Lamination speed enhancer and method for enhancing it

Abstract

To provide a lamination speed improver for use in starch-based adhesives for corrugated cardboard. The present invention provides a lamination speed enhancer for use in starch-based adhesives for corrugated board, which comprises a phenolic resin.

Description

Technical Field

[0001] The present invention relates to a bonding speed improver for use in a starch-based adhesive for cardboard, a starch-based adhesive for cardboard, a method for manufacturing a cardboard sheet, a method for manufacturing a starch-based adhesive for cardboard, and a method for improving the bonding speed in the manufacture of cardboard sheets.

Background Art

[0002] General cardboard sheets used in cardboard boxes for home delivery and packaging of moving goods, etc. have seen a rapid increase in production volume in recent years with the increase in the volume of home delivery handled due to the rapid spread of online shopping.

[0003] The demand for improving the bonding speed in the production of such general cardboard sheets is strong. Furthermore, in recent years, due to the increasing interest in environmental issues such as CO2 reduction, methods for improving the bonding speed and manufacturing a larger quantity of cardboard sheets with less energy are being sought. In order to improve the bonding speed, methods such as increasing the amount of alkali (caustic soda) added to the starch-based adhesive for cardboard to lower the gelatinization start temperature and increasing the starch concentration to reduce the drying load have been adopted. However, in the method of increasing the alkali to lower the gelatinization start temperature, if the amount of alkali is increased too much, the viscosity of the adhesive in the straightening tank increases, making it difficult to control the amount of glue adhesion and the flow of the adhesive in the process, the viscosity stability of the adhesive decreases, and it thickens over time, making stable production difficult.

[0004] Also, in the method of increasing the starch concentration, if it is increased too much, the viscosity in the storage tank increases, causing the above-mentioned problems, and there is a problem that sufficient moisture for gelatinization cannot be obtained, and conversely, the adhesive strength decreases.

[0005] Moreover, in the method of increasing the starch concentration, if it is increased too much, the viscosity in the storage tank increases, causing the above-mentioned problems, and there is a problem that sufficient moisture for gelatinization cannot be obtained, and conversely, the adhesive strength decreases.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-284568 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a bonding speed enhancer for use in starch-based adhesives for corrugated cardboard, a starch-based adhesive for corrugated cardboard, a method for manufacturing corrugated cardboard sheets, a method for manufacturing starch-based adhesives for corrugated cardboard, and a method for improving the bonding speed in the manufacturing of corrugated cardboard sheets.

[0008] In view of the aforementioned problems, the inventors conducted extensive research and found that by incorporating phenolic resin into a starch-based adhesive for corrugated cardboard, the viscosity decreases in the storage temperature range of the storage tank, and no problems occur even when the amount of alkali added or the starch concentration is increased. Furthermore, in the temperature range of the heat drying process during lamination, the viscosity rapidly increases and initial adhesive strength is achieved. Thus, the inventors completed the present invention.

[0009] The present invention encompasses the following aspects.

[0010] Item 1, a bonding speed enhancer for use in starch-based adhesives for corrugated cardboard, containing phenolic resin.

[0011] Item 2, the bonding speed improver according to Item 1, wherein the phenolic resin is a resol-type phenolic resin or a novolac-type phenolic resin.

[0012] A starch-based adhesive for corrugated cardboard, comprising a bonding speed enhancer as described in item 3, item 1, or item 2.

[0013] Item 4, the starch-based adhesive for corrugated cardboard as described in Item 3, wherein the solid content of the phenolic resin is 0.5 to 50 parts by mass per 100 parts by mass of the total solid content of the starch in the starch-based adhesive.

[0014] Item 5, a starch-based adhesive for corrugated cardboard according to item 3 or 4, further containing a ketone resin, wherein the solid content of the ketone resin is 75 parts by mass or less per 100 parts by mass of the solid content of the phenolic resin.

[0015] A method for manufacturing a corrugated cardboard sheet, comprising the step of laminating a core and a liner using a starch-based adhesive for corrugated cardboard containing a lamination speed improver as described in item 6, item 1, or 2.

[0016] Article 7, A method for producing a starch-based adhesive for corrugated cardboard, comprising the step of adding a bonding speed improver described in Article 1 or 2 to a starch-based adhesive for corrugated cardboard.

[0017] The method for producing a corrugated cardboard starch-based adhesive according to item 8, wherein the viscosity of the corrugated cardboard starch-based adhesive with the lamination speed improver added, measured using a Rapid Visco Analyzer (RVA) at a heating rate of 5.5°C / min and a rotation speed of 160 r.pm, is 200 RVU or higher, measured at the temperature at which the corrugated cardboard starch-based adhesive before the addition of the lamination speed improver reaches 100 RVU (Rapid Visco Analyzer Units).

[0018] The method for producing corrugated cardboard adhesive as described in item 9, wherein the heating and cooling block of the Rapid Visco Analyzer (RVA) is programmed to remain at a constant 90°C from the start of measurement until the end of measurement, preheated to 90°C, 30g is taken into an aluminum RVA standard can, mounted on the RVA together with the RVA standard paddle, programmed to stir at a paddle rotation speed of 500 r.pm from the start of measurement until the end of measurement, and under the conditions for starting viscosity measurement, the time from the start of viscosity measurement to reaching a viscosity of 150 RVU (Rapid Visco Analyzer Units) is 50 seconds or less.

[0019] A method for improving the lamination speed in the manufacture of corrugated cardboard sheets, comprising the step of adding a lamination speed improver described in item 10, item 1, or 2 to a starch-based adhesive for corrugated cardboard.

Advantages of the Invention

[0020] According to the present invention, there are provided a bonding speed improver for use in a starch-based adhesive for cardboard, a starch-based adhesive for cardboard, a method for manufacturing a cardboard sheet, a method for manufacturing a starch-based adhesive for cardboard, and a method for improving the bonding speed in the manufacture of a cardboard sheet. In particular, by using a phenolic resin as the bonding speed improver, the starch-based adhesive for cardboard exhibits excellent functions in each of the storage temperature range of the storage tank and the temperature range in the heat drying in the bonding process, thereby enabling the manufacture of a cardboard sheet at a high bonding speed.

Brief Description of the Drawings

[0021] [Figure 1] Shows the relationship between the crimping time and the initial adhesion strength. [Figure 2] Schematically shows the method for evaluating the wettability. [Figure 3] Shows the viscosity increase at 90°C.

Modes for Carrying Out the Invention

[0022] Hereinafter, the present invention will be described in detail.

[0023] The present invention relates to a bonding speed improver for use in a starch-based adhesive for cardboard.

[0024] In this specification, the "bonding speed improver for use in a starch-based adhesive for cardboard" refers to a substance for manufacturing a cardboard sheet at a higher bonding speed by adding it to a starch-based adhesive for cardboard. The increase in the bonding speed at this time is preferably achieved without impairing the quality of the product cardboard sheet (for example, the yield excluding defective products in which the core and the liner are peeled off).

[0025] In this specification, "starch-based adhesive" means an adhesive primarily composed of starch that has adhesive properties that utilize the water absorption, swelling, and gelatinization properties of starch, which are exhibited when the adhesive is heated. "Starch-based adhesive for corrugated cardboard" refers to a starch-based adhesive used, for example, to bond corrugated core paper and liner paper. "Adhesive" can also be referred to as "sizing agent," and these terms are used interchangeably in this specification.

[0026] A starch-based adhesive using the lamination speed enhancer of the present invention can be used in the manufacture of corrugated cardboard sheets, without limitation. In one preferred embodiment of the present invention, the starch-based adhesive using the lamination speed enhancer is used in the manufacture of general-purpose corrugated cardboard or water-repellent corrugated cardboard.

[0027] Here, "water-resistant corrugated cardboard" refers to "water-resistant corrugated cardboard" as defined in the corrugated cardboard industry standard "Waterproof Corrugated Cardboard" M0002:2000 (National Federation of Corrugated Cardboard Manufacturers Associations), that is, "corrugated cardboard that has been processed so that its strength does not deteriorate significantly even when immersed for a long time." "Water-repellent corrugated cardboard" refers to "corrugated cardboard that has been surface-treated so that even if water is splashed on it for a short time, it repels water and turns into droplets, preventing water from penetrating." Water-resistant corrugated cardboard and water-repellent corrugated cardboard are collectively referred to as "waterproof corrugated cardboard." "General-purpose corrugated cardboard" refers to corrugated cardboard other than waterproof corrugated cardboard that does not have so-called water resistance and / or water repellency.

[0028] The bonding speed improver of the present invention contains a phenolic resin (phenol-formaldehyde resin, phenol-formaldehyde condensate) as an active ingredient. Here, the active ingredient means a component that is essential for the bonding speed improver of the present invention to exert its effect. In the present invention, the phenolic resin is a resin obtained by condensing phenols and formaldehyde.

[0029] While phenolic resins were conventionally known for their use as components (water-resistant agents) to impart water resistance, their use as bonding speed enhancers was unknown. Furthermore, their effectiveness as water-resistant agents tended to be inferior compared to other water-resistant agents.

[0030] The phenolic resin contained in the bonding speed enhancer of the present invention may be either a resol-type phenolic resin obtained by reacting the raw material compound in the presence of a basic catalyst, or a novolac-type phenolic resin obtained by reacting the raw material compound in the presence of an acidic catalyst.

[0031] Examples of phenols used as raw material compounds in the production of phenolic resins include phenol, cresol, amylphenol, bisphenol A, butylphenol, octylphenol, nonylphenol, and dodecylphenol. Phenols can be used individually or in combination of two or more.

[0032] Phenolic resins can be produced by reacting phenols with formaldehyde in the presence of a basic or acidic catalyst.

[0033] The molecular weight of the phenolic resin improves the bonding speed, and also improves the bonding of starch-based adhesives. It is not particularly limited as long as the attachment function is not hindered.

[0034] The bonding speed improver of the present invention, which contains a phenolic resin, may be the solid component of the phenolic resin itself, or a solution or dispersion (slurry) of the phenolic resin. If it is a solution or dispersion, the medium is an aqueous medium mainly composed of water. In addition to water as the main component, the aqueous medium may contain water-soluble organic solvents (for example, alcohols such as methanol and ethanol). From the viewpoint of ease of mixing with starch-based adhesives, resol-type phenol supplied as a solution or dispersion is more preferred. From the viewpoint of ease of adding the bonding speed improver to starch-based adhesives for corrugated cardboard, resol-type phenol with water as the solvent is even more preferred. In another embodiment, water-soluble phenolic resins that have been conventionally used as water-resistant agents for starch-based adhesives for corrugated cardboard can also be suitably used.

[0035] The lamination speed enhancer of the present invention is intended to enable the manufacture of corrugated cardboard sheets at a higher lamination speed by being added to starch-based adhesives for corrugated cardboard. The starch-based adhesives for corrugated cardboard will be described below.

[0036] In starch-based adhesives for corrugated cardboard, the starch consists of a main starch made from ungelatinized raw starch and a carrier starch which is modified starch completely gelatinized by alkali and heat. Starch-based adhesives for corrugated cardboard are dispersions in which starch is dispersed in an aqueous medium mainly composed of water.

[0037] Typical examples of starch-based adhesives for corrugated cardboard include those containing water, main starch, carrier starch, alkali, and boron compounds.

[0038] The starch used in this invention can be any starch that has been conventionally used in starch-based adhesives for corrugated cardboard. For example, corn starch, high-amylose corn starch, tapioca starch, wheat starch, potato starch, sweet potato starch, etc., and starches that have been oxidized, acid-treated, esterified, or etherified can be used. One or more types of starch can be used in combination.

[0039] In the starch-based adhesive of the present invention, the water-to-over-water ratio is typically around 1.9 to 4.5. By setting the water-to-over-water ratio to 1.9 or higher, sufficient moisture is supplied for the gelatinization of the main starch, resulting in good adhesion. Furthermore, by setting the water-to-over-water ratio to 4.5 or lower, the solid content concentration of the adhesive can be maintained above a predetermined level, achieving good initial adhesion. In this specification, "water-to-over-water ratio" refers to the mass ratio of (total water content / total starch content) in the starch-based adhesive.

[0040] Furthermore, in the starch-based adhesive of the present invention, the carrier ratio is preferably about 5 to 30% by mass. By setting the carrier ratio to 5% or more, good water retention and initial adhesive strength can be achieved. On the other hand, setting the carrier ratio to 30% or less is preferable from the viewpoint of obtaining appropriate viscosity and storage stability as an adhesive for corrugated cardboard.

[0041] In one preferred embodiment of the present invention, the starch-based adhesive contains high-amylose starch as a carrier starch. In this specification, "high-amylose starch" means starch with an amylose content of 50% or more. Examples of high-amylose starch include high-amylose corn starch.

[0042] When high-amylose starch is included as a carrier starch, the carrier starch may consist of high-amylose starch alone or in combination with other starches (one or more). From the viewpoint of improving the initial adhesion rate, the carrier starch may further include rhizome starch in addition to high-amylose starch. Examples of rhizome starches include tapioca starch, potato starch, and sweet potato starch.

[0043] When the carrier starch contains high-amylose starch and rhizome starch, the mixing ratio of high-amylose starch to rhizome starch can usually be around 30:70 to 99:1.

[0044] The starch-based adhesive of the present invention may further contain alkali. The alkali used in the present invention can be those conventionally used in starch-based adhesives for corrugated cardboard, such as sodium hydroxide (caustic soda) or potassium hydroxide. One or more alkalis can be used in combination. The alkali is preferably sodium hydroxide (caustic soda). The causticity of the adhesive of the present invention should be determined according to the adhesive manufacturing conditions in order to obtain an appropriate gelatinization temperature. Generally, the amount of alkali added is preferably in the range of 0.5 to 1.5% by mass as the causticity. In this specification, "causticity" means the mass ratio of (amount of caustic / total amount of adhesive liquid) in the starch-based adhesive.

[0045] The starch-based adhesive of the present invention contains the above-mentioned bonding speed improver (phenol resin). The content of the bonding speed improver is not particularly limited, but preferably it is 0.5 to 50 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of the total solids of the starch. By setting the numerical range in this manner, a high bonding speed improvement effect can be achieved.

[0046] In one preferred embodiment, the starch-based adhesive of the present invention may include thermosetting resins such as ketone resins (ketone-formaldehyde resins, ketone-melamine resins) and melamine resins, epoxy resins, and thermoplastic elastomers such as styrene-butadiene rubber (SBR) as components for imparting water resistance (water-resistant agents). However, in this specification, phenolic resins are not included in thermosetting resins as water-resistant agents. Examples of epoxy resins include epoxy compounds such as polyamide epichlorohydrin, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and glycerol polyglycidyl ether. The content of the water-resistant agent can be typically 1 to 20% by mass, preferably 3 to 10% by mass, based on the total solid content mass of the starch.

[0047] When the starch-based adhesive of the present invention contains a ketone resin as a water-resistant agent, the solid content of the ketone resin is preferably 75 parts by mass or less per 100 parts by mass of the solid content of the phenolic resin, from the viewpoint of achieving a higher bonding speed improvement effect.

[0048] In one of its other preferred embodiments, the adhesive of the present invention does not contain a water-resistant agent.

[0049] The starch-based adhesive of the present invention may further contain a boron compound. The boron compound is thought to pseudo-crosslink the gelatinized starch, thereby exhibiting initial adhesive strength. The content of the boron compound can be approximately 1.5% to 3.3% by mass, preferably 1.6% to 3.3% by mass, more preferably 1.6% to 3.0% by mass, and particularly preferably 0.7% to 2.7% by mass, based on the total solid content of the starch in terms of borax equivalent. By setting the content above the lower limit, sufficient improvement in initial adhesive strength can be achieved. Conversely, by setting the content below the upper limit, the reaction between borax and starch can be suppressed, preventing gelation and / or increased viscosity.

[0050] The starch-based adhesive of the present invention may further contain hydrated inosilicate minerals. Examples of hydrated inosilicate minerals include hydrated magnesium inosilicate and hydrated aluminum magnesium inosilicate. Hydrated inosilicate minerals are found in clay minerals that mainly contain hydrated inosilicate minerals. Examples of clay minerals that mainly contain hydrated inosilicate minerals include those commonly known as "sepiolite," "atapulgite," and "palygorskite," and these can be used in the present invention.

[0051] There are two methods for producing clay minerals mainly composed of hydrated inosilicate minerals: dry grinding and wet grinding. The present invention uses hydrated inosilicate minerals produced by either grinding method as the main component. While clay minerals can also be used, the wet grinding method is preferred because it has a high ability to defibrillate / disperse the fine fibrous structure of clay minerals and can bring out the functionality of hydrated inosilicate minerals.

[0052] In the present invention, the content of hydrated inosilicate minerals is usually about 0.1 to 15% by mass, preferably about 1 to 10% by mass, relative to the total solid content of the starch. By setting the content of hydrated inosilicate minerals to above the lower limit, sufficient effects of including hydrated inosilicate minerals are observed. Setting the content of hydrated inosilicate minerals to above the lower limit is preferable from the viewpoint of economic efficiency and from the viewpoint that thixotropy, one of the characteristics of hydrated inosilicate minerals, is not strongly imparted, and good adhesive properties are achieved.

[0053] The starch-based adhesive of the present invention can be prepared using methods such as a one-tank stain hole method, a two-tank stain hole method, a premix method, or a no-carrier method.

[0054] The one-tank carrier method is a method of adhesive production in which a starch slurry is prepared in a single tank, alkali is added to gelatinize the starch, water is added to dilute the alkaline adhesive solution, the main starch (ungelatinized starch) is added to the diluted alkaline adhesive solution, and borax is added and mixed as needed. When using the one-tank carrier method, the processing temperature is preferably 30 to 45°C from the viewpoint of stabilizing the finished viscosity and viscosity over time of the adhesive. Also, from the viewpoint of loosening and dispersing the fibers of hydrated inosilicate minerals such as sepiolite contained in the adhesive as needed, the rotation speed of stirring during adhesive production is preferably 1000 r.pm or more, and more preferably 1500 to 5000 r.pm. Examples of devices capable of stirring at a rotation speed of 1000 r.pm or more include adhesive devices manufactured by Sarco, Mitsubishi Heavy Industries (MREX), and Kakita Seisakusho.

[0055] A preferred preparation method using a single-tank carrier system is to take 30-45°C warm water into a tank, stir it at 3000-5000 rpm using a homogenizer, add starch to it, and if necessary add hydrated inosilicate minerals, disperse and dissolve them, then add alkali and stir for 10-15 minutes, then add 30-45°C warm water, continue to add the main starch (ungelatinized starch), and if necessary add borax and a water-resistant agent, and stir for 10-15 minutes to produce a starch-based adhesive for corrugated cardboard.

[0056] The timing of adding the bonding speed improver of the present invention is not particularly limited. For example, the bonding speed improver can be added while the mixture is being stirred during the manufacturing process of starch-based adhesive for corrugated cardboard. Specifically, the bonding speed improver can be added after adding starch, alkali, and boron compounds to water and stirring. In another embodiment, the bonding speed improver can be added to water and stirred, and then starch, alkali, and boron compounds can be added to the water to which the bonding speed improver has been added (dissolved or dispersed). In yet another embodiment, the bonding speed improver can be added in the corrugated cardboard sheet manufacturing process to a tank capable of stirring the adhesive, such as a storage tank that supplies the adhesive to a corrugator. The bonding speed improver can also be added multiple times during the manufacturing process of starch-based adhesive for corrugated cardboard.

[0057] In a preferred embodiment of the method for producing a starch-based adhesive for corrugated cardboard according to the present invention, the viscosity of the starch-based adhesive for corrugated cardboard before the addition of a bonding speed improver was measured using a Rapid Visco Analyzer (RVA) at a heating rate of 5.5°C / min and a rotation speed of 160 r.pm, and the viscosity was 100 RVU (Rapid Visco The viscosity of the starch-based adhesive for corrugated cardboard with a bonding speed improver added, measured at a temperature reaching the Analyzer Units (Analyzer Units), is 200 RVU or higher.

[0058] For measurement, the sample of corrugated cardboard starch adhesive was measured using an RVA standard can (aluminum) and paddle (RVA standard Can and Paddle, NSP Pe 30.0 g of RVA is collected in an aluminum RVA measuring can (manufactured by Perten, inner diameter approximately 36 mm, height approximately 65 mm) using a rten (manufactured by Perten) and measured. The starch-based adhesive for corrugated cardboard before the addition of the lamination speed improver contains, for example, the above-mentioned water, main starch, carrier starch, alkali, boron compound, etc., but does not contain phenolic resin, which is the lamination speed improver.

[0059] In another preferred embodiment of the method for producing a starch-based adhesive for corrugated cardboard according to the present invention, the heating and cooling block of RVA is programmed to maintain a constant temperature of 90°C from immediately after the start of measurement until the end of measurement, preheated to 90°C, 30g is taken into an aluminum RVA standard can, attached to the RVA together with the RVA standard paddle, programmed to stir at a paddle rotation speed of 500 r.pm from immediately after the start of measurement until the end of measurement, and under the conditions for starting viscosity measurement, the time from the start of viscosity measurement to reaching a viscosity of 150 RVU is 50 seconds or less.

[0060] Viscosity measurements using a Rapid Visco Analyzer (RVA) should be performed in accordance with standard tests such as AACC (American Association for Clinical Chemistry)-22-08 and ICC (International Color Consortium) standard No. 162. It is possible.

[0061] When measuring viscosity using RVA, the temperature of the starch-based adhesive for corrugated cardboard before heating is approximately 30-40°C.

[0062] The viscosity of the starch-based adhesive for corrugated cardboard of the present invention at the time of completion of the gluing process (immediately after gluing) is not particularly limited. The viscosity can be appropriately set according to the required amount of adhesive to the corrugated cardboard base paper and operating conditions such as the lamination speed. From the viewpoint of ease of adjusting the amount of adhesive to the corrugated cardboard base paper (for example, being able to adjust so that the amount of adhesive to the corrugated cardboard base paper does not become too large) and viscosity stability, the viscosity of the starch-based adhesive for corrugated cardboard of the present invention immediately after gluing (measured by a B-type viscometer) is preferably 700 mPa·s or less, more preferably 600 mPa·s or less, and even more preferably 500 mPa·s or less. Furthermore, from the viewpoint of ease of adjusting the amount of starch-based adhesive for corrugated cardboard that adheres to the corrugated cardboard base paper (for example, being able to adjust so that the amount adhered to the corrugated cardboard base paper does not become too little), and from the viewpoint of suppressing excessive penetration into the base paper and obtaining the desired strength, the viscosity of the starch-based adhesive for corrugated cardboard of the present invention immediately after preparation (measured by a B-type viscometer) is preferably 100 mPa·s or higher. Ideally, the pressure should be 150 mPa·s or higher.

[0063] In this specification, "completion of adhesive preparation" refers to the point in time when all components of the starch-based adhesive for corrugated cardboard, including the bonding speed enhancer of the present invention, have been blended and thoroughly stirred. Stirring can generally be carried out for about 5 to 30 minutes, preferably about 10 to 20 minutes, and more preferably about 15 minutes. The "completion of adhesive preparation" can be defined as within about 15 minutes after the end of stirring.

[0064] The present invention also provides a method for manufacturing corrugated cardboard sheets with improved bonding speed. The manufacturing method of the present invention involves manufacturing a corrugated cardboard sheet using a starch-based adhesive containing the bonding speed improving agent of the present invention, and includes a step of bonding a core and a liner using the starch-based adhesive containing the bonding speed improving agent of the present invention.

[0065] The core and liner used in the method for manufacturing corrugated cardboard sheets of the present invention are not particularly limited. In one preferred embodiment of the present invention, cores and liners used in the manufacture of general-purpose corrugated cardboard or water-repellent corrugated cardboard can be used. This is because the starch-based adhesive for corrugated cardboard penetrates the liner quickly, making it easier to create a deep "adhesive layer" and exhibiting high adhesive strength.

[0066] The liner used in water-resistant corrugated cardboard has a relatively strong water-repellent coating at the bonding surface with the core. On the other hand, the liners used in general-purpose corrugated cardboard are not treated to be water-repellent, and water-repellent corrugated cardboard is not treated to be as water-resistant as water-resistant corrugated cardboard.

[0067] The preferred water repellency of the adhesive surface between the core and the liner used in the corrugated cardboard sheet manufacturing method of the present invention can be determined by the time required for the droplet height to reach 0.50 mm or less when 0.020 g to 0.040 g of "mixed solution for wetting tension test" No. 48.0 (a solution with a wetting tension of 48.0 mN / m) specified in JIS K6768 is dropped from a height of 5.0 to 7.0 mm from the liner using a Pasteur pipette or the like (see Figure 2). The time required for the droplet height to reach 0.50 mm or less is preferably 10 seconds or less, more preferably 5 seconds or less, and even more preferably 2 seconds or less.

[0068] The method for manufacturing corrugated cardboard sheets of the present invention can be carried out using a commonly used corrugator. That is, for example, a corrugator having at least an adhesive roll and means for adhering the corrugated cardboard starch adhesive of the present invention to the adhesive roll can be used to manufacture corrugated cardboard sheets by a method that includes the steps of: bringing the top edge of a corrugated core paper into contact with the adhesive roll and applying the corrugated cardboard starch adhesive of the present invention to the top edge; and laminating liner paper to one or both sides of the core paper to which the corrugated cardboard starch adhesive of the present invention has been applied. For example, corrugated cardboard sheets can be manufactured using the starch adhesive of the present invention with a corrugator equipped with a gravure roll.

[0069] A corrugated cardboard sheet gluing machine consists of an applicator roll and a doctor roll. Applicator rolls (gluing rolls) come in three types: metering rolls, textured rolls, and gravure rolls. Metering rolls and textured rolls are gluing rolls with a smooth surface, while gravure rolls have numerous indentations (cells) on their surface. When a roll is immersed in a glue vat, the adhesive adhering to the roll surface is picked up by rotation, and any excess adhesive adhering to the roll surface is scraped off by the doctor roll. With a roll that has a smooth surface, adhesive that has lost viscosity is not picked up sufficiently by the roll, resulting in uneven application of the adhesive and affecting the bonding performance. On the other hand, with a gravure roll, the adhesive enters the indentations (cells) etched into the roll surface, making it easier to pick up even adhesive that has lost viscosity, and enabling uniform application of the adhesive.

[0070] In corrugated cardboard manufacturing, it is believed that bonding is completed after heating following the lamination of the core and liner, through processes such as (1) swelling of unegelatinized starch, (2) thickening of the adhesive, (3) gelatinization of unegelatinized starch, and (4) drying of the adhesive. Heating is usually performed using a hot plate or similar device. If the bonding is insufficient, the core and liner may separate due to pressure on the bonded area during cutting or slitting. Therefore, to ensure sufficient bonding, the bonding speed (line speed) is adjusted to control the heating time using a hot plate or similar device.

[0071] Although the principle is not entirely clear, by incorporating the lamination speed enhancer of the present invention into a starch-based adhesive for corrugated cardboard, the viscosity is moderately reduced in the storage tank temperature range (e.g., below 45°C). This prevents problems when alkali is added or the starch content is increased, and the adhesive rapidly thickens and develops initial adhesive strength in the temperature range of the heating and drying process in the lamination process (e.g., a heating process at an equipment temperature of 160°C or higher, more preferably 180°C or higher, during which the sheet temperature is 60°C or higher, more preferably 65°C or higher). Therefore, by adding the lamination speed enhancer to a starch-based adhesive for corrugated cardboard, the lamination speed in the manufacturing of corrugated cardboard sheets can be improved.

[0072] Accordingly, the present invention also provides a method for improving the lamination speed in the manufacture of corrugated cardboard sheets, which includes the step of adding a lamination speed improver to a starch-based adhesive for corrugated cardboard. The previous starch-based adhesive for corrugated cardboard contained, for example, water, main starch, carrier starch, alkali, boron compounds, etc., but did not contain phenolic resin, which is a bonding speed enhancer.

[0073] The manufacturing of corrugated cardboard sheets without limitations is subject to the lamination speed improvement method. Specifically, this includes the manufacturing of general-purpose corrugated cardboard, water-repellent corrugated cardboard, and water-repellent corrugated cardboard using starch-based adhesives containing water-resistant agents other than phenolic resin. [Examples]

[0074] <Examples> Example 1 <Preparing the Career Section> Take 600g of water in a 1L stainless steel jug and heat it to 60°C using a water bath. 72g of commercially available cornstarch for corrugated cardboard starch adhesives (manufactured by Oji Cornstarch Co., Ltd.) was added and dispersed using a RoboMix agitator (4500 r.pm) manufactured by Tokushu Kika Kogyo Co., Ltd. to prepare a starch slurry. 50g of a 25% concentration caustic soda solution was added to this starch slurry while stirring, and the mixture was stirred for 15 minutes to produce carrier starch for corrugated cardboard starch adhesive.

[0075] <Preparation of the main part> 840g of water was placed in a 3L stainless steel jug and heated to 35°C using a water bath. 485g of commercially available cornstarch (manufactured by Oji Cornstarch Co., Ltd.) was added, and the mixture was dispersed using a RoboMix agitator (4500 r.pm) manufactured by Tokushu Kika Kogyo Co., Ltd. to prepare the main starch.

[0076] <Preparation of starch-based adhesive for corrugated cardboard> The obtained main starch was stirred using the aforementioned stirrer (4000 r.pm) while carrier starch was added at a rate of 120 g / min using a tube pump. The time required for the addition was 6 minutes.

[0077] While continuing to stir, borax pentahydrate was added.

[0078] Furthermore, while continuing to stir, phenolic resin (PX-24, manufactured by Aica Kogyo Co., Ltd.) was added in the amounts shown in Table 1, and the mixture was stirred for 15 minutes.

[0079] The viscosity of the resulting adhesive was 280 mPa·s (measured with a Type B viscometer).

[0080] Furthermore, 30g of the obtained adhesive was taken into an aluminum cup for measurement using an RVA (Rapid Visco Analyzer, manufactured by NEWPORT SCIENTIFIC), and the temperature-viscosity curve was measured using the same instrument at a heating rate of 5.5°C and a rotation speed of 160 r.pm until 500 RVU was reached. The sample was collected. From the resulting curve, the temperature reached at 100 RVU was measured.

[0081] <Initial adhesive strength> On a standard single-sided corrugated cardboard sheet measuring 50mm x 85mm (liner basis weight: 280g / core basis weight: 180g), the dry weight is 5g / m². 2 Apply cardboard adhesive and attach load cell The pin tester was then set up. A liner (basis weight: 280g) was placed on top of it and pressed down using a 1kg hot plate (180℃). The pressing time was set to 2 seconds, 3 seconds, or 5 seconds. In each case, the liner and the single-sided corrugated cardboard were immediately peeled off after pressing, and the strength at that time was measured using a load cell as the initial adhesive strength.

[0082] Examples 2-5 and Comparative Examples The initial adhesive strength was measured in the same manner as in Example 1, except that the amounts of phenolic resin and ketone resin (water-resistant agent A (manufactured by Oji Corn Starch Co., Ltd.)) were as shown in Table 1. The ketone resin was added immediately after the phenolic resin, while stirring the corrugated cardboard adhesive, similar to the phenolic resin.

[0083] The results are shown in Table 1 and Figure 1.

[0084] Comparative Example 2 <Manufacturing of starch-based adhesive for corrugated cardboard using a single-tank system> 1010g of water was placed in a 3L stainless steel jug and heated to 35°C using a water bath. 99g of commercially available cornstarch for corrugated cardboard adhesives (OHP-C153, manufactured by Oji Cornstarch Co., Ltd.) was added, and 55g of a 25% caustic soda solution was added to the starch slurry while stirring with a Robomix agitator (4500 r.pm) manufactured by Tokushu Kika Kogyo Co., Ltd., and the mixture was stirred for 15 minutes. While continuing to stir, 700g of water was added, along with 545g of commercially available cornstarch (manufactured by Oji Cornstarch Co., Ltd.), and 8.5g of borax decahydrate was added, and the mixture was stirred for another 15 minutes to produce a starch-based corrugated cardboard adhesive. The viscosity of the resulting adhesive was 240 mPa·s (measured with a B-type viscometer). The resulting adhesive was stored while being stirred at 600 r.pm using a Three-One motor, and the RVA measurement and initial adhesive strength measurement described later were performed.

[0085] <Initial adhesive strength> On a standard single-sided corrugated cardboard sheet measuring 50mm x 85mm (liner basis weight: 280g / core basis weight: 180g), the dry weight is 5g / m². 2Applied the corrugated cardboard adhesive and set it on the pin tester equipped with a load cell. Placed a liner (basis weight: 280 g) on it and crimped it with a hot plate (180 °C) weighing 1 Kg by itself. The crimping time was set to 3 seconds, 5 seconds, or 7 seconds. In each case, immediately after crimping, the liner and the single-sided corrugated cardboard were peeled off, and the strength at that time was measured as the initial adhesive strength using a load cell.

[0086] <Viscosity increase at 90 °C using RVA> The heating and cooling block of the RVA (Rapid Viscosity Analyzer, manufactured by Newport Scientific) was programmed to be constant at 90 °C from immediately after the start of measurement to the end of measurement, and preheated to 90 °C. 30 g of the adhesive obtained above was collected in an RVA standard can (aluminum, manufactured by Perten), attached to the RVA together with the RVA standard paddle, and programmed to stir at a paddle rotation speed of 500 r.p.m. from immediately after the start of measurement to the end of measurement.

[0087] Then, the measurement was started to obtain a time-RVA viscosity curve. This measurement was carried out 30 minutes and 150 minutes after the addition of borax decahydrate, which is the chemical added last in the process of preparing the starch-based adhesive for corrugated cardboard.

[0088] Example 7

[0089] A starch-based adhesive was prepared in a one-tank system in the same manner as in Comparative Example 2. Then, 5 minutes after the addition of borax decahydrate, 32.2 g of the resol-type water-soluble phenolic resin trade name PR-967 (non-volatile content concentration 40%, manufactured by Sumitomo Bakelite Co., Ltd.) as it was, was added. This is an amount that is 5% by mass based on the total amount of starch (the total amount of carrier starch and main starch). The viscosity at the time when the stirring for 15 minutes after the addition of borax was completed was 230 mPa·S. Then, the initial adhesive strength was measured in the same manner as in Comparative Example 2. Also, the viscosity increase at 90 °C was measured in the same manner as in Comparative Example 2. Incidentally, this measurement was carried out 30 minutes and 150 minutes after the addition of the phenolic resin, which is the chemical added last when manufacturing the corrugated cardboard adhesive of Example 7. Example 8 Except for changing the amount of resol-type water-soluble phenolic resin added to 64.4 g (10% of the total starch amount), the production of a starch-based adhesive, measurement of initial adhesive strength, and RVA measurement were performed in the same manner as in Example 7. The viscosity after 15 minutes of stirring following the addition of borax was 210 mPa·s.

[0090] The results obtained are shown in Table 2 and the graph in Figure 3.

[0091] The starch-based adhesive for corrugated cardboard containing the bonding speed enhancer of the present invention showed a tendency for a shorter viscosity increase initiation time. It is presumed that this shorter viscosity increase initiation time improves initial adhesive strength and enables an improvement in bonding speed. Furthermore, the starch-based adhesive for corrugated cardboard containing the bonding speed enhancer of the present invention also showed a tendency for less decrease in initial adhesive strength even after time has elapsed since bonding. Because the decrease in initial adhesive strength is small, it is expected that the pot life will be extended.

[0092] [Table 1]

[0093] [Table 2]

Claims

1. A lamination speed improver for use in a starch-based adhesive for corrugated board, comprising a resol-type phenolic resin, A lamination speed improver in which the starch-based adhesive for corrugated cardboard contains raw starch (excluding, however, those in which the resol-type phenolic resin is a cationic phenolic resol resin emulsion (A) obtained by condensation polymerization of phenols and aldehydes in the presence of a water-soluble or water-dispersible thermosetting resin (a) obtained by reacting a polyamide-based resin having substantially a secondary amino group with epihalohydrin, and a water-soluble polymer (b) in the presence of the water-soluble or water-dispersible thermosetting resin (a) obtained by reacting a polyamide-based resin having a secondary amino group with epihalohydrin).

2. The lamination speed enhancer according to claim 1, wherein the resol-type phenolic resin in the lamination speed enhancer is used in an amount of 0.5 to 4.8 parts by mass in terms of solid content per 100 parts by mass of the total solid content of the starch contained in the starch-based adhesive for cardboard.

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