JP7531367B2 - Washing Instructions - Google Patents

Description

The present invention relates to a washing method.

Compared to powder detergents, liquid detergents are easier to use because they leave no residue and can be applied directly to the stained area.
In addition, in recent years, washing machines equipped with a function to automatically dispense liquid detergent from a tank containing the detergent via a dispensing pipe into the washing tub (automatic detergent dispensing function) have been put to practical use. The automatic detergent dispensing function not only eliminates the need to measure, but also allows even a small amount of liquid detergent to be accurately measured, making it easier to achieve sufficient cleaning power and avoiding waste due to overuse.

On the other hand, liquid detergents tend to have inferior cleaning power compared to powder detergents.
In response to these problems, for example, Patent Document 1 proposes a liquid detergent that contains a builder made of a water-soluble inorganic salt, and one or more selected from a surfactant and a water-miscible organic solvent, and has a specific electrical conductivity.
Patent Document 2 proposes a liquid detergent containing a nonionic surfactant, a hydrophilic solvent, an alkaline solid compound, and a specific polymer.
The liquid detergents in Patent Documents 1 and 2 aim to improve the cleaning power.

JP 2003-27100 A JP 2004-155937 A

However, there is a demand for improved cleaning power in liquid detergents.

Therefore, the present invention aims to provide a washing method that can further enhance the cleaning power of liquid detergent.

The present invention has the following aspects.
[1] A washing method comprising: a first step (I) of contacting an article to be washed with a first laundry liquid containing a liquid detergent containing a surfactant in a washing tub; and a second step (II) of supplying both water and the liquid detergent or either one of them into the washing tub to prepare a second laundry liquid, and contacting the article to be washed that has been subjected to the first step (I) with the second laundry liquid in the washing tub; wherein a dilution ratio of the first laundry liquid with water is 2000 times or less per volume part of the liquid detergent, a dilution ratio of the second laundry liquid with water is 800 times or more per volume part of the liquid detergent, and a pH of the second laundry liquid at 25°C is 8.0 or more.
[2] The washing method according to [1], wherein the second step (II) comprises adding water to the first washing liquid in the washing tub to obtain the second washing liquid.
[3] The washing method according to [1] or [2], wherein the liquid detergent and the water are supplied to the washing tub to prepare the first washing liquid in which the liquid detergent is diluted with the water, and the dilution ratio of the first washing liquid is 100 to 2000 times by volume per 1 volume part of the liquid detergent, and the water is added to the first washing liquid in the washing tub to prepare the second washing liquid, or the water and the liquid detergent are supplied to the washing tub to prepare the second washing liquid, and the dilution ratio of the second washing liquid is 800 to 6000 times by volume per 1 volume part of the liquid detergent.
[4] The washing method according to any one of [1] to [3], wherein the concentration of the surfactant in the first washing liquid is 100 ppm or more by mass, and the concentration of the surfactant in the second washing liquid is 50 ppm or more and 350 ppm or less by mass.
[5] The washing method according to any one of [1] to [4], wherein the liquor ratio in the first step (I) represented by [mass of the first washing liquid]/[total mass of the items to be washed] is 4 or more, and the liquor ratio in the second step (II) represented by [mass of the second washing liquid]/[total mass of the items to be washed] is 6 or more.
[6] The washing method according to any one of [1] to [5], wherein the surfactant is at least one selected from alkylbenzene sulfonate, alkyl ether sulfate, alkenyl ether sulfate, polyoxyalkylene alkyl ether, and polyoxyalkylene alkenyl ether.
[7] The washing method according to any one of [1] to [6], wherein the liquid detergent contains an alkaline agent, and a part or all of the alkaline agent is present in a solid state.
[8] The washing method according to any one of [1] to [6], wherein the liquid detergent contains a chelating agent, and a part or all of the chelating agent is present in a solid state.
[9] The washing method according to any one of [1] to [8], wherein the liquid detergent further comprises one or more structuring agents selected from bacterial cellulose, non-bacterial cellulose, and hydrogenated castor oil.

The washing method of the present invention can further improve the cleaning power of liquid detergent.

[Washing instructions]
The washing method of the present invention has a first step (I) and a second step (II).
The first step (I) (hereinafter, also simply referred to as "step (I)") is a step of contacting the first washing liquid containing a liquid detergent containing a surfactant with the items to be washed in the washing tub.
The second step (II) (hereinafter also simply referred to as "step (II)") is a step of supplying both or either one of water and liquid detergent to the washing tub to prepare a second washing liquid, and bringing the second washing liquid into contact with the items to be washed that have been subjected to step (I) in the washing tub.
Examples of items to be washed include textile products such as clothing, dishcloths, towels, sheets, curtains, etc. The material of the textile products is not particularly limited, and may be any of natural fibers such as cotton, silk, wool, etc., and chemical fibers such as polyester, polyamide, etc.
Hereinafter, the washing method of the present invention will be described in detail with reference to embodiments.

First Embodiment
The washing method of this embodiment is a method in which a first laundry liquid of any concentration is brought into contact with an item to be washed for any period of time to wash the item (step (I)), both water and/or liquid detergent are supplied to the first laundry liquid to prepare a second laundry liquid of any concentration, and this second laundry liquid is brought into contact with the item to be washed for any period of time to wash the item (step (II)).

<Step (I)>
In step (I) of this embodiment, a first washing liquid of any concentration is brought into contact with the article to be washed for any time. By bringing the first washing liquid into contact with the article to be washed, dirt components can be removed from the article to be washed, and the article to be washed can be washed. The first washing liquid may be a liquid that has been diluted in advance, or the first washing liquid may be prepared by diluting a liquid detergent with water in a washing tub.
In this specification, "dilution" refers to adding water to a liquid detergent (product) to dilute the concentration of the liquid detergent. The water already contained in the liquid detergent (product) is different from the water used for dilution.

The washing tub is not particularly limited, and may be not only the washing tub of a washing machine, but also a container such as a basin or bucket.
Examples of the washing machine include a two-layer washing machine, a fully automatic washing machine, a washing machine with an automatic detergent dispensing function, a commercial washing machine, and the like, and a washing machine with an automatic detergent dispensing function is particularly preferred.
The automatic detergent dispensing function automatically dispenses liquid detergent from a tank containing the liquid detergent into the washing tub via a dust filter located at the bottom of the tank and a dispensing pipe.
A measuring means such as a syringe pump is provided in the middle of the supply pipe, so that a fixed amount set according to the amount of laundry, etc., can be transferred from the tank to the washing tub.
Using the automatic detergent dispensing function not only saves you the trouble of measuring out the detergent, but also prevents liquid detergent from getting on your hands when measuring out the detergent, or from spilling and soiling the washing machine or surrounding area.

In step (I) of this embodiment, it is preferable to immerse the items to be washed in the first washing liquid and agitate the items for treatment. By agitating the items for treatment, mechanical force can be applied to the items for washing, which increases the efficiency of contact with the first washing liquid and further enhances the cleaning power.

The concentration of the first washing liquid can be determined by, in addition to the content of cleaning components such as surfactants, values such as spectroscopy (ultraviolet absorption spectroscopy (UV spectroscopy), fluorescence spectroscopy, infrared absorption spectroscopy (IR spectroscopy), etc.), viscosity, liquid specific gravity, shear stress, turbidity, ultrasound, microwaves, electrical conductivity, alkalinity, pH, etc., as indicators of concentration.
Liquid detergents will be described later.

In this embodiment, the dilution ratio of the first washing liquid with water is 2000 volumes or less per volume part of liquid detergent, preferably 100 to 2000 volumes, more preferably 200 to 1800 volumes, even more preferably 300 to 1500 volumes, and particularly preferably 500 to 1200 volumes. When the dilution ratio of the first washing liquid with water is equal to or less than the upper limit, the cleaning power can be further improved. When the dilution ratio of the first washing liquid with water is equal to or greater than the lower limit, recontamination can be suppressed. Recontamination refers to the phenomenon in which dirt that has peeled off from the washed item reattaches to the washed item. In addition, when the dilution ratio of the first washing liquid with water is equal to or greater than the lower limit, the amount of the first washing liquid can be increased, making it easier to apply mechanical force when using a washing machine, and the cleaning power can be further improved.

The dilution ratio of the first washing liquid with water is expressed as the volume (capacity) of the first washing liquid relative to the volume (capacity) of the liquid detergent. That is, the dilution ratio can be calculated by the following formula (1).
Dilution ratio (volume times) = volume of first washing liquid (L) / volume of liquid detergent (L) ... (1)

For example, when 15 mL of liquid detergent is diluted with water to obtain 30 L of the first washing liquid, the dilution ratio is 30/15×10 ⁻³ =2000 (volume times).
The dilution ratio is calculated based on the volume at room temperature (1° C. to 30° C.).

The surfactant concentration in the first washing liquid is preferably 100 ppm or more, more preferably 200 ppm or more, and even more preferably 400 ppm or more by mass. When the surfactant concentration in the first washing liquid is equal to or more than the lower limit, the cleaning power can be further improved.
The upper limit of the surfactant concentration in the first laundry liquid is not particularly limited and may be 2000 ppm. The surfactant concentration in the first laundry liquid is determined by first determining the mass (mass%) of the surfactant relative to the total mass of the liquid detergent, and then dividing the mass by the dilution ratio of the first laundry liquid.

The pH of the first washing liquid at 25°C is not particularly limited, but is preferably 6.0 to 11.5, more preferably 7.0 to 11.0, even more preferably 8.0 to 10.5, and particularly preferably 9.0 to 10.0. When the pH of the first washing liquid at 25°C is equal to or higher than the lower limit, the cleaning power can be further improved. When the pH of the first washing liquid at 25°C is equal to or lower than the upper limit, damage to clothes can be suppressed.
The pH of the first washing liquid at 25° C. can be measured with a pH meter (portable pH/ORP/ION meter D-73, manufactured by Horiba, Ltd.) with the measurement object at 25° C.

The time for which the first laundry liquid is brought into contact with the laundry in step (I) (hereinafter also referred to as the "treatment time in step (I)") is preferably 3 minutes or more, more preferably 5 minutes or more, and even more preferably 10 minutes or more. When the treatment time in step (I) is equal to or more than the above lower limit, dirt on the laundry can be sufficiently removed, and cleaning power can be further improved. There is no particular limit to the upper limit of the treatment time in step (I), but it may be about overnight (12 hours), and 8 hours or less is preferable, and 90 minutes or less is more preferable. When the treatment time in step (I) is equal to or less than the above upper limit, the washing time can be shortened, and washing efficiency can be further improved.

The treatment temperature in step (I) is preferably 10 to 80°C, more preferably 20 to 70°C, even more preferably 30 to 60°C, and particularly preferably 40 to 50°C. When the treatment temperature in step (I) is equal to or higher than the above lower limit, the liquid detergent can exhibit sufficient cleaning power, and cleaning power can be further enhanced. When the treatment temperature in step (I) is equal to or lower than the above upper limit, deterioration of the liquid detergent can be suppressed. In addition, when the treatment temperature in step (I) is equal to or lower than the above upper limit, the energy required by the washing machine can be saved, and the environmental burden can be reduced.

The liquor ratio in step (I) expressed by [mass of the first washing liquid]/[total mass of the items to be washed] (hereinafter also referred to as "liquor ratio in step (I)") is preferably 4 or more, more preferably 5 to 30, even more preferably 7 to 25, and particularly preferably 8 to 20. When the liquor ratio in step (I) is equal to or less than the upper limit, the detergent components of the first washing liquid can sufficiently penetrate into the items to be washed, and the cleaning power can be further improved. When the liquor ratio in step (I) is equal to or more than the lower limit, the mechanical force can be easily applied when using a washing machine, and the cleaning power can be further improved.
In this specification, the "total mass of the items to be washed" refers to the total mass of the items to be washed immediately before the start of washing.

In this embodiment, step (I) ends when the supply of water or liquid detergent to the first laundry liquid begins after the first laundry liquid has been brought into contact with the items to be washed.

<Step (II)>
In the step (II) of this embodiment, water and/or liquid detergent are supplied to the first washing liquid to prepare a second washing liquid of any concentration. By contacting the second washing liquid with the article to be washed for any time, the dirt components can be removed from the article to be washed, and the article to be washed can be washed. By including the step (II), the dirt on the article to be washed can be removed more reliably, and the cleaning power can be further improved.
The liquid detergent used in step (I) and the liquid detergent used in step (II) may be the same or different.

The second washing liquid comprises liquid detergent and water, i.e., no concentrate of liquid detergent is used as the second washing liquid.
The dilution ratio of the second washing liquid may be greater than that of the first washing liquid, may be less than that of the first washing liquid, or may be the same as that of the first washing liquid. When the dilution ratio of the second washing liquid is the same as that of the first washing liquid, the washing liquid prepared after the end of step (I) is the second washing liquid.
The dilution ratio of the second laundry liquid is preferably greater than that of the first laundry liquid. That is, the second laundry liquid preferably has a lower surfactant concentration than the first laundry liquid. By making the second laundry liquid lower in concentration than the first laundry liquid, the rinsing property can be improved and the total time required for washing can be shortened. The rinsing property refers to the ease of rinsing off the cleaning components attached to the laundry with water.

The dilution ratio of the second washing liquid with water is 800 or more by volume, preferably 800 or more to 6000 or less by volume, more preferably 900 or more to 5000 or less by volume, even more preferably 1200 or more to 4500 or less by volume, and particularly preferably 2000 or more to 4000 or less by volume. When the dilution ratio of the second washing liquid with water is equal to or more than the lower limit, the mechanical force applied to the washed item can be easily applied, and the cleaning power can be further improved. In addition, when the dilution ratio of the second washing liquid with water is equal to or more than the lower limit, recontamination can be suppressed. When the dilution ratio of the second washing liquid with water is equal to or less than the upper limit, sufficient cleaning power can be obtained, and the dirt on the washed item can be more reliably removed.
The dilution ratio of the second washing liquid with water is determined in the same manner as the dilution ratio of the first washing liquid.

The value obtained by dividing the dilution ratio of the second washing liquid by the dilution ratio of the first washing liquid (hereinafter also referred to as the "difference in dilution ratio") is preferably 0.8 to 50, more preferably 1.0 to 20, and even more preferably 1.0 to 15. When the difference in dilution ratio is equal to or greater than the above lower limit, recontamination can be suppressed. In addition, when the difference in dilution ratio is equal to or greater than the above lower limit, rinsing properties can be improved. When the difference in dilution ratio is equal to or less than the above upper limit, sufficient cleaning power can be obtained, and dirt on the washed items can be removed more reliably.

The surfactant concentration of the second washing liquid is preferably 50 ppm to 350 ppm by mass, more preferably 80 ppm to 300 ppm by mass, and even more preferably 100 ppm to 250 ppm by mass. When the surfactant concentration of the second washing liquid is equal to or higher than the lower limit, sufficient cleaning power can be obtained. When the surfactant concentration of the second washing liquid is equal to or lower than the upper limit, rinsing performance can be improved and the total time required for washing can be shortened.
The concentration of the surfactant in the second washing liquid is determined by first determining the mass (mass %) of the surfactant relative to the total mass of the liquid detergent, and then dividing this by the dilution ratio of the second washing liquid.

The time for which the second laundry liquid is brought into contact with the laundry in step (II) (hereinafter also referred to as "treatment time in step (II)") is preferably 3 minutes or more, more preferably 5 to 30 minutes, and even more preferably 5 to 15 minutes. When the treatment time in step (II) is equal to or more than the above-mentioned lower limit, dirt on the laundry can be sufficiently removed, and cleaning power can be further improved. When the treatment time in step (II) is equal to or less than the above-mentioned upper limit, the washing time can be shortened, and washing efficiency can be further improved.
In the washing method of the present embodiment, by carrying out the treatment of step (II) after step (I), high detergency can be obtained even if the treatment time of step (II) is shortened. Therefore, even if the total time required for washing is shortened, the detergency can be further improved.

The treatment temperature in step (II) is preferably 10 to 80°C, more preferably 20 to 70°C, even more preferably 30 to 60°C, and particularly preferably 40 to 50°C. When the treatment temperature in step (II) is equal to or higher than the lower limit, the liquid detergent can exhibit sufficient cleaning power, and cleaning power can be further enhanced. When the treatment temperature in step (II) is equal to or lower than the upper limit, deterioration of the liquid detergent can be suppressed. In addition, when the treatment temperature in step (II) is equal to or lower than the upper limit, the energy required by the washing machine can be saved, and the environmental impact can be reduced.

The liquor ratio in step (II) expressed by [mass of second washing liquid]/[total mass of items to be washed] (hereinafter also referred to as "liquor ratio in step (II)") is preferably 6 or more, more preferably 6 to 40, even more preferably 8 to 36, and particularly preferably 10 to 30. If the liquor ratio in step (II) is equal to or more than the lower limit, the mechanical force can be more easily exerted when the washing machine is used, and cleaning power can be further improved. If the liquor ratio in step (II) is equal to or less than the upper limit, the amount of water added can be reduced, and the environmental impact can be reduced.

In step (II), it is preferable to immerse the items to be washed in the second washing liquid and agitate the liquid for treatment. By agitating the items to be washed, mechanical force can be applied to the items to be washed, which increases the efficiency of contact with the second washing liquid and further enhances the cleaning power.

The pH of the second washing liquid at 25° C. is 8.0 or more, preferably 8.0 to 10.5, more preferably 8.0 to 10.0, and even more preferably 8.0 to 9.5. When the pH of the second washing liquid at 25° C. is equal to or more than the lower limit, the liquid detergent can exhibit sufficient cleaning power, and the cleaning power can be further improved. When the pH of the second washing liquid at 25° C. is equal to or less than the upper limit, damage to clothes can be suppressed.
The pH of the second washing liquid at 25°C can be measured in the same manner as the pH of the first washing liquid at 25°C.

In this embodiment, step (II) starts when the supply of water and/or liquid detergent to the first washing liquid is started, and ends when the second washing liquid is brought into contact with the items to be washed and then the discharge of the second washing liquid is started, or when the items to be washed are removed from the second washing liquid.

In this embodiment, the second washing liquid is prepared, for example, by supplying both or either one of water and liquid detergent to a washing tub so as to have an arbitrary dilution ratio.
Supplying only water to the washing tub will produce a second washing liquid having a lower surfactant concentration than the first washing liquid, whereas supplying only liquid detergent to the washing tub will produce a second washing liquid having a higher surfactant concentration than the first washing liquid.
The concentration of the surfactant in the second washing liquid can be appropriately adjusted depending on the degree of dirt on the items to be washed.
The water or liquid detergent may be supplied in a predetermined amount at a constant rate (supply amount (L/min)), or the supply rate may be changed midway.

<Other processes>
The washing method of the present embodiment may include steps other than step (I) and step (II) (hereinafter also referred to as "other steps").
Examples of other steps include a draining step, a rinsing step, a spin-drying step, a drying step, and cleaning steps other than steps (I) and (II) which are performed in general washing.
The other step may be provided before or after step (I) and step (II), or may be provided between step (I) and step (II). Two or more other steps may be provided. In addition, step (I) and step (II) may be repeated two or more times after the other step, or another step may be provided after step (I) and step (II) are repeated two or more times.

The draining process in this embodiment is a process of draining the second washing liquid that has been in contact with the article to be washed from the washing tub. The draining process refers to the period from when the discharge of the second washing liquid starts to when the discharge of the second washing liquid is completed. From the viewpoint of removing the second washing liquid that has adhered to the article to be washed, it is preferable that the washing method of this embodiment has a draining process.

From the viewpoint of more reliably removing the second laundry liquid adhering to the items to be washed, the washing method of the present embodiment preferably includes a rinsing step.
The concentration of the surfactant in the rinsing step is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 30 ppm or less. When the concentration of the surfactant in the rinsing step is equal to or less than the upper limit, the surfactant contained in the second washing liquid adhering to the laundry can be sufficiently washed off. The concentration of the surfactant in the rinsing step can be calculated from the concentration of the surfactant in the second washing liquid and the amount of water used for rinsing.
The liquor ratio in the rinsing step, expressed as [mass of water used for rinsing]/[total mass of the items to be washed] (hereinafter also referred to as "liquor ratio in the rinsing step"), is preferably 6 or more, more preferably 6 to 40, even more preferably 8 to 36, and particularly preferably 10 to 30. When the liquor ratio in the rinsing step is equal to or more than the lower limit, the second laundry liquid adhering to the items to be washed can be sufficiently washed off. When the liquor ratio in the rinsing step is equal to or less than the upper limit, the amount of water used for rinsing can be saved.

From the viewpoint of removing moisture adhering to the items to be washed, the washing method of the present embodiment preferably includes a dehydration step.
From the viewpoint of more reliably removing moisture adhering to the items to be washed, the washing method of the present embodiment preferably includes a drying step.

Washing steps other than step (I) and step (II) (hereinafter also referred to as "other washing steps") are steps in which the items to be washed are treated by contacting them with other washing liquids containing liquid detergent. The other washing liquids are washing liquids prepared before the start of step (I) or after the end of step (II). The surfactant concentration of the other washing liquids may be different from or the same as the surfactant concentration of the first washing liquid. The surfactant concentration of the other washing liquids may be different from or the same as the surfactant concentration of the second washing liquid.
When step (I) is the first washing step and step (II) is the second washing step, examples of the other washing step include a third washing step and a fourth washing step.
More specifically, examples of the other washing steps include a step of directly applying a liquid detergent to the items to be washed, a step of preparing another washing liquid in a container other than the washing tub used in steps (I) and (II) and immersing the items to be washed in the other washing liquid and leaving it to stand, and a step of additional washing after step (II).
The number of washing steps is not particularly limited, but in consideration of washing efficiency, it is preferable that there are two steps, step (I) and step (II). That is, it is preferable that the washing method of the present embodiment does not have any washing steps other than step (I) and step (II).

The washing method of the present embodiment includes step (I), and therefore can remove dirt components from the items to be washed and can clean the items to be washed.
The washing method of the present embodiment includes step (II), so that dirt on the items to be washed can be removed more reliably, and the cleaning power can be further improved.
The washing method of the present embodiment has two processing steps, step (I) and step (II), which can reduce the total time required for washing. In addition, by having two processing steps, step (I) and step (II), the washing power can be further improved compared to conventional washing methods.

According to the washing method of the present embodiment, the cleaning power of the liquid detergent can be further improved.
In addition, the washing method of this embodiment results in cleaner washed items.

<Liquid detergent>
The liquid detergent used in the washing method of the present embodiment contains a surfactant.
The surfactant is not particularly limited as long as it is a surfactant used in conventional liquid detergents, and examples thereof include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, and semi-polar surfactants.
The surfactant may be used alone or in combination of two or more kinds.
From the viewpoint of further enhancing the cleaning power, the surfactant preferably contains a nonionic surfactant and an anionic surfactant. As the surfactant, the nonionic surfactant and the anionic surfactant may be used in combination with one or more of a cationic surfactant, an amphoteric surfactant, and a semi-polar surfactant.

Examples of nonionic surfactants include polyoxyalkylene-type nonionic surfactants, alkylphenols, alkylene oxide adducts of fatty acids having 8 to 22 carbon atoms or amines having 8 to 22 carbon atoms, polyoxyethylene polyoxypropylene block copolymers, fatty acid alkanolamines, fatty acid alkanolamides, polyhydric alcohol fatty acid esters or alkylene oxide adducts thereof, polyhydric alcohol fatty acid ethers, alkyl (or alkenyl)amine oxides, alkylene oxide adducts of hydrogenated castor oil, sugar fatty acid esters, N-alkyl polyhydroxy fatty acid amides, and alkyl glycosides.
As the nonionic surfactant, a polyoxyalkylene type nonionic surfactant is preferable, and among them, in particular, a compound represented by the following formula (2) and a compound represented by the following formula (3) are more preferable, and a compound represented by the following formula (2) is even more preferable.

R ¹¹ -O-[(EO) _s / (A ¹¹ O) _t ]-(EO) _u -R ¹² ...(2)
In formula (2), R ¹¹ is a straight or branched chain hydrocarbon group having 8 to 22 carbon atoms. R ¹² is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkenyl group having 2 to 6 carbon atoms. A ¹¹ O is at least one of PO (oxypropylene group) and BO (oxybutylene group). t is a number from 0 to 6 indicating the average number of repeats of A ¹¹ O. u is a number from 0 to 20 indicating the average number of repeats of EO.

R ¹³ -X-[(EO) _p /(A ¹² O) _q ]-(EO) _r -R ¹⁴ ...(3)
In formula (3), R ¹³ is a hydrocarbon group having 7 to 21 carbon atoms. -X- is -COO- or -CONH-. R ¹⁴ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A 12 is an oxypropylene group or an alkenyl group having 2 to 6 carbon atoms. EO is an oxyethylene group. p is a number from 3 to 25 indicating the average number of EO repetitions. A ¹³ is an oxypropylene group or an alkenyl group having 2 to 6 carbon atoms. q is a number from 0 to 6 indicating the average number of repetitions of A ¹² O; and r is a number from 0 to 20 indicating the average number of repetitions of EO.

Examples of the anionic surfactant include carboxylic acid type anionic surfactants such as linear alkylbenzenesulfonic acid or a salt thereof (LAS), α-olefinsulfonic acid or a salt thereof (AOS), linear or branched alkyl sulfate or a salt thereof (AS), polyoxyalkylene alkyl(alkenyl)ether sulfate or a salt thereof (AES), alkanesulfonic acid having an alkyl group or a salt thereof, α-sulfofatty acid ester or a salt thereof, internal olefinsulfonic acid or a salt thereof (IOS), hydroxyalkanesulfonic acid or a salt thereof (HAS), alkyl ether carboxylic acid or a salt thereof, polyoxyalkylene ether carboxylic acid or a salt thereof, alkylamide ether carboxylic acid or a salt thereof, alkenylamide ether carboxylic acid or a salt thereof, and acylamino carboxylic acid or a salt thereof; and phosphate type anionic surfactants such as alkyl phosphate ester or a salt thereof, polyoxyalkylene alkyl phosphate ester or a salt thereof, polyoxyalkylene alkylphenyl phosphate ester or a salt thereof, and glycerin fatty acid ester monophosphate ester or a salt thereof.
Examples of the salt form of the anionic surfactant include alkali metal salts (sodium salt, potassium salt, etc.), alkaline earth metal salts (magnesium salt, etc.), alkanolamine salts (monoethanolamine salt, diethanolamine salt, etc.), and the like.
As the anionic surfactant, LAS, AOS, AS, and AES are preferred, and among them, LAS and AES are more preferred from the viewpoint of further enhancing the detergency. The liquid detergent preferably contains at least AES, and more preferably contains both LAS and AES.

The polyoxyalkylene alkyl(alkenyl) ether sulfate or its salt (AES) is represented by the following formula (4).
R ¹⁵ -O- [(EO) _m / (PO) _n ]-SO ₃ ^- M ⁺ ... (4)
(In formula (4), R ¹⁵ is a linear or branched alkyl group having 8 to 20 carbon atoms or a linear or branched alkenyl group having 8 to 20 carbon atoms. EO is an oxyethylene group. PO is an oxypropylene group. m is a number of 0.1 or more representing the average number of repetitions of EO. n is a number of 0 to 6 representing the average number of repetitions of PO. [(EO) _m /(PO) _n ] indicates that there is no limitation on the order of arrangement of EO and PO, and M ⁺ is a counter cation.)

Examples of cationic surfactants include long-chain aliphatic amidoalkyl tertiary amines or salts thereof, such as caprylic acid dimethylaminopropylamide, capric acid dimethylaminopropylamide, lauric acid dimethylaminopropylamide, myristic acid dimethylaminopropylamide, palmitic acid dimethylaminopropylamide, stearic acid dimethylaminopropylamide, behenic acid dimethylaminopropylamide, and oleic acid dimethylaminopropylamide; aliphatic ester alkyl tertiary amines or salts thereof, such as palmitate ester propyl dimethylamine and stearate ester propyl dimethylamine; palmitic acid diethanolaminopropylamide, stearic acid diethanolaminopropylamide; and quaternized compounds such as alkyl trimethyl ammonium salts, dialkyl dimethyl ammonium salts, alkyl benzyl dimethyl ammonium salts, and alkyl pyridinium salts.
Examples of the salt form of the cationic surfactant include alkali metal salts (sodium salt, potassium salt, etc.), alkaline earth metal salts (magnesium salt, etc.), alkanolamine salts (monoethanolamine salt, diethanolamine salt, etc.), and the like.

Examples of amphoteric surfactants include alkyl betaine type, alkyl amide betaine type, imidazoline type, alkyl amino sulfone type, alkyl amino carboxylic acid type, alkyl amide carboxylic acid type, amide amino acid type, and phosphate type amphoteric surfactants.

Examples of semi-polar surfactants include alkylamine oxides and alkylamidopropyldimethylamine oxides.

The surfactant content is preferably 15 to 85% by mass, more preferably 15 to 80% by mass, and even more preferably 30 to 65% by mass, based on the total mass of the liquid detergent. If the surfactant content is equal to or greater than the lower limit, the cleaning power can be further improved. If the surfactant content is equal to or less than the upper limit, the rinsing performance can be improved.

The liquid detergent may contain optional components other than the surfactant. As the optional components, components generally contained in liquid detergents for clothing can be used.
Examples of optional components include water-miscible organic solvents, water, chelating agents, enzymes, alkaline agents, coating agents, structuring agents, hydrotropic agents, detergent builders, stabilizers, antibacterial agents, texture improvers such as silicone, softeners, defoamers, anti-redeposition agents (soil release agents), preservatives, fluorescent agents, dye transfer inhibitors, pearlizing agents, antioxidants, general-purpose dyes or pigments as colorants, emulsifiers, fragrances, insoluble particles, pH adjusters, and the like.
These optional components may be used alone or in combination of two or more.

Examples of the water-miscible organic solvent include alcohols such as ethanol, glycerin, 1-propanol, 2-propanol, 1-butanol, etc., glycols such as propylene glycol, butylene glycol, hexylene glycol, etc., polyglycols such as dipropylene glycol, etc., alkyl ethers such as diethylene glycol monobutyl ether (butyl carbitol), diethylene glycol dimethyl ether, 3-methoxy-3-methyl-1-butanol, etc. Among these, ethanol, glycerin, propylene glycol, diethylene glycol monobutyl ether (butyl carbitol), and 3-methoxy-3-methyl-1-butanol are preferred in terms of availability, liquid stability of the composition, flowability, etc.
In this specification, the water-miscible organic solvent refers to an organic solvent that dissolves in an amount of 50 g or more in 1 L of water at 25°C.

Water is not particularly limited, but examples include tap water, distilled water, purified water, ion-exchanged water, etc.

The liquid detergent of the present embodiment preferably contains a chelating agent from the viewpoint of further enhancing cleaning power.
Examples of the chelating agent include malonic acid, succinic acid, malic acid, diglycolic acid, tartaric acid, citric acid, and zeolite.
It is preferable that the chelating agent exists in a solid state in whole or in part, from the viewpoint that the solubility can be controlled by the amount of water, the concentration of the surfactant, etc., and the pH of the washing liquid can be more easily controlled.
The chelating agent may be coated with a coating agent described later. By coating the chelating agent with a coating agent, the dispersion stability in the liquid can be further improved. Here, the dispersion stability refers to a stable dispersion state when the solid particles are dispersed in the liquid.

Examples of enzymes include protease, amylase, lipase, cellulase, mannanase, cellulase, etc.

The liquid detergent of the present embodiment preferably contains an alkaline agent from the viewpoint of further enhancing cleaning power.
Examples of the alkaline agent include alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine, and inorganic alkaline agents such as sodium carbonate, sodium hydrogen carbonate (sodium bicarbonate), and sodium silicate.
The alkaline agent is preferably present in a solid state in whole or in part, from the viewpoint that the solubility can be controlled by the amount of water, the concentration of the surfactant, etc., and the pH of the washing liquid can be more easily controlled.
The alkaline agent may be coated with a coating agent described below. By coating the alkaline agent with a coating agent, the dispersion stability in the liquid can be further improved.

Examples of coating agents include hydroxypropylmethylcellulose, methylcellulose, polyacrylic acid or its salts, acrylic acid-maleic acid copolymer or its salts, acrylic acid-maleic anhydride copolymer or its salts, polyvinyl alcohol, etc. A coating agent that is difficult to dissolve in liquid detergent and easily dissolves in the first or second washing liquid is preferred. Examples of such coating agents include hydroxypropylmethylcellulose, methylcellulose, acrylic acid-maleic acid copolymer or its salts, etc.

The liquid detergent of the present embodiment preferably contains a structuring agent from the viewpoint of further enhancing the dispersion stability of the granular chelating agent or granular alkaline agent.
Structuring agents include bacterial cellulose, non-bacterial cellulose (microfibrillated cellulose), hydrogenated castor oil, and the like.
In this specification, the term "structured" refers to a state in which the viscosity changes before and after the application of force.

The content of the optional components is preferably from 0.1 to 85 mass %, more preferably from 15 to 70 mass %, and even more preferably from 30 to 65 mass %, based on the total mass of the liquid detergent.
The total amount of the components constituting the liquid detergent does not exceed 100% by mass.

The viscosity of the liquid detergent at 25° C. is preferably 5 to 10,000 mPa·s, more preferably 10 to 5,000 mPa·s, and even more preferably 100 to 1,000 mPa·s. When the viscosity of the liquid detergent at 25° C. is equal to or higher than the lower limit, the cleaning components of the liquid detergent are likely to penetrate into the items to be washed. When the viscosity of the liquid detergent at 25° C. is equal to or lower than the upper limit, the detergent is likely to disperse uniformly when diluted with water.
The viscosity of the liquid detergent at 25° C. is a value measured using a Brookfield viscometer (manufactured by TOKIMEC Corporation) (measurement conditions: rotor No. 2, rotation speed 60 rpm, viscosity after 1 minute).

The liquid detergent is produced by a conventionally known production method.
A liquid detergent can be produced, for example, by dispersing a surfactant and, if necessary, any optional ingredients in water.

Second Embodiment
In this embodiment, between step (I) and step (II), there is a first drainage step of draining the first washing liquid from the washing tub. By having the first drainage step, the first washing liquid adhering to the washed article can be removed. That is, the first washing liquid containing the dirt components from the washed article can be removed. Therefore, the washing efficiency in step (II) can be further improved.
In addition, in the washing method of the present embodiment, since it is possible to perform the step (II) after draining the first washing liquid containing the soiling components, re-contamination of the washed items can be suppressed.
The washing method of the present embodiment may include a spin-drying step after the first draining step.

<Step (I)>
Step (I) of this embodiment is similar to step (I) of the first embodiment.
The concentration of the first washing liquid in this embodiment is similar to that of the first embodiment.
In this embodiment, the end point of the step (I) is the time when the first laundry liquid starts to be discharged after the first laundry liquid has been brought into contact with the items to be washed.

<First drainage process>
The first drainage step is a step of draining the first washing liquid from the washing tub after the step (I). The first drainage step refers to a period from when the drainage of the first washing liquid starts to when the drainage of the first washing liquid is completed.
The drainage method is not particularly limited, and a drainage method used in general washing can be adopted. When the articles to be washed are immersed in the first washing liquid and agitated in step (I), the agitation is stopped, the drain outlet of the washing tub is opened, and the first washing liquid is drained.

<Step (II)>
Step (II) of this embodiment is a step of supplying both water and liquid detergent to the washing tub to prepare a second washing liquid, and bringing the second washing liquid into contact with the items to be washed that have been subjected to the first step (I) in the washing tub.
Step (II) of this embodiment differs from step (II) of the first embodiment in that both water and liquid detergent are always supplied to the washing tub.
In this embodiment, water and liquid detergent are poured into the washing tub containing the laundry. At this time, water may be poured in first and then liquid detergent, or liquid detergent may be poured in first and then water. Water and liquid detergent may be poured in separately, or liquid detergent may be diluted with water before pouring in.

The concentration of the second washing liquid in this embodiment is similar to that of the second washing liquid in the first embodiment.
In this embodiment, step (II) begins when the supply of water or liquid detergent to the washing tub is started after the first drainage step, and ends when the discharge of the second washing liquid is started after the second washing liquid has been brought into contact with the items to be washed, or when the items to be washed are removed from the second washing liquid.

<Other processes>
The washing method of the present embodiment may include other steps.
The other steps of this embodiment are similar to those of the first embodiment.

The liquid detergent of this embodiment and the method for producing the liquid detergent are the same as the liquid detergent of the first embodiment and the method for producing the liquid detergent of the first embodiment.

Third Embodiment
In this embodiment, the liquid detergent concentrate is not diluted and is used as the first washing liquid. That is, the first washing liquid in step (I) is a liquid detergent. Therefore, the washing method of this embodiment is suitable for removing dirt that is firmly attached to the washing object.

<Step (I)>
In the step (I) of the present embodiment, the liquid detergent is brought into contact with the article to be washed as the first washing liquid. The liquid detergent may be brought into contact with the article to be washed in the washing tub, or the article to be washed that has been brought into contact with the liquid detergent may be put into the washing tub.
In step (I) of this embodiment, it is preferable to bring the liquid detergent into contact with the object to be washed by applying or spraying it. By applying or spraying the liquid detergent to the object to be washed, a high concentration of detergent component can be selectively brought into contact with the soiled parts of the object to be washed, thereby further enhancing the cleaning power.

In this embodiment, step (I) ends when the supply of water or liquid detergent to the washing tub begins after the first washing liquid has been brought into contact with the items to be washed.

<Step (II)>
Step (II) of this embodiment is a step of supplying both water and liquid detergent to the washing tub to prepare a second washing liquid, and bringing the second washing liquid into contact with the items to be washed that have been subjected to the first step (I) in the washing tub.
Step (II) of this embodiment is similar to step (II) of the second embodiment.

The concentration of the second washing liquid in this embodiment is similar to that of the second washing liquid in the first embodiment.
In this embodiment, step (II) begins when the supply of water or liquid detergent to the washing tub is started after step (I), and ends when the discharge of the second washing liquid is started after the second washing liquid has been brought into contact with the items to be washed, or when the items to be washed are removed from the second washing liquid.

<Other processes>
The washing method of the present embodiment may include other steps.
The other steps of this embodiment are similar to those of the first embodiment.

The liquid detergent of this embodiment and the method for producing the liquid detergent are the same as the liquid detergent of the first embodiment and the method for producing the liquid detergent of the first embodiment.

In the step (I) of the present invention, fine bubbles may be generated or formed in the first washing liquid, and the bubbles may be used for washing. By using the bubbles for washing, the detergent components attached to the bubbles penetrate into the gaps between the fibers of the laundry to be washed, and the cleaning power can be further enhanced.
In the step (I) of the present invention, the first washing liquid may be sprayed in the form of a mist in the washing tub to wash. By spraying the first washing liquid in the form of a mist, the detergent components penetrate deep into the fibers of the laundry to be washed, thereby enhancing the cleaning power.
In the step (I) of the present invention, hot air (for example, 40 to 50° C.) may be supplied to the washing tub to warm the items to be washed before washing. By warming the items to be washed before washing, the activity of the detergent components can be increased, and the cleaning power can be further improved.
In the step (I) of the present invention, the first washing liquid may be heated (for example, at 40 to 50° C.) and sprayed in the form of a mist in the washing tub for washing. By spraying the heated first washing liquid in the form of a mist, the detergent components with enhanced activity penetrate deep into the fibers of the laundry to further enhance the cleaning power.
In the step (II) of the present invention, the same cleaning method as in the step (I) can be applied.

In the step (I) of the present invention, it is preferable to detect the pH and temperature of the first washing liquid and the degree of dirt on the laundry by a sensor, and to appropriately adjust the treatment temperature, treatment time, dilution ratio of the second washing liquid in the step (II), etc. For example, when the temperature of the first washing liquid is low (e.g., 10°C), the washing power can be further increased by heating the washing tub or lengthening the treatment time. When the degree of dirt on the laundry is high, the washing power can be further increased by lengthening the treatment time or decreasing the dilution ratio of the second washing liquid.
In the step (II) of the present invention, it is preferable to detect the pH, temperature, and degree of dirt of the second washing liquid by a sensor, and appropriately adjust the treatment temperature, treatment time, rinse step time, bath ratio, surfactant concentration of other washing liquids in other washing steps, etc. For example, when the pH of the second washing liquid is low, the cleaning power can be further improved by providing a third washing step and increasing the pH of the third washing liquid (e.g., pH 10.5). When the surfactant concentration of the second washing liquid is high, the rinsing ability can be further improved by extending the rinse step time or increasing the bath ratio.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description.
The raw materials and measurement/evaluation methods used in each of the examples and comparative examples are as follows.

[Ingredients used]
<Surfactant>
Nonionic: nonionic surfactant, AE (7EO), polyoxyethylene alkyl ether (manufactured by Lion Specialty Chemicals Co., Ltd., product name "Leox CL-70", a compound in which, in formula (2), R ¹¹ is a linear alkyl group having 12 carbon atoms (C12) and a linear alkyl group having 14 carbon atoms (C14) (mass ratio of C12:C14=75:25), the carbon atom of R ¹¹ bonded to an oxygen atom is a primary carbon atom, R ¹² is a hydrogen atom, s is 7, t is 0, and u is 0).
Anionic: anionic surfactant, LAS, linear alkylbenzene sulfonic acid having an alkyl group having 10 to 14 carbon atoms (manufactured by Lion Specialty Chemicals Co., Ltd., product name "Lipon (registered trademark) LH-200").
Anion: anion interface, AES, polyoxyalkylene alkyl ether sulfate (a compound represented by formula (4), in which R ¹⁵ is a linear alkyl group having 12 carbon atoms (C12) and a linear alkyl group having 14 carbon atoms (C14) (mass ratio of C12:C14=75:25), m is 1, n is 0, M is sodium, and the proportion of compounds in which m is 0 and n is 0 relative to the total amount of AES is 43 mass%. Synthesized by the synthesis method described below.).

(Synthesis of AES)
Into a 4 L autoclave, 400 g of Procter &Gamble's trade name CO1270 alcohol (a mixture of an alcohol having 12 carbon atoms and an alcohol having 14 carbon atoms in a mass ratio of 75/25) was charged as a raw material alcohol, and 0.8 g of potassium hydroxide catalyst was charged as a reaction catalyst. The atmosphere inside the autoclave was replaced with nitrogen, and the temperature was raised with stirring.
Subsequently, 91 g of ethylene oxide was introduced while maintaining the temperature at 180° C. and the pressure at 0.3 MPa or less, and reacted to obtain an alcohol ethoxylate.
Analysis using a gas chromatograph: GC-5890 manufactured by Hewlett-Packard (hereinafter, HP), a detector: a flame ionization detector (FID), and a column: Ultra-1 (manufactured by HP, L25m×φ0.2mm×T0.11μm) showed that the average number of moles of ethylene oxide added in the obtained alcohol ethoxylate was 1.0. In addition, the amount of compounds to which ethylene oxide was not added (those that ultimately became component (b-0)) was 43% by mass based on the total amount of the obtained alcohol ethoxylate.
Next, 237 g of the alcohol ethoxylate obtained above was placed in a 500 mL flask equipped with a stirrer, and after replacing with nitrogen, 96 g of liquid sulfuric anhydride (sulfan) was slowly added dropwise while maintaining the reaction temperature at 40° C. After the dropwise addition was completed, stirring was continued for 1 hour (sulfation reaction) to obtain polyoxyethylene alkyl ether sulfate. This was then neutralized with an aqueous sodium hydroxide solution to obtain AES.

<Optional ingredients>
- Defoaming agent: coconut fatty acid (manufactured by NOF Corporation, product name "Coconut Fatty Acid").
Structuring agent: CELLULON (bacterial cellulose (manufactured by CPKelco U.S., trade name "CELLULON (registered trademark) L27")).
Stabilizer: Sodium sulfite (sodium sulfite, manufactured by Mitsui Chemicals, Inc., trade name "Sodium Sulfite").
(Water-miscible organic solvent)
Ethanol: Manufactured by Japan Alcohol Sales Co., Ltd., product name "Specific Alcohol 95% Synthetic".
- Propylene glycol: Manufactured by The Dow Chemical Company, trade name "Propylene Glycol."
- Glycerin: Manufactured by Fujifilm Wako Pure Chemical Industries, product name "Glycerin".
(Alkaline agent)
MEA: Monoethanolamine (manufactured by Nippon Shokubai Co., Ltd., product name "Monoethanolamine").
Sodium carbonate: Sodium carbonate (manufactured by Soda Ash Japan Co., Ltd., product name "grain ash").

Enzyme: Protease (Novozymes Japan Co., Ltd., product name "Progress Uno 100L", enzyme liquid preparation).
Fragrance: Fragrance composition A described in Tables 11 to 18 of JP-A No. 2002-146399.
- Colorant: manufactured by Kishi Chemical Co., Ltd., product name "Green No. 3".
- Antibacterial agent: Diclosan (manufactured by BASF Corporation, product name "Tinosan HP100").
・Water: Ion-exchanged water.

[Examples 1 to 4, Comparative Examples 1 to 3]
A liquid detergent was prepared according to the composition in Table 1. Using the obtained liquid detergent, soiled cloths shown in the evaluation method below were washed through the steps shown in Table 2, and the detergency (for sebum stains and protein stains) was evaluated. The results are shown in Table 2. In Table 1, the unit of content is "mass %" and indicates the amount converted into pure content. In Table 2, "-" indicates that the corresponding step was not included.

<pH Measurement>
100 mL of the first washing liquid was prepared, and the pH of the first washing liquid was measured using a pH meter (portable pH/ORP/ION meter D-73, manufactured by Horiba, Ltd.) in an environment of 25° C. The results are shown in Table 2.
100 mL of the second washing liquid of each example was sampled, and the pH of the second washing liquid was measured in the same manner as for the first washing liquid in an environment of 25° C. The results are shown in Table 2.

<Method for evaluating sebum cleansing power>
An artificially soiled cloth (manufactured by the Laundry Science Association, a general incorporated foundation) was prepared by impregnating an unsoiled cloth with artificial soil, and the resulting cloth was cut into a size of 10 cm x 10 cm to prepare a soiled cloth.
A washing machine (JW-Z23A model, manufactured by Haier Co., Ltd.) was used as the cleaning test machine.
A liquid detergent having the composition shown in Table 1 was added to 15 L of water (15°C, 3°DH) so as to obtain the surfactant concentration (ppm, volume basis) shown in Table 2, and the mixture was stirred for 30 seconds to obtain a first washing liquid.

The first washing liquid, the five soiled fabrics described above, and the washed knitted fabric were placed in a washing tester, and washed at 15°C for the treatment time shown in Table 2 in accordance with the liquor ratio shown in Table 2 (step (I)).
Next, water (15°C, 3°DH) and a liquid detergent having the composition shown in Table 1 were added so as to obtain the surfactant concentration (ppm) shown in Table 2 to prepare a second washing liquid, and washing was performed at 15°C with the liquor ratio shown in Table 2 for the treatment time shown in Table 2 (step (II)).
Thereafter, the fabric was dehydrated for 5 minutes, rinsed in 23 L of water for 12 minutes, and air-dried.
The reflectance of the unsoiled cloth and the soiled cloth before and after cleaning was measured using a color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SE7700 Model"), and the cleaning rate (%) was calculated using the following formula (i).
Cleaning rate (%)=(K/S of soiled cloth before cleaning−K/S of soiled cloth after cleaning)/(K/S of soiled cloth before cleaning−K/S of unsoiled cloth)×100 (i)
Here, "K/S" is a value calculated by (1-R/100) ² /(2R/100) (R indicates the reflectance (%) of an unsoiled cloth and of a soiled cloth before and after washing).

The larger the value of the cleaning rate obtained by the above formula (i), the higher the cleaning power. The average value of the cleaning rates of the 10 soiled cloths was calculated, and the cleaning power for sebum stains was evaluated based on the following evaluation criteria.
Evaluation Criteria
◎: The average cleaning rate was 70% or more.
◯: The average cleaning rate was 65% or more and less than 70%.
Δ: The average cleaning rate was 60% or more and less than 65%.
×: The average cleaning rate was less than 60%.

<Method for evaluating protein cleaning power>
The cleaning rate (%) was calculated in the same manner as in the above <Method of evaluating sebum cleaning power>, except that EMPA116 (protein stain, manufactured by Swissatest Testmaterialien AG) was used instead of the artificially soiled cloth. The average cleaning rate of the five soiled cloths was calculated, and the cleaning power for protein stains was evaluated based on the following evaluation criteria.
Evaluation Criteria
◎: The average cleaning rate was 70% or more.
◯: The average cleaning rate was 65% or more and less than 70%.
Δ: The average cleaning rate was 60% or more and less than 65%.
×: The average cleaning rate was less than 60%.

As shown in Table 2, Examples 1 to 4 in which the present invention was applied were evaluated for sebum cleansing power and protein cleansing power as "◎" or "◯", and were excellent in cleansing power.
On the other hand, in Comparative Example 1, in which the pH of the second washing liquid at 25° C. was less than 8.0, the protein detergency was evaluated as “Δ”. In Comparative Example 2, which did not have step (II), the protein detergency was evaluated as “Δ”. In Comparative Example 3, which did not have step (II), the sebum detergency was evaluated as “Δ” and the protein detergency was evaluated as “×”.

These results demonstrate that the cleaning power of liquid detergents can be improved according to the present invention.

Claims (3)

A first step (I) of contacting a first laundry liquid containing a liquid detergent containing a surfactant with an article to be washed in a washing tub;
Supplying water to the washing tub or supplying water and the liquid detergent to form a second washing liquid;
A second step (II) of contacting the second washing liquid with the article to be washed that has been subjected to the first step (I) in the washing tub,
The liquid detergent contains a nonionic surfactant, an anionic surfactant, and an alkaline agent,
The surfactant content of the liquid detergent is 30 to 65% by mass based on the total mass of the liquid detergent,
The dilution ratio of the first washing liquid with water is 1000 to 2000 times by volume relative to 1 part by volume of the liquid detergent,
The concentration of the surfactant in the first washing liquid is 200 ppm or more and 430 ppm or less by mass,
The first washing liquid has a pH of 8.0 to 10.5 at 25°C ,
The dilution ratio of the second washing liquid with water is 1500 to 6000 times by volume per 1 volume part of the liquid detergent, and is greater than the dilution ratio of the first washing liquid;
the concentration of the surfactant in the second washing liquid is 50 ppm or more and 350 ppm or less by mass and is lower than the concentration of the surfactant in the first washing liquid;
The washing method, wherein the pH of the second washing liquid at 25°C is 8.0 or higher. The liquor ratio in the first step (I) represented by [mass of the first washing liquid]/[total mass of the laundry to be washed] is 4 or more;
The washing method according to claim 1 , wherein the liquor ratio in the second step (II) expressed as [mass of the second washing liquid]/[total mass of the items to be washed] is 6 or more. The time for contacting the first washing liquid with the laundry in the step (I) is 3 minutes or more;
The washing method according to claim 1 or 2, wherein the time for contacting the second washing liquid with the laundry in the step (II) is 5 to 30 minutes.