KR102499067B1 - Ink composition for 3d inkjet printing to provide high strength of mechanical properties - Google Patents

Abstract

The present invention provides an ink composition for inkjet 3D printing. The ink composition may provide an object having high strength mechanical properties after photocuring by optimizing the curing degree of each layer of the 3D object by using a mixture of photoinitiators having different properties.

Description

Ink composition for 3D inkjet printing providing high strength mechanical properties

The present invention relates to an ink composition for inkjet 3D printing. More specifically, the present invention relates to an ink composition for inkjet 3D printing capable of providing high-strength mechanical properties after photocuring by using a mixture of photoinitiators having different properties.

Inkjet 3D printing is a method of forming a laminated body by ejecting a liquid photocurable material by jetting and curing it repeatedly with ultraviolet light or the like. To enable inkjet 3D printing, an ink composition with low viscosity (<100 cP @ 25 ° C) is required, and to enable UV LED photocuring, it must contain a functional group of an acrylic group or an epoxy group.

Photocuring of the acrylic group is achieved by a radical curing mechanism, and oxygen in the air neutralizes the radical to inhibit the curing reaction. Therefore, when acrylic ink is applied to form a 3D printed object by layering, curing of the surface in contact with air is delayed. On the other hand, when UV rays pass through the surface of the ink to cure the deep part, the light is absorbed into the ink as it passes through the ink, resulting in a decrease in the amount of light, and also an effect of delaying photocuring.

Therefore, there is a need to develop an ink composition for 3D inkjet printing capable of providing a high-strength 3D printed object by uniformly realizing light curing characteristics of the deep portion and surface of a coating film of the ink composition.

Regarding the mechanical properties of the conventional 3D printing ink, attempts have been made to improve the mechanical properties by including rubber polymer particles or inorganic nanoparticles or by containing oligomer components. No attempt has been made to provide 3D printed objects.

Japanese patent application JP 2007-209384

An object of the present invention is to provide a 3D printing object having high strength, such as ABS plastic, in inkjet 3D printing by photocuring well on both the surface and the inside of the ink coating film.

In order to solve the above problems, the present inventors, as a result of intensive research, found that it is possible to manufacture an object having high strength mechanical properties after photocuring by optimizing the degree of curing of each layer of a 3D object by mixing and using photoinitiators having different properties. .

According to one embodiment, the ink composition for 3D inkjet printing of the present invention includes a monofunctional acrylate monomer; polyfunctional acrylate monomers; urethane acrylate oligomers; hydroxyketone-based photoinitiators; and a phosphine oxide-based photoinitiator or an aminoketone-based photoinitiator, or both, wherein the weight ratio of the monofunctional acrylate monomer to the multifunctional acrylate monomer is 1:1 to 10:1, and the monofunctional acrylate monomer has a glass transition temperature (Tg) of 50 °C or more, the number of carbon atoms between acrylate functional groups of the multifunctional acrylate monomer is 9 or less, and the hydroxyketone-based photoinitiator is present in an amount of 0.2 to 5% by weight based on the total weight of the composition. contained in an amount of

According to the present invention, it is possible to implement a composition having uniformly excellent photocuring characteristics of the deep part and the surface of the ink coating film by using a mixture of photoinitiators having different absorbances for light wavelengths.

1 is a diagram briefly illustrating steps of manufacturing a 3D sculpture using an ink composition in a 3D inkjet process.
Figure 2 shows a stress strain curve (SS curve) for measuring the mechanical properties of the specimen.
Figure 3 shows the expected curing gradient for each photoinitiator mixed and used according to the present invention.

Hereinafter, the terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, and the inventor appropriately defines the concept of terms in order to explain his/her invention in the best way. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be done.

The present invention provides an ink composition for 3D inkjet printing, comprising a monofunctional acrylate monomer, a polyfunctional acrylate monomer, a urethane acrylate oligomer, and two or more photoinitiators having different properties.

When the ink is irradiated with light having a wavelength in a certain range for photocuring, the longer the wavelength of the light, the higher the penetrating power into the ink. Therefore, when several types of photoinitiators having different absorbances for light wavelengths are mixed and used, it is possible to realize a composition having uniformly excellent photocuring characteristics of the deep part and the surface of the ink coating film.

Photoinitiators that absorb long wavelengths are excellent in internal curing, but due to insufficient surface curing, it is difficult to achieve high strength properties when used alone. A photoinitiator that absorbs intermediate wavelengths is difficult to achieve high-strength properties due to insufficient curing degree when used alone. Photoinitiators that absorb short wavelengths have excellent surface hardening, but due to insufficient internal hardening, it is difficult to achieve high strength properties when used alone.

Therefore, in the present invention, by using a mixture of two or more of the initiators having the above characteristics, photocuring occurs well both on the surface and inside, and accordingly, it is possible to implement an ink composition having excellent mechanical properties of a 3D printed object.

The ink composition for 3D inkjet printing according to the present invention comprises a monofunctional acrylate monomer, a polyfunctional acrylate monomer, a urethane acrylate oligomer, and a photoinitiator absorbing short wavelengths, a photoinitiator absorbing medium wavelengths or a photoinitiator absorbing long wavelengths, or these includes a combination of both.

According to one embodiment, the composition according to the present invention includes a photoinitiator that absorbs short wavelengths, a photoinitiator that absorbs medium wavelengths, and a photoinitiator that absorbs long wavelengths.

The short-wavelength absorbing photoinitiator is a hydroxyketone-based photoinitiator absorbing light in a wavelength range of 240 to 270 nm, examples of which include 2-hydroxy-2-methyl propiophenone (Darocur 1173 from BASF), 2-hydroxy Roxy-2-methyl-4'-tert-butyl-propiophenone, 1-hydroxycyclohexyl phenyl ketone (Irgacure 184 from BASF), 2-hydroxy-4'-(2-hydroxyethoxy)-2 -Methyl-propiophenone, 2-hydroxy-[4'-(2-hydroxypropoxy)]-2-methyl-propiophenone, 2-hydroxy-1-{4-[4-(2-) Hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one (Irgacure 127 from BASF) and the like.

The short wavelength absorption initiator may be included in an amount of 0.2 to 5% by weight, 0.5 to 2% by weight, or 1% by weight based on the total weight of the composition. When the short wavelength absorption initiator is included in less than 0.2% by weight, there is no surface hardening effect by the short wavelength absorption initiator, and collapse may occur during lamination. It does not reach the inside and collapse may occur during lamination due to lack of internal hardening.

The medium-wavelength absorbing photoinitiator is an aminoketone-based photoinitiator absorbing light in a wavelength range of 270 to 350 nm, which is 2-methyl-4'-(methylthio)-2-morpholino-propiophenone (BASF Irgacure 907), 2-benzyl-2-(dimethylamino)-4-morpholinobutyrophenone (Irgacure 369 from BASF), 2-(4-methylbenzyl)-2-(dimethylamino)-4-morph polynobutyrophenone (Irgacure 379 from BASF); and the like.

The medium wavelength absorption initiator may be included in an amount of 0.2 to 5% by weight, or 0.5 to 2% by weight, or 1% by weight based on the total weight of the composition. When the short wavelength absorption initiator is included in an amount of less than 0.2% by weight, it is difficult to form a laminated object due to lack of overall curing, while if the content exceeds 2% by weight, the initiator is included in an excessive amount, resulting in no curing effect and yellowing This can appear very severe.

The long-wavelength absorbing photoinitiator is a phosphine oxide-based photoinitiator absorbing light in a wavelength range of 350 to 420 nm, such as diphenyl-(2,4,6-trimethylbenzoyl)-phosphine oxide (BASF TPO). ), ethyl-(2,4,6-trimethylbenzoyl)phenyl-phosphinate (BASF TPO-L), phenyl-bis-(2,4,6-trimethylbenzoyl)-phosphine oxide (BASF Irgacure 819 ) and the like.

The long-wavelength absorption initiator may be included in an amount of 2% by weight or more, or 2 to 10% by weight based on the total weight of the composition. When the long-wavelength absorption initiator is included in less than 2% by weight, there is no internal curing effect due to the long-wavelength absorption initiator, and collapse may occur during lamination. Not only is it ineffective, but the yellowing can be very severe.

The monofunctional acrylate monomer is a radical curable monomer and has a glass transition temperature (Tg) of 50 ° C. or more, examples of which include isobornyl acrylate, isobornyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacryl rate, dicyclopentadienyl acrylate, dicyclopentadienyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 4-acryloylmorpholine, and the like.

Addition of the monofunctional acrylate monomer contributes to realizing a low-viscosity ink composition.

When the Tg of the monofunctional acrylate monomer is less than 50° C., strength may decrease.

The multifunctional acrylate monomer has 9 or less carbon atoms between acrylate functional groups, and examples thereof include trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethoxylated(3)trimethylolpropane triacrylate, propoxylated(3) ) Glycerin triacrylate, pentaerythritol triacrylate, ethoxylated (3) trimethylolpropane triacrylate, tris (2-hydroxyethyl) isocyanurate triacrylate, ditrimethylolpropane tetraacrylate, etc. can do. The multifunctional acrylate monomer serves to enable the formation of a network structure by increasing the degree of crosslinking in the curing reaction. When a polyfunctional, eg, trifunctional or higher acrylate monomer is present, a three-dimensional network structure can be formed, and furthermore, it contributes to the strength of the final cured product.

When the number of carbon atoms between the functional groups of the multifunctional acrylate monomer is greater than 9, strength may decrease.

The ratio of the monofunctional acrylate monomer to the multifunctional acrylate monomer may be 1:1 to 10:1, specifically 2:1 to 5:1. When the ratio of the monofunctional monomer to the polyfunctional monomer is less than 1:1, that is, when more polyfunctional monomers are included, it tends to be easily broken, and satisfactory strength cannot be achieved. On the other hand, when the ratio of the monofunctional monomer to the polyfunctional monomer exceeds 10:1, that is, when a large amount of the monofunctional monomer is contained, the elastic modulus may be greatly reduced, which is not preferable.

The urethane acrylate oligomer may be a bifunctional or more functional acrylate oligomer having a weight average molecular weight of 2000 to 20000 or less, and the urethane acrylate oligomer is in an amount of 10 to 50% by weight based on the total weight of the composition, or 20 to It may be included in an amount of 40% by weight, or in an amount of 30% by weight. When the content of the oligomer is less than 10% by weight, it may be very brittle and breakage may occur before the yield point. On the other hand, when the content of the oligomer exceeds 50% by weight, the elastic modulus is greatly reduced and the viscosity of the composition is very high, making it difficult to apply the composition to an inkjet process.

Hereinafter, the action and effect of the invention will be described in more detail through specific examples of the invention. However, this is presented as an example of the invention, and thereby the scope of the invention is not limited in any sense.

Example

The compounds used in the following Examples and Comparative Examples are as follows.

(Example 1)

An ink composition containing 25% by weight of ACMO, 35% by weight of IBOA, 17% by weight of TMPTA, 20% by weight of PU256, and 1% by weight of Irgacure 369 and 1% by weight of Irgacure 127 as photoinitiators was stirred and mixed for about 4 hours. A 3D printing ink composition was prepared.

(Examples 2 to 4)

A 3D printing ink composition was prepared by the same method as in Example 1 with the composition shown in Table 2 below.

(Comparative Examples 1 to 13)

3D printing ink compositions were prepared by the same method as in Example 1 with the compositions shown in Tables 1 and 2 below.

(Example of specimen production)

The ink compositions obtained in the above Examples and Comparative Examples were printed at a printing resolution of 600 dpi using Dimatix's Sapphire QS-256/80 AAA, and then irradiated with light with a 365 nm UV LED (intensity: 1 J/cm ² ) to obtain light After curing, lamination printing, and photo-curing again, a 3D model specimen having a total lamination thickness of about 3 mm is prepared.

(experimental example)

[Evaluation of degree of curing]

The degree of curing of the composition was compared by calculating the area of the acrylate-related peak through the IR spectrum, and was evaluated by comparing the acrylate area of the ink and the acrylate area of the cured composition. The curing degree of the composition was classified according to the following evaluation criteria.

○: No uncured monomer/oligomer remains and does not stick to hands

△+: Less than 10% of uncured monomer/oligomer remains and sticks to the hand

△: 10% or more and less than 30% of uncured monomers/oligomers remain and stick to hands

△-: More than 30% of uncured monomer/oligomer remains and smears on hands

[measurement of mechanical properties]

The specimen prepared according to the specimen preparation example may be performed according to the ASTM D638 (tensile test) standard to obtain an S-S curve (stress strain curve) [test specimen: Type I, test speed: 5 mm/min]. Strength, modulus of elasticity, elongation and energy (toughness) can be obtained from the obtained S-S curve, and the curve is shown in FIG. 2.

- Strength: Strength refers to the maximum stress that a material can withstand, and the higher the strength, the higher the mechanical properties.

- Modulus of elasticity: The modulus of elasticity refers to the ratio of stress to strain (stress/strain) in the elastic range, and the higher the elastic modulus, the higher the mechanical properties.

- Elongation: Elongation refers to the tensile elongation at the point where the specimen breaks, and it is not easily brittle when the point where the specimen breaks appears above the yield point.

- Energy (toughness): refers to the energy absorption capacity until failure occurs, and corresponds to the lower area of the stress-strain curve.

The higher the strength and modulus of elasticity, the higher the mechanical properties. In Example 3, the 3D specimen has strength >60 MPa and modulus of elasticity >2.0 GPa, and in this case, it can be said that the specimen has maximum physical properties due to optimized hardening.

Elongation is a reference value to know the properties of the material (ductile, brittle) by checking whether the point where the specimen breaks appears above the yield point. In Example 3, the yield point appears at about 4%, and when the elongation is 4% or more, it can be said that it is not easily brittle and has stable mechanical properties. If the uncured component between each layer acts as a plasticizer, the elongation may be as high as 10% or more, which is not preferable.

In Tables 1 and 2, Comparative Examples 1 to 7 are examples using a single photoinitiator. In particular, as in Comparative Examples 1 and 2, upon application of Darocure TPO having long wavelength absorption (λ _abs = 350 to 420), insufficient surface hardening may occur. In addition, as in Comparative Examples 5 to 7, when Irgacure 127 or Irgacure 184 having short wavelength absorption (λ _abs = 240 to 270) is applied, insufficient internal curing may occur. In the case of Comparative Examples 3 and 4, when Irgacure 369 having medium wavelength absorption (λ _abs = 270 to 350) is applied, mechanical properties may be deteriorated due to lack of overall (surface + interior) curing.

As such, when a single photoinitiator is used, lack of internal curing or insufficient surface curing may occur, making lamination impossible or deteriorating mechanical properties.

Meanwhile, Comparative Examples 8 and 9 and Example 1 show examples in which a medium wavelength absorption photoinitiator and a short wavelength absorption photoinitiator are used in combination. In the case of Example 1, by using a combination of 1 wt% of Irgacure 369 and 1 wt% of Irgacure 127, which is advantageous for surface hardening, surface hardening was improved and the elastic modulus and strength of the specimen were increased. On the other hand, in Comparative Example 8, 1 wt% of Irgacure 369 and 0.1 wt% of Irgacure 127 were used in combination, but the curing degree was not improved due to the small amount. In Comparative Example 9, 0.1 wt% of Irgacure 127 and 1 wt% of Irgacure 369 were used in combination, but the curing degree was not improved due to the small amount.

Therefore, it can be seen that the mechanical properties of the specimen increase when 0.2 to 2 wt% of the medium wavelength absorption (λ _abs = 270 to 350) initiator and 0.2 to 2 wt% of the short wavelength absorption (λ _abs = 240 to 270) initiator are added. there is.

Comparative Examples 10 and 11 and Example 2 show examples in which a long wavelength absorption photoinitiator and a short wavelength absorption photoinitiator are used in combination. In Example 2, by using a combination of 2 wt% of Darocure TPO and 1 wt% of Irgacure 127, which is advantageous for surface hardening, the surface hardening degree was improved and the elastic modulus and strength of the specimen were increased. On the other hand, in Comparative Example 10, 2 wt% of Darocure TPO and 0.1 wt% of Irgacure 127 were used in combination, but the curing degree was not improved due to the small amount. Also, in Comparative Example 11, 1 wt% of Darocure TPO and 1 wt% of Irgacure 127 were used in combination, but internal hardening improvement by TPO was not shown.

Therefore, it can be seen that the mechanical properties of the specimen increase when 2 wt% or more of the long-wavelength absorption (λ _abs = 350 to 420) initiator and 0.2 to 2 wt% of the short-wavelength absorption (λ _abs = 240 to 270) initiator are added.

Comparative Examples 12 and 13 and Example 3 show examples of using a long wavelength absorption photoinitiator and a medium wavelength absorption photoinitiator in combination. In Example 3, by using a combination of 1 wt% of Irgacure 369 and 2 wt% of Darocure TPO, which is advantageous for internal hardening, the internal hardening degree was improved and the elastic modulus and strength of the specimen were increased. On the other hand, in Comparative Example 12, when 0.1 wt% of Irgacure 369 and 2 wt% of Darocure TPO were used in combination, the curing degree was not improved by Irgacure 369. Also, in Comparative Example 13, when 1 wt% of Irgacure 369 and 1 wt% of Darocure TPO were used in combination, internal hardening improvement by TPO was not shown.

Example 4 shows an example in which a long-wavelength absorbing photoinitiator, a medium-wavelength absorbing photoinitiator, and a short-wavelength absorbing photoinitiator are used in combination. In Example 4, it was proved that Darocure TPO 2 wt%, Irgacure 369 1 wt% and Irgacure 127 1 wt% were used in combination to obtain sufficient curing overall and to be suitable as a hard 3D printing ink having excellent mechanical properties.

As described above, specific parts of the present invention have been described in detail, to those skilled in the art, it is clear that these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby. something to do. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (11)

monofunctional acrylate monomers;
polyfunctional acrylate monomers;
urethane acrylate oligomers;
hydroxyketone-based photoinitiators; and
Including a phosphine oxide-based photoinitiator or an aminoketone-based photoinitiator or both,
The weight ratio of the monofunctional acrylate monomer to the polyfunctional acrylate monomer is 1:1 to 10:1,
The glass transition temperature (Tg) of the monofunctional acrylate monomer is 50 ℃ or more,
The number of carbon atoms between the acrylate functional groups of the multifunctional acrylate monomer is 9 or less,
The hydroxyketone-based photoinitiator is contained in an amount of 0.2 to 2% by weight based on the total weight of the composition,
The aminoketone-based photoinitiator is contained in an amount of 0.2 to 5% by weight based on the total weight of the composition,
The phosphine oxide-based photoinitiator is contained in an amount of 2 to 10% by weight based on the total weight of the composition, the ink composition for 3D inkjet printing. According to claim 1, wherein the urethane acrylate oligomer is contained in an amount of 10 to 50% by weight based on the total weight of the composition, the ink composition for 3D inkjet printing. The ink composition for 3D inkjet printing according to claim 1, wherein the hydroxyketone-based photoinitiator absorbs light in a wavelength range of 240 to 270 nm. According to claim 1, wherein the amino ketone-based photoinitiator is to absorb light in the wavelength range of 270 to 350 nm, the ink composition for 3D inkjet printing. The ink composition of claim 1, wherein the phosphine oxide-based photoinitiator absorbs light in a wavelength range of 350 to 420 nm. According to claim 1, wherein the hydroxyketone-based photoinitiator is contained in an amount of 0.5 to 2% by weight based on the total weight of the composition, the ink composition for 3D inkjet printing. delete According to claim 1, The content of the amino ketone-based photoinitiator is 0.5 to 2% by weight based on the total weight of the composition would, 3D inkjet printing ink composition. delete A 3D laminate manufactured by 3D inkjet printing using the ink composition according to claim 1 . The 3D laminate according to claim 10, wherein the laminate exhibits physical properties of an elastic modulus of 2 GPa or more and a strength of 60 MPa or more.

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