JP7718006B2 - Greaseproof paper and heat-sealed greaseproof paper - Google Patents

Description

The present invention relates to grease-resistant paper and heat-sealable grease-resistant paper having a heat-sealable layer.

Greaseproof paper is paper that has the function of preventing the penetration of oil. Greaseproof paper is widely used, for example, as packaging material for ready-made meals such as fried chicken and other fried foods, and as bags for packing hamburgers, French fries, fried chicken, etc. at fast food restaurants, convenience stores, etc. Conventionally, the majority of greaseproof paper has been made by coating a paper base with a fluororesin-based oil-proofing agent such as a perfluorohydrocarbon acrylate or a perfluorohydrocarbon phosphate ester.
However, it has been confirmed that fluorine-based greaseproof paper coated with a fluorine resin-based greaseproofing agent generates perfluoroalcohols, which have a high environmental accumulation potential, when heated to 100 to 180°C. Furthermore, when greaseproof paper containing such fluorine resin-based greaseproofing agents is incinerated after use, fluorine compounds such as perfluorooctanoic acid and perfluorosulfonic acid are generated, raising concerns about adverse health effects on animals, including humans, and on the environment. Furthermore, since other low-molecular-weight fluorine compounds are generally difficult to decompose, greaseproof paper that does not use fluorine compounds is desired, especially for food packaging applications.

Greaseproof paper for food packaging must have oil-resistant properties, such as oil barrier properties that prevent oil from passing through the paper and leaking to the other side, and oil-penetration resistance that prevents oil from spreading across the surface of the paper and causing the paper to appear oily (discoloration of the soaked areas). Furthermore, greaseproof paper for food packaging must be such that the contents are difficult to see from the outside when used to package food, be free of harmful substances, and be recyclable (disintegratable) so that it can be reused as a resource.

Patent Document 1 proposes grease-resistant paper in which a water-soluble polymer is applied to a substrate made of natural papermaking fibers containing a filler. Patent Document 1 aims to achieve recyclability without using fluorine-based compounds, but provides the desired grease-resistant paper by providing a water-soluble polymer layer as an oil-resistant layer on a substrate with high air resistance obtained by highly beating natural papermaking fibers to a freeness of 85 to 90°SR.
Patent Document 2 proposes grease-resistant paper in which an oil-resistant layer consisting of a non-fluorine-based oil-resistant agent and polyethylene wax with an average particle size of 1 to 20 μm is applied to a paper substrate. Patent Document 2 proposes acrylic resin, starch, and polyvinyl alcohol as the non-fluorine-based oil-resistant agent, and provides grease-resistant paper that addresses the issues of operability and cost associated with applying these oil-resistant agents by setting the smoothness and air permeability of the paper substrate within specified ranges.
Patent Document 3 proposes a fluorine-free oil-resistant paper in which the raw materials for the paper base are hardwood pulp/softwood pulp (L/N ratio): 0/100 to 70/30 (mass ratio), the beating degree is 45°SR or higher, the density of the paper produced is 0.45 g/ ^cm3 to 0.75 g/ ^cm3 , and the Steckhide sizing degree is 5 seconds or higher, and this paper base is coated with a styrene-acrylic copolymer resin and paraffin wax in a blending ratio of 90:10 to 10:90 (mass ratio). Patent Document 3 explains that the styrene-acrylic copolymer resin provides film-forming properties to the oil-resistant layer, and the paraffin wax plays a role in improving oil resistance by being present in the voids in the paper base.

Patent Documents 4 and 5 propose oil-resistant paper that uses one or more of modified starch, amylose, and polyvinyl alcohol as an oil-resistant agent. The paper substrate is primarily made of pulp fibers, and Patent Document 4 uses an impregnation method to apply the oil-resistant layer, while Patent Document 5 uses a spray coating method between the layers of multi-layer paper. Neither document specifies the basis weight of the paper substrate, but the examples are carried out in a basis weight range of 200 to 300 g/ ^m2 or more.
Patent Document 6 proposes grease-resistant paper in which a paper substrate is coated with a polylactic acid resin and a polyvinyl alcohol resin and/or a starch compound in a ratio of 70:30 to 98:2 (dry weight ratio) at 3 g/ ^m2 or more and 20 g/ ^m2 or less. Patent Document 6 provides grease-resistant paper that has heat-sealing properties while also taking into consideration the prevention of the generation of harmful substances when burned and decomposition when released into the environment, by blending a biodegradable resin without using a fluorine-based compound in the oil-resistant layer.

Patent No. 4520138 Patent No. 5994455 Japanese Patent Application Laid-Open No. 2020-122250 Japanese Patent Application Laid-Open No. 2005-29943 Patent No. 4604466 Japanese Patent Application Laid-Open No. 2020-128616

An objective of the present invention is to provide grease-resistant paper that uses a non-fluorine-based grease-resistant agent. Another objective of the present invention is to provide grease-resistant paper that has uniform quality and little variation in oil resistance performance across a wide range of paper base weights.

The means for solving the problems of the present invention are as follows.
1. A paper substrate is impregnated with an oil-resistant paint containing a non-fluorine-based oil-resistant agent and a water-soluble polymer,
The paper base material has a basis weight of 20 g/m2 or ^more , contains 30% by weight or more of hardwood pulp as raw material pulp, with an average ratio (l/D) of lumen width (l) to fiber width (D) of 0.50 or less, and the pulp constituting the paper base material has a Schopper-Riegler freeness of 25°SR or more and 45°SR or less.
2. The amount of the oil-resistant paint applied is 1.3 g/ ^m2 or more in dry weight,
1. The greaseproof paper according to 1, wherein the impregnated surface has a Kit value of 2 or more as measured according to J. TAPPI No. 41:2000.
3. The oil-resistant paper according to 1. or 2., which is subjected to an oil resistance test using the irregular kit method and shows a change in opacity of 10% or less before and after contact with oil.
(Irregular kit method)
Rapeseed oil (first-class reagent) was used as the test liquid, and the test liquid was dropped onto a sample that had been conditioned for 10 hours in an environment of 23°C and 50% RH. After leaving the sample in an environment of 23°C and 50% RH for 3 hours, the rapeseed oil on the surface was wiped off. The rate of change in opacity was calculated from the opacity before contact with the oil using the following formula.
Opacity change rate={(O _B −O _A )/O _B }×100
_OB : Opacity before contact with oil _OA : Opacity after contact with oil 4. The greaseproof paper according to any one of 1 to 3, having a maceration freeness of 250 ml CSF or more and 500 ml CSF or less.
5. The oil-resistant paper according to any one of 1. to 4., wherein the water-soluble polymer contained in the oil-resistant paint is one or more selected from starch-based, acrylic-based, and polyvinyl alcohol-based resins.
6. The greaseproof paper according to any one of 1. to 5., having a tensile strength of 1.5 kN/m or more.
7. A heat-sealable grease-resistant paper having a heat-seal layer on at least one surface of the grease-resistant paper according to any one of 1. to 6.

The grease-resistant paper of the present invention does not use a fluororesin-based oil-proofing agent, thereby reducing adverse effects on health and the environment. The paper base material used in the grease-resistant paper of the present invention is suitable for non-fluorine-based oil-proofing agents, and by applying an oil-resistant layer containing a non-fluorine-based oil-proofing agent, such as a synthetic polymer or natural polymer that has been proposed as an alternative to fluororesin-based oil-proofing agents, the paper surface exhibits uniform oil resistance and can efficiently exhibit the oil-resistant properties of various non-fluorine-based oil-proofing agents.

Greaseproof paper
The oil-resistant paper of the present invention has a paper base impregnated with an oil-resistant paint containing a non-fluorinated oil-proofing agent and a water-soluble polymer. Whether or not the paper is impregnated with the paint can be determined by observing the cross section with a microscope or the like.
The paper base material used in the present invention contains 30% by weight or more of hardwood pulp having an average ratio (l/D) of lumen width (l) to fiber width (D) of 0.50 or less. Hereinafter, in this specification, the ratio (l/D) of lumen width (l) to fiber width (D) will also be simply referred to as "l/D".

Hardwood pulp fibers have an internal cavity called a lumen. l/D is a value that indicates the ratio of lumen width to fiber thickness, with smaller values indicating smaller lumens and thicker fiber walls. Pulp l/D can be measured using the following procedure.
1. Dilute the pulp suspension to a concentration of 0.05%.
2. Using a dropper tube, drop the diluted solution onto a clean glass slide, disperse the fibers evenly using a dissecting needle if necessary, and allow to dry.
3. Drop three drops of staining solution C onto the fibers dispersed on the slide glass, place a cover glass on top taking care not to trap air bubbles, remove excess staining solution with blotting paper, and prepare a preparation.
4. Observe the preparation using an optical microscope, move the preparation horizontally or vertically on a movable stage, measure the fiber width (D) and lumen width (l) at the center of the pulp lengthwise, and calculate l/D.
When preparing a paper stock, the l/D of 100 or more pulps of the pulp to be blended is determined by the above method, and the average value can be used as the l/D of the pulp. From the paper made, the paper is disintegrated in the same manner as in the preparation of a slurry for measuring the disintegration freeness of the paper, and 200 or more pulps are distinguished using a dye solution that produces different colors depending on the tree species, etc., and the l/D is determined by the above method, whereby the blending amount of hardwood pulp and the l/D of the pulp can be determined.

(Hardwood pulp with l/D of 0.50 or less)
Hardwood pulp with an l/D ratio of 0.50 or less forms low-density sheets with thick fiber walls that are resistant to crushing. Although the degree of this varies depending on the wood species and other pulp blends, using a stock containing 30% by weight or more of hardwood pulp with an average lumen width (l) to fiber width (D) ratio (l/D) of 0.50 or less as the raw pulp material allows for a low density, i.e., highly breathable, paper base material to be obtained even after the beating treatment required to obtain the paper strength required in the manufacturing process. The high breathability of the paper base material allows the oil-resistant paint to be quickly impregnated and uniformly applied throughout the entire paper base material, thereby reducing unevenness in the oil resistance of the resulting grease-resistant paper. Hardwood pulp with an l/D ratio of 0.50 or less preferably has an l/D of 0.45 or less, and more preferably 0.40 or less.

Hardwood pulp with an l/D of 0.50 or less is not particularly limited and includes mechanical pulp (MP), thermomechanical pulp (TMP), sulfite pulp (SP), kraft pulp (KP), and their bleached pulp (BP) and unbleached pulp (UP). One or a mixture of two or more of these can be used. Among these, kraft pulp (KP), which has excellent strength, is preferred.

(Other pulps)
Other pulps that can be combined with hardwood pulp having an l/D of 0.50 or less include, without particular limitation, hardwood pulp having an l/D of more than 0.50, refined pulp such as softwood pulp, regenerated cellulose, mercerized pulp, dissolving pulp, and non-wood pulp such as bast fibers such as flax, kenaf, paper mulberry, and mitsumata, hard fibers such as bagasse, bamboo, and esparto, seed fibers such as cotton linters, and leaf vein fibers such as Manila hemp and sisal. The pulp that constitutes the paper base material may be a mixture of hardwood pulp and other pulp and then beaten, or the hardwood pulp and other pulp may be beaten separately and then mixed.
The paper base material of the present invention contains 30% by weight or more, preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 60% by weight or more of hardwood pulp having an l/D of 0.50 or less relative to the total pulp used as the papermaking raw material.

The paper base material of the present invention has a Shopper-Riegler freeness of 25°SR or more and 45°SR or less for the pulp constituting the paper base material. The "pulp constituting the paper base material" refers to all pulp contained in the paper base material. Paper base materials with a Shopper-Riegler freeness of less than 25°SR have low paper base strength, which can lead to breakage of the paper base material and significant deterioration of the paper base material's texture when impregnated with an oil-resistant coating, resulting in uneven oil resistance. Furthermore, a Shopper-Riegler freeness of more than 45°SR can lead to uneven absorption of the paper base material when impregnated with an oil-resistant coating, resulting in uneven oil resistance of the greaseproof paper. The Shopper-Riegler freeness is preferably 27°SR or more and 40°SR or less, and more preferably 27°SR or more and 35°SR or less.

(Other additives)
Other additives may be added to the paper base material as needed, such as fillers, pigments, sizing agents, coagulants, fluorescent whitening agents, aluminum sulfate, retention aids, drainage aids, dry strength agents, wet strength agents, coloring dyes, coloring pigments, and waterproofing agents, which may be used alone or in combination.

(Manufacturing method)
The paper substrate can be produced using a method known in the art for papermaking, such as a Fourdrinier paper machine, a cylinder paper machine, a short wire paper machine, a twin-wire paper machine, an on-top hybrid paper machine, or a gap former machine.

The basis weight of the paper substrate is 20 g/ ^m2 or more. If the basis weight is less than 20 g/ ^m2 , the tensile strength will be weak, and the paper substrate may break during papermaking and oil-resistant layer processing. In addition, the lower the basis weight of the substrate, the more likely it is that uneven adhesion of the oil-resistant agent will occur, which is thought to be due to the influence of the pulp fiber formation, causing uneven oil resistance. The basis weight of the paper substrate is not particularly limited as long as it is 20 g/m2 or ^more , but can be, for example, 30 g/ ^m2 or more and 400 g/ ^m2 or less.

From the perspective of oil-resistant agent penetration, it is preferable that the paper substrate have an Oken air resistance of 100 seconds or less. The Oken air resistance of the paper substrate is more preferably 50 seconds or less, even more preferably 30 seconds or less, and even more preferably 20 seconds or less. It is preferable that the Oken air resistance of the paper substrate is 2 seconds or more.

Oil-resistant paint The oil-resistant paint used in the present invention contains a non-fluorine-based oil-resistant agent and a water-soluble polymer, but does not contain a fluorine-based oil-resistant agent. Furthermore, the paint containing a non-fluorine-based oil-resistant agent preferably does not contain a low-molecular-weight fluorine compound, and more preferably does not contain a fluorine-based compound.

(non-fluorine-based oil resistant agent)
Non-fluorine-based oil-proofing agents can be used without particular limitation, and examples thereof include natural polymers such as starch, cellulose derivatives, gelatin, casein, and soybean protein, and synthetic polymers such as polyvinyl alcohol, polyisoprene, polymers or copolymers of chloroprene, polydiene, polyalkene, polymers or copolymers of vinyl monomers, synthetic rubber latex, polyurethane resins, polyester resins, polyamide resins, olefin-maleic anhydride resins, silicone resins, acrylic resins, melamine resins, fatty acid ester resins, vegetable waxes, animal waxes, mineral waxes, and petroleum waxes, and these can be used alone or in combination of two or more. Among these, acrylic resins and fatty acid ester resins are preferred from the viewpoint of oil resistance, and acrylic resins are more preferred from the viewpoint of oil penetration prevention.

(Water-soluble polymer)
The water-soluble polymer acts as a hydrophilic binder that fixes the non-fluorine-based oil-proofing agent to the pulp fibers of the paper substrate without inhibiting the performance of the oil-proofing agent. Examples of water-soluble polymers include anionic polyelectrolyte salts such as carboxyalkylcellulose salts, alginates, pectinates, polyacrylates, polymethacrylates, carboxyalkylated starch, phosphated starch, anionic modified polyvinyl alcohol resins, and anionic polyacrylamides, nonelectrolytes such as methylcellulose, hydroxyalkylcellulose, polyvinyl alcohol resins, polyvinylpyrrolidone, polyalkylene oxides, polyvinyl alkyl ethers, hydroxyalkylated starch, oxidized starch, and pregelatinized starch, water-soluble polysaccharides such as guar gum, tolanthus gum, xanthan gum, gum arabic, carrageenan, galactomannan, pullulan, dextran, and dextrin, and water-soluble proteins such as gelatin and casein. These may be used alone or in combination of two or more. Among these, from the viewpoints of processability, oil resistance, and material cost, starch-based materials (carboxyalkylated starch, phosphated starch, hydroxyalkylated starch, oxidized starch, pregelatinized starch), acrylic resins, and polyvinyl alcohol-based resins are preferred, with acrylic resins being more preferred due to their excellent oil resistance. Furthermore, it is preferable that the water-soluble polymer has a neutral charge or the same charge as the non-fluorinated oil-proofing agent. However, when an aqueous solution of 10% by weight of the non-fluorinated oil-proofing agent and 10% by weight of the water-soluble polymer is prepared, those that do not form a uniform aqueous phase (for example, due to phase separation, aggregation, etc.) cannot be used.

From the viewpoint of material costs, the oil-resistant paint preferably contains 5 to 100 parts by weight of a non-fluorinated oil-resistant agent per 100 parts by weight of the water-soluble polymer, more preferably 10 parts by weight or more, even more preferably 15 parts by weight or more, and more preferably 70 parts by weight or less, even more preferably 50 parts by weight or less.
In addition to the non-fluorine-based oil-resistant agent and the water-soluble polymer, the oil-resistant paint may also contain additives such as surfactants, antifoaming agents, surface sizing agents, paper strength agents, water retention agents, thickeners, release agents, and anti-slip agents, as long as the additives do not impair the performance of the paint.

The oil-resistant paper of the present invention preferably has an oil resistance of 2 or more on the impregnated surface in terms of kit value as defined in J TAPPI No. 41:2000. If the oil resistance is less than 2, oil from the food stored inside may seep out, causing the outer surface to become stained with oil. This kit value may be 3 or more, 4 or more, or 5 or more. Here, the kit value is expressed as a number from 1 to 12, with a higher number indicating better oil resistance (oil barrier properties). Even if the kit value is low, the oil-resistant paper of the present invention has excellent oil penetration prevention properties, is resistant to oil penetration, and is resistant to discoloration. The upper limit of the kit value of the oil-resistant paper of the present invention can be, for example, 7 or less, 6 or less, or 5 or less.
In order to prevent paper tearing during papermaking, etc., the grease-resistant paper of the present invention preferably has a tensile strength measured in accordance with JIS P8113:2006 of 1.5 kN/m or more, more preferably 1.7 kN/m or more, and even more preferably 2.0 kN/m or more.

(Impregnation method)
The method of impregnation of the oil-resistant paint is not particularly limited, and known impregnation methods and coating methods can be used. Specifically, an appropriate method can be selected from impregnation coating using a mangle, size press, etc., and surface coating using a gate roll coater, blade coater, bar coater, champlex coater, gravure coater, die coater, curtain coater, air knife coater, spray coater, etc. Among these, size press is preferred because it has excellent paint impregnation properties.
The oil-resistant paint may be either a water-based paint using a solvent such as water or a solvent-based paint using a solvent such as an organic solvent, but from the viewpoint of safety and hygiene, a water-based paint is preferred.

To obtain oil-resistant paper with a kit value of 2 or more, the amount of oil-resistant paint applied is preferably 1.3 g/m2 or ^more in dry weight, more preferably 1.4 g/ ^m2 or more, and even more preferably 1.5 g/m2 or ^more . There is no particular upper limit to the amount of oil-resistant paint applied, but for example, a dry weight of 10 g/m2 or ^less is preferred. Even if the amount of oil-resistant paint applied exceeds 10 g/ ^m2 in dry weight, there is almost no further improvement in oil resistance, and the cost increases.
The amount of non-fluorine-based oil-resistant agent adhered varies depending on the proportion of the non-fluorine-based oil-resistant agent in the oil-resistant paint, but the amount of non-fluorine-based oil-resistant agent adhered is preferably 0.2 g/ ^m2 or more in dry weight, more preferably 0.25 g/m2 or ^more , and even more preferably 0.3 g/ ^m2 or more. There is no particular upper limit to the amount of non-fluorine-based oil-resistant agent adhered, but for example, a dry weight of 5 g/m2 ^or less is preferred. Even if the amount of oil-resistant paint adhered exceeds 5 g/ ^m2 in dry weight, there is almost no further improvement in oil resistance, and the cost becomes high.

The grease-resistant paper of the present invention is preferably subjected to an oil resistance test using the following irregular kit method, and the rate of change in opacity before and after contact with oil is preferably 10% or less. When oil penetrates into the grease-resistant paper, light scattering decreases, resulting in a decrease in opacity (becoming transparent). Therefore, the smaller the value of the rate of change in opacity, the better the oil penetration prevention properties. For the grease-resistant paper of the present invention, this rate of change in opacity is more preferably 9% or less, even more preferably 8% or less, even more preferably 7% or less, even more preferably 6% or less, even more preferably 5% or less, and even more preferably 4% or less.
(Atypical kit method)
Rapeseed oil (first-class reagent) was used as the test liquid, and the test liquid was dropped onto a sample that had been conditioned for 10 hours in an environment of 23°C and 50% RH. After leaving the sample in an environment of 23°C and 50% RH for 3 hours, the rapeseed oil on the surface was wiped off. The rate of change in opacity was calculated from the opacity before contact with the oil using the following formula.
Opacity change rate={(O _B −O _A )/O _B }×100
_OB : Opacity before contact with oil _OA : Opacity after contact with oil

The grease-resistant paper of the present invention preferably has a remaced freeness of 250 ml CSF or more and 500 ml CSF or less. The remaced freeness is the Canadian standard freeness measured in accordance with JIS P8121-2:2012 after remacing the grease-resistant paper using the method specified in JIS P8220-1:2012. The remaced freeness is preferably 300 ml CSF or more and 450 ml CSF or less, and more preferably 350 ml CSF or more and 450 ml CSF or less.

"Heat-sealed oil-resistant paper"
The heat-sealable grease-resistant paper of the present invention has a heat-sealable layer on at least one side of the grease-resistant paper described above. The heat-sealable layer can be provided on both sides, but if provided on only one side, it is preferably provided on the processed surface impregnated with the oil-resistant paint. When applying a heat-sealing agent to the grease-resistant paper, the heat-sealing layer may not be applied uniformly in the case of grease-resistant paper with a high kit value due to the relationship between the wettability of the heat-sealing agent and the grease-resistant paper. Therefore, when producing heat-sealable grease-resistant paper, if the heat-sealing layer cannot be applied uniformly, it is necessary to adjust the viscosity and solvent composition of the heat-sealing agent coating solution.

(Heat seal layer)
The heat-seal layer is formed by applying a coating material containing a thermoplastic resin with heat-sealing properties to at least one surface of the greaseproof paper. The thermoplastic resin contained in the heat-seal layer may be any known resin without particular limitation, and examples thereof include polyethylene-based resins and polypropylene-based resins. Examples of polyethylene-based resins include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-vinyl acetate copolymer (EVA), carboxylic acid-modified polyethylene, ionomers, derivatives thereof, and mixtures thereof. Examples of polypropylene-based resins include polypropylene (PP) homopolymer, random polypropylene (random PP), block polypropylene (block PP), chlorinated polypropylene, carboxylic acid-modified polypropylene, derivatives thereof, and mixtures thereof. Among these, resins with a glass transition temperature of 100°C or less are preferably used. The thermoplastic resin preferably has a glass transition temperature of −20° C. or more and 85° C. or less, and a melting point of 70° C. or more and 140° C. or less. The glass transition temperature and melting point refer to the midpoint glass transition temperature and melting peak temperature, respectively, measured in accordance with JIS P7121:2012.

In addition to the thermoplastic resin, the heat seal layer may also contain surfactants, waxes, inorganic pigments, dispersants, thickeners, etc., as needed.
The heat seal layer preferably has a heat seal strength of 2.3 N/15 mm or more, more preferably 2.9 N/15 mm or more, as measured by the following method.
(Measurement conditions)
The heat-sealable surfaces of the heat-sealable greaseproof papers were brought into contact with each other and heat-sealed using a heat seal tester (TP-7018, manufactured by Tester Sangyo Co., Ltd.) at a pressure of 160°C, a pressure of 98 kPa, and a pressure time of 1 second.
After heat sealing, the sample was left to stand at 23°C and 50% RH for 10 minutes, and in this atmosphere, the sealed portion of the measurement sample was peeled off at a pulling rate of 300 mm/min using a Tensilon universal testing machine RTG-1210 (A&D Co., Ltd.), to determine the heat seal strength (N/15 mm).

The method for coating the heat seal layer is not particularly limited, and coating can be performed using known coating equipment and coating systems. Examples of coating equipment include blade coaters, bar coaters, air knife coaters, curtain coaters, spray coaters, roll coaters, reverse roll coaters, size press coaters, gate roll coaters, gravure coaters, die coaters, and blade coaters. Coating systems include water-based coatings using solvents such as water, and solvent-based coatings using solvents such as organic solvents. However, water-based coatings are preferred for their safety and environmental friendliness.

The amount of coating per side of the heat seal layer is not particularly limited, but is preferably 2.0 g/ ^m2 or more in dry weight, and more preferably 2.5 g/ ^m2 or more. If the amount of coating is less than 2.0 g/ ^m2 , it is difficult to form a heat seal layer of sufficient thickness, and sufficient heat seal strength may not be obtained. The higher the amount of coating per side of the heat seal layer, the better the heat seal strength tends to improve, but if it is too high, the energy cost and material cost for drying increase, so the dry weight is preferably 20 g/ ^m2 or less, and more preferably 10 g/m2 or ^less . The heat seal layer may be a single layer or may be composed of two or more layers. When the heat seal layer is composed of two or more layers, it is preferable that the total amount of coating of all coating layers be within the above range.

Greaseproof paper
Example 1
A papermaking stock was prepared by mixing softwood kraft pulp (NBKP) with l/D = 0.85 and hardwood kraft pulp (LBKP) with l/D = 0.34 at a ratio of 25% by weight/75% by weight, and beating the mixture to a freeness of 30°SR according to the Schopper-Riegler method. This papermaking stock was used to prepare a paper base material by hand-making to a dry basis weight of 40 g/ ^m2 .
An acrylic resin (Unidyne XP-8001, nonvolatile content 18%, Daikin Industries, Ltd.) was used as an oil-resistant agent, and starch 1 (Penford Gum 290, nonionic hydroxyethylated starch, manufactured by Incredion) which is a water-soluble polymer was mixed at a solids weight ratio of 30 parts by weight/100 parts by weight to prepare an oil-resistant paint with a solids concentration of 3.5%. This was impregnated and coated using a size press method, and dried at 100°C for 1 minute in a KRK rotary dryer (manufactured by Kumagaya Riki Kogyo Co., Ltd.) to obtain a sample.
The amount of the oil-resistant paint adhered was 2.0 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.5 g/m ² in dry weight.

Example 2
Samples were obtained in the same manner as in Example 1, except that the amount of oil-resistant paint applied was changed.
The amount of the oil-resistant paint adhered was 3.9 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.9 g/m ² in dry weight.
Example 3
A papermaking stock was prepared by beating LBKP with l/D = 0.34 so that the freeness according to the Schopper-Riegler method was 30°SR. This papermaking stock was used to prepare a paper substrate by hand-making so that the dry basis weight was 40 g/ ^m2 . The oil-resistant paint was impregnated and coated onto the paper substrate in the same manner as in Example 1 to obtain a sample.
The amount of the oil-resistant paint adhered was 2.5 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.6 g/m ² in dry weight.

Example 4
A 50% by weight mixture of NBKP (l/D = 0.85) and LBKP (l/D = 0.34) was beaten to a freeness of 30°SR by the Schopper-Riegler method to prepare a paper stock. This paper stock was then hand-made to a dry basis weight of 40 g/ ^m² .
An acrylic resin was used as an oil-resistant agent, and starch 2 (SK-100, anionic oxidized starch, manufactured by Nippon Cornstarch Co., Ltd.), a water-soluble polymer, was mixed at 30 parts by weight/100 parts by weight to prepare an oil-resistant paint with a concentration of 3.5%. This was impregnated and coated using a size press method, and dried at 100°C for 1 minute in a KRK rotary dryer (manufactured by Kumagaya Riki Kogyo Co., Ltd.) to obtain a sample.
The amount of the oil-resistant paint adhered was 1.5 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.3 g/m ² in dry weight.
Example 5
The paper substrate obtained in Example 4 was used. The oil-resistant paint used fatty acid ester resin 1 (BW200, non-volatile content 40%, manufactured by Riken Green Co., Ltd.) as an oil-resistant agent, and the water-soluble polymer and blending amounts were the same as in Example 4. The paper substrate was impregnated and coated to obtain a sample.
The amount of the oil-resistant paint adhered was 3.0 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.7 g/m ² in dry weight.

Example 6
The paper substrate obtained in Example 4 was used. The oil-resistant paint used fatty acid ester resin 2 (T-EF201, non-volatile content 30%, manufactured by Seiko PMC Corporation) as an oil-resistant agent, and the water-soluble polymer was impregnated and coated onto the paper substrate in the same amounts as in Example 4 to obtain a sample.
The amount of the oil-resistant paint adhered was 2.5 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.6 g/m ² in dry weight.
Example 7
The paper substrate used was the same as in Example 1. The oil-resistant paint was prepared in the same manner as in Example 4 and was impregnated and coated onto the paper substrate to obtain a sample.
The amount of the oil-resistant paint adhered was 1.9 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.4 g/m ² in dry weight.

(Example 8)
The paper substrate obtained in Example 1 was used. An acrylic resin was used as an oil-resistant agent, and a water-soluble polymer, polyvinyl alcohol (28-98, manufactured by Kuraray Co., Ltd.), was mixed at 30 parts by weight and 100 parts by weight to prepare an oil-resistant paint with a concentration of 3.5%. This was impregnation-coated using a size press method, and dried at 100°C for 1 minute in a KRK rotary dryer (manufactured by Kumagaya Riki Kogyo Co., Ltd.) to obtain a sample.
The amount of the oil-resistant paint adhered was 2.1 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.5 g/m ² in dry weight.
Example 9
A papermaking raw material was prepared in the same manner as in Example 4. A paper substrate was hand-made using this papermaking raw material so that the dry basis weight was 50 g/ ^m2 . The oil-resistant paint was impregnated and coated onto the paper substrate in the same manner as in Example 1 to obtain a sample.
The amount of the oil-resistant paint adhered was 2.2 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.5 g/m ² in dry weight.
Example 10
A papermaking raw material was prepared in the same manner as in Example 4. A paper substrate was hand-made using this papermaking raw material so that the dry basis weight was 102 g/ ^m2 . The oil-resistant paint was impregnated and coated onto the paper substrate in the same manner as in Example 1 to obtain a sample.
The amount of the oil-resistant paint adhered was 2.9 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.7 g/m ² in dry weight.

Example 14
A sample was obtained in the same manner as in Example 1, except that the solid weight ratio of the acrylic resin as the oil-resistant agent to the starch 1 was 10 parts by weight/100 parts by weight.
The amount of the oil-resistant paint adhered was 1.9 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.2 g/m ² in dry weight.
Example 15
A sample was obtained in the same manner as in Example 1, except that the solid weight ratio of the acrylic resin as the oil-resistant agent to the starch 1 was 40 parts by weight/100 parts by weight.
The amount of the oil-resistant paint adhered was 2.1 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.6 g/m ² in dry weight.

"Heat-sealed oil-resistant paper"
Example 11
A polyolefin resin (Zaixen AC, non-volatile content 30%, glass transition temperature 51°C, manufactured by Sumitomo Seika Chemicals Co., Ltd.) was applied as a heat sealing agent to the processed surface of the greaseproof paper produced in Example 2 using a bar coater to obtain a sample.
The coating weight of the heat seal layer was 2.6 g/m ² in dry weight.
Example 12
A heat sealing agent was applied to the processed surface of the greaseproof paper prepared in Example 10 in the same manner as in Example 11 to obtain a sample.
The adhesion amount of the heat seal layer was 7.1 g/m ² in dry weight.
Example 13
The same heat sealing agent was applied to the same greaseproof paper as in Example 12 to obtain a sample.
The coating weight of the heat seal layer was 3.6 g/m ² in dry weight.

(Comparative Example 1)
A 25% by weight/75% mixture of NBKP (l/D = 0.85) and LBKP (l/D = 0.55) was beaten to a freeness of 30°SR by the Schopper-Riegler method to prepare a papermaking raw material. This papermaking raw material was used to prepare a paper substrate by hand-making to a dry basis weight of 40 g/ ^m² . The oil-resistant paint was impregnated and coated in the same manner as in Example 2 to obtain a sample.
The amount of the oil-resistant paint adhered was 2.8 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.6 g/m ² in dry weight.
(Comparative Example 2)
A papermaking raw material was prepared by mixing NBKP (l/D = 0.85) and LBKP (l/D = 0.34) at a ratio of 80% by weight/20% by weight and beating the mixture to a freeness of 30°SR according to the Schopper-Riegler method. This papermaking raw material was used to prepare a paper substrate by hand-making to a dry basis weight of 40 g/ ^m² . The oil-resistant paint was impregnated and coated in the same manner as in Example 2 to obtain a sample.
The amount of the oil-resistant paint adhered was 2.2 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.5 g/m ² in dry weight.

(Comparative Example 3)
The paper substrate used was the one obtained in Example 4. Instead of the oil-resistant paint, a coating solution containing only starch 1, a water-soluble polymer, without blending any oil-resistant agent was prepared, and the coating was impregnation-coated using a size press method, followed by drying at 100°C for 1 minute in a KRK rotary dryer (manufactured by Kumagai Riki Kogyo Co., Ltd.) to obtain a sample.
The amount of the water-soluble polymer deposited was 1.7 g/m ² in dry weight.
(Comparative Example 4)
A papermaking raw material was prepared in the same manner as in Example 4. A paper substrate was hand-made using this papermaking raw material so that the dry basis weight was 15 g/ ^m2 . The oil-resistant paint was impregnated and coated in the same manner as in Example 2 to obtain a sample.
The amount of the oil-resistant paint adhered was 2.0 g/m ² in dry weight, and the amount of the non-fluorine-based oil-resistant agent adhered was 0.5 g/m ² in dry weight.

The obtained paper substrate, grease-resistant paper, and heat-sealable grease-resistant paper were evaluated as follows. The results for the grease-resistant paper are shown in Tables 1 and 2, and the results for the heat-sealable grease-resistant paper are shown in Table 3.
(Evaluation method)
- Freeness (Schopper Riegler)
Measurement was carried out in accordance with JIS P8121-1:2012.
Basis weight: Measured in accordance with JIS P8124:2011.
・Air permeability resistance (Ouken style)
The measurement was carried out in accordance with JIS P8117:2009 using an Oken-type air resistance smoothness measuring instrument (manufactured by Asahi Seiko Co., Ltd.).
Tensile strength was measured in accordance with JIS P8113:2006.

Disintegration freeness The greaseproof paper was disintegrated by the method specified in JIS P8220-1:2012, and the freeness was measured in accordance with JIS P8121-2:2012.
Oil barrier property and unevenness of oil barrier property According to "Paper and paperboard - Oil repellency test method - Kit method" described in J. TAPPI No. 41:2000, kit values were measured for five test pieces to evaluate the oil barrier property.
Furthermore, unevenness in oil barrier properties was evaluated using the liquid number with the highest kit number that did not soak into each of the five test pieces, according to the following evaluation criteria.
(Evaluation criteria for unevenness in oil barrier properties)
○: Three or more sheets have the same liquid number, and the difference in liquid number is within one point.
×: There are two or fewer sheets with the same liquid number, or the difference in liquid number is two or more points.

- Opacity change rate (irregular kit method)
Rapeseed oil (first-class reagent) was used as the test liquid, and the test liquid was dropped in a circle with a diameter of 5 cm or more onto greaseproof paper that had been conditioned for 10 hours in an environment of 23°C and 50% RH. After leaving it in an environment of 23°C and 50% RH for 3 hours, the rapeseed oil on the surface was wiped off.
The opacity of the area where the rapeseed oil was dropped was measured before and after contact with the oil using a spectrophotometer/color difference meter (PF7000, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS P8149:2000, and the rate of change in opacity was calculated based on the following formula.
Opacity change rate={(O _B −O _A )/O _B }×100
_OB : Opacity before contact with oil _OA : Opacity after contact with oil

Heat seal strength The heat seal surfaces of the heat sealable greaseproof papers to which a heat seal layer had been added were brought into contact with each other, and heat sealed using a heat seal tester (TP-7018, manufactured by Tester Sangyo Co., Ltd.) at a pressure of 160°C, a pressure of 98 kPa, and a pressure time of 1 second.
After heat sealing, the sample was left to stand at 23°C and 50% RH for 10 minutes, and in this atmosphere, the sealed portion of the measurement sample was peeled off at a pulling rate of 300 mm/min using a Tensilon universal testing machine RTG-1210 (A&D Co., Ltd.), to determine the heat seal strength (N/15 mm).

Results From Examples 1 to 3 and Comparative Examples 1 and 2, it was confirmed that oil-resistant paper whose paper base material contains 30% by weight or more of hardwood pulp with an average l/D of 0.50 or less as raw material pulp has little unevenness in oil resistance and can be coated with oil-resistant paint evenly.
Examples 4 to 6 and Comparative Example 3 confirmed that the specific paper substrate of the present invention can be uniformly impregnated with an oil-resistant paint and has excellent oil barrier properties, regardless of the type of non-fluorinated oil-proofing agent used. However, it was confirmed that acrylic non-fluorinated oil-proofing agents are superior in terms of preventing oil penetration.
From Examples 1, 7, and 8, it was confirmed that the specific paper substrate of the present invention can be uniformly coated with an oil-resistant paint and has excellent oil resistance, regardless of the type of water-soluble polymer.
Examples 9 and 10 and Comparative Example 4 confirmed that the oil-resistant paper of the present invention has practical oil resistance and tensile strength over a wide range of basis weights.
From Examples 1, 14 and 15, it was confirmed that oil resistance can be controlled by adjusting the ratio of the water-soluble polymer to the non-fluorinated oil-proofing agent.
From Examples 11 to 13, it was confirmed that the heat-sealable oil-resistant paper of the present invention, which is formed by coating a heat-seal layer on the oil-resistant paper, has practical oil resistance and heat-seal strength.

Claims (7)

The paper substrate is impregnated with an oil-resistant paint containing a non-fluorine-based oil-resistant agent and a water-soluble polymer,
The paper base material has a basis weight of 20 g/m2 or ^more , contains 30% by weight or more of hardwood pulp as raw material pulp, the ratio (l/D) of lumen width (l) to fiber width (D) being an average of 0.50 or less, and the Schopper-Riegler freeness of the pulp constituting the paper base material is 25°SR or more and 45°SR or less ,
The grease-resistant paper , wherein the non-fluorine-based oil-resistant agent contains an acrylic resin . The amount of the oil-resistant paint adhered is 1.3 g/m ² or more in dry weight,
2. The greaseproof paper according to claim 1, wherein the impregnated surface has a Kit value of 2 or more as measured according to J. TAPPI No. 41:2000. 2. The oil-resistant paper according to claim 1, wherein the change in opacity before and after contact with oil is 10% or less when the oil resistance test is carried out using the irregular kit method.
(Irregular kit method)
Rapeseed oil (first-class reagent) was used as the test liquid, and the test liquid was dropped onto a sample that had been conditioned for 10 hours in an environment of 23°C and 50% RH. After leaving the sample in an environment of 23°C and 50% RH for 3 hours, the rapeseed oil on the surface was wiped off. The rate of change in opacity was calculated from the opacity before contact with the oil using the following formula.
Opacity change rate = {(OB - OA) / OB} x 100
OB: Opacity before contact with oil OA: Opacity after contact with oil The greaseproof paper according to claim 1, having a maceration freeness of 250 ml CSF or more and 500 ml CSF or less. The oil-resistant paper according to claim 1, wherein the water-soluble polymer contained in the oil-resistant paint is one or more selected from starch-based, acrylic-based, and polyvinyl alcohol-based resins. The greaseproof paper according to claim 1, having a tensile strength of 1.5 kN/m or more. Heat-sealable greaseproof paper having a heat-seal layer on at least one side of the greaseproof paper described in any one of claims 1 to 6.