particle-stretched polyolefin porous membrane.

Fig. 4 is an SEM image of a wet process polyolefin porous membrane.

Fig. 5 is an SEM image of uniaxially-stretched and biaxially stretched dry-process porous polyolefin membranes.

DESCRIPTION

Laminate Material

A laminate material for use in the manufacture of desiccant bags is disclosed herein. The laminate material has properties that make it better than prior materials used for this purpose. For example, the laminate material described herein may have higher water resistance, higher dimensional stability, lower cost, increased environmental friendliness, etc. At least one layer of the laminate is a dry process porous polyolefin membrane. The dry-process porous polyolefin membrane may be an internal or external layer of the laminate. The laminate may also have additional layers.

The laminate may have one or more, two or more , three or more, four or more, five or more, six or more, seven or more, or all eight of the following properties: is non-dusting; is mold resistant; is mildew resistant; has higher dimensional stability as indicated by a MD shrinkage less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, less than 7%, less than 5%, or less than 3% at 120°C and/or a transverse direction (TD) shrinkage less than 15%, less than 10%, less than 7%, less than 5%, less than 3%, or less than 1% at 120°C; is chemically inert; has a high moisture vapor transmission rate (MVTR) as indicated by a value greater than or equal to 500 g/(m ² *day), greater than or equal to 550 g/(m ² *day), greater than or equal to 600 g/(m ² *day), greater than or equal to 650 g/(m ² *day), greater than or equal to 700 g/(m ² *day), equal to or greater than 710 g/(m ² *day), equal to or greater than 720 g/(m ² *day), equal to or greater thann730 g/(m ² *day), equal to or greater than 740 g/(m ² *day), equal to or greater than 750 g/(m ² *day), or equal to or greater than 760 g/(m ² *day), equal to or greater than 770 g/(m ² *day), equal to or greater than 780 g/(m ² *day) , equal to or greater than 790 g/(m ² *day), equal to or greater than 800 g/(m ² *day) when measured according to ASTM-E96A the desiccant method; has higher water resistance as indicated by a value above 3,000 mmH ₂ 0, above 3,500 mmH ₂ 0 , above 4,000 mmH ₂ 0, above 4,500 mmH ₂ 0 above 5,000 mmH ₂ 0, above 5,500 mmH ₂ 0, above 6,000 mmH ₂ 0, above 6,500 mmH ₂ 0, above 7,000 mmH ₂ 0, above 7,500 mmH ₂ 0, above 8,000 mmH ₂ 0, above 8,500 mmH ₂ 0 or above 9,000 mmH ₂ 0 when measured according to AATC 127; and has heat sealability, meaning a sufficient strength seal can be formed in the bag or packet formation process with minimal effects on the properties of the laminate material.

The thickness of the laminate may be from 5 to 50 mils, from 5 to 40 mils, from 5 to 30 mils, from 5 to 20 mils, or from 5 to 10 mils.

The basis weight of the laminate may be from 10 to 200 gsm, from 20 to 150 gsm, from 30 to 125 gsm, from 40 to 120 gsm, from 50 to 115 gsm, from 60 to 110 gsm, from 70 to 100 gsm, or from 80 to 90 gsm. In some preferred embodiments, the range may be from 20 to 120 gsm.

Dry-stretch porous polyolefin membrane

The dry-stretch porous polyolefin membrane may be an internal or external layer of the laminate. External layer means outermost layers of the laminate. A three-layer laminate would have one internal and two external layers.

The dry-stretch porous polyolefin membrane of the laminate is not so limited. As understood by those skilled in the art, the term dry-stretch refers to the method by which the membrane was formed. Such a method does not involve the use of solvents, oils, diluents, pore-formers, beta-nucleators, nucleating agents, or the like. Due to the difference in how it is made, a membrane made from a dry-stretch process has a completely different structure than a membrane made by a wet process (e.g., a process using solvents, oils, or diluents) or a membrane made by a process that uses other pore forming agents such as beta-nucleators or particles or particulates. For example, see Fig. 3, which includes an SEM image of a membrane formed by a particle-stretch process, Fig. 4, which includes an SEM image of a membrane made by a wet process, and Fig. 5, which includes an SEM image of a membrane made by a dry-stretch process. The Celgard ^® dry-stretch process comprises steps of extruding, annealing, and stretching. Pore formation occurs in the stretching step. The dry-stretch porous polyolefin membranes described herein may have an average pore size from 0.01 to 1.0 microns, from 0.05 to 1.0 microns, from 0.1 to 1.0 microns, from 0.2 to 1.0 microns, from 0.3 to 1.0 microns, from 0.4 to 1.0 microns, from 0.5 to 1.0 microns, from 0.6 to 1.0 microns, from 0.7 to 1.0 microns, from 0.8 to 1.0 microns, or from 0.9 to 1.0 microns.

The dry-stretch porous polyolefin membrane may be a monolayer membrane, a bilayer membrane, a trilayer membrane, or a multilayer membrane having four or more layers. In some preferred embodiments, the dry-stretch porous polyolefin membrane may be a bilayer membrane with one layer comprising polyethylene and the other layer comprising polypropylene. Bilayer, trilayer, and multilayer membranes described herein may be formed by co-extrusion of two or more layers, lamination of two or more layers, or combinations of co-extrusion and lamination such as co-extrusion of two layers and lamination of the two co-extruded layers to a third layer.

The polyolefin of the dry-stretch porous polyolefin membrane is not so limited, but may be a polyethylene homopolymer, copolymer, or terpolymer, a polypropylene homopolymer, copolymer, or terpolymer, or a blend of one or more of the foregoing. In some preferred embodiments, the polyolefin of the dry-stretch porous polyolefin membrane may be a high-density polyethylene (HDPE). In some preferred embodiments, the polyolefin is not a halogenated polyolefin. In particularly preferred embodiments, the polyolefin is not a fluorinated polyolefin. Many fluorinated polymers, e.g., e-PTFE and the like, are known to be harmful to the environment.

The dry-stretch polyolefin membrane may have a thickness from 2 to 50 microns, from 5 to 45 microns, from 10 to 40 microns, from 10 to 35 microns, from 10 to 30 microns, from 10 to 25 microns, from 10 to 20 microns, or from 10 to 15 microns.

Other Lavers of the Laminate

The laminate may also have one or more, two or more, three or more, four or more, or five or more additional layers. In some preferred embodiments, the laminate has three layers. The one or more additional layers of the laminate may comprise, consist of, or consist essentially of a polyolefin membrane, polyolefin mesh or net, or polyolefin non-woven. The additional layers of the laminate may be the same or different from the other. The polyolefin non-woven is not so limited and may comprise, consist of, or consist essentially of polypropylene homopolymers, copolymer, or terpolymers; polyethylene homopolymers, copolymers, or terpolymers; or combinations of the foregoing. The method by which the non-woven is formed is not so limited. The non-woven may be wet-laid, dry-laid (e.g., parallel laid, cross-laid, or random air-laid), or spun laid (e.g., spunbond or meltblown) nonwovens.

The polyolefin mesh net is also not so limited, and may be a woven or non-woven mesh or net. For example, the non-woven mesh or net may be formed by extrusion. In some embodiments, the layer comprising a polyolefin mesh or net, may comprise two or more laminate or cross-laminated polyolefin meshes or nets.

In some preferred embodiments, the laminate consists only of polyolefins, making the laminate recyclable.

The method by which the layers of the laminate are joined together is not so limited and may include the use of an adhesive between the layers of the laminate, application of heat, application of pressure, application of heat and pressure, or any combination of the foregoing. In some preferred embodiments, the laminate is not formed using adhesives or glues. While this is how typical materials for desiccant bags and packets are formed currently, the use of glues and adhesives negatively affects the breathability of the material leading, for example, to lower moisture vapor transmission rates. Further, avoiding glues and adhesive has advantages from a recyclability standpoint, particularly if the layers of the laminate are recyclable, but the glue is a different material that is not recyclable or is not recyclable with the materials of the layers.

Desiccant Bag or Packet with Deliquescent Desiccant

In some embodiments, a laminate material as described hereinabove may be used in the formation of a desiccant bag or packet that includes a deliquescent desiccant therein. As explained above, when a deliquescent desiccant (solid) absorbs water it becomes a liquid brine in the desiccant bag or packet. The liquid brine exerts pressure on the bag or packet. Thus, a laminate material as described hereinabove that exhibits a higher water resistance value would be preferred for use in the formation of a desiccant bag or packet that includes a deliquescent desiccant therein. For example, the laminate preferably has higher water resistance as indicated by a value above 3,000 mmH ₂ 0, above 3,500 mmH ₂ 0 , above 4,000 mmH ₂ 0, above 4,500 mmH ₂ 0 above 5,000 mmH ₂ 0, above 5,500 mmH ₂ 0, above 6,000 mmhhO, above 6,500 mmhhO, above 7,000 mmhhO, above 7,500 mmhhO, above 8,000 mmh O, above 8,500 mmh O or above 9,000 mmhhO when measured according to AATC 127.

In some preferred embodiments, when designing a desiccant bag or packet to be used with a deliquescent desiccant, it is preferred that the dry-stretch porous polyolefin membrane of the laminate be closest to the inside of the packet or bag (where the desiccant is held). Without wishing to be bound by any particular theory, the inventors believe that bags or packets with this design will have maximum water resistance. During use, a bag or packet containing a deliquescent desiccant experience pressure from within as the brine formed in the packet or bag pushes against the inside of the bag or packet. In this situation, a layer of the laminate that is furthest away from the interior of the packet or bag experiences the most pressure.

Low MD shrinkage at high temperature may also preferred for a laminate material used for this type of desiccant packet or bag. An MD shrinkage less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, less than 7%, less than 5%, or less than 3% at 120°C is preferred. Alternatively, or in addition to having the aforementioned MD shrinkage values, the laminate may have a transverse direction (TD) shrinkage less than 15%, less than 10%, less than 7%, less than 5%, less than 3%, or less than 1% at 120°C. However, because bags or packets comprising a deliquescent desiccant cannot be recharged (this type of desiccant is not typically discharged) thermal stability, particularly at such high temperatures, is not necessarily required for this type of bag.

A MIL SPEC Desiccant Bag or Packet

In another aspect, a desiccant bag or packet that satisfies the requirements of MIL-D-3464E for Type I, Type II, or Type III bags is disclosed. The desiccant bag or packet is formed using a laminate material as described hereinabove. The desiccant in the bag or packet is not so limited and may comprise CaO, silica gel, clay, molecular sieves, CaO, CaS04, or combinations thereof. Notably, desiccant bags or packets meeting the requirements of Type I, Type II, Type III, MIL-D-3464E, involves a test of the bags or packets resistance to reactivation temperature (about 118°C), meaning properties measured before reactivation are maintained after reactivation. Rechargeable Desiccant Bag or Packet

The rechargeable or regenerable desiccant bag or packet is formed using a laminate material as described herein and the bag or packet comprise a desiccant that can be recharged or regenerated. Recharging is typically performed by exposing the bags or packets to temperatures around 120°C (118.3°C). Therefore, the thermal stability of the laminate material used to form these types of bags should be high. For example, the laminate should have a low shrinkage at high temperatures. A machine direction (MD) shrinkage less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, less than 7%, less than 5%, or less than 3% at 120°C is preferred. Further, a transverse direction (TD) shrinkage less than , less than 15%, less than 10%, less than 7%, less than 5%, less than 3%, or less than 1% at 120°C may be preferred.

EXAMPLES

Inventive laminates (Cl, C2, C3, C4, C5, and C6) as shown in Fig. 1 were formed and tested. The PE membrane and the PP/PE membrane are microporous dry-process polyolefin membranes as described herein. The PP/PE membrane is a bi-layer membrane comprising a polypropylene-containing layer and a polyethylene-containing layer. The PE support mesh or net comprises polyethylene. The FIDPE/PET non- woven is a non-woven with high-density polyethylene (HDPE) and polyethylene terephthalate (PET)- containing fibers. The PP non-woven is a non-woven of polypropylene (PP) fibers.

Comparative materials including a material including a particle-stretched polyethylene membrane were also tested. Results of the testing are found in Fig. 2. The "PE" example in Fig. 2 is the comparative particle-stretched polyethylene examples.

Desiccant packets or bags were formed using the inventive laminates such that a PE membrane or a PP/PE membrane is closest to the interior of the bags or packets.

As can be seen from the data, the material of the inventive examples exhibit much higher water resistance than the "PE" comparative example, and the material of the inventive examples will be much cheaper and much more environmentally friendly than e-PTFE-containing materials, like Gore-Tex ^® , that have been used in the past. The inventive examples are not halogenated polymer containing materials, like Gore-Tex ^® , which are both expensive and harmful to the environment. Materials with high water resistance are particularly useful for forming desiccant packets or bags where the desiccant in the packet or bag is a deliquescent desiccant that forms water or brine as it absorbs water. As it is formed, the water or brine exhibits pressure on the bag, so if the material of the bag has a high water resistance this is beneficial. As explained above, bags or packets formed with a PE membrane or a PP/PE membrane closest to the interior of the bag or packet (where the desiccant is held) can even better withstand this pressure.

As can also be seen by the data, the material of the inventive examples exhibit lower shrinkage values at high temperatures (eg., 105°C and 120°C) than the comparative "PE" example. In addition, as explained above, the inventive materials are cheaper and safer for the environment than materials containing halogenated polymers, like Gore-Tex ^® , which includes fluorinated polymers (e.g., e-PTFE). Materials with excellent thermal stability, as indicated by low shrinkage values at high temperatures, are desirable, particularly in the formation of rechargeable desiccant bags or packets, which include a desiccant capable of being recharged. Recharging may occur by subjecting the desiccant packet or bag to temperatures of about 120°C (typically 118.3°C).

Testing

MIL-D-3464E Military Specification (MIL SPEC) is a specification of the United States Military for desiccants and desiccant bags. Testing is done according to the MIL SPEC to determine if the required properties for Type I, Type II, and Type III desiccant packets or bags are satisfied.

Machine Direction (MD) shrinkage is measured by obtaining a sample of the laminate material and heating it in an oven unrestrained at a temperature (e.g., 90°C, 105°C, or 120°C). Machine direction width of the sample is measured before (initial width) and after heating (final width), and percent shrinkage is calculated by the following formula (1):

[(Initial width-final width)/(initial width)]*100

After the sample is removed from the oven, let it equilibrate before taking the final measurement. About 15-20 minutes is a sufficient time.

Transverse Direction (TD) shrinkage is measured in a similar manner to MD shrinkage except that transverse direction length of the laminate material is measured before and after heating. Hydrostatic head or water resistance is measured according to AATC 127, with the failure mode being recorded. Possible failure modes include, but are not limited to three drops penetrating the material or rupture of the material. Failure by rupture may indicate that an even higher water resistance could be achieved the material was reinforced. However, no reinforcement should be used to obtain hydrostatic head or water resistance as described herein.

Moisture vapor transmission rate of the laminate is measured according to ASTM E96A, the desiccant method. The chosen desiccant should be the one that the laminate material is intended to be used with.

Thickness is measured using an appropriate ASTM standard for laminate materials that contain a non- woven material. Ten to fifteen measurements should be taken across the laminate. An instrument with a foot size from 0.5 to 0.7 inches and a foot pressure between 5 and 10 psi is desirable.

Basis weight is measured using an appropriate ASTM standard. Basis weight of a sample involves calculating the mass of a sample (g) and the area of a sample (m ² ) to obtain the grams per-square-meter (gsm) measurement.

For tensile property measurements, use of Instron Model 3365 is preferred. Five to ten samples are prepared, with samples being from 20 to 40 inches long across the width of the film (MD direction) for MD sample and along the length of the film (TD direction) for TD sample.