Crosslinkable resin composition and crosslinked resin

Abstract

To provide a crosslinkable resin composition capable of undergoing a reversible crosslinking reaction.SOLUTION: The composition contains: an acid anhydride-modified polyethylene having repeating units represented by the general formula [I], -[CH2-CR1(R2A)] (where R1 is a hydrogen atom or a methyl group, R2 is a direct bond or a divalent organic group, and A represents an acid anhydride group), and repeating units represented by -[CH2CH2]-; and a polyfunctional thiol represented by the general formula [II], R3-[SH]n (where R3 is an n-valent (n is an integer from 2 to 6) organic group).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a crosslinkable resin composition and a crosslinked resin product, and more specifically to a crosslinkable resin composition capable of a reversible crosslinking reaction, and a crosslinked resin product which can be recycled by returning at least a portion of the crosslinked structure to an uncrosslinked state. [Background technology]

[0002] Cross-linked polyethylene has excellent insulation properties, heat resistance, durability, chemical stability, etc., and is used in a wide range of applications, including insulating coating materials for electric wires and various electrical products, as well as water and hot water supply pipes, automobile parts, chemical tanks, solar cell encapsulants, etc. There is also a demand for effective use (recycling) of cross-linked polyethylene waste generated during production and disposal after use as a recyclable resource. However, cross-linked polyethylene cannot be melted by heat or solvents, and recycling methods are limited. Therefore, methods of forcibly cutting the carbon chains by using supercritical water (see Patent Document 1 below) or shearing with a twin-screw extruder (see Patent Document 2 below) have been investigated. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2001-192495 [Patent Document 2] Patent Publication No. 2018-35247 Summary of the Invention [Problem to be solved by the invention]

[0004] These methods require the introduction of new equipment and inevitably result in deterioration of quality, and have hardly been industrialized.

[0005] A first object of the present invention is to provide a crosslinkable resin composition capable of undergoing a reversible crosslinking reaction. A second object of the present invention is to provide a crosslinked resin product having excellent recyclability, in which at least a part of the crosslinked structure can be returned to an uncrosslinked state. [Means for solving the problem]

[0006] The crosslinkable resin composition of the present invention is characterized by containing an acid anhydride-modified polyolefin and a polyfunctional thiol.

[0007] The crosslinkable resin composition of the present invention comprises an acid anhydride-modified polyethylene having a repeating unit represented by the following general formula [I] and a repeating unit represented by -[CHCH]-, It is preferable that the polyfunctional thiol is represented by the following general formula [II].

[0008] [ka]

[0009] (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 represents a direct bond or a divalent organic group, and A represents an acid anhydride group.

[0010] [ka]

[0011] [In the formula, R 3 represents an organic group having a valence of n (n is an integer of 2 to 6).

[0012] The acid anhydride group is preferably a group derived from maleic anhydride.

[0013] The polyfunctional thiol is preferably a mercaptocarboxylic acid derivative, and particularly preferably trimethylolpropane tris(3-mercaptopropionate).

[0014] In the acid anhydride-modified polyethylene, the ratio of the number of repeating units represented by the above general formula [I] to the number of repeating units represented by -[CH2CH2]- is preferably 100:2,000 to 100:3,600,000.

[0015] The ratio of the number of acid anhydride groups in the acid anhydride-modified polyethylene to the number of mercapto groups in the polyfunctional thiol is preferably 100:50 to 100:200.

[0016] In the crosslinkable resin composition of the present invention, it is preferable that the crosslinking temperature (T1) is in the range of 120 to 240°C, the decrosslinking temperature (T2) is in the range of 250 to 350°C, and the temperature difference (T2-T1) is 20°C or more. More preferably, the crosslinking temperature (T1) is in the range of 150 to 200°C, the decrosslinking temperature (T2) is in the range of 280 to 310°C, and the temperature difference (T2-T1) is 80°C or more.

[0017] The crosslinked resin of the present invention is characterized by being represented by the following general formula [III].

[0018] [ka]

[0019] [In the formula, R 3 is an organic group having a valence of n (n is an integer from 2 to 6); R 4 represents a divalent hydrocarbon group substituted with 1 carboxy group, and D represents an organic group having a repeating unit represented by the following general formula [IV] and a repeating unit represented by -[CH2CH2]-.

[0020] [ka]

[0021] (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 represents a direct bond or a divalent organic group.

[0022] The degree of crosslinking of the resin of the present invention is preferably 25% or more. The crosslinked resin of the present invention preferably has a heat deformation rate of 40% or less. Effect of the Invention

[0023] The crosslinkable resin composition of the present invention is capable of reversible crosslinking (crosslinking reaction and decrosslinking reaction), where the crosslinking reaction is carried out at a relatively low temperature and the decrosslinking reaction is carried out at a relatively high temperature. According to the crosslinkable resin composition of the present invention, a crosslinking reaction of the crosslinkable resin composition occurs at a predetermined temperature (a relatively low temperature), and this makes it possible to suitably produce a crosslinked resin product (the crosslinked resin product of the present invention). In the crosslinked resin product of the present invention, at least a part of the crosslinked structure can be returned to an uncrosslinked state by a decrosslinking reaction. According to the crosslinked resin product of the present invention, a decrosslinking reaction of the crosslinked resin product occurs at a predetermined temperature (relatively high temperature), and this makes it possible to suitably regenerate the crosslinkable resin composition. In addition, since the crosslinked structure has a thioester bond (-SC(=O)-), the reaction temperature for decrosslinking can be lowered to a certain degree, so that the thermal deterioration of the reproduced crosslinkable resin composition can be suppressed, and deterioration in the physical properties of the resin crosslinked body due to the crosslinkable resin composition can be prevented. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] <Crosslinkable resin composition> The present invention will now be described. The crosslinkable resin composition of the present invention contains an acid anhydride-modified polyolefin and a polyfunctional thiol.

[0025] <Acid anhydride modified polyolefin> The acid anhydride-modified polyolefin is a copolymer of an α-olefin and an acid anhydride-modified monomer. The acid anhydride-modified polyolefin may contain a repeating unit introduced by a copolymerizable monomer other than the acid anhydride-modified monomer.

[0026] A suitable acid anhydride-modified polyolefin is an acid anhydride-modified polyethylene having a repeating unit represented by the above general formula [I] and a repeating unit represented by --[CH2CH2]--.

[0027] In the above general formula [I], R 1 is a hydrogen atom or a methyl group, R 2 is a direct bond or a divalent organic group, and A is an acid anhydride group.

[0028] The acid anhydride group represented by A is a group having a structure derived from an acid anhydride (-CO-O-CO-), and specific examples thereof include a group derived from maleic anhydride, a group derived from succinic anhydride, a group derived from glutaric anhydride, a group derived from citraconic anhydride, a group derived from itaconic anhydride, and a group derived from phthalic anhydride. Of these, it is preferred that the acid anhydride group is a group derived from maleic anhydride (that is, the acid anhydride-modified polyethylene is maleic anhydride-modified polyethylene).

[0029] In the above general formula [I], the acid anhydride group may be directly bonded to a carbon atom constituting a polyethylene chain, and R 2 It may be bonded to the carbon atom via a divalent organic group represented by the following formula: Here, R 2 Preferred divalent organic groups represented by the formula include -CH2- and -C(=O)O-.

[0030] In the above general formula [I], -R 2 Preferred examples of the structural unit represented by -A include those shown below.

[0031] [ka]

[0032] The acid anhydride-modified polyethylene is composed of a random copolymer, a block copolymer, an alternating copolymer or a graft copolymer of a repeating unit represented by the above general formula [I] and a repeating unit represented by --[CH2--CH2]--. The ratio of the number of repeating units represented by the above general formula [I] to the number of repeating units represented by -[CH2CH2]- is preferably 100:2,000 to 100:3,600,000, more preferably 100:6,000 to 100:720,000, and particularly preferably 100:14,000 to 100:360,000. If the ratio of the repeating unit (acid anhydride group A) represented by the above general formula [I] is too small, the degree of crosslinking of the crosslinked resin obtained by crosslinking a resin composition containing such an acid anhydride-modified polyethylene will be low and the thermal deformation rate will be high, making it impossible for the crosslinked resin to fully exhibit the performance (e.g., heat resistance) required of the crosslinked resin. On the other hand, if the ratio of the repeating unit represented by the above general formula [I] is too high, the properties of the polyethylene such as flexibility and mechanical strength are impaired, which is undesirable.

[0033] <Multifunctional thiol> The polyfunctional thiol constituting the crosslinkable resin composition of the present invention has a plurality of mercapto groups and functions as a crosslinking agent for the acid anhydride-modified polyethylene.

[0034] A suitable polyfunctional thiol constituting the crosslinkable resin composition of the present invention is represented by the above general formula [II]. In the above general formula [II], R 3 is an organic group having a valence of n (n is an integer of 2 to 6). The number of mercapto groups in the multifunctional thiol represented by the above general formula [II] is 2 to 6, preferably 2 to 4, and in one suitable example, it is 3.

[0035] Preferred polyfunctional thiols include derivatives of mercaptocarboxylic acids such as thioglycolic acid derivatives, mercaptopropionic acid derivatives, and mercaptobutanoic acid derivatives (specifically, esters of mercaptocarboxylic acids with polyhydric alcohols).

[0036] Specific examples of polyfunctional thiols include 2,5-dimercapto-1,3,4-thiadiazole, ethylene glycol bisthioglycolate, butanediol bisthioglycolate, trimethylolpropane tristhioglycolate, pentaerythritol tristhioglycolate, pentaerythritol tetrakisthioglycolate, ethylene glycol (3-mercaptopropionate), butanediol bis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3 -mercaptopropionate), tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, dipentaerythritol hexa(3-mercaptopropionate), ethylene glycol (3-mercaptobutyrate), butanediol bis(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptobutyrate), dipentaerythritol hexa(3-mercaptobutyrate), and the like, but are not limited thereto. Of these, trimethylolpropane tris(3-mercaptopropionate) is preferred.

[0037] The crosslinkable resin composition of the present invention is capable of reversible crosslinking (crosslinking reaction and decrosslinking reaction), where the crosslinking reaction is carried out at a relatively low temperature and the decrosslinking reaction is carried out at a relatively high temperature. According to the crosslinkable resin composition of the present invention, a crosslinking reaction of the crosslinkable resin composition occurs at a predetermined temperature (a relatively low temperature), and this makes it possible to suitably produce the crosslinked resin product of the present invention.

[0038] <Crosslinked resin> The crosslinked resin of the present invention has a structural unit represented by the above general formula [III]. In the above general formula [III], R 3 represents an organic group having a valence of n (n is an integer of 2 to 6), and the organic group R 3 is a residue obtained by removing a mercapto group from a polyfunctional thiol constituting the crosslinkable resin composition (before crosslinking). Also, R 4 is a divalent hydrocarbon group substituted with 1 carboxy group (a carboxy group derived from an acid anhydride). R 4 Examples of the group represented by the formula include -CH(CH2COOH)-, -CH2CH(COOH)-, -CH(CH2CH2COOH)-, -CH2CH(CH2COOH)-, -CH2CH2CH(COOH)-, and the like.

[0039] In the above general formula [III], -SC(=O)R 4 The group represented by - is a divalent organic group (thioester bond-containing group) formed by the reaction of an acid anhydride-modified polyethylene with a polyfunctional thiol, and serves as a crosslinking point of the crosslinked resin.

[0040] D represents an organic group having a repeating unit represented by the above general formula [IV] and a repeating unit represented by -[CH2CH2]-, and the organic group D is a residue obtained by removing the acid anhydride group A from the acid anhydride-modified polyethylene constituting the crosslinkable resin composition (before crosslinking). The organic group D (anhydride-modified polyethylene residue) is an organic group R 2 By R 4 is bonded to a group represented by the formula:

[0041] The crosslinked resin of the present invention can be produced by heating the crosslinkable resin composition of the present invention at a predetermined temperature to react the acid anhydride-modified polyethylene with the polyfunctional thiol to form a thioester bond and crosslink the crosslinkable resin composition.

[0042] Here, by using maleic anhydride modified polyethylene as the acid anhydride modified polyethylene and trimethylolpropane tris(3-mercaptopropionate) as the polyfunctional thiol, it is possible to obtain a crosslinked resin having, for example, the structure shown below. [ka]

[0043] The crosslinking temperature (T1) of the crosslinkable resin composition of the present invention [crosslinking temperature measured by the method described in the Examples below] is preferably in the range of 120 to 240°C, more preferably in the range of 150 to 200°C.

[0044] As a heat treatment method for crosslinking, various methods can be adopted depending on the form of the crosslinked resin body, such as a method of heating in an atmosphere of nitrogen, water vapor, silicone oil, molten salt, or the like, or a method of heating during molding in a hot press machine or an injection molding machine.

[0045] By heating the crosslinked resin of the present invention at a predetermined temperature, an acid anhydride-modified polyethylene having a repeating unit containing an acid anhydride group and a polyfunctional thiol having multiple mercapto groups are produced, thereby reproducing the crosslinkable resin composition.

[0046] The decrosslinking temperature (T2) of the crosslinked resin product [the decrosslinking temperature measured by the method described in the Examples below] is preferably in the range of 250 to 350°C, and more preferably in the range of 280 to 310°C. A crosslinked resin having a decrosslinking temperature (T2) in the range of 250° C. or higher has excellent heat resistance.

[0047] Furthermore, a crosslinked resin product having a de-crosslinking temperature (T2) in the range of 350°C or less can suppress the thermal degradation of the acid anhydride-modified polyethylene produced when a crosslinkable resin composition is reproduced from the crosslinked resin product, and can prevent a decrease in the physical properties of the crosslinked resin product due to the reproduced crosslinkable resin composition, so that such a crosslinked resin product has excellent recyclability.

[0048] The crosslinked resin of the present invention has a crosslinked structure based on a thioester bond (-SC(=O)-), and this is the first time that the decrosslinking temperature (T2) can be set to 350°C or lower. In a crosslinked resin product having a crosslinked structure based on an ester bond (-O-C(=O)-), the de-crosslinking temperature cannot be set to 350°C or lower (see Comparative Examples 1 to 3 described later), and a crosslinked resin product made from a crosslinkable resin composition reproduced from such a crosslinked resin product does not have good physical properties.

[0049] The temperature difference (T2-T1) between the decrosslinking temperature and the crosslinking temperature is preferably 20°C or more, and more preferably 80°C or more. When the temperature difference (T2-T1) is 20°C or more, it is possible to easily set and control the treatment temperature in each of the crosslinking step of the resin composition and the de-crosslinking step of the crosslinked resin product.

[0050] <Degree of crosslinking of crosslinked resin> The crosslinked degree of the resin crosslinked product of the present invention is preferably 25% or more, and more preferably 35% or more. If the degree of crosslinking is too low (for example, less than 25%), the resin cannot exhibit sufficient heat resistance and will melt under temperature conditions exceeding the melting point of the resin.

[0051] <Thermal deformation rate of crosslinked resin> The crosslinked resin material of the present invention preferably has a thermal deformation rate (a rate of reduction in thickness due to heating) of 40% or less, and more preferably 20% or less. If the thermal deformation rate of the crosslinked resin is too high (for example, more than 40%), it will not be able to exhibit sufficient heat resistance, and the resin will deform significantly under high temperature conditions, which will be problematic when used in applications such as cables.

[0052] The crosslinkable resin composition of the present invention may contain various substances used in conventional resin compositions as optional components, such as, but not limited to, antioxidants, ultraviolet absorbers, flame retardants, process oils, etc. EXAMPLES

[0053] Examples of the present invention will be described below, but the present invention is not limited to these. In the following Examples and Comparative Examples, the following compounds were used as acid anhydride-modified polyethylene, low-density polyethylene, polyfunctional thiol and polyhydric alcohol.

[0054] (MAA-PE-1) Density=0.92g / cm 3 , MFR (190°C, 2.16 kg) = 1.5 g / 10 min, maleic anhydride content = 1.0 mass% (the ratio of the number of repeating units represented by the above general formula [I] to the number of repeating units represented by -[CH2CH2]- is 100:70,000).

[0055] (MAA-PE-2) Density=0.92g / cm 3 , MFR (190°C, 2.16 kg) = 0.9 g / 10 min, maleic anhydride content = 0.7 mass% (the ratio of the number of repeating units represented by the above general formula [I] to the number of repeating units represented by -[CH2CH2]- is 100:100,000).

[0056] (MAA-PE-3) Density=0.92g / cm 3, MFR (190°C, 2.16 kg) = 1.0 g / 10 min, maleic anhydride content = 0.5 mass% (the ratio of the number of repeating units represented by the above general formula [I] to the number of repeating units represented by -[CH2CH2]- is 100:140,000).

[0057] (TMPTM) Trimethylolpropane tris(3-mercaptopropionate), a trifunctional thiol with molecular weight of 399.

[0058] (TMP) Trimethylolpropane, a trihydric alcohol with molecular weight of 134.

[0059] (DMHD) 2,5-Dimethyl-2,5-hexanediol, a dihydric alcohol with molecular weight of 146.

[0060] <Production of Crosslinkable Resin Composition> Example 1 98.5 parts by mass of maleic anhydride modified polyethylene (MAA-PE-1) and 1.5 parts by mass of trimethylolpropane tris(3-mercaptopropionate) (TMPTM) were charged into a Labo Plastomill and kneaded while heating to obtain a resin composition (crosslinkable resin composition) of the present invention.

[0061] Example 2 A resin composition (crosslinkable resin composition) of the present invention was obtained in the same manner as in Example 1, except that 98.5 parts by mass of maleic anhydride modified polyethylene (MAA-PE-2) and 1.5 parts by mass of trimethylolpropane tris(3-mercaptopropionate) (TMPTM) were charged into a Labo Plastomill.

[0062] Example 3 A resin composition (crosslinkable resin composition) of the present invention was obtained in the same manner as in Example 1, except that 99.5 parts by mass of maleic anhydride modified polyethylene (MAA-PE-3) and 0.5 parts by mass of trimethylolpropane tris(3-mercaptopropionate) (TMPTM) were charged into a Labo Plastomill.

[0063] Comparative Example 1 A comparative resin composition (crosslinkable resin composition) was obtained in the same manner as in Example 1, except that 99.5 parts by mass of maleic anhydride modified polyethylene (MAA-PE-1) and 0.5 parts by mass of trimethylolpropane (TMP) were charged into the Labo Plastomill.

[0064] Comparative Example 2 A comparative resin composition (crosslinkable resin composition) was obtained in the same manner as in Example 1, except that 99.0 parts by mass of maleic anhydride modified polyethylene (MAA-PE-1) and 1.0 part by mass of 2,5-dimethyl-2,5-hexanediol (DMHD) were charged into the Labo Plastomill.

[0065] Comparative Example 3 A comparative resin composition (crosslinkable resin composition) was obtained in the same manner as in Example 1, except that 99.5 parts by mass of maleic anhydride modified polyethylene (MAA-PE-2) and 0.5 parts by mass of trimethylolpropane (TMP) were charged into the Labo Plastomill.

[0066] <Production of Crosslinked Resin (Crosslinking Reaction)> Each of the crosslinkable resin compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was crosslinked by pressing at 200°C for 30 minutes using a hot press (Toho Machinery, TBD-50 model) to obtain a sheet-like crosslinked resin product having a thickness of 1 mm.

[0067] The crosslinking temperature (T1) of each of the crosslinkable resin compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was measured as follows. The results are also shown in Table 1 below.

[0068] (Method of measuring crosslinking temperature (T1)) A sample in which the acid anhydride component and the crosslinker component (polyfunctional thiol, polyhydric alcohol) were mixed in equal amounts was heated at a rate of 10°C / min using a differential scanning calorimeter (DSC7020, Hitachi High-Tech Corporation), and the DSC curve was measured. The exothermic peak temperature observed from this DSC curve was taken as the crosslinking temperature (T1).

[0069] <Reproduction of crosslinkable resin composition (de-crosslinking reaction)> The decrosslinking temperature (T2) of the crosslinked resin products obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was measured as follows. The results are also shown in Table 1 below.

[0070] (Method of measuring decrosslinking temperature (T2)) The dynamic viscoelasticity of a sample made of a crosslinked resin was measured using a rheometer (MCR302, manufactured by Anton Paar) while increasing the temperature from an initial temperature of 130°C under conditions of constant frequency (angular frequency 0.1 rad / s, strain 1%), and the temperature (gel point) at which the storage modulus (G') and loss modulus (G") intersect was defined as the de-crosslinking temperature (T2).

[0071] <Measurement of the degree of crosslinking of crosslinked resin> Test pieces were prepared from the sheet-like crosslinked resin products obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 3, and the degree of crosslinking (gel fraction) was measured in accordance with JIS C3005, except that the test pieces were used. The results are also shown in Table 1 below. The crosslinked resin preferably has a degree of crosslinking of 25% or more.

[0072] <Measurement of Heat Deformation Rate of Crosslinked Resin> Test pieces were prepared from the sheet-like crosslinked resin bodies obtained by crosslinking each of the crosslinkable resin compositions obtained in Examples 1 to 3 and Comparative Examples 1 to 3, and the heat deformation rate (reduction rate of thickness due to heating) was measured in accordance with JIS C3005, except that the test pieces were used. The results are also shown in Table 1 below. The heat deformation rate is preferably 40% or less.

[0073]

Table 1

Claims

1. A crosslinkable resin composition containing an acid anhydride-modified polyolefin and a polyfunctional thiol.

2. A repeating unit represented by the following general formula [I] and -[CH 2 CH 2 and an acid anhydride-modified polyethylene having a repeating unit represented by the formula: The crosslinkable resin composition according to claim 1, which contains a polyfunctional thiol represented by the following general formula [II]: 【Chemistry 1】 (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 represents a direct bond or a divalent organic group, and A represents an acid anhydride group. 【Chemistry 2】 [In the formula, R 3 represents an organic group having a valence of n (n is an integer of 2 to 6).

3. 3. The crosslinkable resin composition according to claim 2, wherein the acid anhydride group is a group derived from maleic anhydride.

4. The crosslinkable resin composition according to claim 2, wherein the polyfunctional thiol is a mercaptocarboxylic acid derivative.

5. 3. The crosslinkable resin composition according to claim 2, wherein the polyfunctional thiol is trimethylolpropane tris(3-mercaptopropionate).

6. In the acid anhydride-modified polyethylene, the number of repeating units represented by the above general formula [I] and the number of repeating units represented by -[CH 2 CH 2 3. The crosslinkable resin composition according to claim 2, wherein the ratio of the number of repeating units represented by the formula (III) to the number of repeating units represented by the formula (III) is 100:2,000 to 100:3,600,000.

7. The crosslinkable resin composition according to claim 2, wherein the ratio of the number of acid anhydride groups in the acid anhydride-modified polyethylene to the number of mercapto groups in the polyfunctional thiol is 100:50 to 100:

200.

8. Crosslinking temperature (T 1 ) is in the range of 120 to 240°C, Decrosslinking temperature (T 2 ) is in the range of 250 to 350°C, Temperature difference (T 2 -T 1 2. The crosslinkable resin composition according to claim 1, wherein the temperature of the crosslinking agent is 20° C. or higher.

9. A crosslinked resin represented by the following general formula [III]: 【Chemistry 3】 [In the formula, R 3 is an organic group having a valence of n (n is an integer from 2 to 6); R 4 represents a divalent hydrocarbon group substituted with one carboxy group; D represents a repeating unit represented by the following general formula [IV] and -[CH 2 CH 2 ]-] is an organic group having a repeating unit represented by the formula: 【Chemistry 4】 (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 represents a direct bond or a divalent organic group.

10. The crosslinked resin according to claim 9, having a degree of crosslinking of 25% or more.

11. The crosslinked resin according to claim 9, which has a heat deformation rate of 40% or less.

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