Release agent for removing plastics, especially polyurethane plastics from molds

A release agent applied to the surface of a mold in the form of a film to permit ready removal of plastic, particularly polyurethane, from the mold. The release agent contains a film-forming substance having an affinity to the plastic and becomes attached to the plastic and is removed with the plastic when taken out of the mold thereby preventing buildup of film-forming substance in the mold. A cross-linking agent and/or a cross-linking catalyst and/or emulsifier and/or tenside may advantageously be incorporated in the release agent.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a release agent for removing plastics, especially 
polyurethane plastics from a mold. The release agent is applied to the 
surface of a mold in the form of a film. 
2. Description of the Prior Art 
As is well known, plastics are removed from closed or open molds through 
the use of release agents, for instance, such as tetrafluoroethylene 
(Teflon.RTM.), silicon or wax type, the latter often being dissolved in 
solvents. The release agents used up-to-date have the disadvantage that 
they must be removed completely from the mold after the molded part has 
been removed from the latter, since otherwise it is not possible to 
varnish the plastic surface of the molded part in the desired manner and 
with the necessary adhesion. This operation of removing the release agent 
film adhering to the surface of the plastic is very laborious and 
comprises vapor degreasing and post-treatment with solvent, which result 
in changes of the plastic surface which necessitates in turn 
post-treatments such as puttying and priming, which overall leads to a 
considerable cost increase of the finished part. On the other hand, due to 
the low affinity of the release agents used heretofore vis-a-vis the 
plastic, particularly polyurethane or polyurea plastic, a film of release 
agent always remains in the mold itself after the molded part is removed. 
The thickness of this film grows with continuous production and must be 
removed from time to time, thereby interrupting the production cycle. For 
health reasons the use of solvents which are required for the release 
agents known heretofore and which furthermore lengthens the cycle time of 
mold removal is objectionable because the solvent must evaporate after the 
application, so that one must frequently operate with multi-station rotary 
table in the production process. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a method and an 
improved release agent for removing plastics, particularly polyurethane 
plastics, from molds, in which the described disadvantages are absent. 
In particular the release agent can be used without a solvent. The 
invention permits the molded parts to be varnished immediately after 
removal from the mold and without additional pretreatment measures. 
With the foregoing and other objects in view, there is provided in 
accordance with the invention a process of casting plastics in a mold in 
which a release agent is applied to the surface of the mold in the form of 
a film to permit ready removal of the cast plastic from the mold, the 
improvement comprising applying a release agent containing a film-forming 
substance having an affinity to the polymer matrix and becomes attached to 
the plastic, removing the plastic together with said film-forming 
substance attached thereto from the mold thereby preventing buildup of 
film forming substances in the mold. 
In accordance with the invention there is provided a release agent for 
application to the surface of a mold in the form of a film to permit ready 
removal of plastic from the mold which comprises a liquid containing a 
film-forming substance having an affinity to the plastic matrix and which 
upon application to the surface of the mold forms a film, and due to the 
affinity of said substance to the plastic becomes attached to the plastic 
and is removed with the plastic when taken out of the mold thereby 
preventing buildup of film-forming substance in the mold. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
release agent for removing plastics, especially polyurethane plastics from 
molds; it is nevertheless not intended to be limited to the details shown, 
since various modifications may be made therein without departing from the 
spirit of the invention and within the scope and range of equivalents of 
the claims. 
The invention, however, together with additional objects and advantages 
thereof will be best understood from the following description. 
DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the invention, a release agent for removing plastics, 
especially polyurethane plastics, from molds which is applied in the form 
of a film to the surface of the closed or open mold, is characterized by 
the feature that the release agent film has been prepared from, or 
consists of, at least one film-forming substance which has affinity to the 
polymer matrix and preferably has few, or non-reactive, end groups. 
Optionally the film-forming substance may be in a mixture with a 
cross-linking agent reactive with building blocks of the plastic to be 
removed from the mold and/or at least one catalyst for the cross-linking 
reaction. 
The release agent according to the invention can be prepared by simple 
mixing of release agent film formers as well as, optionally, cross-linking 
agents and/or catalysts and can be sprayed, brushed or applied in some 
other manner to the mold in the form of a film. If required, a tenside can 
be added to the release agent for improving the wetting of the mold 
surface. If desired, an emulsifier can also be added to the release agent 
to increase the rate of diffusion of the release agent molecule and/or for 
subsequently diffusing the release agent film into the surface of the 
plastic to be removed from the mold. The release agent according to the 
invention may be employed in the form of a homogeneous solution which may 
optionally also contain one or several inorganic or organic solvents. 
With the release agent according to the invention it is possible in a 
technically simple, economical and effective manner to remove plastics, 
especially polyurethane plastics, from molds without problems and without 
the need for complicated and expensive rework of the surface of the 
plastic removed from the mold, i.e. the molded plastic part removed from 
the mold can be subjected to any desired surface treatment, especially to 
immediate varnishing without the need for additional prior treatments. If 
the release agent according to the invention is used, no or only very 
small amounts of release agent film remain on the surface of the mold 
after the plastic has been removed from the mold, so that the production 
interruptions heretofore required in such cases for removing these 
undesirable release agent films become now largely unnecessary. 
From a release agent film wetting the surface of the mold, the reactive 
substances (cross-linking) contained therein, catalyzed or not catalyzed, 
and/or catalysts themselves which may be contained therein counterdiffuse 
with respect to the reactive building blocks such as polyisocyanates, of 
the plastic to be removed from the mold in a controlled manner by means of 
the concentration in the release agent film. This prevents, through 
chemical reaction, a reaction of the reactive substances at the mold 
surface or adsorption of the active reaction products such as polyurethane 
or polyurea groups thereon. In this manner, reactive groups such as 
hydroxyl or amino end groups are placed on the plastic surface in a 
definite manner, which make varnishing on top of these reactive groups 
possible without first removing the release agent film. Due to the 
affinity to the polymer matrix, the release agent film itself diffuses 
into the polymer after removal from the mold wherein the polymer was held 
during the foaming and setting process, because of the little or 
non-reactivity of its end groups. 
The release agent according to the invention is preferably used without 
dilution with solvents. However, it can also be used dissolved in organic 
or inorganic solvents and/or propellants in order to make it more easily 
sprayable. Especially well suited for this are chlorinated or fluorinated 
hydrocarbons, carboxylic acid esters and ketones, to which optionally 
water can also be added. 
Examples for film formers or film forming substances usable according to 
the invention are polyols, polyethers and/or polyesters preferably such 
with secondary end groups and molecular weight (average by weight) of 100 
to 20,000 especially from 800 to 5,000 and their nonfunctional reaction 
products (zerols), which for example are blocked by monofunctional 
isocyanates. 
Suitable as film-forming substances are also polyamines with sterically 
inhibited amino groups or their nonfunctional acyl compounds. However, 
esters of stearic and oleic acid can also be used with low molecular 
polyols. 
The suitability of the film-forming substances usable according to the 
invention is first tested by spraying a film, which has little reactivity 
with isocyanates, onto the mold surface. Zerewitinoff-active compounds are 
very reactive with isocyanates. Compounds which have only a small fraction 
of the reactivity of Zerewitinoff-active compounds are considered of 
little reactivity with isocyanates. If the film is only formed partially, 
the coverage can be perfected by the addition of tensides for lowering the 
surface tension. According to a preferred embodiment, a polyol with little 
reactivity which exhibits affinity vis-a-vis the polyol or polyamine 
contained in the plastic to be removed from the mold, is used for the 
preparation of a release agent film. This will facilitate diffusion of the 
release agent film into the molded body to be removed from the mold. 
As cross-linking agents which diffuse in a controlled manner from the 
release agent film and intercept reactive molecules, such as 
polyisocyanates, and thus prevent them from reacting at the mold surface, 
there can be used, for example: all Zerewitinoff-active compounds, 
preferably amines, polyamines, alcohols, polyols, water, amino-alcohols, 
aminopolyols. Especially suitable are alkylene glycol, butane diol, hexane 
diol, ethylene diamine, 1,6-hexamethylene diamine, aromatic polyamines, 
for instance, tolamine and the nuclear alkylation products thereof as well 
as 4-methyl-3,5-diaminobenzoic-acid ester. Suitable as cross-linking 
agents are also any compounds which are considered as aging protection 
agents for polyurethane systems, especially carbo diiamides and sterically 
inhibited phenols as such, preferably the reactive groups. 
The intercept reaction of the polyisocyanates in the release agent film 
which is important for the removal from the mold, may be aided by 
catalysts of the OH/NCO or the NH.sub.2 /NCO reaction. Thus, diffusion of 
NCO groups toward the mold surface or urethane and urea groups with 
adhesive effect at the mold surface is reliably avoided. Examples for 
catalysts which can be used according to the invention for aiding the 
intercept reaction in the release agent film or can be used as such, are 
tin compounds, especially dibutyl tin dilaurate and/or tin (II) octoate, 
tertiary amines, preferably Dabco.RTM. (triethylene-diamine), and 
caprolactam/water mixtures. Further examples which can be used in a 
mixture with the cross-linking agents and the above-mentioned catalysts or 
alone in the release agent film at the mold surface, are trimerization 
catalysts, especially ammonium acetate, sodium acetate and potassium 
acetate, and carbodiimidization catalysts, especially phospholin oxide. 
The special advantage of the release agent according to the invention, 
besides the ease of removal from the mold attainable thereby and its 
usability without solvents, is that it is possible thereby to 
functionalize the surface of the molded part definitely and 
stoichiometrically via the concentration of the cross-linking agent and/or 
catalysts in the release agent and diffusion film. Since, with the proper 
affine choice, the release agent film remains diffused into the molded 
plastic part, it is possible as a result of the OH- or NH.sub.2 groups 
formed at the surface, to perform a varnishing operation directly without 
further pretreatment, preferably using DD varnishes, with excellent 
adhesion of the varnish without the necessity of removing the release 
agent film. 
The release agent according to the invention contains the cross-linking 
agent preferably in an amount of 0 to 50% and especially, 3 to 15%. By 
using certain polyether film formers (for instance, Desmophen.RTM. 3600), 
it is possible to operate without a cross-linking agent. To improve the 
release action it is advisable, however, also in this case to use a 
cross-linking agent. Particularly good results are obtained if 
polypropylene glycol MG 2000, F-2, which has been reacted with 2 mol 
phenylisocyanate, is used as the sole component of the release agent, or 
also if polypropylene glycol MG 4000 is used as the film-forming substance 
in a mixture with 5% 1,12-diaminododecane, or if polypropylene glycol MG 
2000, F-2, which has been reacted with 2 mol phenylisocyanate, is used as 
the film-forming substance in a mixture with 5% butane diol -1,4 as the 
cross-linking agent, and dibutyl tin dilaurate. Triethylene diamine 
(Dabco.RTM.) or 5% ammonium acetate or 3% phosphine oxide or 5% 
caprolactam in a mixture with water in the volume ratio 4:1 can also be 
used as catalysts. 
The production of polyurethanes is well known. The principal reactants are 
commonly a polyisocyanate and a polyol, the latter usually a polyether or 
a polyester. Various other constituents may be incorporated such as 
catalyst to facilitate the reaction, cross-linking agents, blowing agents 
to induce foaming, coloring agents, etc. To avoid the necessity of users, 
particularly smaller users, of formulating their own mixtures, 
manufacturers sell a polyurethane foam system, in which all the 
ingredients are properly mixed, usually as two liquids, which merely 
require pouring together to form a polyurethane foam.

The invention will be explained in further detail by the following examples 
without being limited thereto, however. 
EXAMPLE 1 
To an aluminum mold was applied a film of release agent which was prepared 
from a mixture of 100 parts by weight polypropylene-oxide diol with an 
average molecular weight of 2,000, 5 parts by weight butane diol -1,4 and 
0.25 parts by weight dibutyl tin dilaurate. Onto the release agent film, a 
polyurethane foam system made by Bayer AG (PU 1777 HT/Desmodur PF-100 T: 
52T) was poured. The molded part so obtained could be removed from the 
mold easily after the molding operation, and was easy to varnish; the 
applied varnish coating adhered firmly thereto. 
REFERENCE EXAMPLE A 
For comparison, the same operation was performed without using a mold 
release agent. The result was that the molded body stuck irreversibly to 
the aluminum mold. 
REFERENCE EXAMPLE B 
Using the known mold release agent Akmosil-180 ST.RTM. or Baysilan Release 
Agent V.RTM., the molded body could be removed from the mold as easily as 
when the release agent according to the invention was used. Before this 
molded body could be varnished durably, however, the film of release agent 
adhering to the surface of the molded body had to be removed in several 
operations. 
EXAMPLE 2 
The procedure was as described in Example 1; however, 5 parts by weight 
1,6-hexamethylene diamine was used as the cross-linking agent in the 
release system. The effects are the same as in Example 1. 
EXAMPLE 3 
The procedure is the same as described in Example 1; however, 15 parts by 
weight 1,12 duodecamethylene diamine is used as the cross-linking agent in 
the release system. Again good release action is obtained with at the same 
time good direct varnishing of the molded body. 
EXAMPLE 4 
The procedure is as in Example 1; however, 5 parts by weight 4-methyl-3, 
5-diamino-benzoic-acid 2-ethylvinyl ester is used as the cross-linking 
agent in the release system, and as catalyst, 0.25 parts by weight dibutyl 
ester of phosphoric acid. Release and varnishability are excellent. 
EXAMPLE 5 
The procedure is as described in Example 4; however, 10 parts by weight 
bisethyl-2, 4-toluylene diamine are used as the cross-linking agent in the 
release system. The release action and the varnishability are excellent. 
EXAMPLE 6 
The mold is wiped with an adduct of 1 mol polypropylene oxide diol 
(M=2,000) and 2 mol stearyl-isocyanate. The system described in Example 1 
was used as the PU system. The release action and varnishability are good. 
EXAMPLE 7 
The procedure is as described in Example 6; however, 5 parts by weight 
bisethyl-2, 4-toluylene diamine are used per 100 parts by weight of the 
polyether with non functional groups (zerol). The release action and the 
varnishability are very good. 
EXAMPLE 8 
The procedure is as described in Examples 6 and 7; however 0.5 parts by 
weight dibutyl ester of phosphoric acid are added to the release system. 
The release action and the direct varnishability, recognizable from the 
ease of removal from a closed mold held at 50.degree. C. and the good 
adhesion of DD.RTM. varnish with heavy curvature of the molded part and in 
the drum rotation test, are excellent.