CN105017734A - Polymeric material for 3D printing and preparation method of polymeric material - Google Patents

Abstract

The invention relates to a polymer material for 3D printing. The raw material includes the following components: 20-100 parts by weight of polybutylene succinate; 0.1-80 parts of modifier; wherein, the modifier is selected from One or more of polylactic acid, reinforcing filler, and nucleating agent. The polymeric resin that can be used for 3D printing in the present invention not only has relatively high toughness, but also has relatively high mechanical strength and heat resistance; it has broad application prospects in 3D printing materials.

Description

A kind of polymer material and preparation method thereof for 3D printing

technical field

The invention relates to a polymer material for 3D printing and a preparation method thereof, in particular to a polymer material mainly composed of PBS.

Background technique

In recent years, 3D printing has received more and more attention because of its unique advantages in forming and processing. 3D printing, also known as additive manufacturing technology, generally refers to the technology of using digital model files to directly form three-dimensional entities in a layer-by-layer manner by controlling the printing nozzle through a program. Compared with traditional molding methods, 3D printing does not require complicated molds and operating techniques. The processing process is controlled by a computer program, which is simple and safe, greatly shortens the molding processing cycle, and quickly forms parts with complex structures, which can be customized. With the deepening of research, 3D printing has gradually been widely used in medicine, aviation, construction, automobile and other fields.

Material filament melt extrusion technology, also known as fused deposition modeling technology, is one of the most widely used technologies in 3D printing technology. After the flow state, it is extruded through a nozzle onto the platform, and the layers are deposited into three-dimensional solids.

At present, the fused deposition molding matrix materials used in the market can be divided into two categories according to whether they are biodegradable, namely non-biodegradable materials represented by acrylonitrile-butadiene-styrene copolymer (ABS) And biodegradable materials represented by polylactic acid (PLA). ABS has excellent impact strength, and the printed parts have good dimensional stability, wear resistance, good dyeability, and a heat-resistant temperature of nearly 100°C, but its non-biodegradability cannot meet people's increasingly strengthened environmental protection requirements. PLA has low shrinkage and low melt strength. It does not need to heat the platform during printing, and basically does not warp. However, its heat resistance is relatively poor, and the heat distortion temperature is only about 60°C. The thermal stability, toughness and crystallization properties of polybutylene succinate (PBS) are significantly better than PLA, and it is expected to become a new generation of 3D printing materials. However, PBS has high crystallinity, large molding shrinkage rate, and low elastic modulus, so it is easy to warp and deform during 3D printing. These shortcomings greatly limit its application as a 3D printing material.

Although 3D printing technology has very broad application prospects, it is also facing great challenges. One of the main factors limiting its development is the small variety and limited performance of 3D printable materials. Chinese Patent Publication No. CN103467950A discloses a 3D printing modified polylactic acid material and its preparation method. The invention uses low-temperature pulverization and mixing reaction technology to modify polylactic acid. The prepared polylactic acid has the advantages of toughness, impact strength and heat The deformation temperature and other aspects have been greatly improved. However, the low-temperature pulverization and mixing reaction technology is suitable for small batch production, and there are difficulties in large-scale industrialization. Chinese Patent Publication No. CN103992628A discloses a UV-crosslinkable 3D printing material. PBS is modified and polymerized with other substances to prepare a 3D printing material, but this material is mainly used for UV 3D printing.

Contents of the invention

(1) Technical problems to be solved

Aiming at the defects of high molding shrinkage and low elastic modulus in the prior art when PBS is directly applied to 3D printing, the present invention provides a polymer material mainly composed of PBS.

(2) Technical solution

The polymer material of the present invention, its raw material includes the following components by weight: 20-100 parts of polybutylene succinate; 2-80 parts of modifier; wherein, the modifier is selected from polylactic acid , one or more of reinforcing fillers and nucleating agents.

The polymer material of the present invention comprises the following components by weight: 20-90 parts of polybutylene succinate; 10-80 parts of polylactic acid, the total amount of which is 100 parts.

The polymer material of the present invention preferably comprises the following components in parts by weight: 20-80 parts of polybutylene succinate; 20-80 parts of polylactic acid, the total of which is 100 parts.

The raw material of the polymer material in the present invention comprises the following components: 100 parts of polybutylene succinate; 5-10 parts of reinforcing filler.

The raw material of the polymer material in the present invention comprises the following components: 100 parts of polybutylene succinate; 0.1 to 5 parts of nucleating agent.

The polymer material of the present invention, its raw material includes the following components: 20-90 parts of polybutylene succinate; 10-80 parts of polylactic acid; 2-10 parts of reinforcing filler, the polybutylene succinate The total amount of ester and polylactic acid is 100 parts.

The raw materials of the polymer material in the present invention further include 1-5 parts by weight of color masterbatch and 1-5 parts by weight of blending additives suitable for 3D printing.

In the present invention, the masterbatch includes inorganic pigments and organic pigments; the inorganic pigment chromate, one of titanium dioxide, carbon black, and iron-based pigments; the organic pigments are selected from phthalocyanine pigments or permanent pigments. Solid pigments.

In the present invention, the blending auxiliary agent suitable for 3D printing can be polyethylene low molecular weight wax, or any other agent that can play the same role.

In the polymer material of the present invention, the molecular weight of the polybutylene succinate is 20,000-200,000, and the degree of crystallinity is 25-65%; the molecular weight of the polylactic acid is 20,000-200,000, and the degree of crystallinity is 0 -40%; the reinforcing filler includes one or more of titanium dioxide, attapulgite, boron nitride, calcium carbonate, talcum powder and clay; the nucleating agent includes boron nitride, TMC300, TMC306 and One or more of polybutylene fumarate. By adding reinforcing fillers, the elastic modulus of the material can be increased, thereby improving the ability of the material to resist deformation. By adding nucleating agents, the curing rate can be increased, thereby speeding up 3D printing.

In the polymer material of the present invention, the molecular weight of the polybutylene succinate is preferably 60,000-150,000. The molecular weight of the polylactic acid is preferably 4-100,000; the crystallinity of the polylactic acid is preferably 0-30%. Polylactic acid in this range not only has good mechanical properties, but also has good melt processing properties.

Another object of the present invention is to provide the preparation method of polymer material of the present invention, comprises the steps:

1) Premix the raw materials of the polymer material after drying, add them into the twin-screw extruder, mix them evenly, and then extrude and cut into pellets to obtain spare materials; the temperature of the first, second, third and die heads of the twin-screw extruder 140-150°C, 165-170°C, 180-185°C, 180-185°C respectively; main engine speed is 40-200rpm;

2) Add the spare material into the single-screw extruder, and draw it with a tractor after extrusion to make a wire rod for 3D printing; the first, second, third and die heads of the single-screw extruder The temperatures are 130-135°C, 150-155°C, 160-165°C, 150-155°C; the screw speed is 10-30rpm, and the draw ratio of the tractor is 1.1-3.2.

The last object of the present invention is to provide a method for 3D printing using the materials described in the present invention, specifically, printing by using fusion deposition technology, controlling the printing speed to 20-42mm/s, printing temperature at 170-215°C, and high printing layer 0.05~0.15mm, wire diameter 1.6~2.0mm.

(3) Beneficial effects

The material of the present invention has the following beneficial effects:

1) The polymer material that can be used for 3D printing based on polybutylene succinate according to the present invention: effectively improves the molding shrinkage that exists when directly using polybutylene succinate for 3D printing Large and low elastic modulus defects, the prepared material has high tensile strength and tensile modulus, and retains the good toughness of the original PBS, and its performance indicators such as elongation at break and impact strength are good.

2) Compared with the existing 3D printable polymer materials, polybutylene succinate blend materials not only have relatively high toughness, but also have high heat resistance, and their Vicat softening point temperature is high at 80°C;

3) The prepared polybutylene succinate and polylactic acid blend material has bright color, its L value is greater than 90, a and b values are both less than 5, and has good biodegradability;

4) The present invention can obtain products with different colors and different mechanical properties by changing the added reinforcing fillers and pigments and the parts by weight of polylactic acid.

Detailed ways

The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

Example 1

This embodiment relates to a polymer material for 3D printing, and its raw material composition is 60 parts by weight of polybutylene succinate, 40 parts by weight of polylactic acid and 1 part by weight of iron yellow.

Example 2

This embodiment relates to a polymer material for 3D printing, and its raw material composition is 20 parts by weight of polybutylene succinate, 80 parts by weight of polylactic acid and 1 part by weight of iron yellow.

Example 3

This embodiment relates to a polymer material for 3D printing, and its raw material composition is 100 parts by weight of polybutylene succinate, 5 parts by weight of attapulgite and 1 part by weight of phthalocyanine blue.

Example 4

This embodiment relates to a kind of polymer material for 3D printing, and its raw material is composed of 100 parts by weight of polybutylene succinate, 2 parts by weight of polybutylene fumarate, and 1 part by weight of permanent violet .

Example 5

This embodiment relates to a polymer material for 3D printing, and its raw material composition is 80 parts by weight of polybutylene succinate, 20 parts by weight of polylactic acid and 2 parts by weight of attapulgite.

Example 6

This implementation involves an example of using the raw materials described in Example 1 to prepare a polymer material for 3D printing and print a hollowed-out rabbit. The steps are as follows:

1) Dry the polybutylene succinate, polylactic acid and iron yellow at 80° C. for 2 hours.

2) take by weighing the polybutylene succinate of 60 weight parts after drying, the polylactic acid of 40 weight parts, after the iron yellow of 1 part is premixed, extrude and pelletize with a twin-screw extruder, get standby material, The temperatures of zone 1, zone 2, zone 3 and the die head of the twin-screw extruder are 140°C-150°C, 165-170°C, 180-185°C, 180-185°C, and the speed of the main engine is 60rpm.

3) Extrude the spare material into filaments with a diameter of 1.75±0.05mm using a single-screw extruder. The temperatures of the first zone, second zone, third zone and die head of the single-screw extruder are 130-135°C, 150-155°C, 160-165°C, 150-155°C respectively. The screw speed is 10rpm, and the draft ratio is 1.1-2.4.

4) The filaments obtained in step 3) are collected into rolls, sent into the heating chamber through the gear in front of the nozzle of the Aod printer, and heated and melted in the heating chamber. The nozzle moves according to the pre-set 3D printing model program, and the molten material is extruded to a glass platform under the push of the wire. The extruded material gradually cools and solidifies on the platform. After printing one layer, the platform descends and lays down the next layer. Utilizing the viscous flow characteristics of the material itself, it is piled up and formed layer by layer to form a hollowed-out bunny product. The parameter settings during printing are shown in Table 1.

Table 1. Parameter settings for PBS60/PLA40 printing

Perform performance characterization of the material obtained in step 2), and the characterization results are shown in Table 2.

Table 2. Performance parameters of PBS60/PLA40

Tensile strength/MPa 45.6 Tensile modulus/MPa 1545.9 Elongation at break/% 297 Impact strength/kJ m-2 14.7 Zero shear viscosity/Pa·s 1697

In the above-mentioned tests, the tensile properties were determined according to ASTM D638, and type II specimens were selected, and the tensile speed was 50mm/min during the test.

In the above test, the impact strength is measured according to ASTM D648.

In the above test, the melt viscosity was measured at 160° C. with a strain of 1% using a frequency sweep of 0.01 to 100 Hz.

Example 7

This implementation involves an example of using the raw materials described in Example 2 to prepare a polymer material and further print a hollowed-out bunny. The steps are as follows:

1) The mixture of polybutylene succinate, polylactic acid and iron yellow was vacuum-dried at 60° C. for 12 hours.

2) After mixing 20 parts by weight of polybutylene succinate, 80 parts by weight of polylactic acid and 1 part of iron yellow, extrude and pelletize with a twin-screw extruder to obtain spare materials. The temperatures of zone 1, zone 2, zone 3 and the die head of the twin-screw extruder are 140°C-150°C, 165-170°C, 180-185°C, 180-185°C, and the speed of the main engine is 60rpm.

3) extruding the spare material with a single-screw extruder into filaments with a diameter of 1.75±0.05mm. The temperatures of the first zone, second zone, third zone and die head of the single-screw extruder are 130-135°C, 150-155°C, 160-165°C, 150-155°C respectively. The screw speed is 10rpm, and the draft ratio is 1.1-2.4.

4) The filaments obtained in step 3) are collected into rolls, sent into the heating chamber through the gear in front of the nozzle of the Aod printer, and heated and melted in the heating chamber. The nozzle moves according to the pre-set 3D printing model program, and the molten material is extruded to a glass platform under the push of the wire. The extruded material gradually cools and solidifies on the platform. After printing one layer, the platform descends and lays down the next layer. Utilizing the viscous flow characteristics of the material itself, it is piled up layer by layer to form a hollowed-out bunny. The parameter settings during printing are shown in Table 3.

Table 3. Parameter settings for PBS20/PLA80 printing

Perform performance characterization of the material obtained in step 2), and the characterization results are shown in Table 4

Table 4. Performance parameters of PBS20/PLA80

Tensile strength/MPa 55.6 Tensile modulus/MPa 2150 Elongation at break/% 93 Impact strength/kJ m ^-2 12.9

Zero shear viscosity/Pa·s 4837

In the above-mentioned tests, the tensile properties were determined according to ASTM D638, and type II specimens were selected, and the tensile speed was 50mm/min during the test.

In the above test, the impact strength is measured according to ASTM D648.

In the above test, the melt viscosity was measured at 160° C. with a strain of 1% using a frequency sweep of 0.01 to 100 Hz.

Example 8

This implementation relates to an example of using the raw materials described in Example 3 to prepare a polymer material and further print a business card holder. The steps are as follows:

1) The polybutylene succinate and attapulgite were vacuum-dried at 60° C. for 12 hours.

2) After premixing 100 parts by weight of polybutylene succinate, 5 parts by weight of attapulgite, and 1 part of phthalocyanine blue, extrude and pelletize with a twin-screw extruder to obtain spare materials, twin-screw The temperature of zone 1, zone 2, zone 3 and die head of the extruder are 140-150°C, 165-170°C, 180-185°C, 180-185°C respectively, and the speed of the main machine is 60rpm.

3) Extrude the spare material with a single-screw extruder and process it into filaments with a diameter of 1.75±0.05mm. The temperatures of the first zone, second zone, third zone and die head of the single-screw extruder are 130-135°C, 150-155°C, 160-165°C, 150-155°C respectively. The screw speed is 30rpm, and the draft ratio is 1.1-2.4.

4) The filaments obtained in step 3) are collected into rolls, sent into the heating chamber through the gear in front of the nozzle of the Aod printer, and heated and melted in the heating chamber. The nozzle moves according to the pre-set 3D printing model program, and the molten material is extruded to a glass platform under the push of the wire. The extruded material gradually cools and solidifies on the platform. After printing one layer, the platform descends and lays down the next layer. Using the viscous flow characteristics of the material itself, it is piled up and formed layer by layer to form a business card holder. The parameter settings during printing are shown in Table 5.

Table 5. Parameter settings when printing PBS/Att nanocomposites

Perform performance characterization of the material obtained in step 2), and the characterization results are shown in Table 6.

Table 6. Performance parameters of PBS/Att nanocomposites

Tensile strength/MPa 34.3 Tensile modulus/MPa 706.6 Elongation at break/% 134

In the above-mentioned tests, the tensile properties were determined according to ASTM D638, and type II specimens were selected, and the tensile speed was 50mm/min during the test.

Example 9

This implementation relates to an example of using the raw materials described in Example 4 to prepare a polymer material and further print a mobile phone case. The steps are as follows:

1) Dry polybutylene succinate, polybutylene fumarate and permanent violet in vacuum at 60°C for 12 hours.

2) After premixing 100 parts by weight of polybutylene succinate, 2 parts by weight of polybutylene fumarate, and 1 part of permanent violet, extrude and pelletize with a twin-screw extruder to obtain spare materials , the temperatures of the first, second, third and die heads of the twin-screw extruder are 140-150°C, 165-170°C, 180-185°C, 180-185°C, and the speed of the main engine is 40rpm.

3) extruding the spare material into filaments with a diameter of 1.75±0.05mm with a single-screw machine. The temperatures of the first, second, third and die heads of the extruder are 130-135°C, 150-155°C, 160-165°C, and 150-155°C, respectively. The screw speed is 10rpm, and the draft ratio is 2.1-3.2.

4) The filaments obtained in step 3) are collected into rolls, sent into the heating chamber through the gear in front of the nozzle of the Aod printer, and heated and melted in the heating chamber. The nozzle moves according to the pre-set 3D printing model program, and the molten material is extruded to a glass platform under the push of the wire. The extruded material gradually cools and solidifies on the platform. After printing one layer, the platform descends and lays down the next layer. Using the viscous flow characteristics of the material itself, it is piled up layer by layer to form a mobile phone case. The parameter settings during printing are shown in Table 7.

Table 7. Parameter settings when printing PBS/PBF blend materials

The product E is purple, the crystallinity of the sample is 52%, and the tensile breaking strength is 35 MPa.

Example 10

This implementation relates to an example of using the raw materials described in Example 5 to prepare a polymer material and further print a mobile phone case. The steps are as follows:

1) Dry polybutylene succinate, polylactic acid and attapulgite in vacuum at 60°C for 12h.

2) After premixing the polybutylene succinate of 80 parts by weight, the polylactic acid of 20 parts by weight and the attapulgite of 2 parts by weight, extrude and pelletize with a twin-screw extruder to obtain the spare material, and the twin-screw extruder The temperatures of the first, second, third and die heads are 140-150°C, 165-170°C, 180-185°C, 180-185°C respectively, and the speed of the main machine is 200rpm.

3) extruding the spare material into filaments with a diameter of 1.75±0.05mm with a single-screw machine. The temperatures of the first, second, third and die heads of the extruder are 130-135°C, 150-155°C, 160-165°C, and 150-155°C, respectively. The screw speed is 10rpm, and the draft ratio is 2.1-3.2.

4) The filaments obtained in step 3) are collected into rolls, sent into the heating chamber through the gear in front of the nozzle of the Aod printer, and heated and melted in the heating chamber. The nozzle moves according to the pre-set 3D printing model program, and the molten material is extruded to a glass platform under the push of the wire. The extruded material gradually cools and solidifies on the platform. After printing one layer, the platform descends and lays down the next layer. Using the viscous flow characteristics of the material itself, it is piled up layer by layer to form a mobile phone case. The parameter settings during printing are shown in Table 8.

Table 8. Parameter settings when printing PBS/PLA/Att blend materials

Perform performance characterization of the material obtained in step 2), and the characterization results are shown in Table 9.

Table 9. Performance parameters of PBS/PLA/Att nanocomposites

Tensile strength/MPa 36.3 Tensile modulus/MPa 682 Elongation at break/% 267

Comparative example 1

This comparative example relates to a polymer material for 3D printing, and its raw material composition is 100 parts by weight of polybutylene succinate and 1 part by weight of titanium dioxide.

Comparative example 2

This comparative example relates to the example of using the raw material components described in Comparative Example 1 to prepare a polymer material for 3D printing and print a small gecko. The steps are as follows:

1) Dry polybutylene succinate at 60°C for 12 hours;

2) After premixing 100 parts by weight of polybutylene succinate and 1 part of titanium dioxide, extrude and pelletize with a twin-screw extruder to obtain spare materials; The temperatures of the three zones and the die head are 140-150°C, 165-170°C, 180-185°C, and 180-185°C respectively, and the speed of the host machine is 40rpm.

3) Add the spare material into the single-screw extruder, draw it with a tractor after extrusion, and process it into filaments with a diameter of 1.75±0.05mm. and the temperature of the die are respectively 130-135°C, 150-155°C, 160-165°C, and 150-155°C. The screw speed is 20rpm, and the draft ratio is 1.0-2.0.

4) The filaments obtained in step 3) are collected into rolls, sent into the heating chamber through the gear in front of the nozzle of the Aod printer, and heated and melted in the heating chamber. The nozzle moves according to the pre-set 3D printing model program, and the molten material is extruded to a glass platform under the push of the wire. The extruded material gradually cools and solidifies on the platform, and after printing one layer, the platform descends and lays down another layer. Using the viscous flow characteristics of the material itself, the layers are piled up and formed to form a small gecko. The parameter settings during printing are shown in Table 10.

Table 10. Parameter settings for pure PBS printing

Perform performance characterization of the material obtained in step 12), and the characterization results are shown in Table 11.

Table 11. Performance parameters of pure PBS

Tensile strength/MPa 31.5 Tensile modulus/MPa 554 Elongation at break/% 324 Impact strength/kJ m-2 7.2 Zero shear viscosity/Pa·s 678

In the above-mentioned tests, the tensile properties were determined according to ASTM D638, and type II specimens were selected, and the tensile speed was 50mm/min during the test.

In the above test, the impact strength is measured according to ASTM D648.

In the above test, the melt viscosity was measured at 160° C. with a strain of 1% using a frequency sweep of 0.01 to 100 Hz.

It can be seen from this example that only PBS is used as the 3D printing material, and its tensile modulus, impact strength, zero shear viscosity and other properties are obviously not as good as those after adding auxiliary materials such as polylactic acid, so the mixed material of the present invention is the same as pure Compared with the PBS material, its tensile strength, tensile modulus and impact strength can be significantly improved, the warping deformation of 3D printed products is significantly improved, and the dimensional accuracy is improved.

Although the present invention has been described in detail with general descriptions and specific embodiments above, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.

Claims (9)

1., for the polymer materials that 3D prints, it is characterized in that, its raw material comprises the component of following weight part: poly-succinic fourth diester 20 ~ 100 parts; Properties-correcting agent 0.1 ~ 80 part; Wherein, described properties-correcting agent is selected from one or more in poly(lactic acid), reinforcing filler, nucleator.

2. polymer materials according to claim 1, is characterized in that, its raw material comprises the component of following weight part: poly-succinic fourth diester 20 ~ 90 parts; Poly(lactic acid) 10 ~ 80 parts, the two total amount is 100 parts.

3. polymer materials according to claim 1, is characterized in that, its raw material comprises the component of following weight part: poly-succinic fourth diester 100 parts; Reinforcing filler 5 ~ 10 parts.

4. polymer materials according to claim 1, is characterized in that, its raw material comprises the component of following weight part: poly-succinic fourth diester 100 parts; Nucleator 0.1 ~ 5 part.

5. polymer materials according to claim 1, is characterized in that, its raw material comprises the component of following weight part: poly-succinic fourth diester 20 ~ 90 parts; Poly(lactic acid) 10-80 part; Reinforcing filler 2-10 part, the total amount of described poly-succinic fourth diester and poly(lactic acid) is 100 parts.

6. according to the arbitrary described polymer materials of claim 1-5, it is characterized in that, described raw material also comprises the colour batch of 1 ~ 5 weight part and the blended used additives being suitable for 3D printing of 1 ~ 5 weight part.

7. the polymer materials according to any one of Claims 1 to 5, is characterized in that, the molecular weight of described poly-succinic fourth diester is 2-20 ten thousand, and degree of crystallinity is 25-65%;

The molecular weight of described poly(lactic acid) is 2 ~ 200,000, and degree of crystallinity is 0-40%;

Described reinforcing filler comprise in titanium dioxide, attapulgite, boron nitride, calcium carbonate, talcum powder and potter's clay one or more;

Described nucleator comprise in boron nitride, TMC300, TMC306 and poly-fumaric acid fourth diester one or more.

8. the preparation method of polymer materials described in any one of claim 1 ~ 7, is characterized in that, comprise the steps:

1) by premix after the raw material drying of the polymer materials described in claim 1 ~ 7, add in twin screw extruder blended evenly after extrude pelletizing, obtain lay-by material;

The temperature of twin screw extruder one district, 2nd district, 3rd district and die head is respectively 140 ~ 150 DEG C, 165 ~ 170 DEG C, 180 ~ 185 DEG C, 180 ~ 185 DEG C; Engine speed is 40 ~ 200rpm;

2) described lay-by material is joined in single screw extrusion machine, extrude rear tractor drawing-off, make the wire rod printed for 3D;

The temperature of single screw extrusion machine one district, 2nd district, 3rd district and die head is respectively 130 ~ 135 DEG C, 150 ~ 155 DEG C, 160 ~ 165 DEG C, 150 ~ 155 DEG C; Screw speed is 10 ~ 30rpm, and the ratio of drawing of tractor is 1.1 ~ 3.2.

9. utilize the arbitrary described polymer materials of right 1 ~ 7 to carry out the method for fusion stacking 3D printing, it is characterized in that, control print speed 20 ~ 42mm/s, print temperature 170 ~ 215 DEG C, print floor height 0.05 ~ 0.15mm, gauge or diameter of wire 1.6 ~ 2.0mm.