RU2244335C2 - Photopolymerizable composition for visible-region laser stereolithography - Google Patents

Abstract

FIELD: polymer materials.

SUBSTANCE: invention provides photopolymerizable composition for lithography utilizing visible-region light comprising (i) acryl oligomers and (ii) initiating system, said acryl oligomers being hexanediol diacrylate or trimethylolpropane triacrylate and ethoxylated diphenylolpropane diacrylate and said initiating system being a mixture of Bengal rose with dimethylethanolamine in 1-vinyl-2-pyrrolidone, and, additionally, (iii) polymethylmethacrylate. Composition possesses light sensitivity high enough to manufacture three-dimensional variably shaped articles under laser 3D-stereolithography conditions using inexpensive and small-size lasers with λ=530 nm.

EFFECT: expanded lithographic possibilities at lower cost.

2 tbl, 11 ex

Description

The invention relates to photopolymerizable compositions based on acrylic oligomers and can be used in laser stereolithography.

In recent years, in high-tech industries, methods of forming three-dimensional objects have been intensively developed not by removing material (turning, milling, electrical discharge machining) or changing the shape of the workpiece (forging, stamping, pressing), but by layer-by-layer building of the material by changing the phase state of the substance in a given areas of space. Photochemical technologies are based on the effect of a local change in the phase state of a homogeneous medium (liquid – solid transition) as a result of photoinitiation in a given volume of polymerization.

Laser stereolithography includes creating a computer image of the part, dividing it into thin layers, calculating the trajectory of the laser beam that fills each section and sequentially reproducing the corresponding cross sections on the surface of the liquid photopolymerizable composition with a focused beam initiating the polymerization of laser radiation.

Currently, laser stereolithography is used around the world using UV lasers, the quantum energy of which is sufficient to break the chemical bond in the photoinitiator. The resulting free radicals chain polymerize the photopolymerizable composition to form a solid polymer. These processes are widely used in modern technology - in the United States alone, turnover reaches $ 2.5 billion. However, UV lasers have significant drawbacks: high energy consumption, comparable to metal processing centers, large size and the known harmful effects of ultraviolet radiation on the environment [Hagiwara T. Recent Progress of Photo-Resin For Rapid Prototyping, "Resin For Stereolithography". Macromolecular Symposia. 2001.175. PP.397-402].

At the same time, economical and small-sized solid-state lasers based on a crystal of neodymium-doped aluminum yttrium garnet with diode pumping, generating radiation of 1.06 μm, are known. Frequency doubling (2nd harmonic) gives a wavelength of 532 nm. Until now, the use of visible light with such a large wavelength in laser stereolithography installations is not known. This is due to the fact that the energy of photons with λ = 530 nm is not enough to break the chemical bond with the formation of initiating radicals. For polymerization initiated by long-wave visible light, rather complex initiating systems are used, consisting of at least a dye-sensitizer and a proton donor [Lee J.H., Prud'homme R.K., Aksay I.A. Cure Depth In Photopolymerization: Experiments And Theory. Journal of Materials Research. 2001.16. PP.3536-3544]. Such initiation is very inefficient, which is why it is not possible to implement such a complex technological process on lasers with λ> 500 nm.

Photopolymerizable compositions for laser stereolithography consist of mixtures of oligomers and monomers of acrylic type (epoxy compositions are much less common). For example, US Pat. No. 6,025,114 (2000) proposes a fairly typical stereolithographic composition consisting of (meth) acrylate with functionality ≥ 3, urethane (meth) acrylate with 2-4 functionality, (meth) acrylate based on diphenylolpropane and an initiating system for UV light. In Pat. US 6432607 (2002), the composition additionally contains bismaleimide-based di (meth) acrylates, which improves the size accuracy of “grown” products. These compositions are analogues of the present invention, but they cannot serve as a prototype, since they are used in installations with UV lasers, i.e. in dramatically excellent conditions.

Closest to the proposed composition (prototype) is a photosensitive composition based on acrylic oligomers, polymerizing under the influence of visible light with a wavelength of 380-490 nm, mainly 410 nm, in the presence of an initiating system based on titanocene and carbonyl compounds, which may additionally contain benzoin derivatives , aminobenzophenones, thiosubstituted ketones, acylphosphine sulfides, thioxanthones, cyanine dyes, etc. (US Pat. USA 6468711, MKI ⁶ G 03 F 7/004, 10/22/2002).

Such compositions are widely used to obtain coatings for various purposes, for example, by the lithographic method, but cannot be used in 3D laser stereolithography even at optimal wavelengths near 410 nm due to the low polymerization rate, for example, a coating with a thickness of 50-100 microns is formed in 3-5 min of irradiation (at λ = 530 nm, the formation of a solid polymer does not occur).

The objective of the present invention is to provide an acrylic composition capable of forming a three-dimensional product under the conditions of laser stereolithography using a laser emitting light with λ> 500 nm. As indicated above, similar compositions and the specified method to date have not been created.

The solution of this problem is achieved by the proposed photopolymerizable lithography composition using visible light, including acrylic oligomers and an initiating system, which, according to the invention, contains hexanediol diacrylate or trimethylolpropane triacrylate and ethoxylated diphenylolpropane diacrylate as a rose mixture, as the initial mixture with dimethylethanolamine in 1-vinyl-2-pyrrolidone, and additionally contains polymethyl methacrylate, as follows m ratio of components, wt. hours:

Polymethylmethacrylate 0.1-0.8

Bengal rose 0.20-0.22

Dimethylethanolamine 1.82-2.05

1-vinyl-2-pyrrolidone 3.00-5.22

Ethoxylated diacrylate

diphenylolpropane 47.1-79.21

Hexanediol diacrylate or

trimethylolpropane triacrylate 13.96-47.40.

The basis for solving this problem is the manifestation of the “gel effect” known for acrylic oligomers — a sharp acceleration of the polymerization rate after reaching the gel point. For ordinary difunctional acrylic oligomers, gel-point is achieved at 4-5% conversion of double bonds, for systems containing, as in the above analogues, polyfunctional (> 2) (meth) acrylates, 3-4% conversion. Naturally, any factor accelerating the achievement of the gel point, and, therefore, the stage of a sharp increase in the rate of formation of a solid polymer, can increase the photosensitivity of the composition, i.e. reduce specific energy consumption for the formation of 1 g of solid polymer. This is especially significant when using low-energy lasers.

It was unexpectedly found that microadditives of a high molecular weight polymer - polymethylmethacrylate (PMMA) to compositions based on acrylic oligomers dramatically increase the speed of photopolymerization without significantly changing the macro viscosity of the composition. The effect is most pronounced when using 0.2-0.8 wt.% PMMA. Below this limit, an increase in speed is not enough to implement the laser stereolithography method, and at a higher polymer content, the viscosity of the composition increases significantly, which prevents the leakage of liquid onto the substrate and reduces the process productivity.

Many high polymers, including PMMA, are often added to oligomeric compositions in an amount of 5-90% to increase mechanical strength, especially impact resistance, films and coatings. For example, in Pat. US 6486234 (2002) to increase the impact resistance of coatings in the composition based on acrylic oligomers enter 1-20 wt.% PMMA or another polymer, and in US Pat. US 6462129 (2002) for this purpose use 40-99 mph PMMA or other polymer at 61-120 mph other components. Obviously, such an approach has nothing to do with the proposed technical solution.

In the examples below, the experimental conditions for obtaining the proposed compositions and control samples are disclosed, and tables 1 and 2 present data on the photopolymerization rate (V _p ) of the studied compositions, including under conditions simulating the method of laser stereolithography.

The compositions were prepared as follows: to prepare the initiating system, a weighed photosensitizer — a Bengal rose (BR) and N, N-dimethylethanolamine (DMEA) was dissolved in a reaction diluent — 1-vinyl-2-pyrrolidone (VP). A viscous difunctional oligomer was mixed with a reaction diluent (monofunctional reagent) and a photoinitiator solution was added, mixed thoroughly. In the cases indicated in the examples, a multifunctional oligomer, for example, trimethylolpropane triacrylate, was added to a mixture of mono- and difunctional oligomers. PMMA was previously dissolved in the least viscous oligomer and added to the composition. The resulting compositions were placed in a desiccator and vacuumized for 2-3 hours, then kept under vacuum for 10-12 hours to remove air bubbles. The composition was stored in a refrigerator in a brown glass container or shielded black paper.

Preliminary tests of photopolymerization were carried out by irradiating a drop of the composition on a glass slide under a 100 W halogen lamp with a filter transmitting light with λ> 530 nm at a distance of 10 cm for 1 min.

The polymerization rate of the compositions was determined by IR spectroscopy. The composition was placed between NaCl glasses and the IR spectrum was recorded in the range of 1700-1400 cm ^-1 to determine the optical density of the strip ν _{C = C} = 1613 cm ^-1 and the optical density of the internal standard, ν _C-CH3 = 1443 cm ^-1 . Then the composition was irradiated with visible light with λ _excitation = 480-540 nm and an intensity of 100 W / m ² and the IR spectrum was recorded. The conversion of double bonds was calculated by the formula:

K = 100% -D $\genfrac{}{}{0ex}{}{\text{t}}{\text{1613}}$ D $\genfrac{}{}{0ex}{}{\text{0}}{\text{1443}}$ / D $\genfrac{}{}{0ex}{}{\text{0}}{\text{1613}}$ D $\genfrac{}{}{0ex}{}{\text{t}}{\text{1443}}$ · 100%,

where d $\genfrac{}{}{0ex}{}{\text{0}}{\text{1613}}$ - optical absorption density of double bonds before irradiation (t = 0);

D $\genfrac{}{}{0ex}{}{\text{0}}{\text{1443}}$ - absorbance of the C — CH ₃ groups before irradiation (t = 0);

D $\genfrac{}{}{0ex}{}{\text{t}}{\text{1613}}$ is the optical density of absorption of double bonds after irradiation, t = τ;

D $\genfrac{}{}{0ex}{}{\text{t}}{\text{1443}}$ is the absorbance of the C — CH ₃ groups after irradiation, t = τ.

Examples

Example 1. 0.22 g of a Bengal rose photosensitizer (BR) was dissolved in 4.65 g of 1-vinyl-2-pyrrolidone (VP) and in 2.05 g of N, N-dimethylethanolamine (DMEA). 0.4 g of PMMA (M.M. 60000-70000) was dissolved in 13.96 g of hexanediol diacrylate (DAGD) and 78.72 g of ethoxylated diphenylolpropane ethoxylated (Bis GMA) was mixed.

CH ₂ = C (CH ₃ ) COOCH ₂ CH (OH) CH ₂ OC ₆ H ₄ C (CH ₃ ) ₂ C ₆ H ₄ OCH ₂ CH (OH) CH ₂ OOCC (CH ₃ ) = CH ₂

Bis-GMA

Then the oligomers were mixed with the prepared solution of the initiating system, mixed thoroughly, placed in a desiccator and vacuum for 2-3 hours, then the composition was left under vacuum for 10-12 hours to remove air bubbles from the composition.

The content of components in the resulting composition is, wt. hours:

Polymethylmethacrylate (PMMA) 0.4

Bengal rose (BR) 0.22

Dimethylethanolamine (DMEA) 2.05

1-Vinyl-2-pyrrolidone (VP) 4.65

Ethoxylated diacrylate

diphenylolpropane (bis-GMA) 78.72

Hexanediol diacrylate (DAGD) 13.96.

The resulting composition on a glass slide or under conditions simulating the method of laser stereolithography was irradiated with light λ = 530 nm and a solid polymer was obtained. The test results are shown in tables 1 and 2.

Example 2. The composition was prepared as in example 1, but without the addition of PMMA, in the following ratio of components, wt. hours:

PMMA 0

BR 0.2

DMEA 2.0

VP 4.34

Bis-GMA 79.5

DAGD 13.96.

Example 3. The composition was prepared, as in example 1, in the following ratio of components, wt. hours:

PMMA 0.1

BR 0.21

DMEA 1.86

VP 4.66

Bis-GMA 79.21

DAGD 13.96.

Example 4. The composition was prepared, as in example 1, in the following ratio of components, wt. hours:

PMMA 1.0

BR 0.23

DMEA 1.82

VP 4.69

Bis-GMA 77.8

DAGD 13.96.

Example 5. The composition was prepared, as in example 1, in the following ratio of components, wt. hours:

PMMA 0.8

BR 0.2

DMEA 2.0

VP 5.22

Bis-GMA 77.82

DAGD 13.96.

Example 6. The composition was prepared, as in example 1, in the following ratio of components, wt. hours:

PMMA 0.3

BR 0.2

DMEA 2.0

VP 3.0

Bis-GMA 47.1

Trimethylolpropane triacrylate

(TATMP) 47.4.

Example 7. The composition was prepared, as in example 1, in the following ratio of components, wt. hours:

PMMA 0.5

BR 0.2

DMEA 2.0

VP 3.0

Bis-GMA 69.5

TATMP 24.8.

Example 8. The composition was prepared, as in example 1, in the following ratio of components, wt. hours:

PMMA 0.4

BR 0.2

DMEA 2.0

VP 3.0

Bis-GMA 62.6

DAGD 31.8.

Example 9. The composition was prepared, as in example 1, in the following ratio of components, wt. hours:

PMMA 0.5

BR 0.05

DMEA 2.0

VP 3.0

Oligoester acrylate MDF-2 93.45.

Example 10. The composition was prepared as in example 9, but without the addition of PMMA, in the following ratio, wt. hours:

PMMA 0

BR 0.05

DMEA 2.0

VP 3.0

Oligoester acrylate MDF-2 93.95

Example 11. The composition consists of 98.00 parts by weight of MDF-2 oligoester acrylate and 2.00 parts by weight UV photoinitiator “Durakur-4265”.

Table 1. The photopolymerization rate of the proposed compositions and control samples Example No. Initiating system, parts by weight PMMA additive, parts by weight V _p mol / l s Preliminary tests VP DMEA BR 1 4.65 2.05 0.22 0.4 8.8 Normal dense stretch film 2 4.34 2.0 0.2 0 3.6 Very soft film 3 4.66 1.86 0.21 0.1 4,55 Stretch film 4 4.69 1.82 0.23 1,0 7.62 Thick uneven film 5 5.22 2.0 0.2 0.8 - Normal Thick Film 6 3.0 2.0 0.2 0.3 5.67 - 7 3.0 2.0 0.2 0.5 7.19 Stretch film 8 3.0 2.0 0.2 0.4 6.88 Normal Thick Film nine 3.0 2.0 0.05 0.5 3.2 Very soft film 10 3.0 2.0 0.05 0 1.46 Poor quality film eleven UV initiator “Durakur 4265” 0 10,2 Normal Thick Film

Table 2. Energy parameters of photopolymerization of compositions under conditions simulating laser stereolithography (λ = 530 nm) Example Critical exposure,
MJ cm ^-2 Effective penetration depth,
mm Minimum layer thickness, microns 1 23.9 0,094 16 2 not polymerized 4 227.9 0.713 2800 6 29.9 0,023 thirteen 8 74,2 0.1 48

As follows from the data in the tables, the introduction of small PMMA additives allows one to achieve photopolymerization rates comparable with lime for typical UV-initiated compositions, for example MDF-2 oligoester acrylate under UV irradiation (Example 11) and the proposed composition according to Example 1 when irradiated with λ = 530 nm polymerize at approximately the same rate, while MDF-2 is successfully processed using UV laser stereolithography. The use in the proposed composition as acrylic oligomers of hexanediol diacrylate or trimethylolpropane triacrylate in the declared amounts (from 13.96 to 47.40 parts by weight) leads to the achievement of the same technical result. In the absence of PMMA, even the most photoactive composition according to Example 1 polymerizes ~ 4 times slower, which excludes its use in laser stereolithography. As far as different requirements for the photoactivity of the composition are presented upon initiation by visible and UV light, examples 10 and 11 illustrate, the difference in the photopolymerization rates reaches 8-10 times.

The above analysis is confirmed by data on the preparation of samples under conditions simulating the method of laser stereolithography (table 2). The compositions according to examples 1, 6 and 8 show quite acceptable energy characteristics for this method, while in the absence of PMMA even the best composition does not give a solid polymer, and with a high content of PMMA a thick polymer layer is unacceptably slowly formed.

Thus, the proposed composition has sufficient photosensitivity for the manufacture of three-dimensional products of arbitrary shape in 3D laser stereolithography using economical and small-sized lasers with λ = 530 nm.

Claims (1)

A photopolymerizable lithography composition using visible light lithography, including acrylic oligomers and an initiating system, characterized in that it contains hexanediol diacrylate or trimethylolpropane triacrylate and ethoxylated diphenylolpropane diacrylate as an initiating system - a mixture of Bengal roseol vinyl-2-pyrrolidone, the composition further comprises polymethyl methacrylate in the following ratio, wt. hours: Polymethyl methacrylate 0.1-0.8 Bengal rose 0.20-0.22 Dimethylethanolamine 1.82-2.05 1-vinyl-2-pyrrolidone 3.00-5.22 Ethoxylated diacrylate diphenylolpropane 47.1-79.21 Hexanediol diacrylate or trimethylolpropane triacrylate 13.96-47.4