WO2002018116A1

WO2002018116A1 - Method of polymerizing resin composition containing a volatile material, product formed thereby and apparatus for performing the method

Info

Publication number: WO2002018116A1
Application number: PCT/US2001/026932
Authority: WO
Inventors: Roger Mccartney
Original assignee: Fusion Uv Systems, Inc.
Priority date: 2000-08-31
Filing date: 2001-08-31
Publication date: 2002-03-07
Also published as: AU2001286899A1

Abstract

Disclosed is a method for curing a resin composition containing a volatile material, to reduce evaporation of the volatile material, apparatus for performing the method, and a product formed by the method. The method includes two steps. A photoinitiator is included in the resin composition, and in a first step of the method a surface layer (but not a remainder) of the resin composition is cured using ultraviolet light to seal off the surface to prevent volatile material evaporation. The ultraviolet light is produced by a medium or high pressure ultraviolet lamp, and irradiation by the ultraviolet light is performed while there is relative movement between the ultraviolet lamp and the resin composition. The second curing step, to cure the remainder of the composition, can be a room temperature or high-temperature cure, or other type of cure. Where air or cooling fluid flows by the ultraviolet lamp during the first step, a transparent (quartz) shield is placed between the lamp and resin composition to prevent the fluid from damaging the resin composition surface prior to curing. The present invention is particularly effective to avoid volatile monomer evaporation when molding a resin composition in an open mold.

Description

METHOD OF POLYMERIZING RESIN

COMPOSITION CONTAINING A VOLATILE MATERIAL,

PRODUCT FORMED THEREBY AND APPARATUS FOR

PERFORMING THE METHOD

BACKGROUND ART

The present invention is directed to a method of polymerizing a resin composition containing a volatile material, for example, containing a volatile monomer such as styrene, apparatus used to perform this method and a polymerized product formed by this method. In particular, the present invention is directed to a method of curing a resin composition which contains a volatile material, apparatus used to perform this method and the product formed by this method.

TECHNICAL FIELD

The present invention is especially directed to a technique for preventing, or at least reducing, volatilization of the volatile material (for example, the volatile monomer) when curing a resin composition containing such volatile material.

In many industrial processes, volatile diluent monomers such as styrene, vinyl toluene or vinyl ethers are included with oligomers (such as unsaturated polyesters or vinyl esters) in resin compositions, the resin compositions being cured in open molds in the presence of accelerator catalysts, curing being performed at room temperature or under baking oven conditions. This technique can be used in forming molded plastic products such as shower stalls, bath tubs, boats, etc. In the curing cycle, large amounts of the volatile diluent monomer can be lost through surface evaporation, before surface setting of the resin composition is accomplished. Such evaporation occurs, e.g., where the curing is an exothermic reaction, or where curing occurs under temperature conditions where the volatile material evaporates. This evaporation causes environmental pollution, is hazardous to surrounding workers, and causes bulk weight losses and compositional changes in the finished cured product. For example, the finished polymer loses a percentage of its bulk weight, and suffers compositional changes (and changes in properties).

Attempts have been made to reduce this evaporation of volatile material by various techniques to change the evaporation rate of the volatile material. For example, materials have been added to hold the volatile material, such as styrene, in the composition to a greater extent

(for example, to reduce evaporation rates). Alternatively or in addition, paraffin has been utilized as a surface sealing material on the resin composition, to stop evaporation of the volatile material.

However, these attempts have shortcomings. For example, adding relatively large amounts of material as necessary for paraffin surface sealing adversely affects the composition which is cured. In addition, these techniques do not sufficiently reduce evaporation of volatile components.

Japanese Patent Document No. Sho54[1979]-144884 describes a process of using ultraviolet light to surface cure a resin composition in forming reinforced plastic moldings, reducing escape of styrene from the resin composition. The technique described in this Japanese patent document includes irradiating a resin composition containing unsaturated polyester resin and/or vinyl ester resin and photosensitizer with a low-pressure ultraviolet lamp for surface curing, and then heat curing in a hot air furnace. This patent document discloses that the lamp is to be a low-pressure ultraviolet lamp; that when high-pressure ultraviolet lamps were used, curing was rapid and the escape of styrene did not diminish, while when low-pressure ultraviolet lamps were used, styrene is prevented from escaping but curing was slow. This patent document describes a static condition for the curing, and discloses reducing styrene emission, during manufacture of reinforced plastic moldings, by 50%.

According to the technique described in this Japanese patent document, using a static condition and a low-pressure lamp, heat was brought to the bulk mass and set off exothermic cure of the composition, causing high-temperature mass gelation and rapid styrene loss.

Accordingly, it is still desired to provide a technique for polymerizing (curing) a resin composition containing a volatile material, which reduces loss of the volatile material during curing, without substantially changing the cured composition and properties thereof.

DISCLOSURE OF INVENTION

The present invention overcomes deficiencies of the above-described techniques, by providing a two-stage method of polymerizing a resin composition containing a volatile material. The first stage of this method is a first polymerization of a surface (e.g., exposed surface) of the resin composition, performed by irradiating the surface of the resin composition with ultraviolet light from a medium pressure or high pressure ultraviolet lamp, with this irradiating being performed during relative movement between the lamp and the resin composition. The resin composition includes a photoimtiator (photosensitizer) during this first polymerization, to facilitate the polymerization by irradiating with ultraviolet light. This first polymerization freezes or hardens a surface layer of the resin composition, to seal off the surface. This sealing off of the surface achieves an effect called "cocooning" in this disclosure. A remaining portion of the resin composition, in a depth direction, is not polymerized in this first stage. The second stage of the polymerization is a second polymerization of the resin composition, to polymerize a remainder of the resin composition not polymerized in the first polymerization.

In performing the first polymerization, the surface of the body of the resin composition is sealed off to reduce loss of volatile material. Illustratively, and not to be limiting of the present invention, the resin composition can be a liquid and provided in an open mold system; by initially conducting the first polymerization as discussed previously, prior to polymerization of the remainder of the resin composition, e.g., at room temperature or high temperature conditions, in the presence of a catalyst, loss of volatile material is reduced.

The resin composition according to the present invention includes a small amount of the photoinitiator, and includes use of a high powered (medium or high pressure) ultraviolet light source, with the ultraviolet light source moving relative to the surface of the body of the resin composition in order to, e.g., sweep or scan the entire surface in order to seal off the surface. Only a small amount of the photoinitiator need be included in the resin composition; accordingly, the final product is not substantially affected by incorporation of the photoinitiator.

According to another aspect of the present invention, the present invention includes the product formed by this two-stage polymerization. Since only a small amount of an additional material (photoinitiator) is included in the resin composition polymerized in forming the product, properties of the product are those desired. By retaining the volatile material, such as a volatile monomer, a more desired product through polymerization is achieved.

As a still further aspect of the present invention, the present invention also includes polymerization or curing apparatus, including first and second polymerization stations. At the first polymerization station, a surface layer of a body of a resin composition is cured. At a second polymerization station, a remaining part of the body of the resin composition, other than the surface layer, is cured. The first polymerization station includes a medium or high pressure ultraviolet lamp for irradiating ultraviolet light on the surface layer on the body of the resin composition, and structure to move the body of the resin composition relative to the ultraviolet lamp while the ultraviolet lamp irradiates the surface layer of the body of the resin composition with ultraviolet light. This moving structure can either move the ultraviolet lamp, or move the body of the resin composition. Desirably, the medium or high pressure ultraviolet lamp is an electrodeless ultraviolet lamp. More desirably, the electrodeless ultraviolet lamp includes an elliptical reflector, to concentrate and focus ultraviolet light from the ultraviolet lamp on the surface layer of the body of the resin composition, to more effectively and efficiently cure only the surface layer without substantially curing any remaining portion (e.g., in the depth direction) of the body of the resin composition.

Generally, according to the polymerization apparatus of the present invention, utilizing the ultraviolet lamp, the lamp, including the bulb thereof, is cooled, for example, by passing a cooling fluid, such as air, to the lamp and past the bulb, to cool the lamp. In any event, air generally passes by the ultraviolet lamp, h order to avoid this cooling fluid and/or air from adversely affecting the surface of the body of the resin composition, during the polymerization by irradiating with ultraviolet light (for example, to prevent rippling of the surface of the body of resin composition), a transparent shield (transparent to the ultraviolet light) is provided between the ultraviolet lamp and body of the resin composition, to block the cooling fluid and/or air passing by the ultraviolet lamp, from contacting the surface of the resin composition. As can be appreciated, the faster that the surface of the resin composition is set, the greater the retention of the volatile monomer, for example, for use in subsequent polymerization. Listed in the following are some of the factors (illustrative factors) which will speed up the surface polymerization, and enhance the effect of setting the surface to reduce or eliminate volatile material loss: (a) matching the photoinitiator to the lamp source, that is, providing a lamp source which outputs ultraviolet light at a wavelength at which the photoinitiator has maximum sensitivity;

(b) use of short-wave ultraviolet radiation for surface curing, so as to avoid penetration of the radiation into the body of the resin composition; (c) increasing the percentage of photoinitiator;

(d) increasing the power of the lamp;

(e) providing the surface of the resin composition at a focal point of a reflector system of the lamp; (f) decreasing the relative speed (e.g., line speed) between the body of the resin composition and the ultraviolet lamp;

(g) increasing the response of the resin to ultraviolet light (for example, increasing unsaturated polyester or decreasing monomer concentration, so that the composition is more reactive to ultraviolet light); (h) including additional ultraviolet curable oligomers, ultraviolet curable cross-linking monomers or any combination thereof, in the resin composition;

(i) increasing a temperature of the curing system (but this also speeds up evaporation); and

(j) placing an inert gas blanket over the resin composition (this can speed up setting of the surface ("cocooning") with use of less photoinitiator and less ultraviolet energy).

That is, the faster that the surface is set, the less will be the styrene loss. Time for setting the surface layer is reduced by greater lamp focus, increased lamp power, increased dose of irradiation, and shorter wavelength lamp spectra output. Sweeping the surface at a faster speed also increases the surface area covered. It is desired that this first step of the polymerization (e.g., curing), using the medium-or high-pressure ultraviolet light and relative movement, only set the surface. The remainder of the resin composition, extending from the sealed-off surface, is then polymerized in the second polymerization (e.g., curing) step. For example, where the second polymerization is a room- temperature or high-temperature curing, a primary peroxide or drier-peroxide reaction then occurs to perform the room temperature or high-temperature curing, for a peak exothermic time and temperature, in the second polymerization. Catalyst for the second polymerization can be included in the resin composition, e.g., prior to the first polymerization. It is important to not accelerate the thermal catalyst cure cycle during the first polymerization which is the ultraviolet light polymerization, where the second polymerization is a room-temperature or high-temperature polymerization. Therefore, relative movement between the body of the resin composition and the ultraviolet lamp (for example, a surface sweep or scanning) is utilized, and temperature change during the surface polymerization is monitored and limited.

In the foregoing description, an illustration was given where the second polymerization was a room-temperature or a high-temperature cure. However, the second polymerization is not limited to being a room-temperature or high-temperature cure. For example, the second polymerization can be an ultraviolet polymerization (e.g., curing) procedure. That is, the first polymerization, under procedures discussed previously, can be used to freeze or seal-off the surface of the resin composition; and thereafter a second polymerization can be performed under ultraviolet light, to polymerize or cure a remainder of the resin composition, as known in the art. Where ultraviolet light curing is used for both the first and second polymerization procedures, there is no need for a room-temperature or high-temperature catalyst (e.g., a primary peroxide) in the composition. In general, any type of polymerization or curing can be used as the second polymerization.

It is preferred that in the second polymerization procedure substantially all of the volatile material (e.g., volatile monomer such as styrene) is reacted (used up), e.g., in a crosslinking reaction, in order to avoid later evaporation of remaining volatile material.

The greater the surface area of the body of the resin composition, the greater the volatile material loss prior to forming the surface polymerization layer.

The closer the lamp is to the focal distance and the nearer to the surface of the body of the resin composition, the faster the surface polymerization at a given dose (sweep time). For example, microwave lamps have a focus with the elliptical reflectors of 2.1 inches from the curing surface. The more power of the lamp, in a short-wavelength surface cure, the faster will be the surface polymerization at a given dose or sweep time, at the same distance and reflector system. A 600 watt/inch lamp should cure faster than a 300 watt/inch lamp, all other factors being held constant.

A standard mercury output lamp will cure surfaces better than an iron-doped lamp. However, all of these lamp spectra will surface cure using short-wavelength photoinitiators.

Accordingly, by the present invention, in various aspects thereof, the resin composition containing a volatile material (for example, volatile monomer) can be polymerized (cured, such as by a cross-linking reaction) while retaining the volatile material in the composition. Thus, loss of evaporating volatile material can be, at the least, reduced, to reduce hazardous working conditions and reduce environmental pollution. The surface of the resin composition can be set, to seal off the surface to reduce evaporation of volatile material, and thereafter the remainder of the resin composition can be polymerized or cured by conventional techniques, such as (but not limited to) room temperature or high temperature curing in the presence of a catalyst, or further ultraviolet curing, or other curing techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole figure schematically shows apparatus according to an aspect of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

While the invention will be described in connection with specific and preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. To the contrary, it is intended to cover all alterations, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Throughout the present specification, where materials, methods and apparatus are described as including or comprising specific components or structure or specific processing steps, it is contemplated by the inventor that materials, methods and apparatus of the present invention also consist essentially of, or consist of, the recited components or structure or recited processing steps .

The present invention contemplates, as one aspect thereof, a method of polymerizing a resin composition containing a volatile material. The method includes two steps, a first step which polymerizes only a surface layer of the resin composition, extending from the exposed surface thereof. The first step is to substantially seal off the surface. The second polymerization can be a polymerization conventionally used to polymerize the entire resin composition, e.g., a room temperature polymerization, or a high-temperature polymerization (which heat-cures the remainder of the resin composition), or further polymerization under the ultraviolet light, or other polymerization technique. The first polymerization, which only polymerizes a surface layer, is performed using a medium or high pressure ultraviolet lamp and is performed during relative movement between the lamp and resin composition, with the resin composition including a photoinitiator for ultraviolet light. By including the photoinitiator, utilizing the medium or high pressure ultraviolet lamp, and performing the polymerization during relative movement between the lamp and resin composition, only a surface layer is polymerized, to seal off the surface of the resin composition; the surface can be quickly polymerized; and the surface can be polymerized while retaining volatile material in the resin composition. Thus, by speedily setting the surface, retention of the volatile material is increased, for use in the later second polymerization (for example, a later open mold polymerization under room temperature or high-temperature conditions). The resin composition which is polymerized can have a resin content, illustratively, of 60-

70% by weight, of the total weight of the composition; and the volatile material content can be, for example, 30-40% by weight, of the total weight of the composition.

Generally, any resin can be used, as long as it can be polymerized according to the present invention. For example, the resin can be an unsaturated resin, such as an alkyd resin, epoxy resin, urethane, ether resin, acrylic resin, etc.

The polymerization utilized for polymerizing the resin composition can be, e.g., a free radical polymerization, cationic polymerization or auto-oxidation polymerization.

The volatile material can be any material utilized in the polymerization. For example, the volatile material can be a diluent, e.g., a volatile monomer. Various volatile monomers which can be included within the resin composition utilized according to the present invention can, illustratively, be styrene, vinyl toluene, divinyl benzene and vinyl ether, among others.

The resin composition utilized according to the present invention also includes a photoinitiator (photosensitizer). Illustratively, and preferably, the amount of photoinitiator included in the composition is limited, in order to limit the cost and to reduce polymerization of more than a thin surface layer of the body of the resin composition. In addition, by adding only a little photoinitiator, the photoinitiator does not substantially change properties of the final product. Illustratively, the composition preferably includes 0.25%-10% by weight, of the total weight of the composition, of the photoinitiator (photosensitizer). A preferred range is 0.25-1% by weight of the total weight of the composition, of the photoinitiator. Furthermore, if the first polymerization takes place under a nitrogen (N₂) atmosphere, the amount of photoinitiator included in the composition can illustratively range from 0.1%-20% by weight, of the total weight of the composition. Where the resin composition includes an unsaturated polyester and styrene, together with the photoinitiator, the first polymerization is to be performed under a nitrogen atmosphere, since in general oxygen at the surface of the resin composition quenches the photoinitiator.

The photoinitiator which can be utilized can be any of known photoinitiators for ultraviolet polymerization. For example, benzophenone can be utilized as the photoinitiator. Low- volatility photoinitiators are better to utilize, in order to avoid evaporation of the photoinitiator from the resin composition. On the other hand, liquid photoinitiators are easier to use. Moreover, combinations of various photoinitiators can be utilized, for purposes of the present invention.

A specific photoinitiator which can be used according to the present invention is "Darocur" 1173, having the chemical name 2-hydroxy-2-methyl-l-phenyl-propan-l-one (HMPP),

C₁₀Hι₂O₂, sold by Ciba Specialty Chemicals Corp.

Other photoinitiators are discussed in the following. These photoinitiators are illustrative of those which can be used, and not to be limiting of the present invention. These are all photoinitiators for free radical polymerization, and are each produced by Ciba Specialty Chemicals Corp. A first is 2-benzyl-2-N,N-dimethylamino-l-(4-morpholinophenyl)-l-butanone

(DBMP), having the chemical formula C₂₃H₂₈O₂N₂, and sold under the name "Irgacure" 369. A second is 1-hydroxycyclohexyl phenyl ketone (HCPK), having the chemical formula C₁₃H₁₆O₂ and sold under the name "Irgacure" 184. A third is "Irgacure" 500, which is a mixture of HCPK and benzophenone; at a 1:1 ratio by weight of the two components of this mixture, these two solid photoinitiators form a eutectic mixture that results in a liquid system. A fourth is 2,2-dimethoxy-

2-phenyl acetophenone (BDK), having the chemical formula C₁₆H₁₆O₃, and sold under the name "Irgacure" 651. A fifth is bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide, sold under the name "Irgacure" 819. Another is 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-methylpropyl) ketone, having the chemical formula C₁₂H₁₆0₄, and sold under the name "Irgacure" 2959. And another is "Darocur" 4265, which is a liquid blend (50:50 blend) of HMPP and 2,4,6-trimethylbenzoyl- diphenylphosphine oxide (TPO), TPO having the chemical formula C₂₂H₂₁O₂P. Moreover, TPO can be used by itself as the photoinitiator.

As indicated previously, according to the present invention a medium or high pressure lamp is used. Illustratively, and not to be limiting, the medium/high pressure lamp would have an output of 20-400 watts/cm. Preferably, the medium or high pressure ultraviolet lamp would have an output of 120-240 watts/cm.

Either an electrode or electrodeless lamp can be used for the surface polymerization of the resin composition. Electrodeless (microwave) lamps are preferred, because of lamp power, ability to focus the output light and versatility to sweep three-dimensional surfaces. Use of the electrodeless lamp, particularly as part of a system including a reflector that focuses the output light, can provide the most effective surface polymerization, without polymerizing more than a surface layer of the resin composition; can provide the desired surface polymerization without using a large amount of photoinitiator; and can limit the number of lamps. A preferred lamp is the lamp designated as F-600 sold by Fusion UV Systems, Inc.

As indicated previously, together with use of ultraviolet light from the medium or high pressure ultraviolet lamp, during the surface polymerization there is relative movement between the ultraviolet lamp and the body of the resin composition. This can be accomplished either by moving the body of the resin composition under the ultraviolet lamp or plurality of ultraviolet lamps (for example, passing the body of the resin composition, in an open mold, past the ultraviolet lamp(s)), during the irradiation, or by moving the lamp to scan or sweep across the entirety of the surface of the body of the resin composition, illustratively, the body of the resin composition can be moved at a line speed of 5-40 feet per minute by the ultraviolet lamp, in achieving the surface polymerization according to the present invention. Of course, by increasing the amount of photoinitiator, the line speed can be increased while still hardening the surface layer and achieving the "cocooning" effect according to the present invention.

It is desirable to limit the curing by ultraviolet radiation to a surface layer, in order to avoid wrinkling or crazing of the surface layer. For example, it is desired to utilize a photoinitiator which is sensitive to short wavelengths of ultraviolet light, together with an ultraviolet lamp which outputs only shorter wavelength ultraviolet light, to achieve only surface curing in the first polymerization by the ultraviolet light curing.

Illustrative apparatus for performing the above-described process is shown schematically in the accompanying figure, and will be discussed in the following. That is, curing apparatus 1 includes first polymerization station 2 and second polymerization station 3. Open mold 4 is moved in the direction represented by arrow 6 to first polymerization station 2 and subsequently to second polymerization station 3.

At first polymerization station 2, open mold 4 is moved therethrough while light from ultraviolet lamp 7 is irradiated on the surface of the body of resin composition in mold 4. For example, and as illustrated in the figure, lamp 7 includes bulb 9 and reflector 8. Desirably, the reflector 8 is an elliptical reflector with bulb 9 at one focal point of the elliptical reflector and a surface of the body of the resin composition in open mold 4 passing through the other focal point of elliptical reflector 8. Open mold 4 is transferred from first polymerization station 2 to second polymerization station 3, in the direction designated by arrow 6, by, for example, transfer conveyor 5.

At second polymerization station 3, the resin composition, also including a catalyst for room temperature or high temperature curing, is maintained to achieve curing (hardening or setting) of a remainder of the body of resin composition in open mold 4, other than the polymerized surface layer.

Shown at second polymerization station 3, in the figure, is heater 12, representing, e.g., a baking oven for high-temperature curing, as known in the art. As can be appreciated, such heater would be used for high-temperature curing, but it generally would not be necessary for room temperature curing.

Also shown in the figure is fluid supply pipe 10, e.g., for supplying a cooling fluid to lamp 7, for cooling, e.g., bulb 9. Moreover, in order to protect the surface of the resin composition in open mold 4 from being affected by movement of the cooling fluid (or by movement of heated air at lamp 7, shield 11 is provided between lamp 7 and open mold 4. Shield 11 is transparent to ultraviolet light, of the wavelength irradiated from lamp 7 and to which the photoinitiator of the resin composition is sensitive, and, e.g., is made of quartz.

In the following are set forth specific examples according to the present invention, showing the effect of various processing parameters on the surface polymerization. As can be appreciated, various examples within the scope of the present invention are merely illustrative, and are not limiting of the present invention.

Example I

An unsaturated polyester XR-1270-C was obtained from AOC Corporation. The polyester contains 35% styrene that will be considered the source of monomer evaporation. One percent of photoinitiator, Darocur 1173, was added to give ultraviolet (UV) activation. The resultant mixture was a liquid composition. To test for % volatile loss (% V loss) the liquids were drawn down on aluminum Q panels using either a #28 (2.3 mils) or #70 (6 mils) wire wound draw bar. The panels were weighed uncoated, coated, UV cured and then reweighed after 30 minutes of sitting at room temperature. Data was reported as the % loss of volatile from the original drawn down mass. The UV cure condition consisted of a microwave-powered lamp F-300-H, by Fusion UV

Systems, Inc., of 300 watts/in. (120 watts/cm), at a distance of 2.5 inches from the panel, at a sweep condition, the panels being on a conveyor and moving at 5 feet/minute. The lamp was equipped with a standard mercury lamp spectra. The results are shown in the following Table 1. Table 1

Conclusions: The XR-1270-C lost 21.7% of styrene (63% loss of available styrene) during the room temperature sitting condition. UV irradiation without photoinitiator did not improve the styrene losses. UV irradiation with photoinitiator, and a quick sweep condition, lowered the styrene losses to 8% or a total loss of only 23% of available styrene for the large surface area with a low film thickness. This is a factor of 2.75 lower than without UV and photoinitiator. The 8.0% loss occurs from the time of weighing and then running the panel under the lamp. This loss can be eliminated or reduced by sweep curing immediately after draw down application.

Example H

The same experimental procedure and set-up as in Example I, was used except a F-600-H lamp made by Fusion UV Systems, Inc., was used (600 watts/in., or 240 watts/cm), compared to a

F-300-H lamp (300 watts/in., or 120 watts/cm). Percent volatile was measured and listed after the 30 minute waiting period for final panel reweighing. The results are shown in Table 2.

Table 2

Conclusion: Both lamps compared equally at 5 ft/min. Example IH

The same experimental procedure was used as in Example 1, except line speed was varied and other electrode lamps were tested. Results are shown in the following Table 3. Table 3

Conclusion: The higher wattage of the 600 watt microwave lamp allowed the volatiles (evaporation) to remain reduced at a higher sweep speed. The 300-400 watt lamps worked well at

5ft/min and 2.5 inches in distance. The electrodeless lamps reduced volatiles better at all speed ranges than the medium pressure electrode lamps.

Example IV

Experimental conditions were maintained as in Example I, except bulb spectra were examined with line speed. Mercury bulbs were compared along with halide doped bulbs. Results are shown in the following Table 4. Table 4

Conclusion: Reduced evaporation (effective "cocooning") occurs at 5-10 ft/min with the three lamps but drops off with increased line speed. Example V

Conditions were the same as in Example I, except a line speed of 10 ft/min was used, and a variable power source (VPS) was used with the F-600W-H lamp to lower power from 100% to 25%. The lamp had a 2.5 in. focus. Results are shown in the following Table 5. Table 5

Conclusion: Reduced evaporation (effective "cocooning") drops off with lower power levels at the same line speed. Example VI Same procedure as in Example I was used, except a mercury electrode arc lamp system from UV Process Supply (American Ultraviolet lamp), at various power settings and line speeds, was used. The lamp has an 11-inch bulb (electrode to electrode) and was placed 2.5 inches from the aluminum panel on the conveyor. Results are shown in the following Table 6.

Table 6

Conclusion: The electrode arc mercury lamp reduces evaporation (effectively "cocoons") at 200 watts/in. and 300 watts/in. at 5ft/min, but effectiveness drops off with reduced power and increased line speed. The electrode arc mercury lamp does not reduce evaporation as well as the higher powered, higher focused F-600 watt microwave lamp. Example VH

This experiment uses the procedures as in Example I, except the photoinitiator concentration of Darocur 1173 is varied and studied with line speed using a F-600W-H at 2.5 inches from the panel. Results are shown in the following Table 7. Table 7

Conclusion: As the percentage of concentration of the photoinitiator is increased, sufficiently reduced evaporation (effective "cocooning") can be accomplished at faster line speeds.

Example VHI This experiment uses the procedures as in Example 1, except a speed of lOft/min is used and various electrode and electrodeless lamps are compared at varied distances from the panel. The results are shown in the following Table 8. Table 8

Conclusion: Reduction of evaporation (effective "cocooning") drops off with lamp distance from the substrate at a given line speed.

Example IX

This example illustrates that by introducing curable oligomers and monomers to an unsaturated polyester resin system, the surface polymerization process can occur faster and thus further maintain volatiles. A UV blend was made as follows:

75% (60% Epoxy Acrylate CN-120, (from Sartomer, Inc.) + 40% HDDA (hexanediol diacrylate))

25%) dipentaerythritol pentaacrylate.

(A) 15% of the UV blend was added to 85% of XR-1270 + 1% 1173 (B) 15% of the UV blend was added to 85% of XR-1270 + 5% 1173.

Blend (A), (B) and XR-1270 + 1% 1173 were put on aluminum Q panels and UV cured at various line speeds using a F-600-H lamp at 2.5 inches with the VPS (variable power supply) on 100%.

% volatile losses were measured after UV curing and again after another 30 minutes. Results are shown in the following Table 9. Table 9

Conclusion: Increased photoinitiator and UN oligomer-monomer addition can greatly increase the speed of effective "cocooning" and reduce % volatile loss even at speeds of 40 ft/min.

Examples X-Xπ

An unsaturated polyester XR-1270-C was obtained from AOC Corporation. 35-40% styrene by weight was added to the unsaturated polyester, and will be the source of monomer evaporation. To test for % volatile loss the liquid composition was drawn down on aluminum panels using either a #28 (2.3 mils) or #70 (6.3 mils) wire wound draw bar. The panels were weighed uncoated, coated, UV cured, and then weighed after 30 minutes of sitting at room temperature. Data was reported as the % loss of volatile from the original drawn down mass.

Each specific UV lamp source was evaluated at a given distance, given power level, with a given wavelength bulb by placing the coated Q aluminum panel on a conveyor belt at a given conveyor speed passing the lamp.

A time procedure was used to weigh, cure and reweigh panels to provide consistent and repeatable evaporation loss data.

An analytical Mettler balance accurate to four decimal places was used for weighing accuracy.

"RT" means room temperature. "MEK peroxide" is methyl ethyl ketone peroxide. "1173" in Darocur 1173 photoinitiator. "PI" means photoinitiator.

Table 10

Comparing % volatile weight loss (% V loss) of XR-1270-C and with changed conditions compared to the base resin. An F-300-H lamp was used.

Conclusions: At room temperature and with baking, the present invention greatly lowers volatile evaporation. The further loss after bake, can be reduced by the present invention.

Table 11

Comparing microwave, arc lamps and bulbs in processing of XR-1270-C + 1% Darocur 1173. All lamps were 2.5 inches from the aluminum panel and % volatile loss was measured after UV cure and again after 30 minutes.

Conclusion: Shorter wavelength bulbs and higher-powered lamps provide better "cocooning". No "cocooning" occurs with resin and no photoinitiator. Table 12 Bulk mass effect versus large surface area effect was shown by comparing % volatile loss after UV and after UV + 30 minutes with XR-1270-C + 1% 1173 using the panel method and for bulk mass (a weighing aluminum dish of small surface area, 1 %" circumference, with a material depth of ^lA"). An F-600-H was used at 2.5 inches with line speed variations.

Conclusion:

Volatile loss decreases with reduced surface area. "Cocooning" occurs in both conditions. % volatile loss increases with line speed. One can qualitatively feel "cocooning" by feeling the surface of the panel or dish. The less tack you have, the greater will be the "cocooning" and the less volatiles will be lost.

Accordingly, by the present invention a resin composition containing volatile material, such as a volatile monomer, can be polymerized (for example, cured) without substantial loss of the volatile material. According to the present invention, utilizing a resin composition including a photoinitiator, and using the medium or high-pressure lamps and relative movement between the lamps and resin composition in a first polymerization, to set a surface layer of the polymer, loss of the volatile material can be reduced to 1-10% of the total amount of volatile material initially in the composition. Moreover, by modifying various parameters, including increasing photoinitiator amount and/or adding ultraviolet curing oligomers and monomers, the effect of the present invention can be even further increased, further limiting loss of volatile material. Thus, by limiting loss of volatile material, environmental pollution and hazardous working conditions for workers can be reduced. While several embodiments in accordance with the present invention have been shown and described, it is understood that the same is not limited thereto, but is susceptible of numerous changes and modifications as known to those skilled in the art. Therefore, I do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. Method of polymerizing a resin composition containing a volatile material, comprising: providing said resin composition including a polymerizable material, the volatile material and a photoinitiator for ultraviolet light; performing a first polymerization, of a surface of the resin composition, by irradiating the surface of the resin composition with ultraviolet light from a medium or high pressure ultraviolet lamp, said irradiating being performed during relative movement between the lamp and the resin composition; and performing a second polymerization of the resin composition, to polymerize a remainder of the resin composition not polymerized in the first polymerization.

2. The method according to claim 1 , wherein the first polymerization polymerizes only the surface of the resin composition, to seal off the resin composition.

3. The method according to claim 1 , wherein the first polymerization cures the surface of the resin composition, and the second polymerization cures said remainder of the resin composition.

4. The method according to claim 3, wherein said second polymerization is a thermal curing or a room temperature curing.

5. The method according to claim 1, wherein said ultraviolet lamp has a light output of 20-400 watts/cm.

6. The method according to claim 5, wherein said ultraviolet lamp has a light output of 120-240 watts/cm.

7. The method according to claim 1 , wherein said relative movement is at a speed of 5 to 40 ft/min.

8. The method according to claim 1, wherein both the first polymerization and the second polymerization are free radical polymerizations.

9. The method according to claim 1, wherein the volatile material is a volatile liquid.

10. The method according to claim 9, wherein the volatile liquid is a diluent in the resin composition.

11. The method according to claim 10, wherein the volatile material is selected from the group consisting of styrene, vinyl toluene, divinyl benzene, and vinyl ether.

12. The method according to claim 11, wherein the polymerizable material is a material with unsaturation, polymerizable by free radical polymerization.

13. The method according to claim 12, wherein the material with unsaturation is an unsaturated polyester, and said volatile material is styrene.

14. The method according to claim 13, wherein the photoinitiator is selected from the group consisting of benzophenone and 2-hydroxy-2-methyl- 1 -phenyl-propan- 1 -one .

15. The method according to claim 14, wherein the photoinitiator is 2-hydroxy-2-methyI- 1 -phenyl-propan- 1 -one .

16. The method according to claim 1, wherein the photoinitiator is a liquid.

17. The method according to claim 1, wherein the resin composition includes 0.1 to 20% by weight photoinitiator, of the total weight of the resin composition.

18. The method according to claim 17, wherein the resin composition includes 0.25-10% by weight photoinitiator, of the total weight of the resin composition.

19. The method according to claim 18, wherein the composition includes 0.25-1.0% by weight photoinitiator, of the total weight of the resin composition.

20. The method according to claim 1, wherein the resin composition is provided in an open mold, and the first and second polymerizations are performed with the resin composition in said open mold.

21. The method according to claim 1, wherein said medium or high pressure ultraviolet lamp is an electrodeless ultraviolet lamp.

22. The method according to claim 1, wherein said first polymerization is performed under an inert gas blanket.

23. The method according to claim 1, wherein the polymerizable material is an oligomer.

24. The method according to claim 1, wherein during said first polymerization a cooling fluid is supplied to said ultraviolet lamp, and wherein said cooling fluid is blocked from flowing to said surface of the resin composition.

25. The method according to claim 1, wherein during said first polymerization air flows pas the ultraviolet lamp, and the air flowing past the ultraviolet lamp is blocked from flowing to said surface of the resin composition.

26. The method according to claim 1, wherein said relative movement between the lamp and the resin composition is performed by sweeping ultraviolet light from the medium or high pressure ultraviolet lamp across the entire surface of the resin composition.

27. The method according to claim 1, wherein said volatile material is a monomer.

28. The method according to claim 1, wherein the resin composition includes the volatile material in an amount of 30-40% by weight, of the total weight of the resin composition.

29. Product formed by the method of claim 20.

30. Product formed by the method of claim 14.

31. Product formed by the method of claim 1.

32. Polymerization product, comprising: a surface polymerization layer, formed by polymerizing a surface region of a body of a resin composition, the resin composition including a mixture of polymerizable material, monomer and photoinitiator, the surface polymerization layer being a layer formed by irradiating ultraviolet light from a medium or high pressure ultraviolet lamp on the surface region while providing relative movement between the lamp and the body of the resin composition; and a remaining polymerized material, formed by polymerizing a remainder of the body of the resin composition other than said surface polymerization layer, by a room temperature or heat polymerization.

33. Polymerization product according to claim 32, wherein said product is a molded product, the surface polymerization layer and the remaining polymerized material having been formed with the body of the resin composition being in an open mold.

34. Polymerization apparatus, comprising: a first polymerization station at which a surface layer of a body of a resin composition is polymerized, the first polymerization station including a medium or high pressure ultraviolet lamp for irradiating ultraviolet light on the surface layer of the body of the resin composition, and structure to move the body of the resin composition relative to the ultraviolet lamp while the ultraviolet lamp irradiates the surface layer of the body of the resin composition with ultraviolet light; and a second polymerization station at which a remaining part of the body of the resin composition, other than the surface layer, is polymerized.

35. Polymerization apparatus according to claim 34, wherein the medium or high pressure ultraviolet lamp is an electrodeless ultraviolet lamp.

36. Polymerization apparatus according to claim 35, further comprising a microwave generator and structure to supply microwaves, generated by the microwave generator, to the electrodeless ultraviolet lamp.

37. Polymerization apparatus according to claim 35, wherein the electrodeless ultraviolet lamp includes an elliptical reflector, to focus ultraviolet light from the ultraviolet lamp on the surface layer of the body of the resin composition.

38. Polymerization apparatus according to claim 34, further comprising a shield between the ultraviolet lamp and the body of the resin composition, to prevent air flow adjacent the ultraviolet lamp from disturbing the body of the resin composition.

39. Polymerization apparatus according to claim 38, further comprising supply structure to supply cooling fluid to the ultraviolet lamp.

40. Polymerization apparatus according to claim 34, wherein the structure to move the body of resin composition relative to the ultraviolet lamp includes sweep structure to move the ultraviolet lamp such that ultraviolet light from the ultraviolet lamp sweeps across the entire surface of the body of resin composition.

41. Polymerization apparatus according to claim 34, further comprising an open mold for holding the body of the resin composition.

42. Polymerization apparatus according to claim 34, further comprising conveying structure to transfer the body of the resin composition from the first polymerization station, where the surface layer of the resin composition is initially polymerized, to the second polymerization station, where said remaining part of the body of the resin composition is polymerized.

43. Polymerization apparatus according to claim 42, wherein said conveying structure includes structure for transferring an open mold containing the body of the resin composition from the first polymerization station to the second polymerization station.