JP7261118B2 - wrapping paper - Google Patents

Description

The present invention relates to packaging paper for reducing the amount of plastic used.

In recent years, the problem of plastic waste has become more serious. The world's plastic production is said to exceed 400 million tons/year, and about half of it is packaging containers, which are also a cause of plastic waste. Plastic does not decompose semi-permanently, and its garbage turns into microplastics in the natural environment, which has a serious adverse effect on the ecosystem. The most commonly used plastics for packaging containers are polyethylene terephthalate (PET), which is used for beverage bottles, etc., and polyethylene (PE) and polypropylene (PP), which are used for laminating plastic bags and containers. . In particular, the pollution of the ocean is remarkable, and it is said that the plastic garbage cannot be collected. In the future, it is necessary for the global environment to reduce the use of plastics.

On the other hand, the application of biodegradable plastics that can be completely decomposed by microorganisms has been proposed all over the world as a countermeasure against plastic waste. Biodegradable plastics decompose in the natural world within a certain period of time, but they are still garbage until they are decomposed. See Patent Documents 1 and 2).

Substitution of paper for plastic has been proposed as an immediate means, but polyethylene and polypropylene will be used in large quantities as heat sealing agents when paper is processed into bags and containers. The amount of lamination of these plastics varies depending on the product concept, but is 20 to 300 g/m ² . About 20 to 50 g/m ² is common. Therefore, even in packaging containers in which paper is substituted for plastic, there is still the problem that the amount of plastic used is not sufficiently reduced, and a means for directly reducing the use of plastic is needed.

JP 2012-148444 A JP 2013-141763 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a packaging paper which can reduce the amount of plastic used and is excellent in oil resistance and heat sealability.

In the wrapping paper of the present invention, an ionomer is used instead of polyethylene and polypropylene in order to reduce the amount of polyethylene and polypropylene used in conventional plastic-laminated paper (hereinafter sometimes abbreviated as poly-laminated paper). Further, in the present invention, in order to impart excellent oil resistance (oil repellency), at least one heat seal layer is provided on at least one side of a paper base material containing an oil resistant agent, and the resin of the heat seal layer is an ionomer and has a tensile strength of 3.5 kN/m or more in the machine direction (MD). Compared to the 20 to 300 g/m ² of polyethylene or polypropylene laminate used for the heat seal layer of conventional polylaminated paper, the amount of plastic used for the heat seal layer is about 25 to 300 g/m 2 . It can be reduced to 80%. However, due to the fact that the ionomer layer is thin and the film is made of emulsion, the tension applied in the MD direction during processing such as bag processing causes the voids in the paper layer to increase, resulting in a decrease in barrier properties and oil resistance. Sometimes. In order to prevent this, it is necessary to control the tensile strength of the packaging paper in the MD direction to 3.5 kN/m or more.

In addition, the provision of the ionomer layer causes the wrapping paper to curl significantly, which may result in poor suitability for bag processing, leading to paper feeding troubles and poor adhesion in bag processing machines. The thinner the paper, the larger the curl. Due to the presence of the layer containing the water-soluble resin on the side opposite to the heat-sealing layer, curling is reduced and even thin paper can be stably processed into bags. In addition, the curl stability over time is also excellent.

Ionomer is a general term for synthetic resins in which macromolecules are aggregated by utilizing the cohesive force of metal ions, and is a resin in which acrylic acid or methacrylic acid is combined with ethylene or the like. Ionomers are produced by intermolecular bonding of acrylic polymers and ethylene by adding metal cations such as sodium and zinc.

A preferred method for producing the packaging paper in the present invention is a method of coating an ionomer emulsion and drying to form the heat seal layer. That is, the manufacturing method of the present invention manufactures packaging paper having at least one heat seal layer on at least one side of a paper substrate containing an oil-resistant agent and having a tensile strength in the MD direction of 3.5 kN/m or more. A method for producing packaging paper, characterized in that a coating liquid containing an ionomer emulsion is applied as a heat seal layer in a coating amount of 1 to 10 g/m ² . In particular, by using a water-based ionomer emulsion, it is possible to control the amount of coating to be low, and VOC emissions are eliminated, which is friendly to the global environment. The heat seal strength (heat sealability) is the quality most strongly required for container packaging base paper.

According to the present invention, it is possible to reduce the amount of plastic used and to manufacture packaging paper having excellent oil resistance (oil repellency) and heat sealability. Even if these paper container products are released into the natural world, the amount of residual plastic can be minimized and the problem of plastic waste can be reduced. In addition, the wrapping paper in the present invention is processed into general packaging containers such as bags, food cups such as ice cream, beverage cups such as coffee, food containers such as hot snacks, and trays, boxes, cases, vessels, envelopes, etc. It is possible.

Next, the present invention will be described in detail with reference to embodiments, but the present invention should not be construed as being limited to these descriptions. Various modifications may be made to the embodiments as long as the effects of the present invention are achieved.

The ionomer as used in the present invention is a general term for synthetic resins in which macromolecules are aggregated by utilizing the cohesive force of metal ions. Acrylic acid or methacrylic acid is combined with ethylene or the like. That is, metal salts of ethylene/methacrylic acid copolymers, metal salts of ethylene/acrylic copolymers, metal salts of ethylene/urethane copolymers, metal salts of ethylene/fluoropolymer copolymers, etc. All are called ionomers. Salt-forming metals are, for example, sodium, potassium, calcium, magnesium, zinc, and the like. In the present invention, the ionomer is preferably a metal salt of an ethylene/methacrylic acid copolymer. It is because it is excellent in heat-sealing property with a low coating weight.

Moreover, in the present invention, the heat seal layer is preferably formed by applying an ionomer emulsion and drying it. It is possible to control the coating amount of the heat seal layer to be low. Furthermore, when the emulsion is a water-based emulsion, VOC emissions are eliminated and the load on the natural environment can be reduced. The coating amount of the heat seal layer is 1 to 10 g/m ² in terms of solid content per one side of the paper substrate. If it is less than 1 g/m ² , the heat seal strength will be low and the adhesiveness will be weak. If it exceeds 10 g/m ² , the quality is excessive and the plastic reduction effect is reduced. Also, the curl becomes larger. More preferably 1 to 5 g/m ² . Although the heat-sealing layer may have pinholes invisible to the naked eye, the heat-sealing property is not adversely affected if the pinholes are small enough. A leveling agent for preventing pinholes may be added to the heat-sealing layer coating solution as long as the effects of the present invention are not impaired. Furthermore, it is preferable that the ionomer emulsion is of a self-emulsification-modified type because the thin film of the heat seal layer becomes uniform. In addition, the said heat-seal layer may have two or more layers.

Moreover, in the present invention, it is preferable to have a layer containing a water-soluble resin on the side opposite to the heat seal layer. Moreover, it is preferable that the layer is composed only of a water-soluble resin and does not contain other components. Even thin paper such as wrapping paper can be made less curled, and troubles in bag processing can be reduced. The coating amount of the layer containing the water-soluble resin is preferably 0.05 to 5 g/m ² , for example 0.4 to 3 g/m ² . If it is less than 0.05 g/m ² , the effect of suppressing curling may be inferior, and if it exceeds 5 g/m ² , curl may be increased. Examples of water-soluble resins usable in the present invention include starch, polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), gelatin, casein, soybean protein and the like. Note that there may be two or more layers containing the water-soluble resin.

Further, in the present invention, the oil-resistant agent contained in the paper base material is preferably a fluorine-based oil-resistant agent, and further contains a perfluoroalkyl group, and further contains a perfluoroalkyl group in a side chain. It is preferable to use a copolymer as a main component. It is because it is more excellent in oil resistance (oil repellency). Furthermore, the oil-resistant agent mainly composed of a perfluoroalkyl group-containing copolymer that does not contain PFOA (perfluorooctanoic acid), PFOA-related substances, and their precursor substances, which are said to accumulate in the body, is environmentally friendly. It is preferable from the aspect of reduction and safety. Examples of such products include the Asahi Guard E series manufactured by AGC and the Unidyne series manufactured by Daikin. Oil resistant agents other than those described above include acrylic resins, urethane resins, paraffin wax compounds, and the like.

Furthermore, it is preferable that the heat seal layer does not contain an inorganic pigment. Excellent heat seal strength. In addition, the amount of coating can be reduced, and the amount of resin can also be reduced.

The pulp fiber used for the paper base material of the paper base material is chemical pulp such as LBKP (broadleaf bleached kraft pulp), NBKP (softwood bleached kraft pulp), GP (groundwood pulp), PGW (pressurized groundwood pulp), RMP ( refiner mechanical pulp), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), CMP (chemi-mechanical pulp), CGP (chemigrind pulp), DIP (deinked pulp), unbleached pulp, etc. Wood pulp and non-wood pulp such as kenaf, bagasse, bamboo and cotton. These can be used alone or mixed in any ratio. In addition, synthetic fibers can be further blended within a range that does not impair the intended effects of the present invention. From the viewpoint of environmental conservation, ECF (Elemental Chlorine Free) pulp, TCF (Total Chlorine Free) pulp, waste paper pulp, and pulp obtained from planted trees are preferred. Also, for example, an appropriate freeness of pulp is 200 to 700 ml CSF, preferably 450 to 600 ml CSF, in terms of Canadian standard freeness (JIS P 8121: 1995 "Pulp freeness test method"). is. In addition, unbleached pulp is preferred in the present invention because it has a low environmental load in the sense that bleaching chemicals are not used in large quantities. In addition, unbleached paper pulp is preferable because it has a natural color and is easy on the eyes.

In addition, in order to increase the tensile strength in the MD direction to 3.5 kN / m or more, add softwood pulp to the paper stock, increase the amount of paper strength enhancer, lower the freeness value, and raise the drying temperature after coating. Measures such as increasing the strength of the resin coating are effective. It is preferable that 5 parts by mass or more of the softwood pulp is blended. More preferably, 10 parts or more, for example, 90 to 100 parts by mass of softwood pulp is used in the total pulp. Specifically, for example, pulp containing 90 to 100 parts by mass of softwood unbleached kraft pulp having a Canadian standard freeness of 480 to 560 mlcsf can be used.

Moreover, a filler may be added to the paper base material of the paper base material. For example, light calcium carbonate, ground calcium carbonate, talc, clay, kaolin, calcined clay, titanium dioxide, aluminum hydroxide can be used. The content of the filler in the paper substrate is, for example, 1 to 30 parts by weight with respect to 100 parts by weight of dry pulp.

In the paper base of the paper base according to the present embodiment, in addition to pulp and filler, internal sizing agents, internal strength agents such as wet strength agents, bulking agents, retention improvers, and drainage Various auxiliaries such as improvers, coloring dyes, coloring pigments, fluorescent whitening agents, fluorescent decolorizing agents, and pitch control agents can be suitably blended according to each product. Various known sizing agents can be used as the internal sizing agent, and are not particularly limited, and examples thereof include a neutral rosin sizing agent, a strong rosin sizing agent, an acidic rosin sizing agent, a weakly acidic rosin sizing agent, AKD, and ASA. For example, 0.05 to 2 parts by mass of internal sizing agent can be used with respect to 100 parts by mass of pulp. As the internal paper strength enhancer, conventionally known paper strength enhancers can be used. is. For example, 0.05 to 2 parts by mass of starch-based paper strength enhancer can be used with respect to 100 parts by mass of pulp.

There are no particular restrictions on the method for making the paper substrate of the paper substrate, and fourdrinier paper machine, fourdrinier multi-layer paper machine, cylinder paper machine, multi-layer cylinder paper machine, fourdrinier cylinder combi multi-layer paper machine. machine, twin wire paper machine, etc. Further, in the present invention, the paper substrate may be a single-layer paper, a multi-layer paper, or a multi-layer pasted product.

A surface sizing liquid may be applied to the paper substrate obtained by the papermaking method according to the present embodiment. Also, it may be size-pressed. Examples of the surface sizing liquid include known water-soluble polymers such as starch, polyvinyl alcohol and polyacrylamide, but the liquid is not particularly limited. From the viewpoint of oil resistance (oil repellency), it is preferable to add the oil resistance agent to the surface size liquid. The paper layer can be efficiently impregnated with the oil resistant agent. The basis weight of the paper substrate is not particularly limited, but is, for example, 10 to 500 g/m ² . It is also possible to use a sizing liquid in which the water-soluble polymer and the oil-resistant agent are mixed. Considering the tensile strength, it is preferably 20 g/m ² or more. It is preferably 25 g/m ² or more, for example, 25 g/m ² to 32 g/m ² .

In the present invention, in addition to the heat seal layer, one or more coating layers may be provided between the heat seal layer and the base material on at least one side of the paper base material. Materials that can be used in the coating layer are described below.

In the present embodiment, the white pigment used in the coating layer contains one or more known pigments used in general printing paper, such as calcium carbonate (heavy calcium carbonate, light calcium carbonate, etc.). , kaolin (including clay), calcined clay, talc, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide, zinc oxide, zinc sulfate, zinc carbonate, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous earth, aluminum hydroxide, water Inorganic pigments such as magnesium oxide, acryl, styrene, vinyl chloride, nylon itself, and organic pigments obtained by copolymerizing these (so-called plastic pigments) can be mentioned.

As a binder for the coating layer, starches such as butadiene-based copolymer latex, cross-linking agent-modified starch, oxidized starch, enzyme-modified starch, esterified starch, etherified starch, cationic starch, amphoteric starch, gelatin, casein, soybean. Examples include proteins, water-soluble polymers such as polyvinyl alcohol, and synthetic resins such as vinyl acetate, ethylene vinyl acetate, polyurethane resins, acrylic resins, polyester resins, and polyamide resins.

Although the total amount of the binder in the coating layer is not particularly limited, it is preferably 5 to 50 parts by weight, 6 to 45 parts by weight, for example, 7 to 40 parts by weight, based on 100 parts by weight of all pigments. is more preferable. If the amount is less than 5 parts by mass, the coating layer may fall off during container packaging processing, and if it exceeds 50 parts by mass, pinholes are likely to occur during coating of the heat seal layer, resulting in variations in heat seal strength. easily occur. However, if pinholes are likely to occur, a leveling agent may be added to the heat seal layer coating solution. As the leveling agent, it is preferable to use a surfactant or alcohol. Examples of surfactants include surfactants for food additives, and examples of alcohols include ethanol and isopropyl alcohol.

Further, in the present invention, in order to uniformly coat the heat seal layer, a known calender such as super calender, gloss calender, shoe nip calender, soft calender, etc. is applied to the paper substrate before the heat seal layer is coated. Calendering can be performed by a calendering device. In addition, processing conditions such as the form of a pressurizing device, the number of pressurizing nips, and temperature conditions during calendering can be adjusted as appropriate.

In addition, the coating layer may optionally contain various auxiliary agents such as viscosity modifiers, softeners, glossing agents, water resistance agents, dispersants, flow modifiers, ultraviolet absorbers, stabilizers, antistatic agents, Agents, cross-linking agents, sizing agents, fluorescent whitening agents, colorants, pH adjusters, antifoaming agents, plasticizers, and preservatives can be added as necessary.

A method for applying the coating layer and the heat seal layer is not particularly limited, and a generally used coating apparatus is used. Air knife coater, blade coater, gravure coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, Champlex coater, metering blade type size press coater, short dwell coater, spray Various known coating devices such as a coater, gate roll coater and lip coater can be used.

The coating amount of the coating layer is not particularly limited, but is, for example, 2 to 40 g/m ² in terms of solid content per side of the paper substrate. However, in the present invention, in order to reduce the coating amount of the resin, the coating layer is not particularly necessary, or the coating amount is preferably 2 to 10 g/m ² in terms of solid content.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In addition, "parts" and "%" in the examples indicate "mass parts" and "mass%", respectively, unless otherwise specified. The number of parts to be added is a value in terms of solid content.

(Example 1)
(Preparation of paper substrate)
100 parts of softwood unbleached kraft pulp with a Canadian standard freeness of 520 mlcsf, 0.2 parts of cationic starch (trade name: Neotac 30T, manufactured by Nihon Shokuhin Kako Co., Ltd.), neutral rosin sizing agent (trade name: CC167, Seiko PMC) A stock was prepared by adding water to 0.1 part of the product, and using a fourdrinier multi-cylinder paper machine, a base paper having a basis weight of 28 g/m ² was produced. This base paper was size-pressed with an oil-resistant agent (trade name: Asahi Guard E Series, AG-E060, manufactured by AGC Co., Ltd.) whose main component is a copolymer composed of a perfluoroalkyl group-containing compound. It was coated so as to be 2 g/m ² and dried to obtain a paper substrate of 30 g/m ² .

(Preparation of wrapping paper)
On one side of the paper substrate obtained above, an aqueous ionomer emulsion (trade name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene/methacrylic acid copolymer, self-emulsifying emulsion, microtrack method An average particle size of 0.5 μm) was coated on the heat seal layer using an air knife coater so that the dry coating amount was 4.8 g / m ² , and starch (trade name: : MS3800, manufactured by Nihon Shokuhin Kako Co., Ltd.) A 3% aqueous solution was coated using an air knife coater so as to give a dry coating amount of 0.8 g/m ² and dried to prepare wrapping paper.

(Example 2)
A wrapping paper was prepared in the same manner as in Example 1, except that the oil resistant agent was changed to an acrylic oil resistant agent (trade name: Saibinol EK-61, manufactured by Saiden Chemical Co., Ltd.).

(Example 3)
A wrapping paper was prepared in the same manner as in Example 1, except that the oil-resistant agent was changed to a urethane-based oil-resistant agent (trade name: Hydran WLI-603, manufactured by DIC Corporation).

(Example 4)
A wrapping paper was produced in the same manner as in Example 1, except that the coating weight of the heat seal layer was changed to 2 g/m ² .

(Example 5)
A wrapping paper was produced in the same manner as in Example 1, except that the coating weight of the heat seal layer was changed to 10 g/m ² .

(Example 6)
A wrapping paper was produced in the same manner as in Example 1, except that the coating weight of the heat seal layer was changed to 15 g/m ² .

(Example 7)
A wrapping paper was produced in the same manner as in Example 1, except that the pulp was changed to 5 parts of bleached softwood kraft pulp and 95 parts of bleached hardwood kraft pulp.

(Example 8)
On one side of the same paper substrate as in Example 1, an aqueous ionomer emulsion (trade name: Chemipearl S-300, manufactured by Mitsui Chemicals, composition: metal salt of ethylene/methacrylic acid copolymer, self-emulsifying emulsion, Microtrack Law average particle diameter 0.5 μm) was applied as the lower layer and upper layer of the heat seal layer using an air knife coater so that the dry coating amount was 3.8 g / m ² and 1 g / m ² respectively, and further the heat A 2% aqueous solution of polyvinyl alcohol (trade name: PVA117, manufactured by Kuraray Co., Ltd.) was applied to the opposite side of the sealing layer using an air knife coater so that the dry coating amount was 1.0 g/m ² , and dried. A wrapping paper was made.

(Example 9)
In Example 1, water-based ionomer emulsion (trade name: MYE-30ER, manufactured by Maruyoshi Chemical Co., Ltd., composition: metal salt of ethylene/methacrylic acid copolymer, self-emulsifying emulsion, microtrack method average particle size 0.2 μm) was applied as a heat seal layer using an air knife coater so that the dry coating amount was 4.8 g/m ² .

(Example 10)
In Example 7, packaging paper was produced in the same manner as in Example 1, except that the basis weight of the paper substrate was 100 g/m ² .

(Comparative example 1)
On one side of the same paper substrate as in Example 1, low-density polyethylene (Petrothene DLZ19A manufactured by Tosoh Corporation) was laminated to 20 g/m ² by an extrusion coater (melt extruder) to form a heat seal layer. was provided to prepare a wrapping paper. No water-soluble resin layer was provided on the opposite side of the heat seal layer.

(Comparative example 2)
Packaging paper was prepared in the same manner as in Example 1, except that the water-based ionomer emulsion was changed to a water-based polyethylene emulsion (SN Coat 289, manufactured by San Nopco).

(Comparative Example 3)
A wrapping paper was produced in the same manner as in Example 1, except that the basis weight of the paper substrate was 15 g/m ² .

(Comparative Example 4)
In Example 1, packaging paper was produced in the same manner as in Example 1, except that the paper base did not contain an oil resistant agent.

The obtained packaging paper was evaluated by the method shown below. Table 1 shows the results obtained.

(1) Heat-sealing strength The resulting packaging paper was cut into two sheets of 8 mm wide and 15 cm long, the heat-sealed layers were superimposed, and a heat-sealing device (manufactured by Palmec, model number: PTS-100) was used. , under certain conditions (adhesion width: 4 mm, temperature: 180°C, pressure: 0.4 MPa, pressing time: 0.5 seconds, pitch: 4 mm). Next, the peel strength of the heat-sealed sample was measured using a peel strength tester (manufactured by Shimadzu Corporation, model number: Autograph AGS-X) under constant conditions (peel rate: 100 mm/min, peel length: 10 cm). and the heat seal strength (gf/4 mm). A higher number is better.

(2) Oil repellency The obtained packaging paper is heat-sealed by a bag processing machine, and after bag molding, TAPPI T-559 cm-02 (oil-retentive paper kit method) is used to measure the oil repellency of the surface of the heat seal layer. evaluated. The higher the value (kit value), the higher the oil repellency. Moreover, the practical level has a value of 5 or more. If it is less than 4, the vegetable oil used for frying tends to permeate.

(3) Curl The packaging paper was cut into a size of 30 cm x 30 cm, and the size of the curl was visually determined as follows.
⊚: Flat with no curl at all.
◯: Slightly curled, but to the extent that processing trouble does not occur with a bag processing machine.
x: Curl is large, and trouble occurs during processing with a bag processing machine.

(4) Tensile strength The tensile strength of the obtained packaging paper in the MD direction was measured according to JIS P8113:2006 "Paper and paperboard - Test method for tensile properties". Autograph AGS-X (manufactured by Shimadzu Corporation) was used for the tensile test.

As is clear from Table 1, in Examples 1 to 10, although the coating amount of the heat seal layer was significantly reduced compared to Comparative Example 1, the heat seal strength was equal to or higher than that of Comparative Example 1, and the oil resistance was improved. was at a practical level. Moreover, compared with Comparative Example 2, the heat seal strength was clearly superior. Moreover, compared with Comparative Examples 3 and 4, the oil resistance was clearly superior. As described above, the experimental results show that, according to the present invention, the amount of resin coating can be significantly reduced compared to the conventional technology that uses polyethylene laminate, contributing to the reduction of plastic waste while improving oil resistance and heat resistance. It is possible to provide packaging paper with excellent sealing properties.

Claims (5)

A packaging paper having at least one heat-seal layer on at least one side of a paper substrate containing an oil-resistant agent, wherein the resin of the heat-seal layer is an ionomer, and the tensile strength in the MD direction is 3.5 kN/m or more. and the basis weight of the paper substrate is 20 g/m ² or more ,
A packaging paper characterized in that the pulp used for the paper substrate is a pulp containing 90 to 100 parts by mass of softwood unbleached kraft pulp having a Canadian standard freeness of 480 to 560 mlcsf. 2. The packaging paper according to claim 1, further comprising a layer containing a water-soluble resin on the opposite side of said heat seal layer. 3. The wrapping paper according to claim 1, wherein the oil-resistant agent is mainly composed of a copolymer containing a perfluoroalkyl group. A packaging paper having at least one heat-sealable layer on at least one side of a paper substrate containing an oil-resistant agent and having a basis weight of 20 g/m ² or more, and having a tensile strength in the MD direction of 3.5 kN/m or more. In the manufacturing method , a paper substrate is prepared from pulp containing 90 to 100 parts by mass of softwood unbleached kraft pulp having a Canadian standard freeness of 480 to 560 mlcsf, and a coating liquid containing an ionomer emulsion is applied as a heat seal layer. is coated at 1 to 10 g/m ² . 5. The method of manufacturing packaging paper according to claim 4 , wherein the ionomer emulsion is a self-emulsifying emulsion.