JP7727367B2 - Lamination speed enhancer and method for enhancing it - Google Patents

Description

The present invention relates to a lamination speed enhancer for use in starch-based adhesives for corrugated board, a starch-based adhesive for corrugated board, a method for producing corrugated board sheets, a method for producing starch-based adhesives for corrugated board, and a method for improving the lamination speed in the production of corrugated board sheets.

The production volume of general-purpose corrugated cardboard sheets used for cardboard boxes used for parcel delivery and packing moving items has been increasing rapidly in recent years due to the rapid spread of internet shopping and the increase in parcel delivery volume.

There is a strong demand for improving the lamination speed in the production of such general cardboard sheets. Furthermore, in recent years, due to growing interest in environmental issues such as _CO2 reduction, there is a demand for a method for improving the lamination speed and producing larger quantities of cardboard sheets using less energy.

To date, methods used to improve lamination speed have included increasing the amount of alkali (caustic soda) added to starch-based adhesives for corrugated board to lower the gelatinization temperature, or increasing the starch concentration to reduce the drying load. However, when increasing the alkali to lower the gelatinization temperature, if the amount of alkali is increased too much, the viscosity of the adhesive in the storage tank increases, making it difficult to control the amount of glue applied and to transport the adhesive within the process, and the adhesive's viscosity stability decreases, causing it to thicken over time, making stable production difficult.

Furthermore, even if the starch concentration is increased, if it is increased too much, the viscosity will increase in the storage tank, resulting in the problems mentioned above. In addition, there will be insufficient moisture for gelatinization, which will in turn result in a decrease in adhesive strength.

JP 2007-284568 A

The present invention aims to provide a lamination speed enhancer for use in starch-based adhesives for corrugated board, a starch-based adhesive for corrugated board, a method for manufacturing corrugated board sheets, a method for manufacturing starch-based adhesives for corrugated board, and a method for improving lamination speeds in the manufacture of corrugated board sheets.

After extensive research in light of the above issues, the inventors discovered that by incorporating a phenolic resin into a starch-based adhesive for corrugated cardboard, the viscosity decreases within 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, the viscosity increases rapidly within the temperature range required for heat drying in the lamination process, achieving initial adhesive strength. This discovery led to the completion of the present invention.

The present invention includes the following aspects:

Item 1: A lamination speed enhancer for use in starch-based adhesives for corrugated cardboard, containing a phenolic resin.

Item 2. The lamination speed enhancer according to Item 1, wherein the phenolic resin is a resol-type phenolic resin or a novolac-type phenolic resin.

Item 3. A starch-based adhesive for corrugated cardboard, comprising the lamination speed enhancer described in Item 1 or 2.

Item 4. The starch-based adhesive for corrugated cardboard according to Item 3, wherein the solids content of the phenolic resin is 0.5 to 50 parts by mass per 100 parts by mass of the total solids content of the starch in the starch-based adhesive.

Item 5: A starch-based adhesive for corrugated cardboard according to Item 3 or 4, further comprising a ketone resin, the solids content of which is 75 parts by mass or less per 100 parts by mass of the solids content of the phenolic resin.

Item 6. A method for producing a corrugated cardboard sheet, comprising the step of laminating a core and a liner using a starch-based adhesive for corrugated cardboard containing the lamination speed enhancer described in Item 1 or 2.

Item 7: A method for producing a starch-based adhesive for corrugated cardboard, comprising the step of adding the laminating speed improver described in Item 1 or 2 to a starch-based adhesive for corrugated cardboard.

Item 8: A method for producing a starch-based adhesive for corrugated board according to Item 7, wherein the viscosity of the starch-based adhesive for corrugated board to which a laminating speed enhancer has been added is 200 RVU or more, as measured using a Rapid Visco Analyzer (RVA) at a temperature rise rate of 5.5°C/min and a rotation speed of 160 rpm, at a temperature at which the starch-based adhesive for corrugated board before adding the laminating speed enhancer reaches 100 RVU (Rapid Visco Analyzer Units).

Item 9: A method for manufacturing a corrugated board adhesive according to Item 7 or 8, wherein the heating and cooling block of a Rapid Visco Analyzer (RVA) is programmed to maintain a constant temperature of 90°C from immediately after the start of measurement until the end of measurement, the RVA is preheated to 90°C, 30 g of the sample is placed in an aluminum standard RVA can, and the can is attached to the RVA together with a standard RVA paddle. The can is programmed to stir at a paddle rotation speed of 500 rpm from immediately after the start of measurement until the end of measurement, and under these conditions, the viscosity rise start time from the start of viscosity measurement until a viscosity of 150 RVU (Rapid Visco Analyzer Units) is reached is 50 seconds or less.

Item 10. A method for improving lamination speed in the production of corrugated cardboard sheets, comprising the step of adding the lamination speed improver described in Item 1 or 2 to a starch-based adhesive paste for corrugated cardboard.

The present invention provides a lamination speed enhancer for use in starch-based adhesives for corrugated board, a starch-based adhesive for corrugated board, a method for manufacturing corrugated board sheets, a method for manufacturing a starch-based adhesive for corrugated board, and a method for improving lamination speeds in the production of corrugated board sheets. In particular, by using a phenolic resin as a lamination speed enhancer, the starch-based adhesive for corrugated board exhibits excellent functionality in both the storage temperature range of the storage tank and the temperature range used for heat drying in the lamination process, thereby enabling the production of corrugated board sheets at high lamination speeds.

The relationship between compression time and initial adhesive strength is shown. The method for evaluating water repellency is shown schematically. Viscosity increase at 90°C is shown.

The present invention is described in detail below.

The present invention relates to a lamination speed enhancer for use in starch-based adhesives for corrugated cardboard.

In this specification, the term "laminating speed enhancer for use in starch-based adhesives for corrugated board" refers to an agent that is added to starch-based adhesives for corrugated board to enable the production of corrugated board sheets at a faster laminating speed. It is preferable that the increased laminating speed be achieved without compromising the quality of the finished corrugated board sheets (e.g., yield excluding defective products in which the core and liner have separated).

In this specification, "starch-based adhesive" refers to an adhesive primarily made of starch that has adhesive properties that utilize the water absorption, swelling, and gelatinization properties of starch, which are manifested when the adhesive is heated. "Starch-based adhesive for corrugated cardboard" refers to a starch-based adhesive used, for example, to bond corrugated core base paper and liner base paper together. "Adhesive" can also be referred to as "glue," and are used interchangeably in this specification.

The starch-based adhesive using the laminating speed enhancer of the present invention can be used in the production of any type of corrugated board sheet. In one preferred embodiment of the present invention, the starch-based adhesive using the laminating speed enhancer is used in the production of general-purpose corrugated board or water-repellent corrugated board.

Here, water-resistant cardboard refers to "water-resistant cardboard" as defined in the cardboard industry standard "Waterproof Cardboard" M0002:2000 (Japan Corrugated Box Association), i.e., "cardboard that has been processed so that its strength does not deteriorate significantly even when submerged for long periods of time." "Water-repellent cardboard" refers to "cardboard whose surface has been treated to repel water, turning it into droplets and preventing water penetration, even when exposed to water for a short period of time," as defined in the cardboard industry standard M0002:2000. Water-resistant cardboard and water-repellent cardboard are collectively referred to as "waterproof cardboard." "General-purpose cardboard" refers to cardboard other than waterproof cardboard that has not been given so-called water resistance and/or water repellency.

The application speed enhancer of the present invention contains a phenolic resin (phenol-formaldehyde resin, phenol-formaldehyde condensate) as an active ingredient. Here, the term "active ingredient" refers to a component that is essential for the application speed enhancer of the present invention to exhibit its effects. In the present invention, the phenolic resin is a resin obtained by condensing a phenol with formaldehyde.

Phenol resins have traditionally been known to be used as components for imparting water resistance (water-resistant agents), but their use as lamination speed enhancers has not been known. Furthermore, their effectiveness as water-resistant agents has tended to be inferior to that of other water-resistant agents.

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

Phenols, which are raw material compounds used in the production of phenolic resins, include phenol, cresol, amylphenol, bisphenol A, butylphenol, octylphenol, nonylphenol, and dodecylphenol. Phenols can be used alone or in combination of two or more.

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

The molecular weight of the phenolic resin is not particularly limited as long as it improves lamination speed and does not inhibit the adhesive function of the starch-based adhesive.

The lamination speed enhancer of the present invention containing a phenolic resin may be the solid content of the phenolic resin itself, or a solution or dispersion (slurry) of the phenolic resin. When it is a solution or dispersion, the medium is an aqueous medium primarily composed of water. The aqueous medium may contain, in addition to the main component water, a water-soluble organic solvent (e.g., alcohols such as methanol and ethanol). From the viewpoint of ease of mixing with the starch-based adhesive, resol-type phenol supplied as a solution or dispersion is more preferred. From the viewpoint of ease of adding the lamination speed enhancer to a starch-based adhesive for corrugated board, resol-type phenol using water as the solvent is even more preferred. In another embodiment, water-soluble phenolic resins, which have traditionally been used as water-resistant agents for starch-based adhesives for corrugated board, can also be suitably used.

The laminating speed improver of the present invention is added to a starch-based adhesive for corrugated board to enable the production of corrugated board sheets at a higher laminating speed. The starch-based adhesive for corrugated board is described below.

The starch in starch-based adhesives for corrugated board contains a main starch consisting of ungelatinized raw starch and a carrier starch, which is a modified starch that has been fully gelatinized using alkali and heat. Starch-based adhesives for corrugated board are a dispersion of starch in an aqueous medium primarily composed of water.

A typical example of the composition of a starch-based adhesive for corrugated cardboard is one that contains water, main starch, carrier starch, alkali, and a boron compound.

The starch used in the present invention can be any starch that has traditionally been used in starch-based adhesives for corrugated cardboard. Examples include corn starch, high-amylose corn starch, tapioca starch, wheat starch, potato starch, sweet potato starch, and starches that have been oxidized, acid-treated, esterified, or etherified. One or more types of starch can be used, or two or more types can be used in combination.

The water fold ratio of the starch-based adhesive of the present invention is typically approximately 1.9 to 4.5. By setting the water fold ratio to 1.9 or higher, sufficient moisture is supplied for the main starch to gelatinize, resulting in good adhesion. Furthermore, by setting the water fold ratio to 4.5 or lower, the solids concentration of the adhesive can be maintained at a predetermined level or higher, achieving good initial adhesion. In this specification, "water fold ratio" refers to the mass ratio (total water amount/total starch amount) in the starch-based adhesive.

In addition, the carrier ratio of the starch-based adhesive of the present invention is preferably typically around 5 to 30% by mass. By setting the carrier ratio to 5% or more, good water retention and initial adhesive strength can be achieved. Furthermore, setting the carrier ratio to 30% or less is preferred from the standpoint of achieving appropriate viscosity and storage stability as an adhesive for corrugated cardboard.

In one preferred embodiment of the present invention, the starch-based adhesive contains high-amylose starch as a carrier starch. As used herein, "high-amylose starch" refers to starch with an amylose content of 50% or more. Examples of high-amylose starch include high-amylose cornstarch.

When high amylose starch is used as the carrier starch, the carrier starch may consist solely of high amylose starch, or may be combined with one or more other starches. From the perspective of improving the initial adhesion rate, the carrier starch may further contain rhizome starch in addition to high amylose starch. Examples of rhizome starch include tapioca starch, potato starch, and sweet potato starch.

When the carrier starch contains high-amylose starch and rhizome starch, the blending ratio of high-amylose starch to rhizome starch can usually be about 30:70 to 99:1.

The starch-based adhesive of the present invention can further contain an alkali. The alkali used in the present invention can be any alkali that has traditionally been used in starch-based adhesives for corrugated board, such as sodium hydroxide (caustic soda) or potassium hydroxide. Alkalis can be used alone or in combination of two or more. The alkali is preferably sodium hydroxide (caustic soda). The caustic content of the adhesive of the present invention can be determined based on the glue-making conditions to obtain an appropriate gelatinization temperature. Generally, the amount of alkali added is preferably in the range of 0.5 to 1.5 mass% in terms of caustic content. In this specification, "caustic content" refers to the mass ratio (caustic content/total glue liquid volume) in the starch-based adhesive.

The starch-based adhesive of the present invention contains the above-mentioned application speed enhancer (phenolic resin). There are no particular restrictions on the amount of application speed enhancer contained, but it is preferably 0.5 to 50 parts by mass, and more preferably 1 to 20 parts by mass, per 100 parts by mass of the total solids content of the starch. By using this range, a high application speed improvement effect can be achieved.

In one preferred embodiment, the starch-based adhesive of the present invention may contain, as a component for imparting water resistance (water-resistant agent), thermosetting resins such as ketone resins (ketone-formaldehyde resins, ketone-melamine resins) and melamine resins, epoxy resins, thermoplastic elastomers such as styrene-butadiene rubber (SBR), etc. However, in this specification, phenolic resins are not included in the thermosetting resins used 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 is typically 1 to 20% by mass, preferably 3 to 10% by mass, based on the total solids mass of the starch.

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

In another preferred embodiment, the adhesive of the present invention does not contain a water-resistant agent.

The starch-based adhesive of the present invention may further contain a boron compound. It is believed that the boron compound pseudo-crosslinks the gelatinized starch, thereby exhibiting initial adhesive strength. The content of the boron compound, calculated as borax, is typically approximately 1.5% to 3.3% by mass, preferably approximately 1.6 to 3.3% by mass, more preferably approximately 1.6 to 3.0% by mass, and particularly preferably approximately 0.7 to 2.7% by mass, based on the total solids mass of the starch. By ensuring that the content is above the above lower limit, sufficient improvement in initial adhesive strength is achieved. Furthermore, by ensuring that the content is below the above upper limit, gelation and/or high viscosity caused by the reaction between borax and starch can be suppressed.

The starch-based adhesive of the present invention may further contain a hydrous inosilicate mineral. Examples of hydrous inosilicate minerals include hydrous magnesium inosilicate and hydrous aluminum-magnesium inosilicate. Hydrous inosilicate minerals are included in clay minerals whose main component is hydrous inosilicate minerals. Examples of clay minerals whose main component is hydrous inosilicate minerals include those commonly known as "sepiolite," "attapulgite," and "palygorskite," and these can be used in the present invention.

There are two methods for producing clay minerals whose main component is hydrous inosilicate mineral: dry milling and wet milling. Clay minerals whose main component is hydrous inosilicate mineral produced by either milling method can be used in the present invention. However, wet milling is preferred because it has a high ability to defibrate and disperse the fine fiber structure of the clay mineral, thereby enabling the functionality of the hydrous inosilicate mineral to be fully utilized.

In the present invention, the content of the hydrous inosilicate mineral is typically about 0.1 to 15% by mass, and preferably about 1 to 10% by mass, based on the total mass of solids in the starch. By ensuring that the content of the hydrous inosilicate mineral is at or above the lower limit, the full effect of including the hydrous inosilicate mineral is observed. Having the content of the hydrous inosilicate mineral at or above the lower limit is preferred from the standpoint of economy and from the standpoint of achieving good adhesive properties without imparting strong thixotropy, one of the properties of hydrous inosilicate minerals.

The starch-based adhesive of the present invention can be prepared using the one-tank Stainhole method, the two-tank Stainhole method, the premix method, the no-carrier method, etc.

The one-tank carrier method is a sizing method 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 paste, the main starch (ungelatinized starch) is added to the diluted alkaline paste, and borax is added as needed. When using the one-tank carrier method, the processing temperature is preferably 30 to 45°C to stabilize the adhesive's final viscosity and viscosity over time. Furthermore, to loosen and disperse the fibers of the hydrous inosilicate mineral, such as sepiolite, which is optionally included, the stirring speed during sizing is preferably 1000 rpm or higher, more preferably 1500 to 5000 rpm. Examples of equipment capable of stirring at speeds of 1000 rpm or higher include sizing equipment manufactured by Sarco, the MREX sizing equipment manufactured by Mitsubishi Heavy Industries, and the sizing equipment manufactured by Kakida Manufacturing Co., Ltd.

A preferred preparation method using the one-tank carrier system involves, for example, placing 30-45°C hot water in one tank and stirring it with a homogenizer at 3,000-5,000 rpm, adding starch, and optionally adding hydrated inosilicate mineral. After dissolving and dispersing, alkali is added and the mixture is stirred for 10-15 minutes, followed by adding 30-45°C hot water, followed by adding main starch (ungelatinized starch), and optionally adding borax and a waterproofing agent, and stirring for 10-15 minutes to produce a starch-based adhesive for corrugated board.

The timing of adding the laminating speed enhancer of the present invention is not particularly limited. For example, the laminating speed enhancer can be added while the material is being stirred during the manufacturing process of a starch-based adhesive for corrugated board. As a specific example, starch, an alkali, and a boron compound can be added to water and stirred, and then the laminating speed enhancer can be added. In another embodiment, the laminating speed enhancer can be added to water and stirred, and then the starch, alkali, and a boron compound can be added to the water to which the laminating speed enhancer has been added (dissolved or dispersed). In yet another embodiment, the laminating speed enhancer can be added to a tank capable of stirring the adhesive, such as a storage tank that supplies adhesive to a corrugator, during the corrugated board sheet manufacturing process. The laminating speed enhancer can also be added multiple times during the manufacturing process of a starch-based adhesive for corrugated board.

In a preferred embodiment of the method for producing a starch-based adhesive for corrugated board of the present invention, the viscosity of the starch-based adhesive for corrugated board to which a laminating speed enhancer has been added is 200 RVU or more, measured using a Rapid Visco Analyzer (RVA) at a temperature rise rate of 5.5°C/min and a rotation speed of 160 rpm, at a temperature at which the starch-based adhesive for corrugated board before the addition of the laminating speed enhancer reaches 100 RVU (Rapid Visco Analyzer Units).

For measurement, 30.0 g of the sample starch-based adhesive for corrugated board is placed in an aluminum RVA measurement can (manufactured by Perten, inner diameter approximately 36 mm, height approximately 65 mm) using an RVA standard can (made of aluminum) and paddle (RVA standard Can and Paddle, manufactured by NSP Perten). Before the addition of the lamination speed enhancer, the starch-based adhesive for corrugated board contains, for example, the above-mentioned water, main starch, carrier starch, alkali, boron compound, etc., but does not contain the phenolic resin used as the lamination speed enhancer.

In another preferred embodiment of the method for producing a starch-based adhesive for corrugated cardboard of the present invention, the heating and cooling block of the RVA is programmed to maintain a constant temperature of 90°C from immediately after the start of measurement to the end of measurement, 30 g of the sample is preheated to 90°C, and the sample is placed in an aluminum standard RVA can and attached to the RVA together with a standard RVA paddle. The can is programmed to stir at a paddle rotation speed of 500 rpm from immediately after the start of measurement to the end of measurement, and under these conditions when viscosity measurement is started, the viscosity increase onset time from the start of viscosity measurement to the time when a viscosity of 150 RVU is reached is 50 seconds or less.

Viscosity measurements using a Rapid Visco Analyzer (RVA) can 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.

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

The viscosity of the starch-based adhesive for corrugated board of the present invention at the completion of the glue production (immediately after glue production) is not particularly limited. The viscosity can be set appropriately depending on the required operating conditions, such as the amount of adhesion to the linerboard and the lamination speed. From the perspective of ease of adjusting the amount of adhesion to the linerboard (for example, being able to adjust the amount of adhesion to the linerboard so that it does not become too great) and viscosity stability, the viscosity of the starch-based adhesive for corrugated board of the present invention immediately after glue production (measured with a Brookfield 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 standpoint of ease of adjusting the amount of starch-based adhesive for corrugated board adhered to the linerboard (for example, adjustment can be made so that the amount adhered to the linerboard does not become too small), and from the standpoint of suppressing excessive penetration into the linerboard and achieving the desired strength, the viscosity of the starch-based adhesive for corrugated board of the present invention immediately after glue production (measured with a Brookfield viscometer) is preferably 100 mPa·S or more, and more preferably 150 mPa·S or more.

In this specification, the term "completion of glue production" refers to the point at which all components of the starch-based adhesive for corrugated board, including the laminating 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 glue production" can be within about 15 minutes after the end of stirring.

The present invention also provides a method for producing corrugated cardboard sheets with improved lamination speeds. The manufacturing method of the present invention produces corrugated cardboard sheets using a starch-based adhesive containing the lamination speed enhancer of the present invention, and includes a step of laminating a core and a liner using the starch-based adhesive containing the lamination speed enhancer of the present invention.

The corrugating medium 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, the corrugating medium and liner 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 "glue foot" and achieving high adhesive strength.

The liners used in waterproof cardboard have relatively strong water-repellent properties on the adhesive surface where they meet the core. On the other hand, liners used in general-purpose cardboard are not water-repellent, and water-repellent cardboard does not have as strong a water-repellent property as waterproof cardboard.

The preferred water repellency of the adhesive surface between the corrugated fiberboard and the liner used in the corrugated fiberboard manufacturing method of the present invention can be determined by the time required for the height of a droplet to reach 0.50 mm or less when 0.020 g to 0.040 g of "Wet Tension Test Mixture" No. 48.0 (a liquid with a wet tension of 48.0 mN/m) as specified in JIS K6768 is dropped using a Pasteur pipette or similar device from a position 5.0 to 7.0 mm above the liner (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.

The method for manufacturing the corrugated cardboard sheet of the present invention can be carried out using a commonly used corrugator. That is, for example, a corrugated cardboard sheet can be produced using a corrugator having at least a glue roll and a means for applying the starch-based adhesive for corrugated cardboard of the present invention to the glue roll, by a method including the steps of bringing the top edge of a corrugated core paper into contact with the glue roll and applying the starch-based adhesive for corrugated cardboard of the present invention to the top edge, and laminating liner paper to one or both sides of the core paper coated with the starch-based adhesive for corrugated cardboard of the present invention. For example, a corrugated cardboard sheet can be produced using the starch-based adhesive of the present invention using a corrugator equipped with a gravure roll.

A corrugated board sheet gluing machine consists of an applicator roll and a doctor roll. Applicator rolls (gluing rolls) come in three types: metaling rolls, textured rolls, and gravure rolls. Metaling rolls and textured rolls have smooth surfaces, while gravure rolls have numerous indentations (cells) on their surface. The roll, immersed in a glue vat, picks up the adhesive adhering to its surface as it rotates, and the doctor roll scrapes off any excess adhesive adhering to the roll surface. With a smooth surface, adhesive with reduced viscosity is not picked up sufficiently by the roll, resulting in uneven application of the adhesive and patchy application, which affects adhesive performance. On the other hand, with a gravure roll, the adhesive penetrates the indentations (cells) engraved on the roll surface, making it easy to pick up even adhesive with reduced viscosity, enabling uniform application of the adhesive.

In the manufacture of corrugated cardboard, heating after laminating the core and liner is thought to complete the bonding process through processes such as (1) swelling of ungelatinized starch, (2) thickening of the adhesive, (3) gelatinization of the ungelatinized starch, and (4) drying of the adhesive. Heating is usually carried out using a hot plate or similar device. If bonding is insufficient, the core and liner may peel apart due to pressure on the adhesive joint during cutting or slitting. Therefore, to ensure sufficient bonding, the lamination speed (line speed) is adjusted to adjust the heating time using a hot plate or similar device.

Although the mechanism behind this is unclear, by incorporating the laminating speed enhancer of the present invention into a starch-based adhesive for corrugated board, the viscosity is appropriately reduced within the storage tank temperature range (e.g., 45°C or below), preventing problems when adding alkali or increasing the starch content. Furthermore, the viscosity is rapidly increased and initial adhesive strength is achieved within the temperature range of the heat drying step in the laminating process (e.g., a heating step at an equipment temperature of 160°C or above, more preferably 180°C or above, with the sheet temperature being 60°C or above, more preferably 65°C or above). Therefore, adding a laminating speed enhancer to a starch-based adhesive for corrugated board can improve the laminating speed in the production of corrugated board sheets.

Therefore, the present invention also provides a method for increasing the lamination speed in the production of corrugated cardboard sheets, which includes the step of adding a lamination speed enhancer to a starch-based corrugating adhesive. The starch-based corrugating adhesive before adding the lamination speed enhancer contains, for example, the above-mentioned water, main starch, carrier starch, alkali, boron compound, etc., but does not contain the phenolic resin that is the lamination speed enhancer.

The lamination speed improvement method is applicable to the production of various types of corrugated cardboard sheets, including general-purpose corrugated cardboard, water-repellent corrugated cardboard, and water-repellent corrugated cardboard that uses a starch-based adhesive containing a water-resistant agent other than phenolic resin.

<Example>
Example 1
<Preparation of carrier part>
600 g of water was placed in a 1-L stainless steel mug and heated to 60°C using a water bath, and 72 g of commercially available cornstarch for starch-based adhesives for corrugated cardboard (manufactured by Oji Cornstarch Co., Ltd.) was added, followed by dispersion using a Robomix mixer (4500 rpm) manufactured by Tokushu Kika Kogyo Co., Ltd. to prepare a starch slurry. While stirring, 50 g of a 25% caustic soda solution was added to this starch slurry, and the mixture was stirred for 15 minutes to produce a carrier starch for a starch-based adhesive for corrugated cardboard.

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

<Preparation of starch-based adhesive for cardboard>
While stirring the obtained main starch with the stirrer (4000 rpm), the carrier starch was added at a rate of 120 g/min using a tube pump. The addition took 6 minutes.

While continuing to stir, borax pentahydrate was added.

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

The viscosity of the resulting adhesive was 280 mPa·S (measured with a Brookfield viscometer).

30 g of the resulting adhesive was placed in an aluminum cup for measuring an RVA (Rapid Visco Analyzer, manufactured by NEWPORT SCIENTIFIC), and a temperature-viscosity curve was obtained using the measuring instrument at a heating rate of 5.5°C and a rotation speed of 160 rpm up to the point where 500 RVU was reached. From the obtained curve, the temperature at which 100 RVU was reached was measured.

<Initial adhesive strength>
A 50mm x 85mm sheet of general-purpose single-faced corrugated cardboard (liner basis weight: 280g/core basis weight: 180g) was coated with 5g/ ^m² of cardboard adhesive (bone-dry weight) and placed in a pin tester equipped with a load cell. A liner (basis weight: 280g) was placed on top and pressed with a 1kg hot plate (180°C). The pressing time was 2, 3, or 5 seconds. After pressing, the liner and single-faced cardboard were immediately peeled off, and the strength at that time was measured with a load cell as the initial adhesive strength.

Examples 2 to 5 and Comparative Example The initial adhesive strength was measured in the same manner as in Example 1, except that the amounts of the phenolic resin and the ketone resin (water-resistant agent A (Oji Cornstarch Co., Ltd.) added were as shown in Table 1. The ketone resin was added immediately after the addition of the phenolic resin while stirring the corrugated board adhesive, just like the phenolic resin.

The results are shown in Table 1 and Figure 1.

Comparative Example 2
<Manufacturing starch-based adhesives for corrugated cardboard using a one-tank system>
1010 g of water was placed in a 3 L stainless steel mug and heated to 35°C using a water bath. 99 g of commercially available cornstarch for starch-based adhesives for corrugated cardboard (OHP-C153, manufactured by Oji Cornstarch Co., Ltd.) was added. While stirring with a Robomix mixer manufactured by Tokushu Kika Kogyo Co., Ltd. (4500 rpm), 55 g of a 25% caustic soda solution was added to the starch slurry and stirred for 15 minutes. While continuing to stir, 700 g of water, 545 g of commercially available cornstarch (manufactured by Oji Cornstarch Co., Ltd.), and 8.5 g of borax decahydrate were added and stirred for 15 minutes to produce a starch-based corrugated cardboard adhesive. The viscosity of the resulting adhesive was 240 mPa·s (measured with a Brookfield viscometer). The resulting adhesive was mixed with a Three-One motor at 600 rpm. The mixture was stored while being stirred at 40°C, and then the RVA measurement and the initial adhesive strength measurement, which will be described later, were carried out.

<Initial adhesive strength>
A 50mm x 85mm sheet of general-purpose single-faced corrugated cardboard (liner basis weight: 280g/core basis weight: 180g) was coated with 5g/ ^m² of cardboard adhesive (bone-dry weight) and placed in a pin tester equipped with a load cell. A liner (basis weight: 280g) was placed on top and pressed with a 1kg hot plate (180°C). The pressing time was 3, 5, or 7 seconds. After pressing, the liner and single-faced cardboard were immediately peeled off, and the strength at that time was measured with a load cell as the initial adhesive strength.

<Viscosity increase at 90°C using RVA>
The heating and cooling block of the RVA (Rapid Visco Analyzer, manufactured by NEWPORT SCIENTIFIC) was programmed to maintain a constant temperature of 90° C. from immediately after the start of measurement until the end of measurement, and was preheated to 90° C. 30 g of the adhesive obtained above was placed in an RVA standard can (made of aluminum, Perten), which was then attached to the RVA together with an RVA standard paddle, and the can was programmed to stir at a paddle rotation speed of 500 rpm from immediately after the start of measurement until the end of measurement.

Measurements were then started, and a time-RVA viscosity curve was obtained. These measurements were taken 30 minutes and 150 minutes after the addition of borax decahydrate, the final chemical added in the process of preparing the starch-based adhesive for corrugated board.

Example 7
A starch-based adhesive was prepared using the one-tank method in the same manner as in Comparative Example 2. Then, 5 minutes after adding the borax decahydrate, 32.2 g of a resol-type water-soluble phenolic resin (trade name PR-967, non-volatile content 40%, manufactured by Sumitomo Bakelite Co., Ltd.) was added in its pure form. This amount was 5% by mass of the total starch amount (total amount of carrier starch and main starch). After 15 minutes of stirring following the addition of the borax, the viscosity was 230 mPa·S. Thereafter, the initial adhesive strength was measured in the same manner as in Comparative Example 2. The viscosity increase at 90°C was also measured in the same manner as in Comparative Example 2. This measurement was performed 30 minutes and 150 minutes after adding the phenolic resin, which is the last chemical added when producing the corrugated board 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), a starch-based adhesive was produced, and the initial adhesive strength and RVA were measured in the same manner as in Example 7. The viscosity was 210 mPa·S after 15 minutes of stirring following the addition of borax.

The results are shown in Table 2 and the graph in Figure 3.

Starch-based adhesives for corrugated board containing the laminating speed enhancer of the present invention tended to have a short viscosity increase time. It is presumed that the short viscosity increase time improves initial adhesive strength, enabling an increase in laminating speed. Furthermore, starch-based adhesives for corrugated board containing the laminating speed enhancer of the present invention also tended to have a small decrease in initial adhesive strength even over time after glue production. Because the decrease in initial adhesive strength is small, a longer pot life can be expected.

Claims (2)

A method for increasing the lamination speed in the production of corrugated cardboard sheets, comprising a step of adding a lamination speed improver for use in a starch-based adhesive for corrugated cardboard, the lamination speed improver comprising a phenolic resin, to the starch-based adhesive for corrugated cardboard,
the solid content of the phenolic resin in the starch-based adhesive for corrugated cardboard is 0.5 to 4.8 parts by mass per 100 parts by mass of the total solid content of the starch;
A method for improving lamination speed, wherein the starch-based adhesive for corrugated cardboard does not contain any water-resistant agent other than the phenolic resin (provided that the 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 an 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 an epihalohydrin ). The method for improving lamination speed according to claim 1, wherein the phenolic resin is a resol-type phenolic resin or a novolac-type phenolic resin.