CN1391625A - Liquid packaging paper - Google Patents

Abstract

Improved liquid paperboard products with reduced edge capillary sizing properties were produced by adding calcium carbonate fillers up to 10.0% by weight. This filler increases the retention and reactivity of sizing agents such as alkyl ketene dimer, thereby further preventing liquid penetration into liquid paperboard substrates.

Description

liquid container cardboard

technical field

The present invention relates generally to paper products, particularly paper containers for packaging liquids and solutions. More particularly, the present invention relates to improved liquid packaging paperboard for use in the production of these liquid containers and methods of making the same.

Background technique

Edgewick sizing is used to prevent liquid penetration in liquid packaging board. This resistance to liquid penetration within the paperboard container along the exposed edges helps to maintain the strength and rigidity of the container over its lifetime. Such unfilled boards have been made in the past because fillers were believed to have a negative impact on board strength, especially sizing properties.

Significant amounts of time and expense are spent each year in the design of artwork that enhances the appearance of packaging materials to attract consumers' attention, and in the development of attention-grabbing concepts. This design includes not only the size and shape of the package, but also the correct combination of color and graphics to determine the success or failure of the packaged product sales.

Liquid materials such as dairy products, juices and other beverages packaged in paper storage containers must overcome several factors in production and storage. Liquids such as these and oils, fats and other solutions can penetrate the paperboard comprising the packaged product with the result that they contaminate exposed package surfaces and detract from the aesthetics of the graphics, colors and designs of the exterior surfaces intended to appeal to consumers and damage the integrity of the container. integrity of the structure. Obviously, this is an undesirable situation.

Past work has focused on overcoming the penetration of liquids, oils and beverages into packaging materials, with work aimed at preventing liquids from penetrating the material. Laminated foil packaging material is one way, but it is quite expensive. Other methods that have been used to prevent grease penetration into packaging materials are polyolefin coatings, fluorocarbon coatings, saturation with paraffin or microcrystalline waxes, coating of one or both sides of the material with polymer reinforced waxes, etc. However, these methods have proven expensive and seldom successful.

Containers for packaging liquid products, especially dairy products such as milk and milk products, are manufactured from coated paperboard. The coating can be on one side of the cardboard, but it is usually on both sides. It is usually coated with polyethylene, and of course other waterproof substances can also be used.

To work effectively in such a container, the cardboard must act as a liquid barrier. For dairy products, the most aggressive penetrating ingredient is generally lactic acid. The most vulnerable part of the cardboard is often its cut edges. Accordingly, manufacturers of paperboard have searched for improved methods of preventing the edges of paperboard from being penetrated by liquids containing lactic acid. It is well known that paperboard sized with ketene dimer (KD) prevents liquids containing lactic acid from penetrating the edges.

In many cases it is undesirable to use a metallized substrate as a packaging material, especially where external coloring and/or printing is required on the surface of the packaging and structural integrity is important. It is also often impractical and expensive to use barriers to absorb liquids, oils and/or fats. In this case, it is necessary to at least provide an easy-to-print packaging material that (may hide the unsightly oily, smudged appearance from the buyer) will prevent liquid penetration into the cardboard from occurring.

There is still much room for improvement in the edge capillary sizing properties of paperboard. In the past, to maintain good edge capillary sizing, especially with regard to lactic acid-containing beverages (i.e., milk), higher alkyl ketene dimers (a cellulose-reactive sizing agent), retention aids, and thermosetting resins (such as Kymene(R) Hercules, Inc. Wilmington, Delaware) was used to facilitate hard sizing along the edges of the paperboard, which are the most sensitive to liquid penetration and degradation. Most paperboard used to make liquid containers needs to be manufactured without fillers as this negatively affects the strength and sizing properties of the board.

It is an object of the present invention to improve the edge capillary sizing properties of paperboard for liquid container manufacture and construction by adding fillers. Yet another object of the invention is to produce paperboard for liquid containers and packaging in which the filler comprises up to 10% of the paperboard (with or without retention aid).

Contents of the invention

The present invention includes paperboard products for the construction and manufacture of liquid containers, aseptic packaging and dairy, juice, carbonated and non-carbonated soft drinks, hot drinks and other liquid packaging and methods of production thereof. Edge capillary sizing of boards can be improved by adding calcium carbonate fillers to increase the retention and activity of sizing agents such as alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA), which prevent liquid penetration performance. Detailed Description of the Invention

When mineral particles, such as calcium carbonate, are used as fillers in the manufacture and production of liquid paperboard, the internal cohesive properties of the paper are impaired because the mineral particles have a larger surface area than wood fibers alone. Mineral particle fillers are expected to interfere with fiber/fiber bonds, resulting in a weaker, inferior product. In order to maintain good marginal capillary sizing properties for lactic and citric acids as ingredients in dairy and fruit juices, large amounts of cellulose-reactive sizing agents of alkyl ketene dimer (AKD), cationic thermosetting resins and retention aids are used to promote "Hard" sizing along the edge of the board. Other sizing agents such as alkenyl succinic anhydride (ASA) were tried but were unable to prevent the penetration of lactic acid.

The present invention improves the edge capillary sizing properties of liquid packaging boards by adding calcium carbonate fillers, preferably ground calcium carbonate or precipitated calcium carbonate (PCC), in amounts up to 10% of the board. Calcium carbonate fillers increase the efficiency of the sizing agent. Also, in the presence of calcium carbonate fillers, alkyl ketene dimers (AKD) or alkenyl succinic anhydrides (ASA), preferably AKD, can be used in these board products. To provide excellent sizing properties.

Surprisingly, it has been found that when calcium carbonate is used as a filler in paperboard for liquid packaging, the combination of calcium carbonate and the Their mixture sizing agents produce mutual synergy, thereby further enhancing the edge capillary sizing performance. This sizing provides liquid container board with greater wet strength, durability as measured according to Technical Association of the Pulp and Paper Industries (TAPPI) Test Method T456, OM-87. When the precipitated calcium carbonate is first surface treated with sodium stearate, acrylic copolymer or salt of C ₁₂ -C ₂₀ fatty acid, the edge capillary sizing performance of the paperboard can be further enhanced. Preferred acrylic copolymers include acrylonitrile consisting of butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, methyl methacrylate, styrene, vinyl acrylate, vinyl chloride, and mixtures thereof copolymer.

Calcium carbonate was added as a filler to liquid container boards, improving the retention of alkyl ketene dimer sizing by 28% and increasing the activity of the dimer by 25%. This provides two advantages, as this improves the edge capillary sizing properties of the board and at the same time, the addition of calcium carbonate causes the board to increase in volume, stabilizing the alkalinity of the system and subsequently reducing or completely eliminating the additional addition of sodium bicarbonate needs. This in turn reduces the need to add expensive thermosetting resins to the stock.

Calcium carbonate fillers also result in increased board brightness, smoothness and better coverage of polyethylene and wax coatings. The paperboard has enhanced stiffness and stiffness because the calcium carbonate stabilizes the alkalinity of the paperboard system and improves the retention of the alkylketene dimer in the system.

The manufacture and production of liquid paperboard containing calcium carbonate filler is very similar to that of ordinary paperboard. The wood pulp is broken, refined and diluted to obtain fiber pulp or feed. Calcium carbonate is added to the supply alone or together with other starches, resins and sizing agents. Ground calcium carbonate (GCC) as well as precipitated calcium carbonate (PCC) can be used as filler in the present invention, and precipitated calcium carbonate can give excellent paper products. Controlling particle size, particle surface area, etc. enables manufacturers to tailor calcium carbonate to specific paperboard products.

The cardboard sheet is then formed on a paper machine, which forces the water out and passes the product through a series of heated drums to dry the paper. The paper is then calendered at high speed to compact to the desired smoothness. Liquid cardboard is typically coated on both sides with a polyethylene film using known film-forming techniques. The thickness of the film depends on the liquid to be included. Controlling factors include acidity and alkalinity, storage temperature, exposure to sunlight, and more.

Calcium carbonate is added to the liquid paperboard in an amount of about 0.5-10.0% of the total weight of the paperboard. Preferably about 3.0-10% by weight, most preferably about 4.0-6.0% by weight. Other ingredients include wet strength agents such as polyamine epichlorohydrin resins to further bind the pulp fibers together to increase the strength and fastness of the paper. Natural rosin can also provide the same bonding function. Retention aids such as anionic polyacrylamides also bind and stabilize system components.

The following non-limiting examples are provided to more particularly discuss and suggest specific embodiments of the invention. However, they are for illustrative purposes only, and additionally, minor variations and changes to process parameters and ingredients not included herein should be considered to be possible, however, to the extent that such changes and changes do not substantially alter or affect the process or final product . It should be understood that such variations are still within the spirit and scope of the invention as determined by the following examples.

Example 1

PCC-filled liquid packaging board for improved edge capillary sizing

PCC filler was used in liquid packaging board to determine its effect on edge capillary sizing properties. Board handsheets were made from Prince Albert bleached northern kraft pulp in a 75% hardwood/25% softwood blend. Hardwood and softwood pulps were refined at 1.6% consistency to endpoints of 400 and 500 Canadian Standard Freeness, respectively. The refined pulp is diluted to 1.0% consistency for papermaking. The weight limit of the target sheet is 225 grams per square meter. The concentration of alkyl ketene dimer (AKD) size (Heron(R) 75, Hercules Inc.) was kept constant and added to the feed at 0.125% (2.5 pounds per ton) on dry sheet weight. Cationic potato starch (Sta-Lok 400(R); A.E. Staley Mfg. Co.) was added to the feed at 0%, 0.5% and 1.0% by dry sheet weight (0, 10 and 20 pounds per ton). The thermosetting resin, polyamidoamine epichlorohydrin (PAE) (Kymene 557H, Hercules Inc.) was added to the feed at 0%, 0.25 and 0.5% (0, 5 and 10 pounds per ton) of dry paper sheet weight . ALBACAR(R) LO PCC was added to the feed at levels adjusted to be approximately 0%, 3% and 6%. The amount of anionic polyacrylamide retention aid (Accurac(R) 171; Cytec Industries) was kept constant and added to the feed at 0.00875% by dry sheet weight (0.175 lbs per ton). After the handsheets were formed on a Formax sheet former (Noble & Wood), two extrusions were made between stainless steel rollers at a pressure of 20 psi. In the first press, the sheet is still sandwiched between sheets of paper machine "wet felt" material on the forming wire. The sheet is then removed from the forming wire sandwiched between two sheets of unsized blotter paper and pressed again. The handsheets were conditioned and tested under TAPPI standard conditions of 23°C and 50% relative humidity. Sheets were laminated, cut to size and soaked in 1% lactic acid solution for 4 hours for edge capillary sizing performance testing. The results of the edge capillary sizing performance test are shown in Table 1.

Table 1

Effect of PCC filler on edge capillary sizing properties Internal starch (%) PAE(%) PCC filler (%) Edge capillary sizing properties (g/100 inches) 0 0 0.0 5.90 0 0 2.8 1.01 0 0 6.0 1.82 0.5 0 0.0 3.46 0.5 0 2.9 0.76 0.5 0 6.0 0.80 0 0.25 0.0 0.79 0 0.25 2.9 0.63 0 0.25 5.7 0.66 0.5 0.25 0.0 0.75 0.5 0.25 2.9 0.62 0.5 0.25 6.0 0.63 1.0 0.5 0.0 0.72 1.0 0.5 2.7 0.69 1.0 0.5 5.8 0.62

Examination of the data showed that PCC filler improved the edge capillary sizing performance of liquid packaging boards under all wet end conditions used for the evaluation. The first set of data showed that the edge capillary sizing value for the board without starch, PAE and PCC fillers was 5.90 g/100 inches of exposed edge. Adding PCC fillers to the paperboard greatly improved this value. Upon further examination of the data, the edge capillary sizing values were lower (better) when the PCC filler was added to the board whether starch, PAE or both were added.

Example 2

  PCC-filled liquid packaging paperboard for improved hot and cold beverage packaging

PCC filler was used in liquid packaging board to determine its effect on hot and cold beverage packaging. Handsheets were made from Prince Albert bleached northern kraft pulp containing a 75% hardwood/25% softwood blend. Hardwood and softwood pulps were refined at 1.6% consistency to endpoints of 400 and 500 Canadian Standard Freeness, respectively. The pulp was mixed in a ratio of 75:25. The refined pulp is diluted to 1.0% consistency for papermaking. The weight of the target sheet is 225 grams per square meter. The concentration of AKD size (Hercon(R) 75, Hercules Inc.) was kept constant and added to the feed in amounts of 0%, 0.5 and 1.0% by dry sheet weight (0, 10, and 20 pounds per ton). PAE (Kymene(R) 557H, Hercules Inc.) was added to the furnish at 0.125% (2.5 pounds per ton) by weight of the sheet. Cationic potato starch (Sta-Lok(R) 400, A.E. Staley Mfg. Co.) was added to the feed at 0%, 0.25% and 0.5% (0, 5 and 10 pounds per ton) on dry sheet weight. ALBACAR(R) LO PCC was adjusted to almost 0%, 3% and 6% added to the feed. The amount of anionic polyacrylamide retention aid (Accurac(R) 171; Cytec Industries) was kept constant and added to the feed at 0.00875% by dry sheet weight (0.175 lbs per ton). After the handsheets were formed on a Formax sheet former (Noble & Wood), two extrusions were made between stainless steel rollers at a pressure of 20 psi. In the first press, the sheets are still sandwiched on the forming wire between sheets of paper machine "wet felt" material. The sheet is then removed from the forming wire sandwiched between two sheets of unsized blotter paper and pressed again. The handsheets were conditioned and tested under TAPPI standard conditions of 23°C and 50% relative humidity.

Cobb sizing test (3 minutes per TAPPI test method T441-OM90) with hot coffee (84°C, 8.4 grams per liter of instant coffee) and cold coffee (23°C, 8.4 grams per liter of instant coffee). Cobb The test results are shown in Table 2.

Table 2

Effect of PCC Filler on Cobb Sizing Internal starch (%) PAE(%) PCC(%) Hot Liquid Cobb Sizing (g/m²) Cold Liquid Cobb Sizing (g/m²) 0 0 0.0 320 279 0 0 2.8 241 64 0 0 6.0 240 75 0.5 0 0.0 296 50 0.5 0 2.9 103 44 0.5 0 6.0 88 47 0 0.25 0.0 63 45 0 0.25 2.9 49 43 0 0.25 5.7 50 42 0.5 0.25 0.0 60 43 0.5 0.25 2.9 49 42 0.5 0.25 6.0 49 39 1.0 0.5 0.0 59 41 1.0 0.5 2.7 48 44 1.0 0.5 5.8 51 45

From this work it is known that PCC filler greatly improves the ability of liquid packaging boards to package hot and cold beverages as determined by the hot and cold Cobb sizing tests. The first set of data showed hot liquid and cold liquid Cobb sizing values of 320 and 279 g/m2 for board without starch, PAE and PCC, respectively. Boards incorporating PCC fillers greatly improved this sizing value. Upon further examination of the data, the Cobb sizing values were always lower (better) when PCC was added to the board irrespective of the presence of starch, PAE or not in the board.

Example 3

  Calcium carbonate-filled liquid packaging board for improved edge capillary sizing

Ground calcium carbonate (GCC) and PCC fillers were used in liquid packaging board to determine the effect on edge capillary sizing properties. The board was made on a pilot paper machine. The fillers evaluated accounted for up to 10% in the liquid packaging board. The fiber feed consisted of 80% bleached kraft hardwood and 20% bleached kraft softwood. The target board weight is 225 grams per square meter. Cationic potato starch (Sta-Lok(R) 400; A.E. Staley Mfg. Co.) was added to the feed in an amount of 10 pounds per ton. AKD sizing (Hercon(R) 79, Hercules Inc.) at 0.2%, PAE (Kymene(R) 557H; Hercules Inc.) was added to the dilute stock at 10 pounds per ton. Calcium carbonate filler should be added as much as possible to the level of 3%, 6% and 9%. The filled boards were conditioned and tested under TAPPI conditions of 23°C and 50% relative humidity. The paper sheets were laminated, cut to size and soaked in 1% lactic acid solution for 4 hours for the edge capillary absorption test, the results of the edge capillary absorption test are shown in Table 3.

table 3

Effect of calcium carbonate filler on edge capillary sizing properties packing type Filling amount (%) Edge capillary sizing (grams/100 inches) unfilled paperboard 0.0 0.53 PCC-Calcite 3.7 0.49 PCC-Calcite 6.9 0.44 PCC-Calcite 9.6 0.39 PCC-aragonite 3.2 0.54 PCC-aragonite 6.2 0.46 PCC-aragonite 9.6 0.46 GCC-Calcite 3.1 0.48 GCC-Calcite 7.1 0.38 GCC-Calcite 10.4 0.51

Examination of the data indicates that different mineral forms of calcium carbonate filler will improve the edge capillary sizing properties of liquid packaging boards. The edge capillary sizing value of the exposed edge of the liquid packaging board without any filler was 0.53 grams per hundred inches (g/100 in.). When calcite PCC filler was added to the paperboard at levels as high as 9.6%, the edge wicking value decreased to 0.39 g/100 inches. With calcite ground calcium carbonate (GCC) filler at 7.1% filler, the edge capillary absorption decreases to 0.38 g/100 inches. With the addition of 10.4%, the edge capillary absorption value increased to 0.51 g/100 inches, but still lower than the value of the unfilled board size.

Example 4

Use of PCC and surface treated PCC in AKD or ASA sized liquid packaging board

Filler to improve edge capillary sizing

Cardboard handsheets were produced following the procedure of Example 1 using a Noble and Wood type sheet former. Hardwood and softwood pulp were mixed in a ratio of 50:50. The target board weight is 225 grams per square meter. Starch was added at 0.5%, cellulose active sizing agent (AKD or ASA) was added at 0.15% (AKD) or 0.1% (ASA). PCC fillers were added to the board to achieve levels of 3%, 6% and 9%. PCC fillers can also be surface treated to further improve edge capillary sizing. For example, surface treatment of PCC fillers with 0.5% acrylic copolymer. The results of these edge capillary sizing tests are shown in Table 4.

Table 4

  Edge capillary sizing of AKD or ASA sized liquid packaging boards using PCC filler

performance impact packing type Packing treatment Filler dosage (%) Sizing agent Edge capillary absorption (g/100 inches) none -- 0.0 AKD 1.62 PCC none 4.8 AKD 0.92 PCC none 9.3 AKD 1.10 PCC 0.5% acrylic copolymer 5.0 AKD 0.90 PCC 0.5% acrylic copolymer 9.1 AKD 0.83 none -- 0.0 ASA 2.40 PCC none 5.4 ASA 1.41 PCC none 10.7 ASA 1.90 PCC 0.5% acrylic copolymer 5.2 ASA 1.20 PCC 0.5% acrylic copolymer 9.3 ASA 1.18

Examination of the data indicated that PCC fillers would improve the performance of edge capillary sizing in liquid packaging boards using AKD as an internal sizing or the less common ASA as an internal sizing. Examination of the data also indicated that surface treatment of PCC fillers with acrylic copolymers further enhanced edge capillary sizing performance. For the AKD sized board without filler, the edge capillary sizing value of the exposed edge reached 1.62 grams per 100 inches (grams per 100 inches). After adding PCC filler at 4.8% and 9.3%, edge capillary sizing values reached 0.92 g/100 inches and 1.10 g/100 inches, respectively. When the PCC filler was surface treated with 0.5% acrylic copolymer (dry weight) and then added to the board at 5.0% and 9.1% the sizing values were further reduced to 0.90 g/100 in and 0.83 g respectively /100 inches.

For board sized with ASA without filler, the edge capillary sizing value at the exposed edge was 2.40 g/100 inches. Adding PCC filler at 5.4% and 10.7% improved the edge capillary sizing values to 1.41 and 1.90 g/100 inches, respectively. When the PCC filler was surface treated with 0.5% acrylic copolymer (dry weight) and then added to the board at levels of 5.2 and 9.3%, the sizing values were reduced to 1.20 g/100 inches and 1.18 g/100 inches, respectively.

Claims (16)

CLAIMS 1. A liquid container board comprising calcium carbonate, wherein said calcium carbonate is used in an effective amount to improve edge capillary sizing properties and reduce liquid penetration. 2. The liquid container paperboard of claim 1, wherein the paperboard further comprises a sizing agent selected from the group consisting of alkyl ketene dimers, alkenyl succinic anhydrides, cationic polyamidoamines, styrene maleic anhydride, and mixtures thereof. 3. The liquid container paperboard of claim 1, wherein said calcium carbonate is selected from the group consisting of ground calcium carbonate and precipitated calcium carbonate. 4. The liquid container paperboard of claim 3, wherein said calcium carbonate is precipitated calcium carbonate. 5. The liquid container paperboard of claim 4, wherein said precipitated calcium carbonate is coated with a surface coating selected from the group consisting of sodium stearate, acrylic copolymers, _C12 - _C20 fatty acid salts, and mixtures thereof. 6. The liquid container paperboard of claim 5, wherein said acrylic copolymer comprises one or more monomers selected from the group consisting of butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2- Hydroxyethyl ester, methyl methacrylate, styrene, vinyl acrylate, vinyl chloride and mixtures thereof. 7. The liquid container paperboard of claim 4 wherein said precipitated calcium carbonate is incorporated into said paperboard at a level of from about 0.5% to about 10.0% by weight of the total weight of the container paperboard. 8. The liquid container paperboard of claim 7, wherein said precipitated calcium carbonate is incorporated into said paperboard in an amount of from about 3.0% by weight to about 10.0% by weight of the total weight of the container paperboard. 9. The liquid container paperboard of claim 8 further comprising a polyethylene film coated on its surface. 10. The liquid container paperboard of claim 9 further comprising a wet strength agent, a retention aid, and an optical brightener. 11. A method of reducing or eliminating edge capillary sizing in liquid packaging board comprising adding an effective amount of precipitated calcium carbonate as filler. 12. The method of claim 11, wherein said paperboard further comprises a compound selected from the group consisting of alkyl ketene dimers, alkenyl succinic anhydrides, cationic polyamidoamines, styrene maleic anhydride, cationic sizing resins, and mixtures thereof sizing agent. 13. The method of claim 11, wherein said precipitated calcium carbonate is pre-treated with a surface coating comprising sodium stearate, acrylic copolymer, _C12 - _C20 fatty acid salt and mixtures thereof. 14. The method of claim 13, wherein said acrylic copolymer comprises one or more monomers selected from the group consisting of butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate esters, methyl methacrylate, styrene, vinyl acrylate, vinyl chloride and mixtures thereof. 15. The method of claim 11 wherein said precipitated calcium carbonate is added to said liquid packaging board in an amount of from about 0.5% to about 10.0% by weight of the total board stock. 16. The method of claim 15, wherein said precipitated calcium carbonate is added to said liquid packaging board in an amount ranging from about 3.0% to about 10.0% by weight of the total board stock.