TWI861276B - Oil-resistant paper and method for producing oil-resistant paper - Google Patents

Abstract

The present invention provides an oil-resistant paper which satisfies the oil resistance and has no coating defects. As a solution, the oil-resistant paper is characterized in that: an oil-resistant layer is formed on at least one side of a base paper, the oil-resistant layer has polyvinyl alcohol resin and styrene-acrylic copolymer resin as main components, and the content of the polyvinyl alcohol resin is 15 to 50 parts by weight relative to 100 parts by weight of the styrene-acrylic copolymer resin.

Description

Greaseproof paper and method for producing the same

The present invention relates to an oil-resistant paper and a method for manufacturing the oil-resistant paper.

Oil-resistant paper can be used in, for example: paper containers, food trays, food packaging paper, cigarette cartons, medical purposes, etc.

As oil-proof agents, the most widely known ones are those that use oil-resistant fluorine-based resins. However, since organic fluorine-based resins accumulate in the human body and produce harmful gases under high temperature conditions, acrylic resins and polyvinyl alcohol resins have also been known in recent years (Patent Document 1). Acrylic resins and polyvinyl alcohol resins ensure oil resistance by forming a film.

In the method of internally adding the oil-resistant agent to the base material, the oil-resistant agent will lead to deterioration of productivity. In addition, the method of applying the oil-resistant agent on the base material by using a printing machine, etc., will also complicate the manufacturing steps. Therefore, from the perspective of reducing the steps and reducing the amount of materials used such as the oil-resistant agent, it is better to apply the oil-resistant agent on the surface of the base paper during the papermaking stage to impart oil resistance, and the coating form is particularly suitable for high-weight paperboard (thick paper).

On the other hand, the coating of paperboard (thick paper) is different from that of low-weight but high-density woodfree paper. Although the specific reason is still unclear (one of the main reasons may be related to the density of the paper), it is believed that part of the oil-resistant liquid will become residue and remain on the surface of the base paper. If the paper is directly polished under this condition, the residue will be transferred to the polishing roller, which will eventually cause stripe-like defects on the paper.

[Prior Art Literature] (Patent Literature)

Patent document 1: Japanese Patent Publication No. 2015-155582.

Therefore, the main problem to be solved by the present invention is to provide an oil-resistant paper which can meet the oil resistance and has no coating defects.

The oil-resistant paper of the present invention that solves the above-mentioned problem is characterized in that an oil-resistant layer is formed on at least one side of the base paper, the oil-resistant layer has polyvinyl alcohol resin and styrene-acrylic copolymer resin as main components, and the content of the polyvinyl alcohol resin is 15-50 parts by mass relative to 100 parts by mass of the styrene-acrylic copolymer resin.

Furthermore, the method for producing oil-resistant paper of the present invention is characterized in that it has the following steps: on at least one side of the base paper obtained by papermaking, an oil-resistant agent is applied at a temperature of 15°C or more and less than 40°C to form an oil-resistant layer, and then a polishing process is performed, wherein the oil-resistant agent is a polyvinyl alcohol resin and a styrene-acrylic copolymer resin as main components; and the content of the polyvinyl alcohol resin is 10 to 50 parts by mass relative to 100 parts by mass of the styrene-acrylic copolymer resin.

According to the present invention, it is possible to provide an oil-resistant paper which can satisfy oil resistance and has no coating defects.

The following is a detailed description of the form used to implement the present invention.

(Oil resistant)

The oil-resistant layer is formed by using the following oil-resistant agent as an oil-resistant agent and applying it on at least one side of the base paper. The oil-resistant agent has polyvinyl alcohol resin and styrene-acrylic copolymer resin as main components, and the content of the polyvinyl alcohol resin is 15 to 50 parts by mass relative to 100 parts by mass of the styrene-acrylic copolymer resin.

The styrene-acrylic copolymer resin is preferably provided in the form of an emulsion.

Examples of polyvinyl alcohol-based resins include unmodified and completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, or modified polyvinyl alcohol. Examples of modified polyvinyl alcohols include ethyl-modified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, acetyl-modified polyvinyl alcohol, and diacetyl-modified polyvinyl alcohol.

The styrene-acrylic copolymer resin and the polyvinyl alcohol resin are preferably contained in a solid content mass ratio of 90:10 to 65:35. More preferably, the solid content mass ratio of the styrene-acrylic copolymer resin and the polyvinyl alcohol resin is 85:15 to 75:25. Moreover, the content of the polyvinyl alcohol resin is preferably 15 to 50 parts by mass relative to 100 parts by mass of the styrene-acrylic copolymer resin.

If the amount of polyvinyl alcohol resin forming the hydrophilic coating is small, it is believed that water resistance tends to be unsatisfactory. Furthermore, polyvinyl alcohol resin has the function of protecting styrene-acrylic copolymer resin, and if the amount of polyvinyl alcohol resin is small, the amount of oil-resistant residues tends to increase. On the other hand, if the amount of polyvinyl alcohol resin is too large, the viscosity of the oil-resistant coating liquid will increase, and pipeline transportability will deteriorate and coating compatibility will tend to deteriorate.

It is further expected that the aforementioned oil-resistant layer contains 1.0 to 10.0 parts by mass of wax oil as a stripping agent relative to 100 parts by mass of the aforementioned styrene-acrylic copolymer resin. Wax oil can also improve oil resistance. In addition, during the polishing process, wax oil can also play an effect of preventing residue from adhering to the polishing roller.

The basis weight of the aforementioned base paper is 180~1310g/ ^m2 , and in particular, when the oil-resistant paper of 250~600g/ ^m2 that can be used for paper containers, etc. is taken as the object, for example, when the total amount of the single-sided coating of the oil-resistant layer is 2.0~8.0g/ ^m2 , especially 2.2~6.0g/ ^m2 , in the papermaking step (coating in the device), the effect of suppressing the aforementioned streak defect will be more significantly manifested.

In order to obtain oil-resistant paper with a high basis weight, the base paper preferably has a middle layer with multiple layers and a pair of surface layers formed on the front and back of the middle layer, and is made of multiple layers. The number of layers of the middle layer is not limited, but it is suitable to be 2 to 7 layers, especially 4 to 5 layers.

The basis weight can be measured according to Japanese Industrial Standard JIS-P8124 (2011). The basis weight of each layer of multi-layer paper does not need to be equal, and the basis weight of the surface layer and the middle layer is not particularly limited, but the basis weight of the surface layer as a single layer is preferably 30~260g/ ^m2 . In addition, the basis weight of the entire middle layer is preferably 600~950g/ ^m2 .

The paper thickness can be measured according to the "Paper and paperboard - Test methods for thickness and density" stated in the Japanese industrial standard JIS-P8118 (2014). The thickness of the multi-layer paper is preferably 180~187μm.

The density of the base paper (excluding the oil-resistant layer) as oil-resistant paper is preferably 0.70-1.00 g/cm ³ , and particularly preferably 0.8-0.95 g/cm ³ . For example, the density of the multi-layer paper can be adjusted by adjusting the pulp freeness and ash content of the surface layer or the middle layer, and the polishing step.

The pulp constituting the base paper, i.e. the pulp of the surface layer and the middle layer, is preferably composed mainly of coniferous kraft pulp and broadleaf kraft pulp. Although recycled pulp can be blended in a range of 20% by weight, such pulp is not suitable for food use, and 100% virgin pulp products are desired.

As the softwood kraft pulp, for example, there can be listed: softwood unbleached kraft pulp (NUKP), softwood semi-bleached kraft pulp (NSBKP), softwood bleached kraft pulp (NBKP), etc. Also, as the broadleaf kraft pulp, for example, there can be listed: broadleaf unbleached kraft pulp (LUKP), broadleaf semi-bleached kraft pulp (LSBKP), broadleaf bleached kraft pulp (LBKP). Among them, from the perspective of both the appearance and strength of the processed product, it is better to use softwood bleached kraft pulp and broadleaf bleached kraft pulp.

The goal is to mix softwood kraft pulp and broadleaf kraft pulp. This will make the paper thicker and ensure sufficient strength.

In addition, when it is a multi-layer oil-resistant paper, by setting the mass ratio of the aforementioned coniferous tree bleached kraft pulp to the aforementioned broad-leaf tree bleached kraft pulp in the surface layer to 5/95 or more and 15/85 or less, the broad-leaf tree kraft pulp, which is relatively rigid and easy to be high-densified, will be contained more, so that a pair of surface layers can obtain high-density and rigid characteristics, and excellent strength. Furthermore, the surface layer has a high inhibitory effect on the penetration of moisture or oil from the packaging object such as food into the interior.

On the other hand, by setting the mass ratio of the softwood kraft pulp to the broadleaf kraft pulp in the middle layer to 20/80 or more and 40/60 or less, the softwood kraft pulp having high softness is mostly contained, so the middle layer has good softness.

Each layer of the multi-layered oil-resistant paper can be appropriately combined with various known pulps for use as needed, such as chemical pulps such as broad-leaved sulfite pulp and coniferous sulfite pulp; or pulp chemically or mechanically made from non-wood fibers such as ramie, hemp, and reed.

The greaseproof paper of the embodiment, when used in paper tableware, for example, is in direct contact with the objects to be contained, such as food. Therefore, as other pulps used for the greaseproof paper, chemical pulps are preferred, and among them, ECF pulp, TCF pulp, and unbleached kraft pulp (UKP) are more preferred. The so-called ECF pulp is a chemical pulp bleached without elemental chlorine, which is produced by bleaching with chlorine dioxide (ClO ₂ ) instead of chlorine (Cl ₂ ). The so-called TCF pulp is a completely chlorine-free bleached chemical pulp bleached with oxygen (O), hydrogen peroxide (H ₂ O ₂ ), and ozone (O ₃ ) instead of chlorine (Cl ₂ ). That is, because the chlorine ion content in ECF pulp and TCF pulp is very small or zero, there is an advantage that even if it is burned at a low temperature, the risk of generating organic chlorine compounds such as dioxins is still low, and as a result, the burden on the environment can be reduced. In addition, when using unbleached kraft pulp, it can be made close to the color of wood (ice bar, etc.), so the bleaching step can be omitted, thereby reducing energy consumption and _CO2 emissions, thereby reducing the burden on the environment.

The base paper (including a multi-layer paper consisting of a surface layer and a middle layer) preferably contains a sizing agent and a paper strength enhancer as additives for papermaking.

(Sizing agent)

In order to further inhibit the penetration of moisture or oil from the packaging object such as food into the interior, the greaseproof paper can be added to each layer. As sizing agents, styrene-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), neutral rosin sizing agents, rosin sizing agents, modified rosin emulsion sizing agents, etc. can be listed. Among them, rosin sizing agents and modified rosin emulsion sizing agents are preferred.

The aforementioned rosin sizing agent is a sizing agent previously known in the field of papermaking and is not particularly limited. Examples of rosin-based substances include reinforced rosin and rosin esters. The reinforced rosin is obtained by modifying rosins with α,β-unsaturated carboxylic acid or its anhydride. The rosins are gum rosin, wood rosin, tall rosin, etc. The α,β-unsaturated carboxylic acid is fumaric acid, maleic acid, acrylic acid, etc. The rosin ester is obtained by reacting the aforementioned rosins with polyols. The polyols are glycerol, trihydroxymethylethane, trihydroxymethylpropane, pentaerythritol, dipropylene glycol, etc. In the present invention, the rosin-based sizing agent includes: those obtained by emulsifying the rosins alone or their mixtures, and those obtained by emulsifying the rosins alone and then mixing them. Furthermore, the emulsified rosins also include those to which various polymers are added in order to improve the sizing performance.

The content of the sizing agent as the surface layer is preferably 0.5 kg/t or more and 5.0 kg/t or less in terms of solid content. The content of the sizing agent as the middle layer is preferably 2.0 kg/t or more and 5.0 kg/t or less in terms of solid content. In addition, "kg/t" represents the mass per ton of pulp (kg). By setting the content of the sizing agent within the above range, water resistance can be improved.

(Paper Strengthener)

The oil-resistant paper can have a paper strength enhancer added to each layer. By adding a paper strength enhancer, each layer can be given various strengths suitable for making paper food containers. Also, by adding a resin-based paper strength enhancer inside, when applying the oil-resistant agent (resin), the oil-resistant agent will become less likely to penetrate into the paper and the application will become easier.

As the paper strength enhancer, various known paper strength enhancers such as polyacrylamide resins, polyamide resins, polyamine resins, acrylic resins, melamine resins, urea resins, polyamide epichlorohydrin resins, etc. can be used. Among them, it is preferable to use an amphoteric paper strength enhancer. As the amphoteric polyacrylamide, there can be listed: a copolymer of acrylamide and the above-mentioned anionic monomer and cationic monomer, a Mannich reaction modified product or Hofmann degradation product of a copolymer of acrylamide and the above-mentioned anionic monomer, etc. In the inventor's opinion, amphoteric polyacrylamide is particularly preferred because it has a self-anchoring function, so even if the amount added is increased to improve the strength between papers, it will not cause excessive cations, and can stably anchor the modified rosin emulsion sizing agent.

The content of the paper strength enhancer in each layer is preferably 12.0kg/t~30.0kg/t in terms of solid content. By setting the content of the aforementioned paper strength enhancer within the aforementioned range, various paper strengths such as interlayer strength can be imparted to the oil-resistant paper. If the content of the paper strength enhancer is lower than the aforementioned range, there is a concern that the interlayer strength is insufficient. On the other hand, if the content of the paper strength enhancer exceeds the aforementioned range, the improvement in interlayer strength will be roughly saturated, further reducing the yield of the added paper strength enhancer, and further causing contamination and foaming in the papermaking machine system, and there is a concern that the operability will be reduced.

(Other additives)

Furthermore, the oil-resistant paper may contain various other papermaking additives within the scope of not impairing the purpose and effect of the present invention. As other additives that can be added to the oil-resistant paper, for example, known papermaking chemicals can be cited.

[Manufacturing method]

When manufacturing oil-resistant paper, an oil-resistant agent is applied on one or both sides of the base paper obtained by papermaking to form an oil-resistant layer, and then the paper is polished. The oil-resistant agent contains polyvinyl alcohol-based resin and styrene-acrylic copolymer resin as main components.

As a further specific example, it is as follows.

(1) Disperse the pulp fibers in water to prepare a slurry. When manufacturing multiple layers of base paper, prepare the slurry corresponding to each of the multiple layers.

(2) Then, the raw material slurry is used to make paper in a papermaking machine under the condition of pH value of 6 or more and 8 or less to obtain base paper. When a plurality of layers of base paper are produced, the papermaking is performed by making each layer by multi-layer papermaking. The papermaking method is not particularly limited, and a known papermaking machine, i.e., a fourdrinier, a cylinder, a hybrid former, a gap former, etc., can be used.

After papermaking, an oil-proofing agent can be applied to at least one of the front and back sides of the base paper using a coating device such as a sizing device, a rod metering size press, a gate roll coater, a doctor blade coater, or a polishing roll to form an oil-proof layer.

The oil-proof agent is preferably applied at a temperature of 15°C or higher and less than 40°C. The oil-proof agent is preferably applied dispersed in water. Here, the temperature adjustment method of the oil-proof agent can use a method known in the papermaking industry.

(3) Next, use a pressure roller to press and remove the water.

(4) Then, dry in a drum dryer.

After drying, you can use a calender such as a nip calender, super calender, machine calender, or soft calender to perform a smoothing treatment. By performing a smoothing treatment, you can give the oil-resistant paper a high gloss and create a high-end product.

〈Other implementation forms〉

The present invention is not limited to the above-mentioned implementation form, and can be implemented in various modified and improved forms other than the above-mentioned forms.

[Implementation example]

Add polyvinyl alcohol to a sample tank filled with a specific amount of water, heat it to dissolve it, and leave it for more than 1 hour. Then, add styrene-acrylic copolymer emulsion and paraffin oil to the sample tank and stir to obtain an oil-resistant agent.

For the base paper shown in the table, papermaking is performed using a cylinder multi-drum multi-layer papermaking machine, and the aforementioned oil-resistant agent is transferred and applied using a calendering roll, and then calendering treatment is performed to obtain oil-resistant paper.

(Precipitation test)

For oil-resistant paper (Test Examples 1 to 7), precipitation tests were performed according to the Maron mechanical stability test (Japanese Industrial Standard JIS K 6828-3 (2003)).

The precipitation rate (%) is calculated using the following formula.

Sedimentation rate (%) = mass of precipitate (g) / mass of coating liquid (oil resistant agent) (g) × 100

The precipitation test results are shown in Table 1.

When the temperature of the oil-resistant agent is set to be roughly constant and the proportion of PVA is increased, the precipitation rate tends to be lower (Test Examples 2 to 4). In addition, when the proportion of the chemical in the oil-resistant agent is set to be constant, if the temperature of the oil-resistant agent is lowered, the precipitation rate tends to be lower (Test Examples 6 and 7).

(Product evaluation test)

For the samples (Test Examples 8 to 18), the oil repellency and streak defect status were evaluated. The results are shown in Tables 2 and 3.

The evaluation of oil repellency is carried out as follows. The oil resistance (oil repellency) is measured according to the JAPAN TAPPI paper pulp test method (No. 41) and the oil repellency test method for paper and paperboard - kit method. The test operation is shown below.

(1) The amount of oil-resistant agent (containing styrene-acrylic copolymer emulsion, wax oil, and polyvinyl alcohol (PVA) in its ingredients), the temperature of the oil-resistant agent, and the physical properties of the base paper were changed in various ways to prepare samples for the oil repellency test (Test Examples 8 to 18).

(2) The base paper is formed by laminating 7 layers of wet paper. The overall mass per unit area (basis weight), paper thickness, and density of the base paper are shown in Table 2 and Table 3.

(3) To measure the oil repellency (oil resistance) of oil-resistant paper having an oil-resistant layer on the surface (felt surface) of the base paper.

(4) The oil release degree of 8 or above is rated as good.

For the above-mentioned test examples 8 to 18, the following standards are used to evaluate the status of the stripe defects.

○: There are no streak defects on the surface of the oil-resistant paper and the appearance is good.

△: Although there are streaks on the surface of the oil-resistant paper, it is still to a degree that does not affect the function.

×: There are many streak defects on the surface of oil-resistant paper, and the streak defects may reduce the oil repellency.

The base paper in the samples (Test Examples 8 to 18) was formulated as follows. The surface layer was made of 100 parts by mass of a pulp slurry having a freeness of 420 mL and a NBKP:LBKP ratio of 20:80. The middle layer was made of 100 parts by mass of a pulp slurry having a freeness of 480 mL and a NBKP:LBKP ratio of 20:80. The pulp slurry was multi-layered using a multi-layer papermaking machine in which the wire member was a cylinder net to form a multi-layer structure of the surface layer, the middle layer, and the surface layer. The basis weight of each layer was 100 g/m ² for a pair of surface layers and 280 g/m ² for the middle layer, so that the total basis weight was 380 g/m ² .

(other)

‧[Basic weight (g/m ² )]

Measured according to "Paper and paperboard - Basis weight determination method" stated in Japanese industrial standard JIS-P8124 (2011).

‧[Paper thickness (μm)]

Measured according to "Paper and paperboard - Test methods for thickness and density" stated in Japanese industrial standard JIS-P8118 (2014).

‧[Density (g/cm ³ )]

Measured according to "Paper and paperboard - Test methods for thickness and density" stated in Japanese industrial standard JIS-P8118 (2014).

‧[Type B viscosity (cps)]

B-type viscosity is measured according to the "Method for Determination of Viscosity of Liquids" of Japanese Industrial Standard JIS-Z8803 (2011). B-type viscosity is the resistance torque when stirring the oil-resistant agent. The higher it is, the more energy is required for stirring.

[Industrial availability]

The oil-resistant paper of the present invention can be used for coating paper tableware, paper medical equipment, and paper furniture.

Claims (9)

An oil-resistant paper, characterized in that an oil-resistant layer is formed on at least one side of a base paper, the oil-resistant layer has a mixture of a polyvinyl alcohol resin and a styrene-acrylic copolymer resin emulsion as a main component, and the content of the polyvinyl alcohol resin is 15-50 parts by mass relative to 100 parts by mass of the styrene-acrylic copolymer resin emulsion, and the oil-resistant layer contains 1.0-10.0 parts by mass of wax oil relative to 100 parts by mass of the styrene-acrylic copolymer resin emulsion. The oil-resistant paper as claimed in claim 1, wherein the density of the base paper is 0.70-1.00 g/cm ³ . The oil-resistant paper as claimed in claim 1 or claim 2, wherein the basis weight of the base paper is 180-1310 g/m ² . The oil-resistant paper as described in claim 3, wherein the base paper has a plurality of middle layers and a pair of surface layers formed on the front and back surfaces of the middle layers, and the pulp of the surface layers and the middle layers is made of coniferous tree kraft pulp and broadleaf tree kraft pulp as the main components. The oil-resistant paper as claimed in claim 3, wherein the total coating weight of the oil-resistant layer on one side is 2.0-8.0 g/m ² . A paper tableware, which is formed from the oil-resistant paper described in claim 3. A paper medical device, which is formed from the oil-resistant paper described in claim 3. A paper furniture, which is formed by the oil-resistant paper described in claim 3. A method for producing oil-resistant paper, characterized in that it has the following steps: on at least one side of a base paper obtained by papermaking, an oil-resistant agent is applied at a temperature of 15°C or more and less than 40°C to form an oil-resistant layer, and then a polishing process is performed, wherein the oil-resistant agent is a mixture of a polyvinyl alcohol resin and a styrene-acrylic copolymer resin emulsion as a main component; and the content of the polyvinyl alcohol resin is 10-50 parts by mass relative to 100 parts by mass of the styrene-acrylic copolymer resin emulsion, and in the oil-resistant layer, 1.0-10.0 parts by mass of wax oil is contained relative to 100 parts by mass of the styrene-acrylic copolymer resin emulsion.