Process for adjusting the sensitivity to radiation of photopolymerizable compositions

• US 5,573,889 A
• Filed: 05/09/1995
• Issued: 11/12/1996
• Est. Priority Date: 10/27/1989
• Status: Expired due to Term

• Current Assignee: 3D Systems, Inc. (3D Systems Corporation)
• Original Assignee: Ciba-Geigy Corporation (Novartis Ag)
• Inventors: Hofmann, Manfred, Schulthess, Adrian, Hunziker, Max, Wiesendanger, Rolf, Klingert, Bernd, Bernhard, Paul
• Primary Examiner(s): Hamilton, Cynthia
• Application Number:
  US08/437,737
• Time in Patent Office: 553 Days
• Field of Search: 430/281, 430/301, 430/269, 430/285, 430/286, 430/281.1, 430/285.1, 430/286.1, 430/269, 522/2, 522/4, 264/22, 264/401
• US Class Current: 430/285.1
• CPC Class Codes: B29C 64/106 using only liquids or viscous materials, e.g. depositing a continuous bead of viscous material
• CPC Class Codes: B29C 64/135 the energy source being concentrated, e.g. scanning lasers or focused light sources
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 70/00 Materials specially adapted for additive manufacturing
• CPC Class Codes: C08F 2/48 by ultraviolet or visible light
• CPC Class Codes: G03F 7/0037 Production of three-dimensional images
• CPC Class Codes: G03F 7/029 Inorganic compounds; Onium compounds; Organic compounds having hetero atoms other than oxygen, nitrogen or sulfur
• CPC Class Codes: G03F 7/031 Organic compounds not covered by group G03F7/029

Abstract

A process is described for the preparation of photopolymerizable compositions, wherein the photopolymerizable compositions can be photopolymerized by the irradiation of emission lines of differing wavelength from a UV/VIS laser light source, and contain a photopolymerizable compound and at least two photoinitiators, by adjusting the sensitivity to radiation. The ratio between the concentrations of the individual photoinitiators is so adjusted that the composition has virtually the same optical density for the radiation of the different emission lines at which the photoinitiators are effective.

Claims

1. A process for the preparation of a photopolymerizable composition to be used in the production of a three-dimensional object by means of stereolithography, which process comprises providing a photopolymer formulation containing at least one photopolymerizable compound and the following steps in the indicated temporal order:

1) selecting a specific UV/VIS laser light source with a set of different emission lines, by the radiation of which emission lines the photopolymerizable composition is to be polymerized;

2) selecting a plurality of photoinitiators, the absorption spectrum of each of the photoinitiators overlapping with at least one of the emission lines intended to cause photopolymerisation of the photopolymerizable composition, with the proviso that no photoinitiator of any pair of two photoinitiators of the selected plurality has a greater extinction coefficient for radiation of the same one of the said emission lines as the other photoinitiator of the pair;

3) defining a ratio for the concentrations of each of the photoinitiators in the composition such that the optical densities of a layer of any given thickness of the composition only differ from one another, for radiation of the defined different emission lines, by +/-20% based on the arithmetic mean of the optical densities, and

4) mixing said plurality of photoinitiators at said concentration ratio into said photopolymer formulation to produce said composition.

2. A process according to claim 1, wherein the laser light source is selected from the group consisting of Ar-ion lasers having a multi-line operation within the UV range and/or within the visible range and copper vapor lasers.

3. A process according to claim 1, wherein two photoinitiators are used and wherein the absorption maximum of longest wavelength of the first photoinitiator is between 350 and 400 nm and the absorption maximum of longest wavelength of the second photoinitiator is at a wavelength shorter than the said absorption maximum of the first photoinitiator.

4. A process according to claim 3, wherein the concentration c₁ of the first photoinitiator is given by equation (11):

space="preserve" listing-type="equation">c.sub.1 =(ε

.sub.2 (λ

.sub.2)A(λ

.sub.1)-ε

.sub.2 (λ

.sub.1)A(λ

.sub.2))/([ε

.sub.1 (λ

.sub.1)ε

.sub.2 (λ

.sub.2)-ε

.sub.1 (λ

.sub.2)λ

.sub.2 (λ

.sub.1)]d) (11),

and the concentration c₂ of the second photoinitiator is given by equation (12);

space="preserve" listing-type="equation">c.sub.2 =(ε

.sub.1 (λ

.sub.1)A(λ

.sub.2)-ε

.sub.1 (λ

.sub.2)A(λ

.sub.1))/([ε

.sub.1 (λ

.sub.1)ε

.sub.2 (λ

.sub.2)-ε

.sub.1 (λ

.sub.2)ε

.sub.2 (λ

.sub.1)]d) (12),

in which λ

₁ and λ

₂ are the wavelength of the emission lines from the UV/VIS laser light source at which the photopolymerizable composition is to be cured,

d is the thickness of the irradiated layer of photopolymerizable material,

ε

₁ (λ

₁) is the extinction coefficient of photoinitiator 1 at the wavelength λ

₁,

ε

₁ (λ

₂) is the extinction coefficient of photoinitiator 1 at the wavelength λ

₂,

ε

₂ (λ

₁) is the extinction coefficient of photoinitiator 2 at the wavelength λ

₁,

ε

₂ (λ

₂) is the extinction coefficient of photoinitiator 2 at the wavelength λ

₂,

A(λ

₁) is the optical density of the photopolymerizable composition at the wavelength λ

₁ and

A(λ

₂) is the optical density of the photopolymerizable composition at the wavelength λ

₂, with the proviso that the optical densities A(λ

₁)=A(λ

₂).

5. A process according to claim 1, wherein the photopolymerizable composition can be polymerized within the range from 250 to 450 nm and has a sensitivity to radiation of less that 200 mJ/cm² or wherein the photopolymerizable composition can be polymerized within the range from 450 to 800 nm and has a sensitivity to radiation of less than 2J/cm².

6. A process according to claim 1, wherein the photopolymerizable compound of the photopolymerizable composition is a compound which can be polymerized by free radicals or a mixture of such compounds.

7. A process according to claim 6, wherein the compound which can be polymerized by free radicals contains 2 to 5 acrylate ester and/or methacrylate ester groups.

8. A process according to claim 1, wherein the photopolymerizable composition has a viscosity of 500 to 8000 mPa. s (at 25°

C.) and a volume shrinkage when passing from the liquid state into the completely polymerized state of less than 8% by volume, based on the liquid composition.

9. A process according to claim 1, wherein the photopolymerizable composition contains di-, tri-, tetra- or penta-functional monomeric or oligomeric acrylate or methacrylate esters and has a viscosity of 500 to 8000 mPa-s (at 25°

C.).

10. A process according to claim 1, wherein the photopolymerizable composition contains, as photopolymerizable monomers:

a) 10 to 80% by weight, based on the mount of components a), b) and c), of at least one difunctional monomeric or oligomeric acrylate or methacrylate having a viscosity of more than 500 mPa. s (at 25°

C.),

b) 5 to 25% by weight, based on the amount of components a), b) and c), of at least one compound of the formula I, II or III ##STR10## in which R₁ is hydrogen, methyl, hydroxyl or a radical of the formula IV ##STR11## and R₂ is a group of the formula V ##STR12## in which n is 0, 1, 2 or 3 and R₃ and R₄ independently of one another are hydrogen or methyl, and

c) 1 to 25% by weight, based on the amount of components a), b) and c) at least one compound of the formula VI ##STR13## in which R₅ is hydrogen or methyl and R₆ is a group of the formula VII ##STR14## in which R₇ is selected from the group consisting of tetrahydrofurfuryl, cyclohexyl, 2-phenoxyethyl, benzyl, isobornyl, glycidyl, dicyclopentenyl, morpholinoethyl, dimethylaminoethyl, diethylaminoethyl or a C₁ -C₂₀ alkyl radical which can be linear or branched, or, if R₅ is hydrogen, R₆ can also be pyrrolidinon-2-yl, imidazolyl, carbazolyl, anthracenyl, phenyl, C₅ -C₈ cycloalkyl, naphthenyl, 2-norbornyl, pyridyl, N-caprolactamyl or tolyl.

11. A process according to claim 10, wherein component a) is a compound of the formula VIII ##STR15## in which p is 0 or 1, t is 0 or 1 and, in the event that p is 0, t can also be 2 or 3, X is --O--, --S--, --SO₂ -- or --C(R₁₀)(R₁₁)--, R₁₀ and R₁₁ independently of one another are hydrogen, trifluoromethyl or methyl, R₇ is hydrogen and, in the event that p is 0, can also be methyl, R₈ is hydrogen if p=0 and is hydroxyl if p=1, and R₉ is hydrogen or methyl.

12. A process according to claim 10, wherein component c) is 1-vinylpyrrolidone, isobornyl acrylate or phenoxyethyl acrylate.

13. A process according to claim 1, wherein the ratio for the concentrations for each of the photoinitiators in the composition is defined such that that the optical densities of a layer of any given thickness of the composition are the same for radiation of the defined emission lines.

14. A method for enhancing the gradient of the degree of polymerization in the region of the transition from virtually unchanged material to gelled material in a photopolymerizable composition to be used in the production of a three-dimensional object by means of stereolithography and obtained by a process, which comprises providing a photopolymer formulation containing at least one photopolymerizable compound and the following steps in the indicated temporal order:

1) selecting a specific UV/VIS laser light source with a set of different emission lines, by the radiation of which emission lines the photopolymerisable composition is to be polymerized;

2) selecting a plurality of photoinitiators, the absorption spectrum of each of the photoinitiators overlapping with at least one of the emission lines intended to cause photopolymerisation of the photopolymerizable composition, with the proviso that no photoinitiator of any pair of two photoinitiators of the selected plurality has a greater extinction coefficient for radiation of the same one of the said emission lines as the other photoinitiator of the pair;

3) defining a ratio for the concentrations of each of the photoinitiators in the composition such that the optical densities of a layer of any given thickness of the composition only differ from one another, for radiation of the defined different emission lines, by +/-20% based on the arithmetic mean of the optical densities, and

4) mixing said plurality of photoinitiators at said concentration ratio into said photopolymer formulation to produce said composition,

said method comprising the irradiation of said composition with radiation of the selected set of emission lines of the UV/VIS laser light source.

15. A method according to claim 14, wherein the ratio for the concentrations for each of the photoinitiators in the composition is defined such that that the optical densities of a layer of any given thickness of the composition are the same for radiation of the defined emission lines.