A method for foaming a composition

Abstract

The present invention relates to a method for foaming a composition, comprising: (a) preparing a composition comprising: (i) an emulsion-based polymer, (ii) a plurality of expandable microspheres having an initial expandable temperature range of 80°C to 110°C; and (b) exposing the composition to dielectric heating, wherein the dielectric heating is radio frequency heating, the radio frequency heating being performed in a range of less than 300 MHz; thereby causing the plurality of expandable microspheres in the composition to expand.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 201880047716.3, entitled “Dielectric Heating Foamable Composition”, filed on July 18, 2018. Technical Field

[0002] This invention relates to dielectric heating foamable compositions. Specifically, this invention relates to using radio frequency (RF) heating to heat foamable compositions to provide thermal insulation during the preparation of articles. Background Art

[0003] There is a search for single-use food packaging and containers that are less environmentally friendly than traditional closed-cell extruded polystyrene foam packaging. Packaging made entirely of plastic typically does not biodegrade in less than 400 years, or, if any, is prohibited by some regulations.

[0004] There is a need for recyclable, biodegradable, and / or compostable alternative packaging. One such package comprises a cellulose-based substrate derived from recyclable and / or compostable renewable materials. The package is manufactured by joining two cellulose substrates together with an air gap between them. Some disadvantages of these alternative packages include poor insulation and poor structural integrity compared to plastic packaging. When the package is handled and bent, the air gap between the two substrates is compressed, reducing insulation in those compressed areas. Insulation can be improved by increasing the air gap between the cellulose substrate layers, increasing the thickness of the cellulose substrate, or inserting a cellulose medium between the two layers.

[0005] Some of the improved packaging mentioned above are described in US 9,580,629, US 8,747,603, US 9,273,230, US 9,657,200, US 20140087109, US 20170130399, US 20170130058, and US 20160263876. The resulting packaging has an air gap providing insulation within a coating / adhesive sandwiched between two substrates. Conventional heating requires a long time and a large space for water evaporation and polymer curing / coalescing. Furthermore, the insulation gap is not always uniform due to varying packaging dimensions. While microwave heating provides tight control over moisture content and uniform air gaps, the penetration depth is limited to approximately 1.5 inches. Therefore, any substrate thicker than approximately 1.5 inches can result in uneven packaging.

[0006] There is a need in the art for methods to provide uniform insulation for packaging of all sizes. This invention provides a method for producing environmentally friendly and economically advantageous packaging that provides uniform insulation for packaging of various sizes. Summary of the Invention

[0007] This invention relates to a method for foaming and coalescing a waterborne composition filled with microspheres.

[0008] One embodiment relates to a method for foaming and agglomerating a composition, the method comprising:

[0009] (a) A composition comprising: (i) a water-based polymer; (ii) a plurality of expandable microspheres having an initial expandable temperature range of about 80°C to about 110°C and a maximum expandable temperature range of about 50°C to about 150°C; and (iii) optionally present additives; and

[0010] (b) Exposing the composition to dielectric heating;

[0011] As a result, the multiple expandable microspheres in the composition expand and the composition aggregates.

[0012] Another embodiment relates to a method for forming an article of article, the method comprising the following steps:

[0013] (a) A composition comprising the following components: (i) a water-based polymer, (ii) a plurality of expandable microspheres having an initial expandable temperature range of about 80°C to about 110°C and a maximum expandable temperature range of about 50°C to about 150°C, and (iii) optional additives.

[0014] (b) Apply the composition to a first substrate;

[0015] (c) Applying a second substrate to the composition to form an article in which the composition is sandwiched between the two substrates;

[0016] (d) Apply dielectric heating to the article;

[0017] As a result, the multiple expandable microspheres in the composition expand and the composition aggregates.

[0018] Dielectric heating provides uniform heating throughout the composition and creates substantially uniform air gap thickness throughout the composition and article. Attached Figure Description

[0019] Figure 1A A photograph shows a composition filled with microspheres that has been activated by RF dielectric heating immediately after the microspheres have expanded.

[0020] Figure 1B A photograph of the microsphere-filled composition, activated by RF dielectric heating after the composition has been completely dried, is shown.

[0021] Figure 2A A photograph shows a composition filled with microspheres that has been activated by convection heating immediately after the microspheres have expanded.

[0022] Figure 2B A photograph is shown of a microsphere-filled composition activated by convection heating after the composition has been completely dried.

[0023] Figure 3A A photograph shows a composition filled with microspheres that has been activated by microwave heating immediately after the microspheres have expanded.

[0024] Figure 3B A photograph is shown of a composition filled with microspheres that has been activated by microwave heating after the composition has been completely dried.

[0025] Figure 4A A photograph of the package, activated by RF after drying at ambient temperature for less than 1 minute, is shown.

[0026] Figure 4B A photograph shows an adhesive on a substrate activated by RF after drying at ambient temperature for less than 1 minute.

[0027] Figure 5A A photograph of the package, activated by RF after drying at ambient temperature for 2 minutes, is shown.

[0028] Figure 5B A photograph shows the adhesive on a substrate activated by RF after drying at ambient temperature for 2 minutes.

[0029] Figure 6A A photograph of the package, activated by RF after drying at ambient temperature for 5 minutes, is shown.

[0030] Figure 6B A photograph shows the adhesive on a substrate activated by RF after drying at ambient temperature for 5 minutes. Detailed Implementation

[0031] This invention provides a method for foaming multiple microspheres and agglomerating and in-situ locking the foamed microspheres in an aqueous composition. The aqueous composition comprises a polymer and multiple microspheres and is applied to one or more cellulose substrates to form a package. Once expanded and in-situ locked, the air gaps within the foamed microspheres provide insulation and structural integrity for the package. This packaging is more environmentally friendly than conventional extruded polystyrene foam packaging.

[0032] Conventional heating requires ovens with long belts, which necessitates large spaces and significant heat output. Traditional heaters typically operate within a temperature range of approximately 212°F (100°C) to approximately 450°F (177°C).

[0033] Microwave heating is another method. Microwave heating provides uniformity in drying and moisture control, and can keep moisture content to around 1%. However, microwave energy dissipates and cannot penetrate to a depth greater than approximately 1.5 inches (4 cm). Furthermore, microwaves are a known radiation hazard, so worker exposure to such harmful radiation should be minimized. To minimize health risks, industrial microwave machines typically have small openings, making it challenging to fit large and oddly shaped containers into these small openings.

[0034] In this document, dielectric heating, electronic heating, radio frequency (RF) heating, and high-frequency heating, used interchangeably, refer to the process of heating dielectric materials using high-frequency alternating electric fields or radio waves. RF heating differs from microwave heating. Industrial radio frequencies operate between approximately 2 MHz and 300 MHz, with typical wavelengths ranging from approximately 141 to approximately 24 feet (43 to 7.3 meters). Industrial microwave systems use frequencies exceeding 300 MHz, with typical wavelengths ranging from approximately 13 to approximately 5 inches (33 to 12 cm). The power utilization efficiency of RF generators is far lower than that of microwave units; therefore, microwave units are typically the preferred heating source.

[0035] This invention provides dielectric heating (particularly RF heating) of foamable aqueous compositions. RF generates an alternating electric field between dielectric materials (polar water molecules in this invention). The article is conveyed between electrodes, causing water molecules in the composition to continuously reorient to face the opposing electrodes. The friction generated by this molecular motion results in rapid heating. RF operates at frequencies far lower than microwave heating and poses lower health risks compared to microwaves. Due to the greater penetration depth of RF, it is also suitable for heating large and oddly shaped containers.

[0036] Furthermore, the method of the present invention may include a combination of dielectric heating and direct heating applications. For example, the expansion of microspheres can be achieved by dielectric heating, while the removal of excess moisture after expansion can be achieved by direct heating.

[0037] RF heating comprises a composition of a water-based polymer and multiple expandable microspheres, providing uniform heating and drying of the water and the expanded microspheres.

[0038] The present invention is also based on the discovery that a composition comprising a water-based polymer and a plurality of expandable microspheres, applied by RF heating to an article, provides the article with improved uniform thermal insulation.

[0039] One embodiment relates to a method for foaming and agglomerating a composition, the method comprising:

[0040] (a) Preparing a composition comprising: (i) a water-based polymer, (ii) a plurality of expandable microspheres, said expandable microspheres having an initial expandable temperature range of about 80°C to about 110°C and a maximum expandable temperature range of about 50°C to about 150°C, and (iii) optionally present additives; and

[0041] (b) Exposing the composition to dielectric heating;

[0042] As a result, the multiple expandable microspheres in the composition expand and the composition aggregates.

[0043] RF heating forces water out of the composition to aggregate the water-based polymer, while simultaneously causing the microspheres to expand when the temperature reaches an activated state. Heating is particularly preferred at RF frequencies of approximately 14, 27, and 41 MHz. The RF device can be designed with operational amplifiers to optimize heating.

[0044] The compositions described herein can be used in multilayer substrates, particularly cellulose substrates. Using these compositions, a larger insulating space can be provided between two substrates, which is connected at the adhesion point. Insulating products used in this invention include paper products for consumer use, such as paper products for purposes such as: hot drink cups and lids, cold drink cups and lids, hot food containers and lids, cold food containers and lids, freezer cartons and boxes, envelopes, bags, etc.

[0045] The composition can be formed as an adhesive or a coating, which are used interchangeably herein. The composition is prepared by forming a mixture of a water-based polymer, a plurality of expandable microspheres, and optionally present additives.

[0046] Aqueous polymers are prepared via emulsion polymerization and can be single-grade or mixtures of synthetic emulsion polymers or polymers of natural origin. Aqueous polymers prepared by emulsion polymerization may include any desired polymer components, including starch, vinyl acetate ethylene dispersions, polyvinyl acetate, polyvinyl acetate polyvinyl alcohol, dextrin-stabilized polyvinyl acetate, polyvinyl acetate copolymers, vinyl acetate ethylene copolymers, vinyl acrylics, styrene acrylics, acrylics, styrene-butyl rubber, polyurethane, starch, and mixtures thereof. Particularly preferred emulsion polymer components are vinyl acetate ethylene dispersions, polyvinyl acetate, and starch. Preferably, the emulsion polymer is stabilized by a hydrophilic protective colloid.

[0047] The water-based polymer may be present in the composition in any amount, and ideally, it is present in an amount of about 60% to about 99.5% by weight, preferably about 65% to about 95% by weight, prior to curing. Depending on the emulsion polymer, the solids content is about 40% to about 65% by weight.

[0048] The expandable microspheres used in this invention can expand in size in the presence of heat and / or RF radiation. Microspheres usable in this invention include, for example, thermally expandable polymer microspheres, including those having a hydrocarbon core and a polyacrylonitrile shell (e.g., under trade names). Those for sale) and other similar microspheres (e.g., under trademarks) (Those for sale). Expandable microspheres can have any unexpanded size, including diameters from about 5 micrometers to about 30 micrometers. In the presence of heat or radiation, the diameter of the expandable microspheres of the present invention can increase by about 3 to about 10 times the original size. When the microspheres in the composition expand, the composition becomes a foam-like material with improved thermal insulation properties. The microspheres are typically made of a plastic or polymer shell with a foaming agent located inside, designed to activate upon reaching a specific temperature.

[0049] Expandable microspheres have a specific temperature at which they begin to expand and a second temperature at which they have reached maximum expansion. Microsphere grades are typically sold with a specific expansion temperature (Texp) and a maximum expansion temperature (Tmax). The initial expansion temperature (Texp) is the typical temperature at which the microspheres begin to expand, and the maximum expansion temperature (Tmax) is the temperature at which approximately 80% of the microspheres have expanded. If the microspheres are exposed to temperatures far above Tmax, they begin to explode and deflate.

[0050] A particularly useful microsphere has a Texp of approximately 80°C to approximately 105°C. The microsphere has reached its maximum expansion temperature (Tmax) ideally between approximately 90°C and approximately 140°C.

[0051] The specific microspheres and their corresponding Texp and Tmax are crucial to this invention. Although any specific grade of microspheres can be used in this invention, the Texp and Tmax of the microspheres should be considered when formulating and activating them under RF conditions. RF radiation evaporates water from the composition, but the temperature of the composition is limited to less than about 100°C. If additives and / or salts are present in the composition, supercritical heating may occur during RF heating, pushing the temperature above 100°C. However, the preferred Texp and Tmax for expandable microspheres are less than about 100°C and less than about 140°C, respectively. Microspheres with higher temperatures will not be activated during RF heating. Once the composition aggregates, the microspheres are essentially locked in situ, making expansion difficult, if not impossible. Surprisingly, RF heating allows the microspheres to expand more robustly. The use of RF activation allows for self-limitation of microsphere expansion and reduces bursting and shrinkage compared to conventional convection heating.

[0052] In a preferred embodiment, it is ideal that the expandable microspheres are present in the composition at an amount of about 0.1 wt% to about 70 wt% of the composition before curing, more preferably at an amount of about 0.5 wt% to about 60 wt% of the composition before curing, and most preferably at an amount of about 1 wt% to about 50 wt% of the composition before curing. The expansion rate of the expandable microspheres and the loading level of the microspheres are related to each other.

[0053] Depending on the amount of microspheres and the type of polymer, the aggregated composition can have adhesive properties. High amounts of microspheres result in low or no adhesive properties, while low amounts (less than about 30% by weight based on the total weight of the composition) result in adhesive properties.

[0054] The amount of expandable microspheres in the composition can be adjusted depending on the size of the fully expanded microspheres. The desired amount of microspheres in the composition can also be varied depending on the specific expandable microspheres used.

[0055] The microspheres further enhance the structural integrity of the aggregated composition upon expansion. While introducing voids into the matrix typically reduces mechanical integrity, microspheres within the polymer matrix provide rigidity when applied to the substrate. This is particularly useful for packaging fragile items.

[0056] In another embodiment, the microspheres may be pre-expanded. If pre-expanded microspheres are added to the composition, they should be selected so that RF heating does not cause the microspheres to begin decomposition. In yet another embodiment, the microspheres may be a mixture of pre-expanded microspheres and expandable microspheres.

[0057] The composition optionally further comprises any plasticizer; tackifier; wetting agent; accelerator; filler; pigment; dye; stabilizer; rheology modifier; polyvinyl alcohol; preservative, such as antioxidant, biocide; and mixtures thereof. The content of these components may be from about 0.05% by weight to about 15% by weight of the composition.

[0058] An exemplary plasticizer is Available benzoic acid esters, such as diethylene glycol dibenzoate, dipropylene glycol dibenzoate, etc.

[0059] The accelerator is a polyvalent cation derived from a water-soluble salt, including common aluminum nitrate (Al(NO3)3), zirconium acetate, and ammonium zirconyl carbonate (available from Zirconium Chemicals as Bacote 20). The addition of the polyvalent water-soluble salt shortens the radiation time required during the expansion of the composition. When added, based on the total weight of the composition, about 0.05% to about 1% by weight, preferably about 0.1% to 0.3% by weight, of the accelerator can be used.

[0060] Exemplary preservatives include 1,2-benzisothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, and 2-methyl-4-isothiazolin-3-one. Typically, a preservative may be used in an amount of about 0.05% by weight to about 0.5% by weight of the composition prior to curing.

[0061] Exemplary fillers include pearl starch, physically modified starch, and chemically modified starch.

[0062] Other materials may be used as needed without adversely affecting the composition and its thermal insulation properties. It is desirable that the composition may include other additives and / or salts to increase the coalescence of the composition.

[0063] Although the composition may begin to coalesce at room temperature, a high moisture content will make the composition essentially fluid until the moisture content reaches about 20 wt%, 19 wt%, 18 wt%, 17 wt%, 16 wt%, 15 wt%, 14 wt%, 13 wt%, 12 wt%, 11 wt%, 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, or 1 wt% of the total weight. Preferably, the moisture content should be maintained at a level greater than about 20 wt% to prevent premature coalescence. Premature coalescence leads to uneven drying, resulting in uneven thickness of the dried composition on the substrate.

[0064] RF heating also allows for the manufacture of articles at high throughput. The composition must be designed to accommodate this high-throughput method to maximize the solids content of the composition. Ideally, water molecules should be effectively removed without leaving unsightly wrinkles or unevenness on the substrate.

[0065] Surprisingly, RF heating provided uniform and smooth activation of the microspheres at a faster throughput, and also allowed water to drain from the composition more quickly. The uniformity and smoothness of the coalesced coating provided uniform insulation for the article and minimized unsightly wrinkles on the substrate, while increasing yield.

[0066] Another embodiment relates to a method for forming an article of article, the method comprising the following steps:

[0067] (a) A composition comprising the following components: (i) a water-based polymer, (ii) a plurality of expandable microspheres having an initial expandable temperature range of about 80°C to about 110°C and a maximum expandable temperature range of about 50°C to about 150°C, and (iii) optional additives.

[0068] (b) Apply the composition to a first substrate;

[0069] (c) Applying a second substrate to the composition to form an article in which the composition is sandwiched between the two substrates;

[0070] (d) Apply dielectric heating to the article;

[0071] As a result, the multiple expandable microspheres in the composition expand and the composition aggregates.

[0072] The products are suitable for use as protective packaging, transport packaging, impact-resistant packaging, and heat-insulating packaging. Packaging includes cups, food containers, boxes, cartons, bags, lids, crates, envelopes, shipping bags, wraps, clamshells, etc.

[0073] Substrates include fiberboard, chipboard, corrugated boards, corrugated mediums, solid bleached boards (SBB), solid bleached sulfite board (SBS), solid unbleached board (SLB), white lined chipboards (WLC), kraft paper, kraft paperboard, coated papers, and binderboards.

[0074] The composition can be applied to the first substrate in any desired configuration, including a series of dots, stripes, waves, checkerboard patterns, any general polyhedral shape with a substantially flat base, and combinations thereof. Additionally, the composition can be applied to the first surface in the form of a series of cylinders. Furthermore, if desired, the composition can be applied to the first surface as a substantially flat sheet, covering the entire first surface (full lamination) or covering a portion of the first surface. A second substrate is applied to the top surface of the composition, forming a sandwich configuration: first substrate – composition with expandable microspheres – second substrate.

[0075] In yet another embodiment, the insulating article comprises a substantially flat substrate and a non-flat circular substrate. The composition is applied to the substantially flat substrate, the non-flat substrate, or both substrates to form the insulating article. The composition can be applied to completely coat the surface of one or more substrates or selectively coat a portion of the surface of one or more substrates. The pattern can be random or a variety of ordered designs. Thus, the resulting article has an insulating space between the lining surfaces. Articles with patterned compositions mimic the spacer inserted between the two substrates. The space between the two substrates is created and maintained by expanded microspheres.

[0076] Optionally, different adhesives may be applied between the two substrates. This is particularly useful for bonding two substrates together if the composition has low or no adhesive properties. Different adhesives may be applied before, simultaneously with, or after the composition is applied to the first substrate. In another embodiment, different adhesives may be applied to the second substrate, the composition may be used to bond the two substrates together, and the different adhesives may be sandwiched between the two substrates. Exemplary different adhesives include hot melt adhesives, pressure-sensitive adhesives, water-based adhesives, and solvent-based adhesives.

[0077] A wet composition is applied between two substrates to form an article, which is then exposed to dielectric heating to cause the composition to coalesce and expand into microspheres. Thus, heating locks the component, comprising multiple expanded microspheres, onto the substrate surface. Dielectric heating generates an alternating electric field between polar water molecules, resulting in rapid heating. In the presence of water, the temperature rises to 100°C, the water evaporates, and the microspheres expand. Microsphere grades with a Texp of about 80°C to about 100°C and a Tmax of about 90°C to about 140°C expand with dielectric heating.

[0078] The use of dielectric heating, particularly RF heating, allows for rapid processing. Therefore, RF methods allow for high throughput and ensure smaller areas compared to convection heating methods. Furthermore, due to the greater penetration depth and the more flexible aperture of the oven compared to a microwave oven, RF processing can be used to manufacture larger and oddly shaped packages.

[0079] Multilayer substrate packaging formed with compositions containing microspheres improves the packaging's ability to withstand strain under elevated and / or decreased temperatures and constant stress. Those skilled in the art will anticipate that the addition of microspheres increases the strain of the composition at elevated temperatures.

[0080] The invention can be better understood by analyzing the following embodiments, which are non-limiting and are intended only to help explain the invention.

[0081] Example

[0082] Example 1: Water-based polymer

[0083] Table 1

[0084] resin emulsion Water-based polymer name emulsion polymers Solid content pH 1 Dur-O-Set C-325 PVAc 54-58％ 4.5-6.0 2 Resyn 1072 PVAc 62-67％ 3.5-5.5 3 Dur-O-Set E-200 EVA 53-59％ 4.0-5.0

[0085] Example 2: Composition

[0086] The compositions were prepared using the following components. Each resin emulsion was used to prepare the following compositions.

[0087] Table 2

[0088]

[0089]

[0090] *Texp 80℃, Tmax 135℃, median particle size 15.2μm, blowing agent isobutane (concentration 10-20%), density ≤10kg / m³ 3

[0091] The compositions are prepared by mixing the components in a container.

[0092] Example 3: Activation

[0093] The composition 4 and resin emulsion 3, in a wet state, were applied to paper substrates (20 lb and 24 lb paper, Golden Kraft) in a series of dot patterns. Each substrate was activated by conventional heating, microwave heating, or RF dielectric heating (40 MHz and 55–62 Amps). The initial height of the coating and the final height after activation are recorded in Table 3. The percentage of moisture immediately after activation was visually determined by calculating the amount of non-expanding segments of the coating.

[0094] Table 3

[0095]

[0096] RF activation provides a superior percentage increase in microsphere expansion and flatness compared to the other two heating methods. Furthermore, RF heating offers much faster drying because the moisture percentage is significantly lower than that of convection and microwave heating.

[0097] Photographs of the activated composition on paper are shown in Figures 1-3. RF heating, such as... Figure 1A and Figure 1B As shown, it provides consistent and smooth expansion, while convection heating ( Figure 2A and 2B ) and microwave heating ( Figure 3A and 3B The composition did not provide consistent expansion.

[0098] Example 4: Solid content

[0099] To understand the rate flux, a package was formed by coating composition 4 (resin emulsion 3) onto a first substrate and placing a second substrate on top of the first substrate. The package was then placed at ambient temperature (approximately 72°F to approximately 90°F) for less than 1 minute, 2 minutes, or 5 minutes before RF activation with 40 MHz and 55-62 Amps.

[0100] exist Figure 4A , 5A The packaging appearance of the coated substrate is shown in Figure 6A. The two substrates are pulled apart and photographed, as shown. Figure 4B , 5B And 6B.

[0101] Table 4

[0102]

[0103] While high solids content allows for faster manufacturing throughput, the surface of high-solids compositions can form a skin, preventing moisture loss. To minimize wrinkles and uneven foaming, the composition should be activated with RF in less than 1 minute. Rapid throughput methods, including coating and activation of the coating in less than 1 minute, allow for maximum benefits.

Claims

1. A method for foaming a composition, comprising: (a) A composition comprising: (i) an emulsion-based polymer selected from starch, polyvinyl acetate, polyvinyl acetate polyvinyl alcohol, dextrin-stabilized polyvinyl acetate, polyvinyl acetate copolymers, acrylics, styrene-butyl rubber, polyurethane, and mixtures thereof; (ii) a plurality of expandable microspheres having an initial expandable temperature range of 80°C to 110°C and a maximum expandable temperature range of 50°C to 150°C; and (iii) optional additives. (b) Apply the composition to a substrate; as well as (c) Exposing the composition to dielectric heating, wherein the dielectric heating is radio frequency heating, and the radio frequency heating is performed in the range of less than 300 MHz; As a result, the multiple expandable microspheres in the composition expand. The time interval between step (b) and step (c) is less than 1 minute.

2. The method according to claim 1, wherein the composition further comprises an accelerator, said accelerator being a polyvalent water-soluble salt.

3. The method according to claim 2, wherein the accelerator is selected from aluminum nitrate, zirconium acetate, zirconium oxycarbonate and mixtures thereof.

4. The method according to claim 1, wherein the radio frequency heating is performed at 13 MHz, 27 MHz or 40 MHz.

5. The method according to claim 1, wherein the emulsion-based polymer is a vinyl acrylate.

6. The method according to claim 5, wherein the emulsion-based polymer is a styrene-acrylic polymer.

7. The method according to claim 1, wherein the emulsion-based polymer is a vinyl acetate-ethylene copolymer.

8. The method according to claim 7, wherein the emulsion-based polymer is a vinyl acetate ethylene dispersion.

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