A styrene-butadiene block copolymer mixture, a composition for hot melt adhesive, a hot melt adhesive, and a method for preparing and using the same

Abstract

This invention relates to a styrene-butadiene block copolymer mixture, a composition for hot melt adhesives, a hot melt adhesive, its preparation method, and its application, belonging to the field of adhesives. The copolymer mixture contains 65-75 wt% styrene-butadiene-styrene block copolymer and 25-35 wt% styrene-butadiene block copolymer; the styrene monomer content in the copolymer mixture is 36-40 wt%; the copolymer mixture has a melt index of 11-21 g / 10 min at 200°C and a breakage elongation of not less than 800%, and a tensile strength of not less than 9 MPa. The mixture provided by this invention has a low molecular weight, a high melt index, low viscosity when preparing hot melt adhesives, and good processing performance. Furthermore, the synthesis method of this mixture is simple, its performance is stable, it does not require the addition of additional coupling agents for coupling, and its cost is low.

Description

Technical Field

[0001] This invention relates to a styrene-butadiene block copolymer mixture, a composition for hot melt adhesives, a hot melt adhesive, its preparation method and application, belonging to the field of adhesives. Background Technology

[0002] Hot melt pressure-sensitive adhesives are solvent-free adhesives made by fusing thermoplastic elastomers with tackifying resins, plasticizers, antioxidants, and other additives. They are used in labeling, furniture, packaging, wood processing, and shoemaking. However, conventional label adhesives have a minimum application temperature of 10°C. In low-temperature environments, they easily lose their original tackiness, leading to label peeling and detachment. This can cause serious consequences such as information loss and confusion during cold chain logistics. Therefore, label adhesives must be able to operate and be applied in low-temperature environments, maintaining tackiness and preventing detachment from the adhered surface. Thus, we aim to develop a low-temperature resistant hot melt pressure-sensitive adhesive to meet market demands.

[0003] Chinese patent (publication number CN102504735A) discloses a hot-melt pressure-sensitive adhesive, which is prepared from the following raw materials in parts by weight: 25-40 parts of matrix resin, 48-60 parts of tackifier, 12-22 parts of plasticizer, and 0.6-1.2 parts of stabilizer; wherein the matrix resin is a solution-polymerized styrene-butadiene rubber composed of a styrene-isoprene-styrene triblock copolymer and a styrene-butadiene diblock copolymer, with a weight ratio of 1.2-3.1. However, this hot-melt pressure-sensitive adhesive easily loses its original tackiness at low temperatures.

[0004] Chinese patent (publication number CN105969273A) discloses an environmentally friendly hot-melt pressure-sensitive adhesive, prepared by mixing the following components in weight percentages: 25-50 parts of C5 petroleum resin; 20-35 parts of plasticizer; 10-25 parts of styrene-butadiene-styrene block copolymer; and 2-10 parts of additives. However, this hot-melt pressure-sensitive adhesive exhibits low peel strength at low temperatures. Summary of the Invention

[0005] In view of the problems existing in the prior art, one of the objectives of the present invention is to provide a styrene-butadiene block copolymer mixture with low molecular weight, high melt index, low viscosity when preparing hot melt adhesive, good processing performance, and simple synthesis method, stable performance, no need to add additional coupling agent for coupling, and low cost.

[0006] The second objective of this invention is to provide a composition for hot melt adhesives, wherein the hot melt adhesive prepared from this composition has excellent properties such as high bonding strength, no adhesive residue upon peeling, no label warping at low temperatures, and difficulty in separating the paper face material from the adhesive layer.

[0007] The third objective of this invention is to provide a method for preparing a hot melt adhesive, which is simple and easy to produce.

[0008] The fourth objective of this invention is to provide a hot melt adhesive that has excellent properties such as high bonding strength, no residue upon peeling, no label warping at low temperatures, and difficulty in separating the paper surface from the adhesive layer. Furthermore, the hot melt adhesive provided by this invention does not require the addition of organic solvents and water, has a solid content of 100%, does not generate additional waste during production, and does not emit any unpleasant odor during use, making it both safe and environmentally friendly.

[0009] The fifth objective of this invention is to provide the application of hot melt adhesives in pressure-sensitive adhesives. When this adhesive is used in cold chain transportation, the labels are not easily separated, and the label peeling phenomenon does not occur.

[0010] To achieve the above objectives, a first aspect of the present invention is to provide a styrene-butadiene block copolymer mixture, the copolymer mixture containing 65-75 wt% of a styrene-butadiene-styrene block copolymer and 25-35 wt% of a styrene-butadiene block copolymer; wherein the content of styrene monomer in the copolymer mixture is 36-40 wt%.

[0011] The copolymer mixture has a melt index of 11-21 g / 10 min at 200°C and a breaking elongation of not less than 800%, and a tensile strength of not less than 9 MPa.

[0012] The inventors discovered that mixing a certain proportion of styrene-butadiene-styrene block copolymer and styrene-butadiene block copolymer, and ensuring the performance parameters of the mixture are within the aforementioned range, results in a hot melt adhesive with high bonding strength, no residue upon peeling, no label curling at low temperatures, and minimal separation between the paper surface and the adhesive layer. A melt flow index of 11–21 g / 10 min facilitates product processing. If the melt flow index is too high or too low, the product will have either too good or too poor flowability, leading to processing difficulties.

[0013] As a preferred embodiment, the styrene-butadiene-styrene block copolymer has a number-average molecular weight of 55,000 to 75,000, and the styrene monomer content in the styrene-butadiene-styrene block copolymer is 36 to 40 wt%. The inventors have found that, under this preferred condition, the resulting hot melt adhesive provides a higher tack value at low temperatures (ambient temperature below 40°C).

[0014] As a preferred embodiment, the styrene-butadiene block copolymer has a number average molecular weight of 55,000 to 75,000, and the styrene monomer content in the styrene-butadiene block copolymer is 36 to 40 wt%. The inventors have found that under this preferred condition, the hot melt adhesive can provide a higher initial tack value at low temperatures (ambient temperature below 40°C).

[0015] As a preferred embodiment, the copolymer mixture contains 68-72 wt% styrene-butadiene-styrene block copolymer and 28-32 wt% styrene-butadiene block copolymer.

[0016] As a preferred embodiment, the 1,2-butadiene content in the styrene-butadiene-styrene block copolymer and the styrene-butadiene block copolymer is independently 0-16 wt%, more preferably 10-14 wt%, and even more preferably 10-13 wt%. If the 1,2-butadiene content is too high, the glass transition is high, which is not conducive to the low-temperature performance of the adhesive.

[0017] As a preferred embodiment, the preparation method of the styrene-butadiene block copolymer mixture includes: stirring and mixing the styrene-butadiene-styrene block copolymer and the styrene-butadiene block copolymer evenly, followed by coagulation by water precipitation and drying to obtain the final product. The styrene-butadiene block copolymer mixture synthesis method provided by this invention is simple, low-cost, and has stable performance, and does not require the addition of an additional coupling agent for coupling; it only requires a mixing method.

[0018] It should be noted that the present invention does not have any special requirements for the preparation methods of the styrene-butadiene-styrene block copolymers and styrene-butadiene block copolymers; methods known in the art are acceptable. As a preferred embodiment, in an anionic polymerization system, monomers are added sequentially at a temperature of 50–110°C, and the block copolymers are synthesized by initiation with an initiator.

[0019] As a preferred embodiment, the anionic polymerization system contains a nonpolar hydrocarbon solvent, an activator, and an initiator.

[0020] As a preferred embodiment, the initiator is n-butyllithium. There are no special requirements regarding the amount of n-butyllithium added; it can be added according to the molecular weight of the designed polymer.

[0021] As a preferred embodiment, the activator is selected from at least one of tetrahydrofuran, diethyl ether, anisole, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetrahydrofurfuryl ethyl ether, and bis(tetrahydrofurfuryl propane). Tetrahydrofuran is more preferred.

[0022] As a preferred embodiment, the nonpolar hydrocarbon solvent is selected from at least one of cyclohexane, cyclopentane, and n-hexane. More preferably, it is cyclohexane and / or cyclopentane.

[0023] As a preferred embodiment, the styrene and butadiene mixed monomers are fed in a sequential manner, that is, the styrene-butadiene-styrene block copolymer is added in the order of styrene, butadiene, and styrene, and the styrene-butadiene block copolymer is added in the order of styrene and butadiene or butadiene and styrene.

[0024] A second aspect of the present invention provides a composition for a hot melt adhesive, comprising the following components in parts by weight:

[0025] 100 parts of elastomer; wherein the elastomer contains 40-60 parts of styrene-butadiene block copolymer and 40-60 parts of styrene-isoprene-styrene block copolymer;

[0026] Plasticizer 50-90 parts;

[0027] 100-180 parts of tackifying resin;

[0028] The styrene-butadiene block copolymer is the styrene-butadiene block copolymer described in the first aspect above.

[0029] The hot melt adhesive provided by this invention requires no addition of organic solvents and water, has a solid content of 100%, does not generate additional waste during production, and does not emit any unpleasant odor during use, making it both safe and environmentally friendly.

[0030] As a preferred embodiment, the plasticizer is selected from at least one of dioctyl phthalate, dibutyl phthalate, white mineral oil, naphthenic oil, vegetable oil, and liquid paraffin. More preferably, naphthenic oil, and even more preferably, naphthenic oil KN-4010.

[0031] As a preferred embodiment, the tackifying resin comprises at least one of rosin resin, terpene resin, aromatic resin, and C5-C9 synthetic petroleum resin. More preferably, it is a C5-C9 synthetic petroleum resin and / or terpene resin, and even more preferably, it is a C5 synthetic petroleum resin and / or terpene resin.

[0032] As a preferred embodiment, the adhesive composition further contains an antioxidant, the antioxidant being present in an amount of 0.1 to 1.0 wt% of the adhesive.

[0033] As a preferred embodiment, the antioxidant is selected from at least one of antioxidant 1076, antioxidant 168, antioxidant 1135, antioxidant 571, antioxidant 1010 and antioxidant DLTP, and is more preferably antioxidant 1076 and / or antioxidant 1010.

[0034] A third aspect of the present invention provides a method for preparing a hot melt adhesive, the method comprising using the components of the composition described in the second aspect above, including:

[0035] Under a protective atmosphere, the plasticizer and tackifying resin are preheated and melted, and then the antioxidant and elastomer are added and stirred to obtain the hot melt adhesive.

[0036] As a preferred embodiment, the preheating and melting temperature is 110–140°C, the time is 30–60 min, and the stirring rate is 130–170 r / min.

[0037] As a preferred embodiment, the mixing temperature is 150–180°C, the mixing time is 20–45 min, and the mixing speed is 130–170 r / min.

[0038] This invention also provides a method for preparing a hot melt adhesive, resulting in a hot melt adhesive with excellent properties such as high bonding strength, no adhesive residue upon peeling, no label warping at low temperatures, and minimal separation between the paper face material and the adhesive layer.

[0039] This invention also provides the application of hot melt adhesives as pressure-sensitive adhesives at ambient temperatures below 40°C.

[0040] Compared with the prior art, the present invention has at least the following advantages:

[0041] (1) The method for synthesizing the styrene-butadiene block copolymer of the present invention is simple, has stable performance, does not require the addition of a coupling agent for coupling, and has low cost.

[0042] (2) The styrene-butadiene block copolymer of the present invention has a low molecular weight and a high melt index, resulting in low viscosity when preparing hot melt adhesive and good processing performance.

[0043] (3) The removable label paper made of the hot melt adhesive of the present invention has excellent properties such as high bonding strength, no adhesive residue when peeled off, no label curling at low temperature, and the paper surface material and adhesive layer are not easy to separate.

[0044] (4) The hot melt adhesive prepared by the present invention can be used for cold chain transportation. No organic solvents and water need to be added during the preparation of the hot melt adhesive. The solid content reaches 100%. No additional waste is generated during the production process. No unpleasant odor is emitted during use. It is safe and environmentally friendly. The preparation process is simple and does not require special raw materials and production equipment. It has good application prospects. Detailed Implementation

[0045] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0046] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0047] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0048] Styrene-isoprene-styrene block copolymer (SIS): grade YH-1124, purchased from Sinopec Hunan Petrochemical Co., Ltd.

[0049] The preparation method of styrene-butadiene-styrene block copolymer is as follows:

[0050] 2500 ml of cyclohexane solvent, 56.3 g of styrene, and 0.3 g of tetrahydrofuran activator were added to a polymerization reactor. 4.7 mmol of n-butyllithium initiator was added at 60℃~70℃, and the reaction was allowed to proceed for 30 min. Then, 187.5 g of butadiene was added, and the temperature was controlled below 110℃. After the reaction was allowed to proceed for 30 min, 56.3 g of styrene was added again, and the reaction was allowed to proceed for another 30 min. Finally, 5 mmol of methanol was added as a terminator, and the reaction was allowed to proceed for 10 min before the product was discharged. 2 g of 2,6-di-tert-butyl-4-methylphenol antioxidant was added, and the mixture was stirred until homogeneous, yielding styrene-butadiene-styrene block copolymer 1 (abbreviated as SBS1).

[0051] The preparation method of styrene-butadiene block copolymer is as follows:

[0052] 2500 ml of cyclohexane solvent, 112.5 g of styrene, and 0.3 g of tetrahydrofuran activator were added to a polymerization reactor. 4.7 mmol of n-butyllithium initiator was added at 60℃~70℃, and the reaction was carried out for 30 min. Then, 187.5 g of butadiene was added, and the temperature was controlled below 110℃. After the reaction was carried out at high temperature for 30 min, 5 mmol of methanol was added as a terminator. The reaction was carried out for 10 min, and the product was discharged. 2 g of 2,6-di-tert-butyl-4-methylphenol antioxidant was added and stirred evenly to obtain styrene-butadiene block copolymer 1 (abbreviated as SB1).

[0053] Styrene-butadiene-styrene block copolymers and styrene-butadiene block copolymers with different molecular weights, styrene monomer contents, butadiene monomer contents, and structures were synthesized according to the above preparation method. The parameters of the synthesized styrene-butadiene-styrene block copolymers are shown in Table 1, and the parameters of the styrene-butadiene block copolymers are shown in Table 2.

[0054] Table 1

[0055] sample Mn (ten thousand) Styrene content / Butadiene content / Styrene content, all in wt%. 1,2-Butadiene content / wt% SBS1 6.5 19.1 / 61.8 / 19.1 12.5 SBS2 7.0 19.0 / 62.0 / 19.0 12.6 SBS3 6.8 19.1 / 61.8 / 19.1 12.4 SBS4 5.2 18.9 / 62.2 / 18.9 12.3

[0056] Table 2

[0057] sample Mn (ten thousand) Styrene content / butadiene content, both in wt%. 1,2-Butadiene content / wt% SB1 6.6 37.9 / 62.1 12.2 SB2 7.0 38.0 / 62.0 12.1 SB3 6.8 38.2 / 61.8 12.3

[0058] The preparation examples of the present invention are used to prepare styrene-butadiene block copolymer mixtures, and the total amount of SBS and SB used in the following preparation examples is 100g.

[0059] Preparation Example 1

[0060] SBS and SB were mixed at a mass ratio of 7:3 and stirred evenly. The resulting mixture was coagulated and dried to obtain a styrene-butadiene block copolymer mixture. Its physical and mechanical properties were tested, as shown in Table 4.

[0061] The melt flow index was tested using a 17217 model melt flow index tester at 200℃ / 5Kg. Tensile strength, i.e., elongation at break, was tested using an AGX-5KNV model electronic tensile testing machine, according to GB / T528-2009. The types and amounts of substances involved in this preparation example are listed in Table 3.

[0062] Unless otherwise specified, the other preparation examples are carried out in accordance with the method of Preparation Example 1. The difference is that the raw materials and amounts used in each preparation example are not exactly the same, as detailed in Table 3.

[0063] Table 3

[0064] Types of SBS Types of SB SBS and SB dosage by mass ratio name Preparation Example 1 SBS1 SB1 7:3 H1 Preparation Example 2 SBS2 SB2 7:3 H2 Preparation Example 3 SBS3 SB3 6.5:3.5 H3 Preparation Example 4 SBS4 SB1 7:3 H4 Comparative Preparation Example 1 SBS1 SB1 5:5 DH-1

[0065] Table 4

[0066] Types of copolymer blends Melt flow index (5 kg, 200℃) Elongation at break (%) Tensile strength (MPa) H1 14.7 1050 15.2 H2 11.0 1020 15.4 H3 13.8 1120 13.8 H4 20.8 1150 13.3 DH-1 14.2 1140 8.5

[0067] The embodiments of the present invention are used to prepare hot melt adhesives, and each part in the following examples represents 1g.

[0068] Example 1

[0069] Under nitrogen protection, the formulated amounts of naphthenic oil, petroleum resin, and terpene resin are first added to the reactor. The temperature is controlled at 130℃, and the mixture is stirred at 150 r / min for 60 min until it melts. Then, the elastomer and antioxidant are added, the temperature is raised to 170℃, and the mixture is stirred until it is homogeneous. Stirring continues for 30 min at a stirring rate of 150 r / min to obtain the pressure-sensitive adhesive.

[0070] Pour the prepared pressure-sensitive adhesive into the glue tank of the hot melt pressure-sensitive adhesive coating machine. Maintain a constant temperature of 140℃ in the glue tank, 130℃ in the glue hose, and 135℃ in the coating temperature. The application rate is 40g / m. 2 .

[0071] The hot melt pressure-sensitive adhesive formulation is as follows: 50 parts of styrene-butadiene block copolymer (H1), 50 parts of SIS, 60 parts of naphthenic oil, 55 parts of C5 petroleum resin, 60 parts of terpene resin, and antioxidant 1010 at 1.0 wt% of the total adhesive mass.

[0072] Example 2

[0073] This embodiment is carried out in a similar manner to Example 1, except that the types and amounts of raw materials are different. Specifically, 60 parts of styrene-butadiene block copolymer mixture (H1), 40 parts of SIS, 60 parts of naphthenic oil, 55 parts of C5 petroleum resin, 60 parts of terpene resin, and antioxidant 1010 is 1.0 wt% of the total mass of the adhesive.

[0074] Example 3

[0075] This embodiment is carried out in a similar manner to Example 1, except that the types and amounts of raw materials are different. Specifically, 40 parts of styrene-butadiene block copolymer mixture (H1), 60 parts of SIS, 60 parts of naphthenic oil, 55 parts of C5 petroleum resin, 60 parts of terpene resin, and antioxidant 1010 is 1.0 wt% of the total mass of the adhesive.

[0076] Example 4

[0077] This embodiment is carried out in a similar manner to Example 1, except that the types and amounts of raw materials are different. Specifically, 50 parts of styrene-butadiene block copolymer mixture (H2), 50 parts of SIS, 60 parts of naphthenic oil, 55 parts of C5 petroleum resin, 60 parts of terpene resin, and antioxidant 1010 is 1.0 wt% of the total mass of the adhesive.

[0078] Example 5

[0079] This embodiment is carried out in a similar manner to Example 1, except that the types and amounts of raw materials are different. Specifically, 50 parts of styrene-butadiene block copolymer mixture (H3), 50 parts of SIS, 60 parts of naphthenic oil, 55 parts of C5 petroleum resin, 60 parts of terpene resin, and antioxidant 1010 is 1.0 wt% of the total mass of the adhesive.

[0080] Example 6

[0081] This embodiment is carried out in a similar manner to Example 1, except that the types of raw materials are different. Specifically, 50 parts of styrene-butadiene block copolymer mixture (H4), 50 parts of SIS, 60 parts of naphthenic oil, 55 parts of C5 petroleum resin, 60 parts of terpene resin, and antioxidant 1010 is 1.0 wt% of the total mass of the adhesive.

[0082] Comparative Example 1

[0083] This embodiment is carried out in a similar manner to Example 1, except that the types and amounts of raw materials are different. Specifically, 100 parts of SIS, 60 parts of naphthenic oil, 55 parts of C5 petroleum resin, 60 parts of terpene resin, and 1.0% of antioxidant 1010 are used.

[0084] Comparative Example 2

[0085] This comparative example was carried out using a similar method to Example 1, except that the styrene-butadiene block copolymer mixture H1 was replaced with an equal mass of styrene-butadiene block copolymer mixture DH1.

[0086] Test case

[0087] The samples prepared in the above examples were tested and evaluated as follows, and the results are shown in Table 5 below.

[0088] 180° peel strength: Tested according to the method of GB / T17200-2008.

[0089] Low-temperature initial tack: Tested according to GB / T4852, using the inclined plane rolling ball method, with an inclination angle of 30° and a test temperature of -15±2℃.

[0090] Low temperature and high humidity holding power: Tested according to GB / T4851, the test temperature is -15±2℃.

[0091] Table 5

[0092]

[0093] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A styrene-butadiene block copolymer blend, characterized in that: The copolymer contains 65-75 wt% styrene-butadiene-styrene block copolymer and 25-35 wt% styrene-butadiene block copolymer; the content of styrene monomer in the copolymer is 36-40 wt%. The copolymer mixture has a melt index of 11-21 g / 10 min at 200°C and a breaking elongation of not less than 800%, and a tensile strength of not less than 9 MPa.

2. The styrene-butadiene block copolymer according to claim 1, characterized in that: The styrene-butadiene-styrene block copolymer has a number average molecular weight of 55,000 to 75,000, and the styrene monomer content in the styrene-butadiene-styrene block copolymer is 36 to 40 wt%.

3. A styrene-butadiene block copolymer according to claim 1 or 2, characterized in that: The styrene-butadiene block copolymer has a number average molecular weight of 55,000 to 75,000, and the styrene monomer content in the styrene-butadiene block copolymer is 36 to 40 wt%.

4. A styrene-butadiene block copolymer according to claim 1 or 2, characterized in that: The copolymer mixture contains 68-72 wt% styrene-butadiene-styrene block copolymer and 28-32 wt% styrene-butadiene block copolymer.

5. A composition for a hot melt adhesive, characterized in that: It contains the following components by weight: 100 parts of elastomer; wherein the elastomer contains 40-60 parts of styrene-butadiene block copolymer and 40-60 parts of styrene-isoprene-styrene block copolymer; Plasticizer 50-90 parts; 100-180 parts of tackifying resin; The styrene-butadiene block copolymer is the styrene-butadiene block copolymer as described in any one of claims 1 to 4.

6. The composition for a hot melt adhesive according to claim 5, characterized in that: The plasticizer is selected from at least one of dioctyl phthalate, dibutyl phthalate, white mineral oil, naphthenic oil, vegetable oil and liquid paraffin.

7. A composition for a hot melt adhesive according to claim 5 or 6, characterized in that: The tackifying resin includes at least one of rosin resin, terpene resin, aromatic resin, and C5-C9 synthetic petroleum resin.

8. A composition for a hot melt adhesive according to claim 5 or 6, characterized in that: The adhesive composition further contains an antioxidant, the antioxidant being present in an amount of 0.1 to 1.0 wt% of the adhesive.

9. A method for preparing a hot melt adhesive, characterized in that: This method is performed using any of the components in the composition according to any one of claims 5 to 7, comprising: Under a protective atmosphere, the plasticizer and tackifying resin are preheated and melted, and then the antioxidant and elastomer are added and stirred to obtain the hot melt adhesive.

10. The method for preparing a hot melt adhesive according to claim 9, characterized in that: The preheating and melting temperature is 110–140°C, the time is 30–60 min, and the stirring rate is 130–170 r / min; And / or, the mixing temperature is 150-180℃, the time is 20-45 min, and the mixing rate is 130-170 r / min.

11. A hot melt adhesive prepared by the method for preparing a hot melt adhesive according to claim 9 or 10.

12. The application of the hot melt adhesive of claim 11 as a pressure-sensitive adhesive at an ambient temperature below 40°C.

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