Resole phenolic resin, adhesive, and method for producing resol phenolic resin

Abstract

To provide a resol type phenol resin capable of sufficiently suppressing a blowout phenomenon and maintaining productivity even when a high moisture content veneer such as the moisture content of 10% or larger is used, when manufacturing the veneer.SOLUTION: A resol type phenol resin having a weight average molecular weight (Mw) of 20,000 or larger, and a molecular weight distribution having a degree of dispersion (Mw / Mn) that is a ratio of a weight average molecular weight (Mw) and a number average molecular weight (Mn) of 15 or larger. When manufacturing a resol type phenol resin by reacting in multi-stages by dividing and adding phenols and aldehydes in a reactor, the viscosity due to a B type viscometer at 25°C of a reaction liquid is set to 50 to 400 d Pa s at a reaction end of the first stage, and to 3 to 6 d Pa s at the reaction end of a final stage reaction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resol-type phenolic resin that can be produced while maintaining conventional productivity, even when plywood is produced using veneers with a high moisture content of 10% or more, when used as an adhesive for plywood, and a method for producing the same, as well as an adhesive using this resol-type phenolic resin. [Background technology]

[0002] Conventionally, amino resin adhesives, such as melamine-formaldehyde resin and urea-formaldehyde resin, and phenol-formaldehyde resin adhesives have been used as adhesives for plywood.

[0003] Compared to amino resin adhesives, conventional phenol-formaldehyde resin adhesives have the problem of being prone to adhesive failure, known as a "puncture," when the pressure is released during the heat press if the veneer used has a high moisture content. Therefore, when manufacturing plywood, measures must be taken, such as drying the veneer to a moisture content of 6% or less; increasing the heat press temperature; lengthening the heat press time; or minimizing the amount of water added when mixing the adhesive; generally, lengthening the heat press time.

[0004] In order to solve these problems, a resol-type phenolic resin has been proposed in which aldehydes are added in portions to phenols in the presence of an alkaline catalyst and reacted in multiple stages to polymerize the resin (for example, Patent Document 1).

[0005] Patent Document 1 describes, as specific production examples, the following: a first-stage reaction carried out until the viscosity of the reaction solution at the end of the reaction reached 300 mPa·s (3 dPa·s), and a final-stage reaction carried out until the viscosity of the reaction solution at the end of the reaction reached 200 mPa·s (2 dPa·s); a first-stage reaction carried out until the viscosity of the reaction solution at the end of the reaction reached 150 mPa·s (1.5 dPa·s), and a final-stage reaction carried out until the viscosity of the reaction solution at the end of the reaction reached 200 mPa·s (2 dPa·s); and a first-stage reaction carried out until the viscosity of the reaction solution at the end of the reaction reached 300 mPa·s (3 dPa·s), and a final-stage reaction carried out until the viscosity of the reaction solution at the end of the reaction reached 1000 mPa·s (10 dPa·s).

[0006] However, the resol-type phenolic resin disclosed in Patent Document 1 is insufficient in its effect of suppressing punctures. For example, in the case of veneers with a high moisture content of 10% or more, the heat-pressing time must be extended to obtain sufficient adhesive strength, making it difficult to maintain productivity. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-123781 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a resol-type phenolic resin that can sufficiently suppress punctures and maintain productivity even when high-moisture veneers, such as those with a moisture content of 10% or more, are used in the production of plywood. [Means for solving the problem]

[0009] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that a resol-type phenolic resin having a weight-average molecular weight (Mw) of 20,000 or more and a molecular weight distribution in which the dispersity (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), is 15 or more, can solve the above-mentioned problems.

[0010] That is, the gist of the present invention is as follows.

[0011] [1] A resol-type phenolic resin having a weight-average molecular weight (Mw) of 20,000 or more and a molecular weight distribution with a dispersity (Mw / Mn), which is the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), of 15 or more.

[0012] [2] The resol-type phenolic resin according to [1], characterized in that it has a weight-average molecular weight (Mw) of 25,000 or more and a molecular weight distribution with a dispersity (Mw / Mn) of 20 or more.

[0013] [3] A resol-type phenolic resin according to [1] or [2], characterized in that the area ratio when a gel permeation chromatography (GPC) chart is fractionated so that the weight average molecular weight (Mw) is 50,000 is 50% or more, and the resol-type phenolic resin contains mononuclear components in an area ratio of 8% or more on the gel permeation chromatography (GPC) chart.

[0014] [4] A resol-type phenolic resin according to any one of [1] to [3], which is obtained by adding phenols and aldehydes to a reaction vessel in portions and reacting them in multiple stages, characterized in that the viscosity of the reaction liquid measured with a Brookfield viscometer at 25°C is 50 to 400 dPa·s at the end of the first stage reaction and 3 to 6 dPa·s at the end of the final stage reaction.

[0015] [5] An adhesive containing the resol type phenolic resin according to any one of [1] to [4].

[0016] [6] A method for producing a resol-type phenolic resin according to any one of [1] to [3], wherein phenols and aldehydes are added in portions to a reaction vessel and reacted in multiple stages to obtain a resol-type phenolic resin, characterized in that the viscosity of the reaction liquid measured at 25°C by a Brookfield viscometer is 50 to 400 dPa·s at the end of the first stage reaction and 3 to 6 dPa·s at the end of the final stage reaction. [Effects of the Invention]

[0017] The resol-type phenolic resin of the present invention can be used as a plywood adhesive to produce plywood, even when high-moisture veneers, such as those with a moisture content of 10% or more, are used, as it can suppress punctures and achieve sufficient adhesive strength without extending the heat-pressing time, thereby enabling plywood to be produced with high productivity. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below. The following description of the constituent elements is an example (typical example) of an embodiment of the present invention, and the present invention is not limited to these details.

[0019] In the present invention, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the resol-type phenolic resin are values ​​calculated using polystyrene standards as determined by gel permeation chromatography (GPC), and specifically, are determined by the method described in the Examples section below.

[0020] In the present invention, the area ratio when a gel permeation chromatography (GPC) chart is fractionated so that the weight average molecular weight (Mw) is 50,000 (hereinafter, this may be referred to as the "Mw 50,000 area ratio") is determined by the following procedures (1) and (2). (1) From the GPC analysis chart, the region with a weight average molecular weight (Mw) of 50,000 is fractionated. The starting point of fractionation is the rising point of the first peak in the GPC analysis chart. (2) Calculate the ratio of the total peak area of ​​the fraction with Mw=50,000 to the total peak area of ​​the GPC chart.

[0021] Furthermore, the area ratio of the mononuclear component on the GPC analysis chart (hereinafter sometimes referred to as the "mononuclear component area ratio") can be determined as the ratio of the mononuclear peak area to the total peak area on the GPC analysis chart.

[0022] [Resol-type phenolic resin] The resol-type phenolic resin of the present invention has a weight-average molecular weight (Mw) of 20,000 or more and a molecular weight distribution in which the dispersity (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), is 15 or more.

[0023] The weight-average molecular weight (Mw) of the resol-type phenolic resin of the present invention is 20,000 or more, preferably 25,000 or more, more preferably 30,000 or more, and preferably 40,000 or less. If the weight-average molecular weight (Mw) is less than 20,000, sufficient adhesive strength of plywood cannot be obtained with conventional heat-pressing times when the moisture content of the veneer is 10% or more.

[0024] Furthermore, since polymerizing the resin in this manner increases the viscosity of the resin, the dispersity (Mw / Mn) is set to 15 or more, preferably 20 or more, in order to reduce the viscosity. If the dispersity is less than 15, the viscosity of the resol-type phenolic resin increases, causing problems in handling it as an adhesive. The upper limit of the dispersity (Mw / Mn) of the resol-type phenolic resin of the present invention is usually 40 or less, preferably 30 or less.

[0025] Furthermore, when the resol-type phenolic resin of the present invention is fractionated in a gel permeation chromatography (GPC) chart so that the weight-average molecular weight (Mw) of the high molecular weight component is 50,000, the area ratio is preferably 50% or more, more preferably 50 to 70%. If the Mw 50,000 area ratio is less than 50%, sufficient adhesive strength to high-moisture content veneers may not be obtained. On the other hand, the mononuclear component, which is a low molecular weight component, is preferably contained in an area ratio of 8% or more on the GPC analysis chart, more preferably 10 to 12%. If the mononuclear component area ratio is less than 8%, the viscosity of the resol-type phenolic resin increases, which may make it difficult to handle as an adhesive.

[0026] The resol type phenolic resin of the present invention may be partially modified with a substance such as tannin, lignin, polyvinyl butyral, polyvinyl alcohol, or hydroxyethyl cellulose, if necessary.

[0027] [Method of manufacturing resol-type phenolic resin] The method for producing the resol type phenolic resin of the present invention is not particularly limited, but examples thereof include the following methods (1) and (2). (1) A method in which phenols and aldehydes are added to a reactor in separate portions and reacted in multiple stages under specified conditions. (2) Mixing high molecular weight resol type phenolic resin with low molecular weight resol type phenolic resin

[0028] <Method of manufacturing resol-type phenolic resin by multi-step reaction> In this method, the resol-type phenolic resin of the present invention is produced by adding phenols and aldehydes in portions and reacting them in multiple stages. The resol-type phenolic resin is obtained by reacting phenols and aldehydes in the presence of an alkaline reaction catalyst, and the resol-type phenolic resin of the present invention can be produced by adding phenols and aldehydes in portions during this reaction and reacting them in multiple stages under predetermined conditions.

[0029] In producing the resol-type phenolic resin of the present invention, the number of times that phenols and aldehydes are added in multiple stages to react them is not particularly limited. However, in terms of ease of control of the reaction conditions, it is preferable to add the phenols in two or three separate stages to react in two or three stages, and it is particularly preferable to add the phenols in two separate stages to react in two stages.

[0030] In this multi-stage reaction, the molar ratio (F / P) of phenols (P) to aldehydes (F) is set to 2.0-3.0 in the first stage, and the reaction is continued until the viscosity of the reaction solution at 25°C, as measured with a Brookfield viscometer, reaches 50-400 dPa·s. If the viscosity of the reaction solution at the end of this one-stage reaction is less than 50 dPa·s, it is difficult to obtain a resin with a Mw of 20,000 or more. If the viscosity exceeds 400 dPa·s, the viscosity of the reaction solution becomes too high, making reaction control difficult. The viscosity of the reaction solution at the end of the one-stage reaction is preferably 70-350 dPa·s, and more preferably 90-200 dPa·s. The reaction solution at the end of this one-step reaction is usually an aqueous solution with a non-volatile content of about 40 to 50%.

[0031] The molar ratio (F / P) for the second and subsequent stages is then adjusted in the same way as for the first stage, and the reaction is continued until the viscosity of the reaction solution (or the second-stage reaction solution in the case of a two-stage reaction) at 25°C reaches 3 to 6 dPa·s as measured by a Brookfield viscometer. If the viscosity of the reaction solution at the end of this final stage reaction is less than 3 dPa·s, the reaction will not proceed sufficiently and a Mw of 20,000 or more will not be achieved. If the viscosity exceeds 6 dPa·s, a large amount of water or other additives will be required to adjust the viscosity of the final resin, resulting in reduced adhesive strength. It is particularly preferable that the viscosity of the reaction solution at the end of the final stage reaction be 4 to 5 dPa·s. The reaction solution at the end of this final stage reaction is usually an aqueous solution with a non-volatile content of about 40 to 50%.

[0032] When a multi-stage reaction of three or more stages is carried out, there are no particular restrictions on the viscosity of the reaction solution in the stages between the first stage reaction and the final stage reaction, but it is preferable that the viscosity of the reaction solution at the end point of the reaction is reduced stepwise from the viscosity of the reaction solution at the end point of the first stage reaction to the end point of the final stage reaction.

[0033] In order to adjust the viscosity of the reaction solution at the end of each reaction stage to the above-mentioned predetermined viscosity, the reaction temperature, reaction time, etc. of each reaction stage may be adjusted. The higher the reaction temperature and the longer the reaction time, the more the condensation reaction progresses and the higher the viscosity of the reaction solution.

[0034] In such a multi-stage reaction, the reaction temperature when reacting phenols with aldehydes is preferably 70 to 95°C throughout all stages, but the reaction temperature of the first stage reaction is preferably 85 to 95°C, and the reaction temperature of the final stage reaction is preferably 70 to 85°C, which is about 10 to 25°C lower than that. When a multi-stage reaction of three or more stages is carried out, the reaction temperature between the first stage and the final stage is preferably set to an intermediate temperature between them. When an alkaline catalyst is additionally added to the reactor during the multi-stage reaction, it is preferable to cool the reactor to about 70 to 85°C to avoid a sudden rise in temperature.

[0035] As described above, the reaction temperature in the multi-stage reaction is higher than the viscosity measurement temperature. In the present invention, however, the reaction is carried out so that the reaction liquid extracted at the end of the reaction is cooled to 25°C and the viscosity measured with a Brookfield viscometer falls within the above range.

[0036] Examples of raw material aldehydes used in the production of resol type phenolic resins include formaldehyde, paraformaldehyde, and acetaldehyde. On the other hand, the raw material phenols used in producing the resol type phenolic resin are not particularly limited, and examples thereof include alkylphenols such as phenol and cresol; aromatic diols such as resorcinol and catechol; bisphenols such as bisphenol A; and the like.

[0037] Examples of alkaline catalysts include sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, and ammonia, with sodium hydroxide being preferred. The alkali such as sodium hydroxide is preferably used so that the molar ratio of the alkali to the raw material phenols is 0.1 to 0.8.

[0038] When a resol-type phenolic resin is partially modified with a substance such as tannin, lignin, polyvinyl butyral, polyvinyl alcohol, or hydroxyethyl cellulose, these substances may usually be added during the condensation reaction of the phenols and aldehydes, or after the condensation reaction is completed and the reaction liquid is cooled.

[0039] After the above multi-stage reaction, water is added as necessary to adjust the viscosity to an appropriate level depending on the intended use of the resol type phenolic resin.

[0040] <Method of manufacturing resol-type phenolic resin by mixing> The resol-type phenolic resin of the present invention can also be produced by blending a high-molecular-weight resol-type phenolic resin with a low-molecular-weight resol-type phenolic resin. In this case, a high-molecular-weight resol-type phenolic resin having a weight-average molecular weight (Mw) of about 40,000 to 60,000, produced by a conventional method, is blended with a low-molecular-weight resol-type phenolic resin having a weight-average molecular weight (Mw) of about 2,000 to 5,000, so that the weight-average molecular weight (Mw) and polydispersity (Mw / Mn) of the resol-type phenolic resin of the present invention, and preferably the area ratio of Mw50,000 and the area ratio of mononuclear components, fall within predetermined ranges.

[0041] [glue] The resol type phenolic resin of the present invention is useful as an adhesive, particularly as an adhesive for plywood. When used as an adhesive, the resol-type phenolic resin may be used as a modified phenolic resin obtained by modifying it with a substance such as tannin, lignin, polyvinyl butyral, polyvinyl alcohol, or hydroxyethyl cellulose, or an unmodified resol-type phenolic resin may be used in combination with a modified phenolic resin.

[0042] Furthermore, adhesives containing the resol-type phenolic resin of the present invention are typically prepared by adding fillers such as wheat flour, calcium carbonate, and sodium carbonate in addition to the resol-type phenolic resin of the present invention. The amount of filler added is not particularly limited, but preferably 10 to 75 parts by weight of each filler per 100 parts by weight (solids) of the resol-type phenolic resin of the present invention and the modified phenolic resin used in combination as needed. Furthermore, if necessary, water may be added to adjust the viscosity. [Example]

[0043] The present invention will be described in more detail below with reference to examples.

[0044] [Measurement method by gel permeation chromatography (GPC)] A resol type phenolic resin was dissolved in an eluent, heated at 60°C, allowed to cool, and then the precipitate was removed to obtain a GPC measurement sample, which was measured using the following instrument specifications. Main unit: Tosoh Corporation HLC-8320GPC Column: TSK-GEL SUPER AW4000 TSK-GEL SUPER AW3000 TSK-GEL SUPER AW2500 Eluent: DMF Flow rate: 0.6mL / min Detector: UV The elution times of the mononuclear components were determined using orthomethylolphenol, paramethylolphenol, and 2,4,6-trimethylolphenol as standard substances.

[0045] [Example 1] 172.8 parts by weight of phenol (P), 361.1 parts by weight of 37.9 wt% formalin (F) (F / P molar ratio: 2.48), 37.4 parts by weight of water, and 98.0 parts by weight of 30 wt% aqueous sodium hydroxide solution (sodium hydroxide / phenol molar ratio: 0.40) were charged into a reactor, heated to 90°C, and reacted until the viscosity measured with a Brookfield viscometer at 25°C reached 100 dPa·s. Next, while cooling, 43.2 parts by weight of phenol and 90.3 parts by weight of 37.9% by weight formalin (F / P molar ratio: 2.48) were added, and after cooling to 70°C, 122.6 parts by weight of 30% by weight aqueous sodium hydroxide solution (sodium hydroxide / phenol ratio: 0.72) was added and the reaction was carried out at 80°C until the viscosity measured with a Brookfield viscometer at 25°C reached 4 dPa·s. After cooling, the viscosity was adjusted to 2.0 dPa·s with water.

[0046] The weight average molecular weight (Mw) of the obtained resol type phenolic resin measured by GPC was 30,000, and the polydispersity (Mw / Mn) was 24. The area ratio of Mw 50,000 was 59%, and the area ratio of mononuclear components was 10%.

[0047] [Example 2] 190.7 parts by weight of phenol (P), 398.6 parts by weight of 37.9 wt% formalin (F) (F / P molar ratio: 2.48), 36.7 parts by weight of water, and 70.3 parts by weight of 30 wt% aqueous sodium hydroxide solution (sodium hydroxide / phenol molar ratio: 0.26) were charged into a reactor, heated to 90°C, and reacted until the viscosity measured with a Brookfield viscometer at 25°C reached 75 dPa·s. Next, while cooling, 21.2 parts by weight of phenol and 44.3 parts by weight of 37.9% by weight formalin (F / P molar ratio: 2.48) were charged, and after cooling to 70°C, 146.1 parts by weight of 30% by weight aqueous sodium hydroxide solution (sodium hydroxide / phenol ratio: 0.72) was charged and the reaction was carried out at 80°C until the viscosity measured with a Brookfield viscometer at 25°C reached 4 dPa·s. After cooling, the viscosity was adjusted to 2.0 dPa·s with water.

[0048] The weight average molecular weight (Mw) of the obtained phenolic resin measured by GPC was 27,300, and the polydispersity (Mw / Mn) was 18. The area ratio of Mw 50,000 was 54%, and the area ratio of mononuclear components was 6%.

[0049] [Comparative Example 1] 234.6 parts by weight of phenol (P), 433.6 parts by weight of 37.9 wt% formalin (F) (F / P molar ratio: 2.19), 92.1 parts by weight of water, and 239.7 parts by weight of 30 wt% aqueous sodium hydroxide solution (sodium hydroxide / phenol molar ratio: 0.72) were gradually added to a reactor, while the temperature was raised to 95°C and the reaction was carried out for 150 minutes. After cooling, the viscosity was adjusted to 2.0 dPa·s with water.

[0050] The weight average molecular weight (Mw) of the obtained resol type phenolic resin measured by GPC was 23,200, and the polydispersity (Mw / Mn) was 11. The area ratio of Mw 50,000 was 42%, and the area ratio of mononuclear components was 3%.

[0051] Comparative Example 2 220.2 parts by weight of phenol (P), 460.5 parts by weight of 37.9 wt% formalin (F) (F / P molar ratio: 2.48), 38.2 parts by weight of water, and 81.2 parts by weight of 30 wt% aqueous sodium hydroxide (sodium hydroxide / phenol molar ratio: 0.26) were gradually added to a reactor, and the temperature was raised to 90°C and the reaction was carried out for 90 minutes. The temperature was then lowered to 85°C, and 116.1 parts by weight of 30 wt% aqueous sodium hydroxide (sodium hydroxide / phenol molar ratio: 0.63) was added and the reaction was carried out for 60 minutes. After cooling, the viscosity was adjusted to 2.0 dPa·s with water.

[0052] The weight average molecular weight (Mw) of the obtained resol type phenolic resin measured by GPC was 16,400, and the polydispersity (Mw / Mn) was 9. The area ratio of Mw 50,000 was 21%, and the area ratio of mononuclear components was 2%.

[0053] Comparative Example 3 212.3 parts by weight of phenol (P), 444.0 parts by weight of 37.9 wt% formalin (F) (F / P molar ratio: 2.48), and 189.3 parts by weight of 30 wt% aqueous sodium hydroxide (sodium hydroxide / phenol molar ratio: 0.63) were gradually added to a reactor, while the temperature was raised to 90°C and the reaction was carried out for 120 minutes. The temperature was then lowered to 85°C, and 112.0 parts by weight of 30 wt% aqueous sodium hydroxide (sodium hydroxide / phenol molar ratio: 1.00) was added and the reaction was carried out for 160 minutes. After cooling, the viscosity was adjusted to 2.0 dPa·s with water.

[0054] The weight average molecular weight (Mw) of the obtained resol type phenolic resin measured by GPC was 17,200, and the polydispersity (Mw / Mn) was 15. The area ratio of Mw 50,000 was 25%, and the area ratio of mononuclear components was 3%.

[0055] [Adhesive preparation and evaluation] 100 parts by weight of the resol type phenolic resin obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were mixed with 30 parts by weight of calcium carbonate, 10 parts by weight of wheat flour, 5 parts by weight of sodium carbonate, and 10 parts by weight of water to obtain a paste (adhesive).

[0056] Using this glue, a 30 x 30 cm plywood board was made from larch wood with a moisture content adjusted to 10-12%. The boards were 1.8 mm and 3.7 mm thick, and the five plies were 1.8 / 3.7 / 1.8 / 3.7 / 1.8 mm thick, for a total thickness of 12 mm. Five 3.7 mm thick veneers were stacked on top of each other, with 20 g of glue applied to each side of the middle veneer. The veneers were then cold pressed at 1.0 MPa for 30 minutes, and then hot pressed at 125°C and 0.8 MPa for 5 minutes to obtain plywood. The obtained plywood was subjected to a special test evaluation (evaluation of special adhesive strength, average wood breakage rate, and pass rate) by a repeated steaming test based on the Japanese Agricultural and Forestry Standards for Plywood: Seihei 15.2. The results are shown in Table 1.

[0057] [Table 1]

[0058] Table 1 shows that the adhesives using the resol-type phenolic resins of Examples 1 and 2 have higher specific adhesive strength, average wood breakage rate, and pass rate than the adhesives using the resol-type phenolic resins of Comparative Examples 1 to 3, and can maintain productivity even when plywood is manufactured using veneers with a moisture content of 10% or more.

Claims

1. A resol-type phenolic resin having a weight-average molecular weight (Mw) of 20,000 or more and a molecular weight distribution in which the dispersity (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), is 15 or more, A resol-type phenolic resin having an area ratio of 50% or more when a gel permeation chromatography (GPC) chart is fractionated so that the weight average molecular weight (Mw) is 50,000, and containing mononuclear components in an area ratio of 8% or more on the gel permeation chromatography (GPC) chart.

2. 2. The resol-type phenolic resin according to claim 1, wherein the resol-type phenolic resin has a weight-average molecular weight (Mw) of 25,000 or more and a molecular weight distribution with a dispersity (Mw / Mn) of 20 or more.

3. An adhesive containing the resol type phenolic resin according to claim 1 or 2.

4. A method for producing the resol-type phenolic resin according to claim 1 or 2, A method for producing a resol-type phenolic resin, in which phenols and aldehydes are added in portions to a reaction vessel and reacted in multiple stages to obtain a resol-type phenolic resin, characterized in that the viscosity of the reaction liquid at 25°C, as measured by a Brookfield viscometer, is 50 to 400 dPa·s at the end of the first-stage reaction and 3 to 6 dPa·s at the end of the final-stage reaction.

Images